Tiller Distance Effects in SWB Recumbent Handling and Design

Here’s another post regarding short wheelbase recumbent bike design.  This time we will focus mostly on tiller distance, and what effects it has on handling.

Tiller distance, as I and most other people define it, is the distance from your hands (when positioned in the normal spot on the handlebars) to the steering axis, as measured along a line that is perpendicular to the steering axis.  Sometimes this is thought of as how far your hands are behind the steering axis when the bike is viewed from the side.  While this is one obvious aspect, hand width adds to it too.  Tiller length is a dimension that lives in 3D, and as a result, the true tiller distance is only observable in a 2D image when looking in line with / along the steering axis. Tiller distance is the radius of the arc your hands travel along when you steer the bike.

A word about nomenclature for a moment.  Notice I am using the term ’tiller distance’ to help distinguish it from the handlebar/steering type of nearly the same name, tiller steering.  This is sometimes also known as ‘preying mantis’ (PM), or even ‘hamster’ steering (but hamster is debatably slightly different).  All recumbent steering types I have ever seen, short of a joystick or tank type steering, have some amount of positive tiller, unlike upright road bikes which normally have negative tiller.  Beach cruisers have positive tiller.  Make sense?  Ok.

Tiller distance is an important factor that helps determine how a recumbent bike handles.  Basically, for good handling, you don’t want the tiller distance to not be too much, and not too little, although too little is a fairly rare problem.  Just to be clear, however, tiller is one factor among at least a dozen others that influences bike handling, so let’s not oversell its importance.  These numerous variables are being considered one at a time, because to try to understand them all at once would be overwhelming for just about all of us.

I postulate that if tiller length is excessive, you tend to have low speed handling problems.  My theory is that as you try to balance the bike and make small, precise steering corrections, your hands have to move a relatively far distance when you have a long tiller distance  to affect the same balance correction. This tends to produce overshoot. And you have to then correct in the opposite direction to compensate, and you might overshoot in that direction too.  Too often, you end up rapidly swinging your hands left and right repeatedly, overshooting each time, and it’s just about the most unpleasant thing you can imagine.  As 2-wheel bent riders, just about all of us have experienced this.  You are really not in control in such cases. Shorter tiller distances calm this down and help you make more precise steering corrections because the inertia of your hands/bars/brake+shift levers/stem are less at work. They are less at work because they only need to move a shorter distance to affect a certain steering correction, and have less chance to be accelerated to a speed that requires a challenging deceleration to be made.  As a result, choosing lightweight brake levers, shift levers, grips, and handlebars can help with this issue a little bit.

Now if you go too far and you have an extremely small tiller distance, you start to have a different problem with overshoot – but this time it’s due to a lack of leverage at bars. To overcome friction at the contact patch, you might need to apply too much force to the bars – again, it’s an effort that is hard to modulate.  And if there is enough leverage/tiller distance to prevent that specific problem, you still might find high speed steering to suffer (i.e. be ‘twitchy’), because even tiny movements of the hands can cause oversteering.  Imagine trying to hold onto the riser/steering tube just above the headset and trying to steer from that location.  Sounds impossible, right?  Probably is.

The Zevo only works well with superman / open cockpit (OC) / tweener bar type steering because of how far the head tube is pushed forward in order to accommodate the particular steering geometry I wanted (steep steering angle + negative fork rake). If I had put tiller / PM /hamster steering on that bike, the tiller distance would have been huge, and this would have resulted in poor handling.  Superman / OC / tweener steering is normally set up with the rider having straight arms, and this cuts down on tiller distance by about 8″ or so compared to tiller steering.   Said another way, for a given bike, superman steering has roughly 8″ less tiller distance than tiller /PM / hamster steering since the bend at the rider’s elbow goes from about 80-110 deg. to about 10-20 deg.

I should note that Bacchetta stick bikes are another bike design that has a far forward head tube, and works best with OC than tiller steering, for the reasons mentioned above. 

Now, I could have made tiller steering work with the Zevo steering geometry, but it would have required an indirect steering setup (like is commonly seen on USS bikes). For purposes of tiller and how it affects control, this brings the steering axis back to where the actual handlebar pivot, behind the head tube of the bike. But I didn’t go this route, because I personally prefer the feel / ergonomics of superman / OC / tweener steering anyway. Avoiding the complication of indirect steering is icing on that cake.

Long tiller distances tend to go along with another design problem that affects low speed handling.  The further the center of mass is behind the steering axis, the more difficult it is for steering changes to affect balance, which also encourages overshoot / oversteering.  Why is that?  Well, imagine this – the rear wheel doesn’t steer, all it can do is pivot around it’s contact patch, so when a given balance correction is made by steering the front wheel, any mass located directly over the rear wheel cannot be given as much lateral acceleration by that given steering correction as mass that is located right over the front wheel.  Of course, what matters is where the center of mass / center of gravity (COG) is located, and typically this ends up somewhere close to the rider’s navel, assuming the bike and luggage are reasonably light.

The counterpoint to wanting your COG far forward are issues of weight distribution (to be covered in a separate, future post), and issues of pedal steer.  Pedal steer is the tendency for the act of pedaling to create steering input. This usually presents itself as a wobbly sensation. My observation has been that the further forward the rider’s legs are relative to the steering axis, the greater the pedal steer.   The act of pedaling causes your legs to primarily accelerate and decelerate in a front-to-back manner with every pedal stroke, however there is always some amount of lateral movement at work too.  It should be noted that some riders have more of this lateral movement in the pedaling than others, but it’s present to some degree with everyone.

Somehow, the Zevo seems to have resolved this conflict.  The COG is seemingly close enough to the steering axis that its steering is responsive and efficient for affecting balance, yet there is zero pedal steer.  (I was expecting some pedal steer before I actually rode it, so that was a nice surprise.)  However, upon further consideration, I think the error in my thinking is that it’s not the distance of the COG behind the steering axis per se that slows your ability to make balance corrections, but the distance behind the front tire contact patch.  That’s where the forces between the bike and road are actually exerted, after all.  If that concept is correct, then it helps explain how the Zevo can resolve both issues (steering-balance response and pedal steel) at once.   The secret is the reverse rake.  It pushes the steering axis forward (for minimizing pedal steer), but keeps the rider COG pretty close to the front contact patch for good balancing.

Getting back to the main subject – tiller distance….  I postulate that tiller distance wants to be somewhere in a sweet spot, and I would estimate it to be somewhere in the 8″ to 16″ range, generally speaking.  Of course, a little less or little more can certainly “work” too, but most designs want it to be somewhere in this ballpark.  To refine this further, if you have really steep steering angles (e.g. 80 deg. and higher), you can more easily tolerate a figure near the top of that range. Slack steering angles (e.g. 70 deg) tend to make the bottom of that range more appropriate.  But why?  Why is that the steeper the head angle, the more tiller you should have, to provide steering stability?

The steeper the head angle, the fewer the number of degrees the steering needs to be turned in order to effect a directional and balance change.  (A constant wheelbase is being assumed.)  For a ‘proof’ of this, try this thought experiment:  If the steering angle is 90 deg, rotating the bars 45 deg. causes the front of the bike to have a new heading 45 deg. off of the previous heading. Now, imagine the other extreme – a steering angle of zero (i.e. horizontal). In that case, no matter how much you rotated the steering, you’d have no change in direction. All you’d be doing is changing the camber angle of the front wheel, not actually steering the bike into a new direction.

Practical evidence of the same is the following: My two Wishbones, each with quite unconventionally steep steering angles (about 80 deg.), have hard interference, and tons of soft interference, yet I never have any trouble with either when actually riding them. Whereas, bikes with no hard interference, and less soft interference, have made these overlaps known in practice. It doesn’t seem coincidental that those bikes had steering angles in the low 70-71 deg range, typical of most current SWB recumbent designs. 

I will also note that both Wishbones have long tiller dimensions (with somewhat wide OC / tweener bars), yet it doesn’t bother me. I certainly don’t feel like I am swinging my hands and arms around a lot when steering. Their low flop geometry may be helping here too – I don’t make a lot of unintended over-steers trying to balance the bike.

So, in a way, if one were to keep the tiller distance short on a bike with a steep steering angle, then this means your hands would not move very far (arc length being short), making the steering seem “twitchy” / overly responsive. However, if you lengthen tiller, the more your hands need to move (arc length) for a given rotation angle of the steering, thus reducing the “twitchyness” of the design.  

The Zevo’s tiller distance is about 14″.  On the long side of average.  So, while the tiller distance on the Zevo is not particularly short, it’s seemingly partially compensated for by the steep steering angle which seems to reduce the number of degrees you need to turn the bars to affect a certain balance correction.   

Striking the right balance in tiller length against other design choices is probably the right path.  Extremes should be avoided.  Unfortunately, the interplay of the multiple independent variables associated with the overall handling characteristics of a bike makes any sort of ‘formula’ one might be tempted to develop quite complicated, and possibly underivable from a practical point of view.

In all of the above, I haven’t attempted to make any claims about which of the two steering/handlebar types I think is “best” – OC / superman / tweener vs. tiller / preying mantis / hamster.  I believe handlebar / steering type selection should be mostly an issue of personal ergonomic preference.  Whichever you find easier to make fine steering movements is best for you.  But as was alluded to above regarding the steering type on the Zevo, you do need to consider the bike design and the resulting tiller distance before going away from the steering type the bike was originally designed around.  Some bike designs work much better with one or the other, but those designs with the head tube/steering axis closer to the rider are a little more versatile and can work ok with either steering type.  Examples of this are the Metabike and the Schiltter Freestyle.  

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The Zevo Recumbent Bike

Somewhat recently I posted about the ideas behind the semi-novel steering geometry of the Zevo.  But what about the rest of the bike?  What’s it like, in a general sense, to ride this thing?

Before I go further, I should note that I was holding off on finishing this up because till recently I had been using the bike with a temporary fork, and although the two critical dimensions of the temporary fork (axle-to-crown and offset/rake) were quite close to the final, intended design, they weren’t exactly the same, either.  With the new fork now fitted and some miles have passed underneath me since, I feel like I can properly comment on the handling.   I’m also gonna take the time to discuss the design as a whole, because there is more to a bike than how it handles (although that’s pretty damn important, in my opinion).

Before I started down the path of designing a bike, I had articulated the following list of wants and needs in a recumbent bike:

1. Body angle of about 140 deg. with 25 deg. seat:  This is an entirely personal thing, as it’s the position I have gravitated towards over the years as what works best for me, while maintaining a good balance between aerodynamics, power delivery, and comfort.  I worked out that this would require a BB height above the seat of about 9.0 inches or so.  For someone who does a lot of climbing, it’s harder to tolerate quite as low of a seat angle. I spent some time years ago running about 18-19 degrees and while it worked well on the flat and gentle uphills, it didn’t feel good on steep climbs. I felt it also reduced my ability to see traffic, road conditions, etc. For me a good compromise is about 25 degrees. 

2.  Seat height no higher than 23 inches:  Somewhat similar to considerations of seat angle, being able to see and be seen is affected by the height of the seat.  Having ridden both mid- and high-racers in the past, as well as several different very low trikes, I have come to the general conclusion that I feel more confident in traffic situations and other less than perfect scenarios being reasonably high up.  The limiter being a seat low enough to make starts and stops easy by making them flat-footed, not tippy-toe affairs.

3. Low flop steering geometry for excellent low speed handling:  You’ve read enough about that already here:  https://rothrockcyrcle.wordpress.com/2020/09/26/steering-geometry-of-short-wheelbase-recumbent-bikes/  

4. Clearance for 2″ wide 650B or 32mm-700c with fenders, front and rear:  I wanted the versatility of an efficient road going setup, as well as one well suited to gravel / mixed-surface riding.  I have always been most interested in versatile bikes, and the Zevo is not meant to be a specialized, single-use machine.

5. Made of steel or titanium, and very durable and suitable for gravel roads and general abuse:  I don’t want to baby this thing.  If I feel like riding on Rothrock rocks, I’m gonna do it.  If I design this thing right, I’ll want to ride it for a couple decades.  It’s gotta last.

6. Stiff under hard pedaling / climbing:  I find this to be the most important issue for good climbing on a recumbent.  So many recumbent bikes and trikes flex like big bows under chain tension, and you can feel this mush in the pedals.  In my experience this does nothing good for a recumbent’s ability to climb.  I was hoping to achieve stiffness through a combination of three things. First, I didn’t skimp on material usage.  I used wall thicknesses almost double what typically is used in 2″ diameter steel stick bents, for example. I used 1.55 mm thick tubing for the three main tubes instead a more common 0.9mm. This almost accounts for the reduced modulus of elasticity of Ti compared to steel.  Second, I aligned the powerside chain line as close to the main tubes as possible. The angle between them doesn’t exceed 10 deg. or so. This required a second power side idler, but I used high quality oversized toothed idlers and mounted them in a very rigid way to the main tubes. This, of course, minimizes the bending moment on the tubes.  Lastly, I triangulated as much as I could, and at the location of the powerside idlers, so the reaction forces at the idler bolts would produce the least bending.  Another nice effect is that the direction of force during the fat part of the power stroke has the first segment of powerside chain almost exactly in opposition. An FEA model would be a nice thing to do to back up my seat of the pants engineering, but I don’t have access to the software or the expertise to use it. I need to find a college student who needs a project.  Some folks will howl about the extra power side idler saying it sucks up power.  Obviously, I am not so sure about that.  Unscientifically I will note that my Windcheetah has two power side idlers and doesn’t have a lot of drivetrain drag, and climbs very well, partly I think because the power side chain follows the main tube very closely.  Velomo also has a double idler bike (Hi-Fly). I am encouraged that I am not the only arrogant dolt trying this.

7. Ability to take a 50T rear cog:  This also has its roots in wanting to climb well.  But it’s not just about getting a low gear, but by getting a low gear using a reasonable large chainring.  The smaller the chainring, the higher the chain tension.  The higher the chain tension, the greater the frame flex.  I also thought it might be nice to have a bike with a single or, at most, double chainring.  A monster cassette makes that practical.

8. Rear Wheel Drive and Weight Distribution of about 55% rear and 45% front:  I feel this produces the best handling, and this is especially important for non-pavement use.  Both wheels need good weight distribution, and when going up steep hills that may not be paved, or may not be clean and dry, demands RWD.

9. Braze-ons where I want them:  It’s a custom bike.  Why not?

10. All external cable routing for ease of maintenance:  As you can probably tell, I am a pragmatist.  I like the looks of a sleek racy bike with hidden cables, but I don’t really want to live with one of those.

11. Clearance to the rear wheel for a seat bag:  Some dual 700C bikes with reasonably low-elevation, laid back seats can’t take my favorite form of baggage due to conflict with the rear tire.   This wasn’t a deal breaker, but I really wanted to try to sneak this one in if possible.

12. A “Future proof” rear dropout system:  Industry standards, especially for disc brake bikes, are in flux.  I wanted a dropout that could be converted from the QR wheels I currently use to 12mm 142mm TA, or perhaps some future standard that hasn’t been pushed on consumers yet.  The finished bike ended up with Paragon sliding dropouts, as a result.  

You can name any number of commercial bikes that can hit half, 2/3rds, or even 3/4ths of these items. But not all. I also had the urge to just simply come up with my own thing. I had some ideas floating around in my head for quite a while.   So that’s when I decided to see if all of these could be satisfied in a single design.  In the end, I am happy to say the answer was ‘yes’, and became the Zevo.  Of course, if you have perused this blog, you see the types of rides I like to do.  Obviously, the design criteria was shaped by those.  This bike is for me, after all.  I could care less if anyone else wants a bike like this (although folks are more than welcome to emulate the aspects that appeal to them in their own design).

So how does the bike handle?  Initial riding impressions were very good. The bike felt weird for the first minute or two, but that sensation went away very quickly and I really liked how it felt. At very low speed you need to more deliberately steer it. The bike doesn’t flop into the turn at all, you need to guide it fully through the turn. At first I thought this aspect of the handling was odd, and the steering felt a little heavy to me, but that quickly faded and then it just simply felt calm. At 15 mph and higher it feels like a lot of other bikes but below that the handling and feel barely changes, unlike most other bikes which markedly change in their handling behavior the slower you go.  At high speed and in fast turns it’s incredibly solid and confidence inspiring.  In fact, I think it’s a little dangerous because it inspires a level of confidence that my actual skills can’t fully support.   I’ve got about 1,000 miles on the bike at this point, and these initial impressions have proved to be lasting.  The bike is just easy to ride.  It’s the first dual 700c bike I have ridden that didn’t feel clumsy or ponderous. I can claim, without exaggeration, that this is the best handling recumbent bike I’ve ever ridden. It’s just so stable that it makes balancing the bike a mindless task, even at walking speeds.

The bike is a very good overall performer, and is quite fast. I wish I had more hard data to share, but I just have been riding it and not worrying much about speed. I did track my rides for the first month, though. Data from then shows it to be a little faster on mixed terrain rides than the Wishbone RT, which was previously the fastest bike I’ve ever had. On my one benchmark route, I managed averages in the 18.1 to 18.7 mph range, where the RT on that route was typically 17.7 to 18.2 mph or so in the month prior to getting the Zevo rolling. So about 0.5 mph difference. That benchmark route has no major climbs but a bunch of shorter, very steep ones, with an overall climbing rate of about 64 ft/mile.

Regarding frame stiffness under hard pedaling, the bike feels extremely stiff and solid.  On steep climbs and during hard accelerations and the bike just simply goes.  No mush in the pedals at all.  I will say it’s very slightly shy of the rigidity of the Wishbone Classic, but that bike’s stiffness is otherworldly.  On the Zevo, I can see a little lateral movement of the boom when pushing very hard.  Doesn’t seem to be twisting or moving down at all – just side to side a little.  I think the flex is real because I can sight the BB and f. derailleur post against the head tube as I am held very still in the seat.  It isn’t enough to be felt in the pedals, so it doesn’t strike me as a bad thing.  I get the impression that might even add to a nice, springy feedback sensation I experience at certain cadences and power outputs when climbing. Speed-wise, it’s every bit the equal as the previous climbing Champ, the Reynolds Wishbone. The Zevo might have and edge. It’s too close to call. The Zevo is pretty clearly a bit better uphill than the P38, though.

That said, the bike better be stiff.  It’s not light.  I knew it would be a little chunky, as I very much wanted to err on the side of stiffness and strength. I am a firm believer that even a couple extra pounds that makes a frame stiffer will pay back more than the weight penalty will take away.  Now, I do think it’s possible to have a frame so stiff that the extra weight is simply wasted and offers no benefit. I am not sure if we are at that point here or not. Might be close, but not quite. I think I’d have to build a lighter version of it and see if the stiffness is compromised too much.   However, logically, even if I am carrying around 1 or 2 lbs of extra/unnecessary weight in the frame, it’s not going to slow me down much since it’s slightly less than 1% of the total system weight. Here is where I remind myself that I need to lose about 15 lbs.

I also need to remind myself that this is actually a prototype.  Even with some small flaws there and there, all of the major design goals were achieved, and I feel a big weight off my shoulders. I had risked so much time, effort, and money into this gamble. I knew it was possible it would turn out to be a dud. I have generated  a list of things that I would change, but they are all minor things so far.  I am a perfectionist which is both a blessing and a curse.  The probability of me personally commissioning another one anytime in the next 5 years is low.  V1.1 is up to someone else to finance.  If that’s you, I’d be happy to do the CAD work to revise the design to suit your slightly larger x-seam, weight/stiffness priority, seat height / BB height relative to the seat preference, and preferences related to braze ons or other features.  

I would be remiss if I finished this write up and I didn’t give some credit to the bikes of George Reynolds that partially inspired the Zevo.  George’s bikes are super stiff, climb amazingly well, and handle great.  The Zevo’s steering geometry took the design of the Reynolds Wishbone and extended it to a relative extreme. The steering angle on the Zevo being a good 6 degrees steeper, and with more negative rake.  Hats off, George.  You really were onto something with your designs.

Further Information:

For the insomniacs in your life, here are some videos of me on the Zevo:

If the inbedded links below don’t work, go here: https://youtube.com/user/SuperKettMan

Also, compare the beginning of this video of me on the Zevo… (which you’ve seen already)  https://youtu.be/age43S0kwD4   …to this video from 5 years ago of me on the same section of road on the Metabike:

The difference in handling is plain to see, actually.

Here is a BROL thread about the design evolution: http://www.bentrideronline.com/messageboard/showthread.php?t=149640

Here is a Google picture folder of the Zevo in various states of completion and environs:

https://photos.app.goo.gl/Y4J9THYjwF7Vt5RW7

And lastly, here is a video of me talking about the bike:

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Steering Geometry of Short Wheelbase Recumbent Bikes

I’ve been riding and studying recumbents in all their forms intently for about 12 years now, and ideas have been slowly forming in my head regarding what they should and should not be, mostly specifically in the non-MBB short wheelbase bike category.  And as I have learned more, and my opinions started solidifying, I realized that what I really wanted to ride simply didn’t exist in the current market, nor in the last 30 or 40 years of recumbent development (as best I could tell).  So as a result, I decided back in February I wanted to design my own short wheel base recumbent bike.

The Zevo is the result.  90% designed by me and built from Grade 9 titanium by Carver  (http://carverbikes.com/).

Zevo

There were a number of design goals with this bike, and there are several unique (or at least quasi-unique) features, but at this time I am going to focus on one of them – the steering geometry.  It has a very steep steering angle and a reverse rake fork.  Ok, what the fudge is that all about?  I was striving for stability at all speeds, but with the main target being low speed.  I want to crawl up stupidly steep hills in more or less a straight line.  Recumbents have a deservedly poor reputation for bad handling at low speeds, with many contraption captains making tons of steering corrections in a desperate attempt to ride straight, but failing miserably unless the grade wasn’t too steep and they could keep their speed up a bit.

I believe the main problem is that the vast majority of short wheelbase recumbent bikes use steering geometry that is essentially derived from upright bikes, and this is probably a mistake.  Upright bikes have a number of different constraints related to traditional upright rider positioning, the desire to have forward stem extensions for the bike to handle well with the rider out of the saddle, clearance between the toes and the back of the front wheel, and reasonable weight distribution both seated and standing.

As a result, most short wheelbase recumbent bikes have head tube angles in the 70-72 deg. range, and fork rakes somewhere between 40 and 48mm.  This usually leads to trail figures between 58 and 70 mm, and flops in the 18 to 22 mm range.  Trail-to-flop ratios are usually somewhere between 3.0 to 4.0. Ok, what does all that mean?  Be patient, and remember to come back to these representative numbers after reading further.

Obviously, recumbent bikes have a whole different set of constraints, and additionally have different design requirements than upright bikes, and it seems objectively dumb to just recycle head tube angles and fork rakes that upright bikes use, without considering how things perhaps should be different.  The only advantage I see is so you can use stock forks.  But before we consider alternative geometries, let’s review some some basic terms and variables – head tube angle (sometimes called steering angle), trail, rake (sometimes called fork offset), and flop.  Please pardon my sorta crappy drawings included herein.

In the drawing immediately below, you can see how trail, rake, and head tube angle are defined.  Near the bottom, you can also see how that if you turn the bars to the left or right, the effect of trail is to center the steering.  Trail is the lever arm with which rolling resistance drag at the tire’s contact patch with the road is exerted through to create a steering torque that seeks to center the steering, so you can to roll straight down the road without having to constantly put lots of attention into doing so.  Since riding straight is what we want to do the vast majority of the time, trail is our friend, our buddy.  Note that the higher rolling resistance is, the higher the centering force of trail.  You can think of trail centering as being ‘powered’ by rolling resistance.

trail

In this first sketch above, rake is shown in it’s typical, or positive direction.  But rake can be negative too, and turn the other direction, towards the back of the bike.  Like this:

negative rake

So, trail, head tube angle, and rake are as defined / shown above.  But what about flop?  Flop is probably the least well known of these four variables.  Flop is the vertical distance the end of the fork and the front wheel axle drops when you turn the bars.  It’s measurement is standardized to the drop that is produced by turning the handlebars 90 degrees.  See the following diagram:

flop

I postulate that flop is evil, and flop must be defeated.

Why is flop not a good thing, generally?  Well, it is critical to understand that flop fights against the stabilizing force of trail.  Trail wants to center the steering as noted above, but flop wants to do the opposite and take any small turn of the bars and turn into a bigger turn.  Flop does this because Mother Earth is always trying to bring us down (literally), and flop helps gravity out by lowering the elevation of our center of mass.  Flop also makes the steering torque higher because it forces you to do work to lift the front end of the bike (and rider/bike system center of mass too, of course) when you try to straighten the handlebars.  This likely leads to over-correcting by most riders.  Too much force leads to overshoot, so to speak. Because flop is ‘powered’ by gravity, the heavier you are, or the more forward biased the the bike’s weight distribution is, the worse flop gets.  The following image is an analogy of the effect of varying degrees of flop has on the rider trying to pilot his bike in a straight line.

Flop Analogy

Riding a bike with lots of flop is riding on a knife edge.  A little turn of the bars makes it feel like the bike is trying to take that little molehill nudge and turn it into a mountainous directional change.  Gravity is working with flop to bring you down a hill, in a semi-literal sense.  But what happened to our buddy trail – why didn’t he keep the bars from flopping way over just because we wanted to make a small steering correction?

The self centering force provided by trail increases with speed because the rolling resistance drag force is proportional to speed.  Flop is an essentially constant force, that is independent of speed, because gravity is a constant.  When speeds are decent, the self centering force provided by trail is high enough to win the battle over flop, and the bike feels stable.  BUT, when speeds are low, the center force provided by trail gets weaker, and flop can win, encouraging over correction on the steering.  Again, you’ll end up looking like the stereotypical bent rider zig-zagging all over the road.

But what if we find a way to have a reasonable amount of trail while minimizing flop?  In that case, the meager trail force at low speeds is enough to keep you tracking straight up the hill.  Is that possible?  Heck yeah, it is.

To further your understanding of the interplay between trail and flop, try playing with numbers in this calculator: http://yojimg.net/bike/web_tools/trailcalc.php

For a given wheel and tire size, there are only two independent variables among the four remaining variables (the four we’ve been talking about – head tube angle, rake, trail, and flop). The head tube and and the rake themselves aren’t of any particular importance, in a sense. They, in and of themselves, don’t dictate how the bike will handle. What actually matters are the trail and flop figures. So a bike designer – if they have access to custom fabrication on forks in particular – should really start with a clean slate and choose a head tube angle and rake that provides the trail and flop they are looking for, while also working around other constraints in the overall design of the bike.

Since I commissioned the Zevo with a custom fork, I saw no reason to simply get what I thought would be best.  I ended up with a very steep head tube angle of 85 degrees, and a fork with a negative rake of 40 mm, which is not a common figure in high clearance forks like I was seeking to use.  This geometry gives me very low flop and a little higher than average trail.

To help understand the give and take among head tube angle, rake, trail, and flop, consider some examples – and use the calculator to check my work if you want:

Example No. 1: You will see that if you enter a 90 deg (vertical) head tube angle, it doesn’t matter what the rake is, you will have zero flop. And in this case, the trail will be equal to the rake multiplied by -1. In other words, a positive rake of 40 mm would give you a negative trail of 40 mm (bad!). A negative rake of 40 mm will give you a positive trail of 40 mm (good!).

Example No 2: If you have zero trail, you will also have zero flop, regardless of what the head tube angle is. Let’s assume a 700C wheel with a 28 mm tire. A head tube angle of 65 deg with a rake of 14 5mm gives zero trail and zero flop. A head tube angle of 45 deg and a rake of 242.5 mm has zero trail and zero flop. A head tube angle of 80 deg. and a rake of 60 mm has zero trail and zero flop. I could go on but you get the idea. Now, a bike would be very ride-able with zero flop, but it’s much less so with zero trail. You need at least a little bit of self centering – at least a little bit of positive trail.

Example No 3 (the most important one): You can achieve the same trail figure with different combos of head tube angle and rake, but the flops won’t be the same. Let’s assume a 700C wheel with a 28 mm tire. Let’s try a 72 deg. head tube angle and rake of 45 mm – this yields 64 mm of trail (a very average figure) and 19 mm of flop. This is a 3.36 trail to flop ratio. Now, let’s try a 77 deg head tube angle and 15 mm of rake. This gives you the same 64 mm of trail, but flop of only 14 mm, for a trail to flop ratio of 4.57. For a given speed, you have the same stabilizing force in both scenarios, but reduced destabilizing force in the steeper HTA / smaller rake option. The Musashi was like this, and I liked the low speed handling  of that bike very much.  Big Cat used a 76-77 head tube angle and a small rake fork.

The upshot of all of this is that the amount of flop you get for each mm of trail greatly increases as head tube angles get slacker (lower).

So this leads us to steep head tube angles to minimize flop.  I am not entirely sure that we shouldn’t go Full Monty and to simply have a 90 deg. head tube angle and use whatever amount of negative rake is needed to get the desired trail number (along with zero flop, of course).  The design of the Zevo started out this way, but I chickened out and reduced the head tube angle to 85, and with the negative 40 mm rake fork got me the trail figure I wanted, which was about 70 mm, and a very low flop of 6 mm. This is a whopping trail-to-flop ratio of 11.66.  Compare these numbers to those typically used on short wheelbase recumbent bikes listed near the top of this discussion.

There was another reason to avoid 90 deg. head tube angle – that is that it pushed the head tube so far forward that it would force direct steering to have a negative stem extension (i.e. have it come back towards the rider). There is nothing wrong with this per se, but it would look bad to my eye, and it would increase the tiller dimension too.  Even for a person who doesn’t care about the looks of a negative stem extension, there is a downside to having too much tiller. We’ll talk about tiller’s role another day.   A head tube angle of 90 degrees also eliminates the stabilization / self centering offered by whatever weight the riders hands and arms exert on the end of the handlebars, although it’s true with the head tube angle only 5 degrees away from vertical, the Zevo design won’t have a lot of that phenomenon at work.

Also, what is the downside of trail? It IS possible to have too much of a good thing. We’ll save that for another time too.

Lastly, I’ve made flop out to be the enemy of good handling.  I am not yet convinced that is actually ideal to eliminate it completely.  It should help with turning – that is when you intend to turn the bike, you can let flop do some of the work of turning into the turn.  Without some flop, will the bike feel too stable, and resistant to making turns?  I am honestly not sure yet.  The counter point is that flop is going to fight you when you want to turn the bars straight again.  I am hedging my bets that any reluctance to turn at low speed is worth the clear upsides of straight line stability and ‘overshoot prevention’ in the specific context of recumbents.

Coming soon – trail, tiller, and how the Zevo actually rides. 

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Metabike Daemon Impressions

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The Daemon is the most recent incarnation of the Metabike recumbent bike. I recently had a chance to keep a Metabike Daemon and ride it for a couple weeks. I owned, rode, and loved a previous generation of Metabike for about 6 years, and I was intrigued to see how the changes in the design that spawned the Daemon turned out.

First, the big picture hasn’t changed. It’s still a Taiwan built (by Performer Cycles), Z-framed SWB high racer made from type 7005 aluminum. Some details are the same too. It still has huge tire clearance in the back, a rear disc brake mount, telescoping boom, fixed seat (with a couple position options), integrated headset, internal cable routing in the boom and main frame tube, and telescoping seat stays that are joined together near the top for lateral rigidity. The shape of the chainstays and how they connect to the central main tube is essentially the same. Head tube angle (steering angle) with a road fork is 72 degrees. These are all good things that I am glad were kept.

So what were the changes? Well, I don’t actually have my old Metabike anymore to take precise measurements, so I am going to have to go partially by memory, and some information provided to me by RBR. Seat is lower by approximately 2″, with the bottom of the seat rim 23″ high. Wheelbase is longer by about the same amount, now at 45.5″. The bottom bracket, when fitted for my 42.5” x-seam, is 9″ above the bottom of the seat rim, or about 8″ above the top of the seat pad, about a half inch lower than it was before. The somewhat iconic triangulating boom brace is gone. The boom is not dead level, but is slightly upsloping (about 7 degrees). The front outer portion of the boom is 60 mm diameter, 5 mm larger than before.  (Note:  The diameter of the curved, middle frame tube hasn’t changed, and is still 60mm, as before.)  The chainline is a little more complicated now, with three return idlers rather than one. The fork steerer is now tapered, instead of straight 1-1/8”. Other changes became evident on the road….

Frame stiffness has improved, which improves climbing. Metabikes have always been known as pretty damn good in this department, but the Daemon is considerably better. There is less mush or ‘biopacing’ in the pedals on steep grades. The fatter tubes which are possibly thicker too (not entirely sure), plus the power side chain aligning more closely with the main frame tube and boom are the likely reasons. The front triangulation may be gone, but the other frame design changes clearly more than make up for it. The bike climbs very well. It’s very nearly as effective uphill as both my beloved square tubed Reynolds Wishbone Classic and my P-38. One variable to keep in mind is the front chainring size. The small ring on my test bike is a relatively large 39T, and this helps keep chain forces that work to turn the bike into a longbow, in check. If I had tried the bike with a granny ring and smaller rear cogs, I would have no doubt felt a little more give in the frame when climbing and accelerating hard.

The bottom bracket is at a more typical height than before, and this will likely make more people happy than the previous bike, which had a BB height that was higher than average relative to the seat. It was probably a bit much for some folks. I should say this wouldn’t have been my personal choice. For whatever reason about 8.5 to 9.0 inches of difference feels right to me and seems most effective for power generation, but I suspect I may be an exception. Note that taller riders will end up with a little higher BB as they will need to extend the boom more than I.

I was surprised that this bike has more soft (heel) interference with the front wheel. In fact, with 28mm tires, 170mm cranks, and my 42.5” xseam, I am only about 2 mm away from having hard interference between crank and tire. Hard inference really should be avoided, while soft interference is par for the course with SWB designs. I don’t find it excessive, but not everyone is equally sensitive to these issues. But this does suggest that if you have a significantly shorter x-seam than me, you will probably want to plan for the use of shorter cranks. Notably, there is clearance to mount the seat further forward than it was on my test bike, and would permit another 1.5 to 2 inches or so of shorter x-seam (say, 40.5” to 41”) before cranks shorter than 170mm are needed to avoid hard interference.

New riders to Metabikes would often comment on the presence of a certain amount of pedal steer these bikes possessed. That is, the act of pedaling would create a noticeable amount of steering input. Given time, this phenomenon would tend to subside for most riders as they adapted to the machine, but the Daemon doesn’t have any of that, even when first riding it. I am not entirely sure why that’s the case, but it’s certainly a good thing. My best guess is that the revised geometry places the rider a little further behind the head tube and front wheel, so that leg imbalance forces produce less torque on the front end of the bike. It seems that the extension of the wheelbase was accomplished primarily by moving the front wheel forward relative to the seat, rather than extending the rear wheel backwards. This would also explain the slightly reduced heel clearance.

Overall, the bike has a more relaxed and planted feel, with less of a “sharks with frickin’ laser beams attached to their heads” kind of attitude about it. It’s more of a mutated sea bass vibe instead. Translation: At moderate and high speeds, it’s somewhat easier to ride than the original Metabike, and demands a little less skill and concentration from the rider to keep the bike on-course. At low climbing speeds, I didn’t get the impression that as much had changed. The handling is a little floppy, as it is with most recumbents. The Daemon isn’t any worse than most other high racers in this way, just not all that much better.

Ride quality is fairly rough. This is not surprising for an efficiently stiff bike made from aluminum with high pressure skinny tires as I had fitted on my test bike. The very thick Ventisit-like seat pad takes off the edge pretty well, but if you ride rough roads, you should take advantage of the impressive level of versatility that the generous frame and fork clearances offers and mount some fatter tires. With lots of fast and fat tires on the market these days, this should not have any negative effects on the bike’s speed potential, but will improve ride quality and safety. It even makes the bike suitable for gravel road excursions.

This may surprise some due to the number of idlers and the presence of a chain tube, but the drivetrain does not have excessive friction. The tension in the return path is so low that the three idlers don’t seem to create much drag. Rather they just work very well to control the chain and keep it out of the way, especially when using a clutch type rear derailleur. There is no chain slap and no interference with the fork or front wheel. On the power side of the chain there is a single idler – standard stuff for a SWB highracer. The chain tube offers very little noise or drag surprisingly, which is probably due to the unconstrained manner in which it is attached, allowing it to exactly follow the chain’s ‘natural’ path.

The only downside to any of the frame and proprietary parts that I see is that the idlers are only of so-so quality. The return idlers lead a pretty easy life and will likely do just fine, but I wonder if the power side idler will hold up as well over the long haul. A Terracycle idler could always be retrofitted, but note that a TC idler is bigger in diameter than the stock idler, and the seat would need to be raised with some rubber washers an additional 1/4” to 3/8” or so for clearance.

I should note that the Daemon was conceived as a dual 700C highracer, but since it has disc brakes front and back, any pair of equal sized wheels would work if you wanted an even lower seat and/or less soft interference with the front wheel. My test bike has a dual 700C wheelset, and is how most riders my size and taller will probably want to outfit their Daemon.

However, one experiment I conducted was to use a 559 front wheel while keeping the 622 (700C) rear wheel. I did this because it is how I rode the most miles on the original Metabike I owned. As with the old bike, I found this change tightened up the slow speed handling and made heel strike a near impossibility. The 1” smaller radius wheel steepens the head tube angle (steering angle) by almost 2 degrees, reducing both trail and flop. If you don’t use a high clearance cross fork like my test bike had, and opt for a shorter road fork instead, you can achieve a similar result with a 700C front wheel, as the fork’s axle-to-crown length would be approximately 1” less (say, 370 to 375mm vs. 395 to 400mm). It should be noted that the 559 front wheel also drops the seat by a half inch, and lowers the bottom bracket relative to the seat by 3/4”.

The Daemon certainly makes for a good option for those seeking a versatile, performance oriented bike for general fitness riding, club rides, centuries, etc. I think it would also be a good choice for randonneuring or credit card touring where the emphasis is on riding and covering ground efficiently, when accessorized appropriately.

All in all, I can say it’s definitely a forward evolution of Metabike design. The fabrication quality is still there, and the design has improved. In talking to Rob Gentry of RBR, he seems to think so too, and as a result, it seems unlikely that any more frames of the original design will be produced going forward.

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HV to BV 200K

First 200K of the year. Happy Valley to Buffalo Valley.  2nd time I have done this perm.  Last time was last summer when I was fit and the days were warm.

On this day we had clear skies, but a headwind no matter which direction we rode, and a 30 deg. F. temperature rise.

I wanted to ride this permanent as a test of sorts.  A test to see if I could ride the Eastern PA Rando’s Fleche on April 9th without suffering inordinately.

While I got through this ride ok, my conclusion is that, while I probably could survive it, I typically need more than just survival to strive for.  The 200K was too difficult, and I certainly could not have kept going for another 100 miles after we stopped without suffering a decent amount.

I rode 3 days later, and it didn’t seem like I got any big fitness boost from the 200K.  One ride can only do so much, right?  When I told EK I was thinking of bagging the Fleche he said “ikillu…take that into consideration.”   Sheesh.  I never knew rando was so dangerous.

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Hairy John

 

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Rebersburg

 

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Rt. 164

 

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RB Winter

 

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Climb up to Hairy Johns

 

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Kellermobile at our beer and hamburger stop.

 

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Bible Road? Don’t remember.

 

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2 miles from the finish as the sun set.

 

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The (Current) Fleet

Somehow I have become a bike collector once again.  Several different times in my life I have purged the redundant machines accumulating in my garage only to have new redundancies appear a few years later.  I guess addiction to novelty is my underlying problem.

I currently have 6 bikes.  There isn’t actually all that much redundancy here, although there is a bit, yes.  I thought it might be cool to post some pics of each of them that haven’t made it onto this blog along with a preceding description of the bike’s raison d’etre.  (Did I spell that right?)   I am going to spend most of my time on the newest to me bike in the bunch (the Volare).

Here they are:

1983 Spectrum:  A racy(-ish), traditional road bike on skinny tires and no fenders for nice days and not-too-terribly-long rides when I want to go fast(-ish).  I ride my tubulars on this bike during much of the summer.  More limited gearing and stretched out position makes this bike not a particular favorite for long or steep climbs.  Aesthetically this bike hits all the right notes for me.

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77′-78′  Schwinn Volare:  My Eroica daydream bike with fenders, super low gearing, and overall condition that doesn’t demand being wiped with a diaper after every ride.  Think of it as my winter / rain bike.  For those times when I don’t want to get the Spectrum or Moulton dirty.  It’s a 1977 or 1978 model – not sure which, with Reynolds 531c tubing (good stuff!).  They were built by Panasonic for Schwinn, at a quality level matching the USA built Paramounts, so they are often referred to as the ‘Japanese Paramount’.

This is a good backdrop to indulge certain ‘retro’ proclivities I possess. I bought it as a frame only and the bike once had orange paint throughout (ok, not exactly – it had chromed / unpainted head tube lugs and fork crown, fork tips and rear stay ends). But apparently they chromed the whole bike and then just painted over top. Well, the bond between paint and chrome must have been poor (obviously).  Probably a surface prep problem because the chrome underneath is as glassy and smooth as chrome is actually meant to be (and unpainted).  You know, I thought about taking off the rest of the paint and just simply having a chromed bike (which would be lovely), but I am liking the ‘beausage’* look so I may just leave it like this indefinitely…

* = beauty through usage

Initial build kit included:
Rivendell ‘Silver’ branded (Tektro 539) Brakes and Grand Compe loopy cable brake levers
Nitto Dirt Drop stem and B132 Rando bars, 44cm width
Suntour Cyclone shifters and rear changer
Dura-Ace seatpost
V-O bottom bracket
Sugino crankset
Suntour Winner Pro 7 speed freewheel

Handling on this bike is great. Riding no hands is easy, and the steering is quite neutral. Turns when I want it to turn, goes straight when I want to go straight. But regrettably it has a speed wobble that randomly shows up (quite oddly) only at moderate speeds (15 to 20 mph range).

In other areas of the riding experience, the Volare is nicely flexy and rides light, and just comes to life underfoot, just like my dearly departed Vitus 979 from the days or yore. I would even dare say that it ‘planes’ in the Jan Heine sense of that word.  I think I may finally know what he is talking about.  I even double dare say it rides better (and is faster too) than the Spectrum and the Moulton.  What a bargain.  I only have about 400 bucks invested in this thing and it’s probably my nicest riding bike.

 Oh, as for the pedals, yes they are SPDs, and I do have a nice set of Campy record pedals (early 80’s vintage) with chromed steel toe clips and white leather campy toe straps in the parts bin, AND I have a pair of black cleated leather shoes in the closet, but I am not really tempted to use them.  I am not THAT retro, and  I think modern pedals and shoes are the bees knees and I wouldn’t go back except for some kind of special Eroica type event. I used to don toe clips and straps for occasional group rides back in my racing days (early 90’s) just to mess with people. But I don’t ride with anyone anymore who would actually be impressed by that  (do I?).

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A relatively recent shot.  I have swapped out the stem and have a better wb cage mount now.

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The bike doesn’t mind getting dirty. And more importantly, neither do I.

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As I bought it.  Photo taken by the seller.

2015 Moulton:  When I feel like being contrarian but not so contrarian that I hop on one of the recumbents.  It offers a pretty different ride feel from the Spectrum and Volare for obvious reasons.

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The Moulton climbs very well despite the weight penalty.  I am used to even heavier ‘bents though.

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Yeah, I ride it in the rain sometimes.

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Unterhausen takes a quick test ride.

1987 Bianchi:  Soon to become my beater bike for retro-styled mountain biking or gravel rides when I choose the upright format.  I got this bike in about 1992 or so.  Used it as a road touring bike and as a winter training bike for a lot of years.  I don’t ride this one much, but I can’t bear to part with it.

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This is a fun bike.

2008 Bacchetta Giro 26 Gravel ‘Bent:  For off-road / mixed surface recumbent riding.  For touring  (if I ever actually do that), or for dirty conditons / rain recumbent riding.  In the past I have raced, rando’ed and credit card toured on this thing.  It does it all.

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At Calvin’s Challenge.  Say Hi to Reddan in the background.

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Gravel roads, here we come.

 

2012 Metabike:  Dedicated purpose paved rando machine.  Makes the miles fly by.

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My main choice for rando.  By a lot.

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Pee break.

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Pre-Fleche porno session.

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This has nothing to do with riding a bike

  • 1st time you listen, you’ll hate it.
  • 2nd time you listen, you’ll hate it.
  • 3rd time you listen, you’ll hate it.
  • 4th time you will think it’s bad.
  • 5th time you will find it interesting
  • 6th time you’ll like it.
  • 7th time you’ll love it.
  • 8th time you’ll think it’s the best album ever made.

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Last 2015 Ride on Gravel?

Was this my last gravel ride of 2015?  The snow is going to fly soon, and not working as close to SC anymore has really cut into my ‘regular’ gravel rides in Rothrock and BESF.  So I only get out there on occasional weekends now.  This particular ride was only 45 miles or so, but it was 85% gravel, so it was an all morning affair, and featured my first ride on Kepler Rd and climbing the backside of PA Furnace.  A few choice pics:

Laurel Run, just above the lower switchback.

Stone Valley. From Winchester Rd., I think.

On the lower slopes of PA furnace (Stone Valley side)

Stone Valley from the top of PA Furnace

Other pics:  http://s771.photobucket.com/user/steamer_03/library/southern%20DNF%20100K%20scout

 

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Monday Morning

Yesterday’s scouting ride for Diet Isolation (aka 100K SI) with ‘the Erics’ was a success.

The main purpose of this ride was to verify that Siglerville-Milroy Pike was decent to ride on (it was), and that this route was do-able in 6 hrs + 45 min.  If it was too much, then the one Eric (not the other Eric) wouldn’t bother submitting it as a permanent.

We did the ride in almost exact 7 hours total time, with over an hour in stops.  Our moving average was pretty slow too though, not quite 11 mph if memory serves.  We aren’t in great shape this year, and we stopped a lot, just because.  So, yeah, it’s do-able.  It’s a hard 100K, though.  Despite it’s modest length, there is plenty of climbing and all of the big climbs of the full-calorie SI are present (although you cross the ridges in different places than on SI).  Plus, the percentage gravel is closer to 60% than the 40% or so on SI.

Aside from all that, I am shamed to say this was my first gravel ride of 2015.  Pathetic, I know.

Some pics:

Eric, Eric, and my ear. Foggy morning.

Fog burned off quickly.

“Why are you taking pictures of me?”

This was self-selected. I can’t imagine what the significance / meaning is.

I wasn’t holding the camera non-level. It’s just that steep.

On our way to A. Seeger NA.

2/3rds the way up the final climb (Bear Meadows)

The gravel ‘bent.  Pic taken at the start (note the lack of dust).

Whole collection:  http://s771.photobucket.com/user/steamer_03/library/SI%20100K%20Scout

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Sunday Morning

8:00 AM.  We’ll start at the start.  Clever huh?

http://ridewithgps.com/routes/6084359

Capture

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