Tubesets for our Bikes: Mule

In addition to individual Kaisei tubes, Compass Cycles offers three tubesets: Superlight, “Mule” and Oversize. Each tubeset is based on bikes that we have found to work extremely well. After describing the Superlight set, today we’ll look at the Mule. Named after my most versatile bike, it features an unusual configuration: an oversized down tube (31.8 mm diameter) for added stiffness, and a standard-diameter top tube (25.4 mm) for the flex characteristics that give our favorite bikes their “lively” feel.

Originally, I built the Mule for a trip to Japan as a Rinko bike that could handle both fast randonneur rides and loaded tours. The bike was intended as a test-bed for components and parts, and it was built in a rush, so we nicknamed it “The Mule”, a name used by Italian race car builders for the bare chassis that they road-tested with rudimentary bodies to finalize suspension and engines, before the car went to the carrozzeria to have its real body added.

What makes the Mule different from most bikes is that it uses an oversized down tube (31.8 mm diameter), but a standard-diameter top tube (25.4 mm). While unusual, this configuration is not without precedent: René Herse built some camping bikes, as well as some tall frames, with similar configurations. Japanese Keirin builders also build bikes with this combination of tubing diameters. And when you look at modern high-performance carbon bikes, they usually have very slender top tubes and relatively massive down tubes.

This is very different from some bikes that use an oversized top tube and a standard down tube, making both tubes the same diameter (28.6 mm). With their stiffer top tubes, these bikes don’t perform well for the BQ Team and many other riders. They also tend to shimmy, probably because both tubes have very similar resonant frequencies.

Going with a smaller top tube and larger down tube was an experiment. Would tweaking the balance of frame stiffness supercharge the Mule’s performance beyond anything we’d experienced thus far? The Mule has performed very well on many rides, but it isn’t a magic bullet: Careful back-to-back testing has shown that, for me, the Superlight tubeset gives the bike slightly better performance.

The Mule’s oversized down tube adds stiffness, yet the standard-diameter top tube keeps the flex characteristics that make for a “lively” feel. That makes the Mule perfect for carrying heavy front panniers. (I avoid loading up the rear, as that requires a much stiffer frame and also makes it difficult to rise out of the saddle.)

But the Mule isn’t just for loaded touring. Some riders who’ve ridden the Mule really like the stiffer, more planted feel compared to the Superlight spec. The Mule doesn’t shimmy as easily – even with a Chris King headset, which is prone to shimmy, the Mule is well-behaved under most conditions.

My Mule is built with a down tube that has just 0.35 mm-thick walls. With the large diameter and super-thin walls, I have found that this tube is very easy to dent. So for the Kaisei tubes, we chose 0.5 mm walls for the unbutted center sections. We offer the tubes with longer thinwall “bellies”, so the overall flex characteristics are very similar.

Even though I prefer the Superlight tubing for all-out performance, I am probably faster on the Mule than on 90% of the bikes we’ve tested at Bicycle Quarterly. I’ve ridden the Mule in a Japanese 600 km Super Randonnée with 11,000 m (36,000 ft) of climbing, and the bike felt great throughout the ride. It was only during the back-to-back testing that I realized its (slight) performance deficit. Would I do the 765-mile Paris-Brest-Paris on the Mule, if my Superlight bike wasn’t available for some reason? Absolutely!

If I could have only one bike, I probably would choose the tubing spec of the Mule. How about you? Obviously, if you plan to go touring, the oversized down tube is a great choice. If you are concerned that the Superlight tubeset may make your frame feel too flexible, especially if you are a heavier or stronger rider, I would recommend the Mule’s tubeset as well. And if you are concerned about shimmy, the very different resonant frequencies of the top and down tubes apparently keep it from developing in most cases. Compared to the more specialized bikes in my stable, the Mule is a great allrounder.

Further Reading:

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
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35 Responses to Tubesets for our Bikes: Mule

  1. Bob says:

    Had the Compass cantilever brakes been ready, would you have built the Mule with room for 584×48 tires instead of center-pull brakes around 584×42 tires?

    • Good question. If it were my only bike, probably not. 650B x 42 mm tires are incredibly versatile, and there are no compromises in making a bike for them. However, since I do have another bike with 650B x 42 mm tires, I probably would have made the Mule for wider tires… Fortunately, the tubeset is suitable for both tire/wheel size combinations.

      • thebvo says:

        Are there fenders to fit 650Bx48mm tires?

      • Fenders ideally are about 18-20 mm wider than the tires to provide good coverage. However, fenders wider than 62 mm don’t work with road chainlines, as the chain hits the fender in the smallest gear. The best solution (unless you use mtb cranks) is to run a 62 mm-wide fender, but place it a bit higher above the tire. It works fine, but it doesn’t look as nice.

  2. buckyrides says:

    I love bicycles like this but why do they have to be so retro, why not update just a little with things like handlebar shifters vs downtube shifters.

    • The Mule needs to pack for Rinko, which requires removing the handlebars. Downtube levers greatly speed up the disassembly time – nothing to disconnect. Furthermore, I find them easier to use – when I let go of the handlebars, my hand automatically drops onto the shift lever, no matter which position on the bars I am using. Brake/shift levers tend to work best from the hoods, but require a bit of a stretch from the other bar positions.

      However, it would be easy to install modern brake/shift levers on the Mule. It’s really a matter of preference that doesn’t change how the bike rides.

  3. William Chitham says:

    Your Mule looks like a cracking bike. As far as I can see it has a lugged frame, is the bb shell custom made (or maybe bi lam?) or is there an off the shelf item made for this mix of tube sizes?
    William Chitham.

  4. drewdevereux says:

    It may be that bikes with low trail (lots of fork offset) are more prone to shimmy. Dave Moulton wrote an article about the subject awhile back. Having ridden many different bikes over the years, I prefer frames/fork designs with lots of trail. Easier to ride hands off too. The only time I ever got shook up was on a custom Woodrup touring bike, which had lots of fork rake.

    • Shimmy is a multi-variate problem, and there are many factors that affect it. High-trail bikes can be easier to ride no-hands, if they don’t carry a load. With a front load especially, they are much harder to ride no-hands due to their greater wheel flop… It’s all quite complex, which is why we spend so much time studying bikes…

    • Matthew J says:

      High trail bikes definitely do not like front loads.

      My road bike has classic Italian 1980s road race specs. It carries several days worth of clothes in a large saddle bag no problem. But a handle bar bag with my Swarovski 10×50 binoculars (which are considered very light in the world of binoculars) got the steering all squirrelly.

  5. MC McBain says:

    I’ve been wondering if replacing the downtube from the Superlight package with a 08/05/08 Columbus SL downtube might achieve somewhat similar results as the Mule as far handling a camping front load. Thoughts?

  6. Shu-Sin says:

    The first touring bike I built for myself was made of oversized tubing that was 9/6/9, if I remember correctly… and the frame was a square 56cm. I’m 5’10”, 140lbs. The bike had shimmy at moderate speeds.

    Earlier this year I finished my second touring bike, this time using superlight tubing, with standard TT and oversized DT, and this time the frame is 59cm/57cm. I took it on a fully loaded tour for two months across Europe this past summer. I had a handlebar bag, two large front panniers, and two medium rear panniers. The bike is Rinko ready and that’s how I travelled when it was necessary. Half way through the trip, I started to have a slight, but quite scary shimmy at very high speeds (mainly when descending mountains). At first I thought it must’ve been the wind, or imbalanced load, or perhaps grabbing the handlebars too tightly. But it was only recently that I realized it was from Rinko-ing/un-Rinko-ing the bike and not tightening the needle bearing headset enough after certain re-assemblies. After ensuring the headset is tight when assembling it now, it never exhibits any shimmy.

    Regarding a loaded rear: I had the majority of my load in the front panniers and handlebar bag. The two rear panniers were for light, but bulky items like sleeping bag. ( This is what the loaded bike looks like. The photo was actually taken half way through my tour, so that is the actual load and actual setup) I had no trouble getting out of the saddle and really rocking the bike when going up steep mountain roads. The advantage of having the rear load was having more traction when going uphill offroad.

    I would assume the only disadvantage is when riding the bike without load. It’s just not that fast. It’s a beast though when it comes to carrying a load. It’s a mule!

    • Jacob Musha says:

      That is an awesome bike! What front-end geometry did you use? Does the bike have low-trail, and is that why you only put lightweight items in the rear panniers?

      • JO says:

        We pack our Santana tandem a similar way for long trips. Flexible frames that feel great unloaded can noodle uncomfortably with a heavy rear load.

        Our first trip on the Santana was the Great Allegheny Passage (GAP) Trail and C&O Canal Trail from Pittsburgh to DC with two large Arkel Panniers on a Blackburn rear rack. There was so much flex and shimmy when standing that it felt dangerous (and we dropped the timing chain twice).

        After reading about Jan’s adventures in Japan (BQ 48) we rode the Camino Santiago (mostly off road) with only a Berthoud handlebar bag and smaller Arkel panniers on a low rider front rack (staying in hostels and small hotels) with no shimmy and cleaning uphill dirt sections that had MTB guys walking.

        This past summer we did a camping trip around Crater Lake from Ashland, OR. All the cooking gear, clothes, tent and food were up front in Berthoud panniers with the sleeping bags and mats in the small Arkel panniers on a rear porteur rack. Great handling, no shimmy and the Compass Rat Trap Pass tires smoothed out Oregon’s chip seal back roads.

        With good weight distribution on a loaded bike, the frame flex can once again work with the rider(s) so they can go back to enjoying the ride!

  7. thebvo says:

    I’m not sure how a stiffer downtube plays a role in loading up lowriders on the front wheel. Isn’t all the weight on the wheel and not on the frame? Weren’t you talking about getting lowriders made for your Herse? It doesn’t seem that different from the other (superlight) tubeset.

    • The front wheel carries the weight, but the load still is out there, and connected to the rider through the frame. I was thinking about having low-rider made for the Herse, but then decided that the Mule would fill that role better. However, if you build a Superlight bike with low-riders, please share your experiences.

  8. Preston R Grant says:

    Jan, You recently stated that you weigh 154 pounds, a rather light weight for your height. I am about your height, but weigh around 180 pounds, and wonder if standard size superlight tubes would work for me on a rando bike. Now being an old timer, I do not pedal with the kind of force I did as a youngster. Your thoughts, please.

    • That is a difficult question. Everybody’s pedal stroke is different, people hold the handlebars differently, there are a lot of factors. I’d work with an experienced builder to figure out what they recommend for you. Among the BQ Team, Hahn is about your weight, but he also is very strong. He prefers OS tubing – but that will be the topic of the third part of this series…

  9. Preston R Grant says:

    Jan, Thanks for the response. BTW, due various joint/old age problems, I no longer use any attachment to the pedals. Have just completed a 30 mile test run with my new Allways pedals, and I am very pleased. Very good grip; very smooth bearings. With my current, less spirited, riding style, and these pedals, I do not miss being attached.

  10. ascpgh says:

    Looking forward to installation three on this subject and perhaps some mention of fabricators who are on your wavelength and open to builds.

  11. Mark says:

    Your post is very informative, I have a A Homer Hilson and a Atlantis from Rivendell, how do the tube sets they use compare to a Mule? I also have a Terraferma Randoneur with very light weight tubes that is quite fast (for me at least).

  12. gasconha says:

    That front bag looks huge! is it a custom Berthoud? I am curious about the volume and how does it handle as a bikepacking front bag?

  13. Paul says:

    Good stuff. This makes me wonder what fork blades you used on your mule. Any experience with a full low-rider load on the Kasai “Toei Special” or similarly compliant fork blades?

    • The Mule uses the Toei Special fork blades. No problems at all with low-riders – the rack is flexible enough vertically to allow the fork blades to move a bit, and the heavier load smoothes out the bumps, too. Laterally, the rack is very stiff, which is good for the handling. So I would have no qualms using the Toei Special blades with low-riders. With a porteur rack, as on my Urban Bike, it’s a different matter. That rack is stiffer and prevents the blades from flexing, so it would be better just to use stiffer blades. As it is now, rack and fork “fight” each other a bit, which leads to the rack bolts coming loose unless they are tightened almost to the point of stripping.

  14. David T. says:

    For individuals who are highly tuned to the performance of their bicycle, why not just take some sandpaper and sand off 0.1 mm from the middle of the top tube, then repaint? It would be easier than buying new bikes with the latest tubing, and would no doubt produce a world of difference in ease of pedaling for discriminating aficionados.

    • Just make sure you uniformly sand off the same amount all around the tube!

      More seriously, thinner-wall tubing must be made from stronger steel, which is why the Kaisei tubing we sell is heat-treated. This isn’t necessary for thicker-wall tubing, because there is more material.

      The idea that you could take an inexpensive part and convert it to a superlight one with a drill and file may be appealing, but it rarely works out well. The materials often are different. For example, reprofiling CNC-machined brakes or cranks to make them as slender and light as forged ones risks catastrophic failures.

      However, it is possible to improve your bike. For example, filing the lugs after the fact will not just improve the aesthetics, but also reduce the stresses at the transition between tube and lug. If you have an older production frame made from thinwall tubing, but with thick lugs, it may be a worth while project.

  15. Pierre-Yves Gauthier says:

    Jan’s, I am not sure where to ask this question. I recently read your articles on tire size / rolling resistance and I am interested in building a 650b wheelset (with hopefully47mm) for my crossbike. The article did not touch on optimum / recommended internal rim width for this. Would 23mm internal be too much? Perhaps 21mm? Thanks!

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