Mark V’s ultimate modal concept bikeComments
by Mark V on Nov 10, 2011 at 9:02 PM
It’s been about 7-8 months that I’ve had my custom titanium travel bike, built by Seattle’s Davidson Cycles. I designed it down to the millimeter based on my own experiences of riding, assembling, wrenching, and designing bikes for myself as well as others. This bike replaces a custom steel Sycip bike that I got in 2005 and took to 20 countries across 3 continents. Like the Sycip, my Davidson MkV (“Mark Five) is fitted with S&S couplings so that I can pack the bike in an airline-friendly travel case. Also like the Sycip, I designed the MkV for maximum versatility so that it could be the best bike for almost any occasion, in potentially any location.
Improvements over my previous design are better tire clearance (I can even cram on a 30mm cyclocross tire), rear eyelets for a rack, and an 1.125” steerer. I also added a couple features that Davidson hadn’t used before, like the 44mm ID head tube for an internal headset and an integrated seatpost. Besides the coolness factor, these two features had concrete advantages for my particular design. The 105mm head tube leaves room for the 35mm top tube and 38mm down tube to be welded on without overlap, but the very short stack of the internal headset allows me to run the bar really low. I don’t think my handlebar position is all that extreme, but for most bikes I need a 17deg down stem slammed on the headset. The MkV is the only bike I own with a 6deg stem.
The integrated seatpost was a risky design choice because it’s nearly impossible to know exactly how the bike will fit in the travel case until you’re actually packing it. There was a chance that the additional height of the extended seatmast might not fit in the case, though I had considered it quite carefully. Thankfully, the seatmast did not turn out to be an issue at all. Indeed, the MkV fits in the case easier than the Sycip even though the MKV has dramatically larger diameter tubes. This is most likely due to the subtler s-bend on the titanium seat stays (compared to the Columbus Zona mtb stays on the Sycip), making the rear triangle slimmer. Will Meyers, the primary builder at Davidson, really nailed the shaping of the seat stay, custom bending the tubes on a jig designed by Bill Davidson. However, my bike is quite small; a seatmast would not work on a more typical size of bike. For my bike, I calculated that I’d save close to a net 100gr with the integrated seatpost design versus a conventional design (factoring all the fittings and titanium tubing), and as I said, it looks cool.
I also had the shifter housing stops welded onto the sides of the head tube. I thought that maybe the cable-splitters for the derailleur cables might rattle less if they were pushed out to the sides of the down tube rather than being suspended directly beneath. Did it work? Yes and no. On mildly irregular surfaces the bike runs quieter, but on truly bumpy roads those splitters jangle horribly (though they’d make noise to some extent in any configuration). Worse: the proximity of the stops to the handlebar, which of course sits very low on my bikes, means that shifter housing is stressed hard whenever the handlebar swings to the extreme right or left. With very careful fitting I’ve gotten just the right length of housing so that it doesn’t kink or break. The stops on the head tube would probably be fine on a non S&S bike with a tall head tube, but I don’t know if I’d do it again for my own bikes.
The Paragon Machineworks titanium track-style dropouts with derailleur hanger are very important to the multi-mode concept. With a 130mm spacing, I can run a standard width road hub to put the bike into any derailleur’ed configuration: crit/road racing, geared commuter, touring. With the track-style rear-entry dropouts and Phil Wood track hub custom-ordered with 130mm spacing, I can run the bike as a get-around urban fixie, or fully badass velodrome-legal racer.
Let’s get one thing straight: no bike can be the best for every situation. My modal concept is all about identifying what’s most important in each situation and then finding the optimum compromise for the frame design. Track geometry is different from road race geometry, which is different also from touring. I knew I’d be using the MkV primarily as a road bike or road fixie, so the geometry is biased towards those situations. The bottom bracket is quite high relative to touring bike, for instance. The chain stays could have been shorter if the bike was going to be primarily a fixed gear/track racer, but while in multi-geared mode I didn’t want to have to pull the wheel back to prevent the tire from hitting the back of the seat tube. So the chain stays are exactly long enough to prevent a 28mm tire from rubbing. I designed the bike with meaty tubing for stiffness, and I knew that bike wouldn’t be a lightweight. At 3.4 pounds with couplings, it’s not quite a tank, but I own bikes with barely 2/3rds the frame weight.
In the Modal concept of bike design, the frame is one-half of the bike and the other half, the component kit, is meant to be readily interchangeable. For the MkV, I have two saddles, 4 handlebars, 2 cranks, 2 sets of pedals, and several wheels. All the parts were chosen and assembled in such a way that I can configure the bike into any mode within 20-25min.
I’ve ridden the bike as a fixed-gear, as a road bike, as a TT bike, and with an archaic Paris-Roubaix suspension fork. Someday I’ll need to try out the touring mode, getting a 2nd fork for low-rider racks and panniers. I’ve taken one airline trip, overjoyed that packing got easier. The MkV handles beautifully…stable on a fast descent, yet crisp and precise in a turn. Stiff in a sprint, yet fairly smooth on hellish surfaces. To me this bike is the solution to the most potential questions to be asked. In this case, titanium is really the optimal material for the task. It’s relatively light, impervious to corrosion and most abuse, can be bent into versatile shapes, and readily works with S&S couplings.