Showing posts with label conversion. Show all posts
Showing posts with label conversion. Show all posts
Wednesday, March 11, 2015
Converting my Gunnar Roadie to low-trail 650B, part 2: First ride impressions
What was the fifth-coldest February on record in Madison provided me with many opportunities to work on the 650B conversion of my Gunnar Roadie. Two days ago I had finally reached the point where it was time for the first test ride. It was already late in the day and so I just went around the block—and was like “Woah! What's going on?!” Little did this have to do with the low-trail geometry of the bike, though. For the past five months I had been riding almost exclusively my fixed gear, studded tire Cross-Check, totally messing with my muscle memory of riding a “normal” bike. In any case, the ride around the block was sufficient to confirm that by and large everything seemed to work and Gunnar was ready for a longer test the next day.
On a beautiful spring afternoon I went out on the Southwest Bike Path, one of Madison's most popular bike paths. I got used to being able to coast and not riding boat anchor tires relatively quickly, and after that the bike mostly felt—not that different from its 700C build. I figured that wasn't a bad thing, and once I had cleared the busier sections of the path, I started experimenting to explore the handling of the bike. Putting into words how a bike feels is difficult. Probably the best way to describe it is that the bike goes exactly where I want it to go, with high precision. The smooth rail trail didn't provide opportunities for, say, high-speed cornering, but adjusting my line a bit felt very precise and required little steering input.
Low-trail geometry is sometimes said to feel unstable at low speeds, but I didn't really notice that. Riding with no hands can be another point where low-trail bikes are different. It should be noted that in general I'm not particularly comfortable with no-hands riding—I suspect that my scoliosis is part of the issue. When taking the hands of the bars, the bike immediately starting shimmying; however the bike stabilized and the shimmy stopped after only a few oscillations. I will have to explore this further. With hands on the bars, shimmy did not occur at all, despite using a regular ball bearing headset. (Roller bearing headsets with their increased friction are said to be a remedy for shimmy in low-trail bikes). Of course, I didn't do any fast descents on this ride.
What did feel weird was getting out of the saddle. It was very different from my Cross-Check, but also different from the 700C build of the Gunnar. However, it seemed like something that I quickly got accustomed to.
One thing to keep in mind with all this is that the bike didn't carry any load. I had taken off the Carradice saddlebag, and the Nitto front rack remained empty. For some low-trail bikes, having a front load apparently is almost a necessity to achieve acceptable handling. This doesn't seem to be the case for Gunnar, and I'm curious to see if/how things change once I add a handlebar bag.
A few remarks on the Panaracer Col de la Vie tires: Using the canonical Frank Berto chart, I pumped the front to 3.5 bar (~50 psi) and the rear to 4.1 bar (60 psi), making them about 35 mm wide (nominally they're 40 mm). While they felt fine, I must say that I didn't have a "magic carpet ride" experience compared to the 25 mm Conti Grand Prix 4000S that where on the bike previously. The Col de la Vie is, of course, what is considered to be a budget tire that didn't fare too well in the tire test by Bicycle Quarterly. Also, the SW Path is smoothly paved, canceling out the potential advantages of wider tires. Aside from subjective impressions, I did end up with a few personal records on Strava, despite not trying all that hard. I'll do some more performance tests on stretches where I more have reliable Strava data from Gunnar's 700C days.
Thursday, January 22, 2015
Converting my Gunnar Roadie to low-trail 650B, part 1
My 2002 Gunnar Roadie is the best bike I've ever ridden. It's fast (it's painted orange; so what did you expect...), looks good, is reliable. Since I first built it up in 2010, I've made some changes, but they were mostly minor -- Grand Bois handlebars replaced the modern bars, as did a 1" steel stem the 1 1/8" aluminum stem, and I upgraded to a generator hub. But now it's time for something more drastic: Converting to 584mm/650B wheels and a fork that will make the bike low trail.
Converting Gunnar is thus the answer to these two points, unlike converting my Cross-Check with ample clearance for wide tires and fenders. I'm on a tight budget and so I spent several months accumulating the parts required for the conversion: A 1" threadless Rawland Stag fork, Shimano Ultegra 6600 rear hub, Shutter Precision PV-8 generator hub for the front, Pacenti SL-23 rims, Sapim double-butted spokes.
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| Gunnar with 25-622 wheels/tires |
Why change an already great bike?
There are two main reasons for this project. The first one is that there is one shortcoming of the frame. It was built to accommodate tires up to 25mm wide, without fenders. I can actually make 28mm tires work, but the clearances at the chain stay then get a little sketchy. Relatively narrow tires have served me pretty well so far. A good tire in combination with the compliant carbon fork make for a comfortable ride, and I've even ridden pretty rough gravel roads on Gunnar. The lack of fenders, on the other hand, is limiting, turning Gunnar basically into a fair-weather bike. I have little patience for getting road spray all over myself, and when the forecast predicts rain, I therefore switch to my fully-fendered Cross-Check. The reason for going to low-trail at the same as changing wheel size is curiosity. Bicycle Quarterly, my favorite bike magazine, has long praised the advantages in handling that low-trail geometry and front loading can bring. Now I don't nearly perceive high trail and rear loads as pernicious as some people make it to be. I regularly ride my Cross-Check with two Ortlieb Back-Rollers full of heavy groceries and yet I'm still alive. But then of course I lack a point of comparison.Converting Gunnar is thus the answer to these two points, unlike converting my Cross-Check with ample clearance for wide tires and fenders. I'm on a tight budget and so I spent several months accumulating the parts required for the conversion: A 1" threadless Rawland Stag fork, Shimano Ultegra 6600 rear hub, Shutter Precision PV-8 generator hub for the front, Pacenti SL-23 rims, Sapim double-butted spokes.
Brakes
Currently I'm running Dura-Ace caliper brakes with a reach of 44mm. Switching to 584mm rims necessitates another 19mm of reach for a total of 63mm. At the local community bike shop I found a pair of Mafac Racer centerpull brakes that at least should work for the rear. The Stag fork is intended to be used with cantilever brakes; so I might do centerpull in the rear and canti in the front.![]() |
| Nice pair of Mafac Racer centerpull brakes |
Clearances
There are two, interconnected challenges with the conversion, tire clearance and ground clearance. As I said, currently the largest 622mm tires that fit are 28mm wide. A 584mm wheel moves the tire further towards the hub and therefore increases clearance at the chain stays—but not by much. The way to figure this out in advance is to measure the distance between the chain stays at 320mm distance from the rear axle. I got about 40mm, but the measurement is a little finicky. So in the best case, I could fit a 38-584 tire without fenders—which of course somewhat defeats one of the main reasons for this conversion—or a 32mm tire with fenders. With the latter option then comes the question whether my pedal-to-ground clearance is still going to be sufficient. When using a typical wide 584mm/650B tire like the Hetre with its 42mm diameter, the outer diameter of a wheel is actually about the same as that of a 622/700C wheel with 28mm tires. Using a narrower tire will lower the bottom bracket and consequently lead to potential pedal strike in corners. The Roadie probably has a bottom bracket of 70mm (though I have to confirm this by measurement), which is on the high end for a 650B conversion, especially when running 175mm cranks.Headset
Low-trail bikes can have problems with shimmy more frequently than high-trail bikes. One possible remedy is the use of a rollerbearing headset to slightly increase friction. For now I will stick with the headset I already have and see how it goes.
What's next?
I'm still waiting for some wheel parts to arrive before I can build them up. I also haven't decided what to do about tires yet. I'm hesitant to spend a lot of money on tires that then potentially are to wide to fit the bike. I could also potentially go for narrow-ish tires in the rear and 42mm tires in the front—but that doesn't make that much sense given the load distribution of a bike. I will report back once I'm getting closer to completion of this project.
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