Originally Posted by almoniyot
I have an old (roughly 1990) Gitane Tour de France road bike (60cm) that has been with me since high school and is still in fine shape. The frame was handmade from Reynolds 531 and is equipped with all Mavic components all around (friction shifting). I want to equip the bike so it is better suited to doing some riding on dirt trails, though no cross racing or anything too rough. I currently have Michelin Tracer road tires size 700x25c, and there appears to be ample clearance all around. I am wondering if it is possible to fit Vredestein Campo 700x28 cross tires. Are there any type of measurements I could do that could approximate whether these tires will fit before I buy them?
Additionally, I am considering buying a new cyclocross fork (something inexpensive) with cantilever bosses attached. Any idea what size I would need? Any suggestions? I presume a new fork would require a new stem too. I already have someone that will weld on cantilever bosses in the back. I currently have shifters on the downtube, and would like to install bar end shifters. What type of bar-end shifter will work with my friction deraileurs?
I know the purists amongst you will recommend that I get a purpose built cross bike, but my budget really does not allow for that now.
When you add up all the costs of all that you're considering (new fork, stem, headset, adding canti bosses, shifters, brakes, cables, housing etc) you might well be better off looking for a used cross frame/ fork on Ebay or something. I often see inexpensive sets going for less than $200. You can keep your wheels, saddle, derailleurs, bar, etc and upgrade as these wear out/break or you can afford them. Honestly, your conversion using your current bike as you describe it probably isn't worth it and will cost more than you think when you add it all up. If you can fit 28c or wider tires on your current frame, then you can ride on dirt roads and smooth trails no problem just the way it is. If your tires won't fit under your (sidepull I assume) brakes you might consider a "downgrade" to the old centerpull brakes that have tons of clearance, stopping power and can be found cheap or free at your LBS or on Ebay, or hell, take a trip out to your county landfill, I guarantee you'll find a pair stuck on an old Ross or something.
If you want bar-end shifters, they all can be set to friction mode to use with any freewheel or cassette, so that's no problem with any derailleur. I'd guess that your frame could fit the 28c vredsteins without any issues, but the only way to know is to eyeball it or measure or try it out. If your 25c tires are a tight fit then probably a no-go. If you have 5mm's on either side of your current tires, youre probably fine for the frame, but the brake clearance may still be a problem- again the old centerpulls work great for cross riding.
Replacing your fork is probably not worth the cost, unless you already have a replacement. But if you insist, the size depends on whether you have a threaded or non- threaded fork. The steer tube on a threaded fork needs to be at least as long as the length of the head tube on your frame, plus the "stack height" of the headset you want to use, plus a few mm's for the cable hanger if you use one that hangs from the headset. Stack height varies by model, but 350mm is about average- check the specs on the model you want/have or measure it yourself. If the fork is a LITTLE (1-2 cms) too long you can fudge it with some headset spacers or just cut it down a little (careful! cut it square or better yet, have a shop do it). A new threadless fork comes longer than you need it to be, and you cut the steer tube down to length- based on the kinds of questions you're asking, I'd get a shop to install it for you and not try a do-it-yourself this time.
Its not so much about being a purist, but major modifications on an older bike are often much more costly than anticipated unless you already have the tools, used parts lying around, and like to tinker- it can get frustrating unless you consider the rebuild process as part of the fun.