Join Date: Apr 2002
Location: Montréal (Québec)
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I think I'm the posted you are referring to, and in my case, weight distribution mostly.
The typical unloaded bike (25" touring frame if that matters) carries about 60-65% of the rider's weight on the rear wheel. When I ride in the city, I often have anywhere between 3-15 lb in rear panniers, and when I tour, in spite of all my efforts to put the heavy stuff in front, my rear panniers are a little bit heavier than the front ones. Add to that the fact that I often tow my daughter on her trailercycle, which means it adds 20-30 lb to the rear wheel.
Regarding weight distribution, on our last tour, our bike+ trailer cycle + gear weighted 40 lb front, 65 lb centre (i.e. rear wheel of main bike), 30 lb rear. With both riders, it was 105 lb, 180 lb and 60 lb respectively.
Even by myself, I found that with 2 700x32 tires, I had to keep the rear tire at 90 psi to avoid pinch flats and the ride on pothole-infested streets was a bit harsh. By using a wider 700x37 tire on the rear wheel, I can keep the pressure at 75-80 psi, even when fully loaded.
As to why I don't use the same size in front?
1. The front tire is still the original 700x32 Continental Top Touring (only 10 000 km so far).
2. The front crown is a little bit too low to fit the 700x37 Top Touring with fenders. They would fit ok in fine weather or even in rain, but certainly not in mud... and the fender would need to remain perfectly straight! I could probably fit something around 700x35, or even a slightly narrower 700x37 (or a wider 700x32) than the Top Touring. However, since I don't have any comfort issue with the 700x32 Top Touring, I'll probably replace it with the same.
BTW, if I were doing a remote tour and carrying a spare tire, I would carry a 700x32.