Originally Posted by
jrich179
what took me by surprise (I did the opposite- went narrower- 32 to 28) was that I had to recalibrate my computer for a different wheel circumference. The compounding of that couple millimeter decrease in circumference resulted in a ride on the same route as my previous ride reading as 1-1.5 miles longer after I switched tires. Wild!
The 20mm difference in circumference
http://www.sheldonbrown.com/cyclecomp_c.html
would lead to a one mile discrepancy over roughly 100 miles... if my math ain't too wonky