Old 10-13-09, 10:54 AM
  #5  
sooprvylyn
I suck, but you're worse
 
Join Date: Jun 2005
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It will also depend on your rims and which part of your frame will be first to get hit by the tire. If the seat or chain stays are gonna be hit first use a narrower rim and this will save a couple mm on tire width. if the rear bridge will hit first use a wider rim and this will save you a couple mm from the tire height.
The rim will only affect the tire width or height by 1-3mm. Also knobbier tires will tend to be wider and taller than tires without knobs. You can save a little room on height too if your tires don't have tall center tread.

keep in mind 5mm is less than 1/4 inch width. divide this by two=1/8 inch. do you have at least this much room between tire and frame on all sides? If so then you should be fine with the 40mm tires, just be aware of the knob height.
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