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Old 06-26-19, 10:09 PM
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Carbonfiberboy 
just another gosling
 
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Join Date: Feb 2007
Location: Everett, WA
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We have had our best results running 28mm Conti 4KIIs, both at 95 lbs. They measure a bit over 31mm on 23mm outside dimension rims. We weigh about 325 all up except for water. We've toured at about 375 lbs. on narrower, real 28mm tires at 115 lbs. on narrower rims. To get some idea of where you are on this, you can contact manufacturers of candidate rims and ask them for a table of max tire pressure vs. tire size. As tire size goes up, rim manufacturers call for lower pressures to reduce the outward force on their rims. I think if you are disk braked you can more safely exceed those pressures by some small amount as you don't have to account for rim wear.

To make a comparison of similar tire drop from different size tires, I do a simple calculation. So we run 31mm tires at 95 lbs. 31*95 lbs.=2945. 2945/28 = 105 lbs. See what I did? For us, ~3000 is a good starting number. For us touring, we'd go 28*115=3220 or 3220/31=104 lbs. for our Conti 4KIIs, Their max sidewall pressure is 115.

If you do these calculations, check out the max recommended pressures. You'll find that not every tire will even be a candidate no matter what size it is. The numbers we are using come from experience, not from any table - we don't pinch flat at those pressures, not even on RR tracks. For some tires it will take some research to discover their inflated width on your candidate rim.
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