On Saturday, January 4, 2014 12:17:13 PM UTC-8, ted wrote: > > 3) For a given tire increasing pressure reduces rolling resistance. >
It depends what you call rolling resistance. If you define it as only the hysteretic losses within the tire, then it's true. However, if you are looking at the OVERALL resistance of the bike, then increasing your tire pressure beyond a certain point doesn't gain anything at all! You just bounce more. So your tire doesn't flex much, but you flex more - the end result is a draw on very smooth roads, and probably a loss on rougher roads. This fact, which is well-documented by now (we ran several tires at pressures from 30 to 200 psi in 10 psi increments), is the reason why wide tires can be fast. If high pressures were faster than lower ones, then you'd have to beef up the casing of wider tires to enable them to run high pressures, and you'd lose all the suppleness. So you'd have a choice of either losing speed due to a sturdy casing, or losing speed because you have to run low pressures. (The load on a wide tire is much greater for the same pressure than it is on a narrow one.) In reality, you can use a supple casing, run your wide tire at relatively low pressures, and you don't lose anything due to the low pressures, but gain due to the supple casing. This finding has revolutionized our understanding of wide tires. No longer is desirable to make wide tires that can handle 100 psi or more - it's in fact counterproductive, since such a strong casing cannot be supple. Of course, none of this is new, it just had been forgotten for a few decades. Jan Heine Editor Bicycle Quarterly www.bikequarterly.com Follow our blog at http://janheine.wordpress.com/ -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
