Originally posted by mrwhipper
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Furthermore, tire pressures for the Kat's safety stickers are listed as minimums for a 140 lb (wet, geared-up) rider riding solo on the Macadams (98+ Kat 600) or Dunlop 205's (98+ Kat 750). Most riders weigh quite a bit more than that, esp. with cargo/passenger/gear/etc.
Let's do a little though exercise that a Metzeler engineer once taught me (this is not verbatim, but covers the same points):
Imagine the bike sitting there on the tires set to their minimum pressure and with no rider on the bike. Think about the size of the contact patch and how much the bottom of the tire is flattened out at that point. Got it so far?
Good...
Now we know how the tire builds heat for modern tires is controlled (literally) by how big that deflection patch is (and the angle the belts/carcass deflects to hit the contact patch and come back out of it)...
Now imagine what's going to happen to that tire once you add on your weight to it. The patch will get bigger, the angles of the tire coming into and out of the contact patch will be larger, and the tire will run hotter as a result. This extra heat and the extra drag as the rubber chunks deform/reform as they come into/out of the contact patch is what causes tires to cup and scallop.
The right answer is to increase the tire pressure to keep the contact patch (and the angles leading into/out of it) the same size with you on the bike as it had been at minimum pressure with you off the bike. Doing this will put the tire back into the right operating temp and will prevent cupping/scalloping (and if existing cupping/scalloping isn't too bad, may wear the tire back to even). And because the tire is now back to the shape it was engineered to be, handling should improve significantly AND tendency towards hydroplaning in the wet will decrease at the same time.
I don't know what Bridgestone's specific recommendations are, but I can tell you that if the tire is cupping out, the tire pressure is (by definition) too low for the total weight on the tire, and it's running hotter than it should as a result.
Cheers
=-= The CyberPoet
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