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How much slower is a worn tire vs. a new tire?(4 posts)

How much slower is a worn tire vs. a new tire?Fez
Dec 17, 2002 1:16 PM
Any opinions, objective or subjective, as to how much slower worn tires are compared to new tires?

I have some old Continentals 700x23 with 3,500 miles. The rear has worn well, but the contact patch is a 1 cm flat area of rubber. They ride fine and there is plenty of rubber left, but I hear a buzzing or squishing sound from these tires constantly.

The new tires (GP3000, 700x23) ride much firmer and quieter. Since they are new, the tread is rounded almost like a tubular and have no flat area yet.

Do the old tires go slower because the much larger contact patch from the flattened tread = more rolling resistance?

Or do the new tires flatten just as much due to rider weight and therefore have equal rolling resistance?

So what has more effect on rolling resistance - the roundness of the tire, or the rubber compound itself?
Not so's you'd noticeKerry
Dec 17, 2002 5:48 PM
The size of the contact patch on the road is the weight the wheel is carrying divided by the pressure in the tire. If there's 100 lbs on that wheel and 100 psi in the tire, you've got a 1 square inch contact patch. In metric units that's a 7 sq. cm contact patch if the wheel is carrying 50 kg and running at 7 bar pressure. The shape of the tire is meaningless (within the range of normal 20-25+ mm tires). Rolling friction from a tire comes largely from casing flex, and the casing will have to flex pretty darn close to the same amount to develop that contact patch.
Not so's you'd noticeFez
Dec 17, 2002 6:29 PM
So casing composition and rubber compound largely determine rolling resistance? And the rolling resistance would stay about the same throughout the useful life of the tire?
You've got it (nm)Kerry
Dec 18, 2002 5:12 PM