I asked my Tire Man..
"I have a quick question for you..will A tire thats say 1/3 worn give
> as good traction as a new tire ? Where's the break off point where a tire
> really won't give good traction at all..
>
> Thanks, Ted O.

He wrote back
"After about 100 or so miles is when a tire achieves its maximum traction wet,
however dry traction can actually improve as the tire wears. Once the tire has
about 3/4 wear on it, the carbon stiffens and you start to lose dry traction, but
wet traction seriously deteriotes about 1/2 worn on most tires. The only tire in
production today that is different from this is some Bridgestone tires,
specifically the tires constructed with Uni-T AQ-II, which maintains wet weather
traction as the tires wears by uncovering a grippy subtread that restores wet
weather traction to like new.
I quit Firestone about 1 month ago, if you hadnt heard through the grapevine.
Good company, lousy management in Baltimore.
Patrick