Old Tires, Higher RR?

[Hockey4mnhs]

yup i think im gonna invest in lrr tires soon

[thisisntjared]

Originally Posted by theclencher

Contact patch is largely a function of weight vs. tire air pressure, so, I doubt it.

and the elasticity of the treads has nothing to do with contact patch? no matter what compound, the lower the tread, the less elastic, right?

[Bill in Houston]

pretty sure clench is right. it would only change in extreme cases where the sidewall starts to support a lot of weight, usually possible only in a verrrrry low profile tire or a run-flat.

[caprice]

I replaced bald tires with a set of 2 year old hardened stock tires from a diesel pick up and I got worse braking traction. Also had other experiences with using older tires. I test drove a Mitsubishi eclipse with dry rotted back tires that made it want to slide out on turns. Usably the old tires had little visible cracks too.

[Bill in Houston]

Oh, yeah, the traction is DEFINITELY going away. Time for new shoes...

[brucepick]

One thing with new tires is the diameter is larger due to tread not worn away.
So actual distance covered per rotation is more - but your speedometer doesn't know this.

The difference vs. a half-worn tire isn't that much - but vs. a worn-away tire the difference is more. If you make speedometer stay at same speed you used to (with worn tires) the engine is actually working harder because it's driving the car faster. But the odometer shows slightly less miles.

If you stay off the gas a bit you likely will get better ACTUAL mpg but it won't show on the odometer. Like having a slightly taller final gear ratio.

[Bill in Houston]

Originally Posted by brucepick

Like having a slightly taller final gear ratio.

I can use all of that that I can get. :-)