New tires--any recommendations?

[Norm Peterson]

Those g forces would be the minimum requirements for the grades, so the 0.07 g is at best a rough idea (you could have a AA that tested at 0.55g and an A at 0.51, for example).

But to use your table numbers which assume just-barely-meet-min-spec tires you have to do a little math. Stopping distance is roughly equal to
[MPH]^2 / (30 x mu), where mu is the g-forces in the above tables (Highway Engineering 101) and it is assumed that those g-levels are maintained all the way down to a complete stop.

From 60 mph, the AA would be expected to stop in about 60^2 / (30 x 0.54) , or about 222 feet.

The A tire would take 60^2 / (30 x 0.47) , or about 255 feet

I'll leave your interpretation of the significance of 33 feet (or 64 feet vs 56 feet = 8 feet at 30 mph) up to you. But I think that 0.07g is a lot, and if I ever needed it but didn't have it, it'd be way too late to wish I'd chosen differently.

FWIW, I've found that once or twice per set of tires I really am looking for every bit of grip that my tires (and brake pads on initial bite) can give me. And that's in street driving, not autocross or other performance driving activity.


Norm

[Rhyder]

How would you quantify it when you include all four tires in contact at the same time? Wouldn't that skew the difference down even more?

I mean I've had to slam on my brakes on the highway around 60mph and I wouldn't think it took me 85 yards (255') to stop, most of a football field. I didn't measure it but that seems a long ways. Im guessing the four wheels on contact shorten that.

so in theory the difference between them would be much less.

[Rhyder]

well the graph here shows all four wheels still equal that, just seems like a long distance. Ill have to try it tonight....


http://www.csgnetwork.com/stopdistinfo.html

[Norm Peterson]

Originally Posted by Rhyder

How would you quantify it when you include all four tires in contact at the same time? Wouldn't that skew the difference down even more?

I mean I've had to slam on my brakes on the highway around 60mph and I wouldn't think it took me 85 yards (255') to stop, most of a football field. I didn't measure it but that seems a long ways. Im guessing the four wheels on contact shorten that.

so in theory the difference between them would be much less.

That 255' is with all four tires contributing. What that g-level really is, is the ratio between the rearward traction force at the tire(s) and the weight carried by each tire. If they're all working at 0.54g and there are no aero lift forces removing car weight from them, the car will decelerate at 0.54g.

Keep in mind that the traction ratings are for wet braking.

The tires fitted to at least SS-level and higher Camaros are good to something a lot closer to 0.9g. But let's be a little conservative and assume that in average hard use youo only achieve an 0.8g overall average rate of deceleration. 60^2 / (30 x 0.8) = 150 feet . . . which ought to "feel" a lot closer to your experience.


BTW, that stopdistinfo link is for dry braking (with nothing-special tires/brake system/pavement/driver).


Norm

[HP_atTheWheels]

great info, thanks

[sjspat]

Well, I just ordered the Hankook Ventus V12 EVO K115. Hopw they turn out ok. My Pirellis on the front are down to the wear bars with only 25000km (15000mi) on them.

[73vette]

Originally Posted by Norm Peterson

That 255' is with all four tires contributing. What that g-level really is, is the ratio between the rearward traction force at the tire(s) and the weight carried by each tire. If they're all working at 0.54g and there are no aero lift forces removing car weight from them, the car will decelerate at 0.54g.

Keep in mind that the traction ratings are for wet braking.

The tires fitted to at least SS-level and higher Camaros are good to something a lot closer to 0.9g. But let's be a little conservative and assume that in average hard use youo only achieve an 0.8g overall average rate of deceleration. 60^2 / (30 x 0.8) = 150 feet . . . which ought to "feel" a lot closer to your experience.


BTW, that stopdistinfo link is for dry braking (with nothing-special tires/brake system/pavement/driver).


Norm

Nice info!!