WTRSCCA, tire sizing guide

One thing to keep in mind when sizing tires for "spirited" driving (autocross, road racing, etc...) is that wider is not always better. The width of the tires need to be matched to the width of the wheels.

A good rule of thumb is that the wheel width needs to be within a certain percentage of the tire's section width:

70% - regular street driving
80% - "spirited" street driving
90% - hard-core handling (autocrossing, road racing, etc...)

So, for the following tires:

Width100%90%80%70%
28511"10"9"8"
27511"10"9"8"
26510"9"8"7"
25510"9"8"7"
24510"9"8"7"
2359"8"7"6"
2259"8"7"6"
2158"7"6"6"

The reason is that the wider the tire, the more the sidewalls bulge out from the rim. the more bulge, the more the tire can squirm under the rim. In extreme cases, the tire can actually pull away from the rim and you end up with an instant blowout (though this is more likely to happen to a wheel that's TOO wide.)

It's very possible that a smaller section width tire will handle better than a larger tire with the same wheels, despite the larger tire's wider tread.