by rshon on Sun Dec 25, 2011 1:34 am
There is also the Bridgestone RE-11 and Hankook R-S3 which come in your stock sizes, and there is the Nitto NT-05, which is more of an AX/DE/TT tire than the Invo (but the rears would be a 335).
The problem with 18" tires in this category is that the sizes tend to stop around the 275-295 range, so you would need to somehow decide if you can give up the extra 10-30mm of rear tread width to use 18" wheels and tires (doing so would make the car a little looser; see below). It is O.K. to use smaller diameter tires so long as you keep the front-to-rear tire diameter ratio the same as stock (25.5/26.3 = .97 Front/Rear). Otherwise your ABS and/or PASM will start to get unhappy at the most inopportune times.
There should be no issues sticking with 19" wheels and tires, however if you should ever decide to change to R-compound tires (100TW and below) and want to use the same wheels, there currently is a better selection in the 18" tire sizes (and 18" tires are generally less expensive than 19" tires).
Now you probably know that the current Street Stock rules allow you to put as wide a wheel and tire that will fit under the fenders WITH NO PENALTY, so long as the treadwear is 140 or above, so maybe the other C4S drivers out there can tell you how much tire your fenders will hold, and what wheel offsets you will need to pull it off without rubbing.
Another consideration you might want to take into account is front-to-rear car balance. The rules for Street Stock severely limit your choices of sway bars to stock factory items that were available as either standard equipment or options on the car, and additional camber adjustment devices are not allowed. So besides slight changes in sway bar sizes, adjusting front-to-rear tire width may be the most effective tool you have to dial out some of the push all the late model cars inevitably come with, and may be a better choice than just fudging with tire pressures.
One possible approach would be to first get a performance alignment from one of the local shops (which will probably include maxing-out the [negative] front camber), run the car on the stock tires at the next autocross, optimizing the tire pressures for best grip front and rear, and then decide if you want your new tire setup to give you more push (more understeer), or be more loose (more oversteer), which is more likely. If you want more push, increase the rear tire width over stock, or if the rears are maxed-out, decrease the front tire width slightly. If you want the car to be looser, either increase the front tire width, or if your are limited by available tire sizes, decrease the rear tire width slightly, relative to the stock width. It's always best to start with a baseline of what you have, and then decide how you want to change it...
Russell
PCA Zone 8 Rules Tech Advisor
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