Piston Slap: Compact Tunerz Edition

Sajeev Mehta
by Sajeev Mehta
piston slap compact tunerz edition

TTAC Commentator Heath writes:

A couple of months ago I got the SVT suspension for my Focus. Not want to blow the budget any more I left the 205/50/16s that the Focus came with and there is a unhealthy amount of sidewall flex with the 50 (Pirelli P6). The SVT had 215/45/17.

My question is when its time for new tires, should I go for 40 or the 45. I’d like to stay on the 16″ rims as don’t really want to get new 17″ rims as well.

Sajeev responds:

If you stay with 16″ rims and go for a lower profile tire, the change in circumference messes up the speedometer, gearing (lower profile means more gear and less economy) and increases the unsightly gap between the tire and the body. We did this for TTAC’s entry for the 24hours of LeMons, and the gearing advantage was totally worth it. On a street car? I doubt it.

If you compensate by fitting a wider tire (225/45/16, for example) on a stock wheel, the tire’s outer tread blocks will not meet the road, and it’ll look like the back end of a steroid-injected baseball player. Which is phat. Except when its not.

So I don’t recommend this. I’ve never seen anyone recommend it. Here’s my question back to you: don’t you want a more responsive tire with more grip? One of my cars still has 60-series tires, and its quite good. I run the stickiest summer tires and their level of precision is even more appealing than keeping my cosmetic tire-to-wheel-to-body ratio in check.

Kevin writes:

Sajeev, I need some more speed in my Astra XE 5MT. It’s new to the US I know but lots of them sold in EU, Brazil and elsewhere since it was introduced in 2005. Isn’t there a 1.6 L turbo version in some markets? Or could I get some GTC parts somehow?

Sajeev responds:

From what I’ve read, you can swap an Ecotec 2.0T or its successor (in Europe), the 1.6T. I would join the appropriate forums to learn the differences between the 2.0 T in the Cobalt SS and the Astra. If the 1.6L is better, find a parts supplier in Europe and ship it here. I’m hoping the 2.0T from the Cobalt works because it’s a well-known package for stateside tuners and finding parts will be a breeze.

Either way, slap the turbo motor in, get a higher flow exhaust, custom tune on a chassis dyno and you should be good to go. Also check the differences between the turbo clutch and yours. And getting a limited slip differential will certainly help the massive torque steer you’ll encounter.

I applaud your creativity, but take it from the guy with a one off, 6-speed, Mercury Cougar: you’d better love that car. Nobody in their right mind will pay anywhere near your final tab for this tweaked Saturn. Not to mention that you (and me) can probably buy a far superior performance car for the same price and much less effort.

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2 of 25 comments
  • Sajeev Mehta Sajeev Mehta on Mar 09, 2009

    Nobody's saying F1 sized tires are right for street cars, just that it proves the point that shorter isn't always better. And maybe we should narrow the scope to one street car: extensive testing of the new M3 showed that it was faster around a track with 18" wheels than 19". Hence why BMW actually has 18" wheels as an option on the car. Heard this from Steve Dinan, FWIW. That guy has resisted putting 20" wheels in his catalog for a while, only now is he making it happen because everyone wants them. That said, going to 17" wheels on Heath's Focus would be nice, but sidewall flex from his 16s isn't reason enough to lower the profile of the tires for that particular 16" wheel.

  • MBella MBella on Mar 09, 2009

    rpn453: Changing offset definitely affects wheel bearings. Tire width can affect wheel bearings. Rim diameter itself will not affect wheel bearings. Yes, but as long as overall diameter, offset, and width are the same, wheel bearings will not be an issue unless you hit something if you decide to go to 17"s form 16"s. You can get some affordable wheels now in 17" sizes. If you take into account that if you buy a wheel and tire combination, tire rack will mount and balance it for free. If you just buy tires, you will have to pay to have them mounted on your old rims. Also, if you plan on using the car in the winter, you need other tires anyway, and you can have snows mounted to the 16"s, and won't have to go to a tire shop every fall and spring.

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