Tire Question?

[Cat]

Our Z's come with stock tires of this size:

Front-265/40/17
Rear-295/35/18

Our selection of replacement tires is pretty darn limited. It seems to down pretty much to F1s again or Pirellis or Michelins at about $1000 to 1300 installed, and that is pretty darn steep for tires that don't hang in there but about 10,000 miles from what I read.

Here is my question. Perusing the tire websites, I have found that there is a metric buttload of tires in the 255/40/17 and 285/35/18 sizes, and they tend to be an order of magnitude cheaper besides!

Aren't these sizes like only 10mm narrower than stock, and for general non-speedy driving wouldn't they work just fine on stock rims? Not being mechanically minded I haven't the vaguest. I just know I don't want to get hammered for four bills for tires!

Thanks for your input, guys.

Miao, Cat

[JimGnitecki]

I will preface this by saying that I'm not sure about this, but here goes:

When I had my C4 (95 Convertible), I lived in Minnesota, used my C4 as my daily car, and contacted Chevrolet about the advisability of mounting snowtires on it for the winter for safety reasons. Chevrlet said NO.

The reason they gave was that the ABS, traction control, and active handling systems were calibtrated for the OEM tires, and a change could lead to some unpredictable and undersirable system responses in the event of a loss of traction or directional stability.

I don't know if this still applies.

It is also possible that Chevrolet was just being very liability conscious, and that the net result might not in fact be dire.

I think you need feedback on this from someone with stronger technical knowledge than most of us on this forum might have.

Jim G

[350bob]

I used to work on the ABS/TCS/Active handling systems for GM. You are correct in saying that tires can have a negative affect on the performance of those systems. However, it really depends on the tire you choose. If you get a normal street tire, the chances are that the electronic brake systems will work pretty much the same. There may be some situations where the systems don't work perfectly, but they will still attempt to do the best job they can with whatever tires are on the car.

As for snow tires, there is actually a Goodyear snow tire made specifically for the C5's (maybe not the Z06, though). And this tire was tested to a point by GM for use with the electronic brake systems.

Regarding the use of reduced width tires, the width isn't so much of a problem as the aspect ratio. The aspect ratio is the center number of a tire size (35 and 40 in this case). This number means that the tire sidewall is X percent as tall as the tire is wide. For example, the front Z06 tire sidewall height would be 0.40 x 265mm = 106mm. If you reduce the width, the sidewall height goes down also, which reduces your rolling radius. The more the rolling radius changes, the more your speedo will be off as well as the electronic signals that the car's computers use. Whether the 10mm change in width is a big deal or not depends on your point of view. Personally, I don't think it's too big of a deal. The best thing to do is to find tires that also have a different aspect ratio along with the width to keep your same rolling radius.

[Cat]

Thanks

I had traction control kick in today when I hydroplaned in the rain. It was most excellent to have it there.

Miao, Cat