Saberspark

Hi all, I've got an '03 Z Touring that I had two of the tires replaced on yesterday. I've currently got (due to what came with the car when I got it and a cheap used tire or two I needed for inspection last year):

225/55/17 in the front - the right tire supposedly being worn unevenly due to needing an alignment that I got over the weekend, which seems to have not exactly straightened the car out.

And in the rear I had the same. However, I just bought a pair of BF Goodrich Comp 2 A/S at the stock sizes, 235/50/17 with intent to replace the front with 225/50/17 when I can afford to. In the meantime, it's Goodrich in the back, old in the front

After getting the new tires put on, I went for a little drive around my area and found that even through gentle turns at say 45-50mph (around the speed limit) the slip light will occasionally trigger and of course limit acceleration from the pedal, which certainly isn't cool. It also went off a time or two if I hit a small bump in the road while pressing the accelerator.

It's not not a horrible issue at the moment, but I don't fully understand why it's happening. Tire pressure seems good too, as that was the first thing I looked at. I'm really concerned about driving in the rain that'll be coming up this week, which was one of the reasons I bought these tires in the first place.

If anyone could offer some helpful advice or information, it would be greatly appreciated. Thanks.

terrasmak

iTrader: (8)

https://my350z.com/forum/2003-2009-n...questions.html

Post #42

Saberspark

Thanks for that. So it sounds like the two biggest contributors to the issue are

1. The slight difference in tire size (that 5mm really makes a difference, eh?)
2. Possible layer on a new tire.

Now the question is - would I be better off if I had TCS disabled in the meantime? I guess that will really depend on how bad it is when I'm driving in the rain. I have a lot of curvy roads to drive on, so it's gonna be a rough time either way I guess.

terrasmak

iTrader: (8)

https://my350z.com/forum/tire_rim_calculator.php Try the calculater, plug in the front tire you're supposed to have and the one you currently have. The difference is not 5mm

Saberspark

Interesting. I came up with:

Diameter difference: -0.89" (-3.43%) - actually 22.6mm damn.

Now what does that actually mean for performance?

Oh, and as for the change I made to the rears from non-stock to stock:

Diameter difference: -0.93" (-3.52%)

terrasmak

iTrader: (8)

It means your front tires are taller than the rears and the computer can not compensate for normal conditions. Once you install the proper front tires, everything will properly work again

karlt

Saberspark,

With the tires you currently have, your rear tires are actually smaller in circumference that the fronts (not accounting for wear). So the TCS thinks the rears are spinning and cuts back the throttle.

Going with different size rears than stock will also change your speedometer calibration. A larger rear tire will result in a lower speedometer reading for the same actual speed.

Saberspark

Yeah. I knew ahead of time that by replacing the rears with stock that there'd be a bit of a height difference, but it turned out to be a lot more significant than I had first thought. Had I just decided to stick to the 55 size, and just increased it up to 235, I wouldn't have had any issues. Damn.

travlee

iTrader: (8)

live and learn.....

terrasmak

iTrader: (8)

I would have moved the fronts to the rear and installed OEM size fronts. That would be perfectly acceptable as far as the computer is concerned.

Saberspark

Really? I mean I know that it makes sense to have the larger ones in the back, but I didn't think the computer would be okay with it since there'd still be that difference.

terrasmak

iTrader: (8)

Back to the tire size calculator https://my350z.com/forum/tire_rim_calculator.php

Plug in the stock front tire and stock rear tire, look if there is a difference in size. Plug in the tire size combo I just mentioned, look at the difference, see if the difference is almost identical or very close.

That post #42 also explains a lot of this too.

Saberspark

Stock Front and rear: 0.39" (1.50%)

New in front, old in rear: 0.49" (1.84%)

I think I see your point. Double the difference with the new in the back versus the front.