I pose the question because I will defer to someone more knowledgeable in this area. I am in the process of getting some new wheels and rubber for my 03 touring and I need some questions resolved regarding the proper F/R tire sizing to avoid the VDC issues. I have read most of the threads on this and other Z sites and have run the calculations regarding proper tire selection to maintain "stock" sizing between the F/R. All my assumptions are going with 18x8.5 F and 18x9.5 R. Here is my issue regarding some statements which have me confused.

There is this discussion regarding the 3% tolerance between the rotational speed difference of the F/R wheels. The stock calculations give the following showing a 2.7% difference:


Selection of comparable front tires going to a 245 width would give the following:


Seems good only 1% difference.

Selection of a 275 width rear gives:

Even better with less than 0.1% difference.

When comparing the new front and rear sets together is where I have some confusion because of the resulting rotation differenece:

This would give a 3.6% difference which I assumed would cause VDC issues, but is widely used.

I have also seen a 245/40/18 front and 275/35/18 rear setup on some Z's but comparison of stock R give the following difference for that rear:


This looks to be a poor choice for rear tires, but when you compare the differences of a 245/40/18 F and 275/35/18 R you get:

Which is a better match than the stock. See my confusion?! Is the final word the fact that the 3% difference is using the stock (2.6%) as the benchmark "zero" point so in actuality you can go any where within around 0-6% total difference. Hell, I guess you could jack the thing up and put 26" rims on if the rotational difference between F/R remained within the allowed range.

Here is the type setup that I was illustrating.


I have seen someone reference the front and rear rotational difference on another Z site using that 2.6% difference, so I figured that comparing F/R with that 1010 tire calculator was the easiest way to derive the numbers. My reason for asking was that there seems to be a limited number of tire makers that have a 275/40-18 tire so was curious about the 275/35 setup. May just have to go with 19".

Thanks for any and all clarifications.

Cheers,
ZGone

 

im running 18x9 fronts, and 18x10 rears with 245/40/18 and 275/40/18 (falken 452s). i've had no problems with VDC. btw, the tires are pretty nice, a lot quieter than stock, plenty of grip as well.

 

halcyon901,

Yea, I running the 452's on the stock rims now and they are great compared to the OEM Potenza's. I am still curious about the difference between the F/R rotational allowances because there have been some people reporting that if they change just one set of tires to a different maker the start having VDC issues even though they are the exact same size as what they were running. I have a feeling that since the rotational difference for the stock configuration is just below the 3% F/R allowance that running different manufactures F/R possibly throws the difference over the limit causing VDC issues. Do you have VDC on yours because the 245/40/18 and 275/40/18 setup would put you over that 3% F/R difference?

 

I have 255/40/18 front and 275/40/18 rear. Looking at the tire calc. both tires are the same rolling dia. as the 225/45/18 front and the 245/45/18 rear. I dont run these on stock rims, I now have 8.5 front and 9.5 rear.

 

3% is your magic #, good luck

http://www.miata.net/garage/tirecalc.html

I went to a 255/40/18F & 275/40/18R w/18x9.5 all around, was difficult to find tires in that combo, so went with Sumitomo, wanted the 452's but they don't make them.

 

It's all explained here...

https://my350z.com/forum/showthread....1&postcount=45

 

Geeze I would have to study all those numbers for half an hour. Choosing tires cannot be this complicated.