Thanks, Dave. That's kinda what I thought but hadn't ever heard 245/40 was a "bad" size so it through me off a bit.

 

sounds like a wheel balance issue...did you get them balanced after you put on the tires?

 

Yes, but I would say the /40/ part is fine, its the /35/ that isn't acceptable, unless its a 315/35/18

 

ok so what if you were to run the same width wheel all around?

for ex. 18 x 8.5 all around. Is it safe to go 245/40 front and then 255/40 rear?

 

I would go 245/40/18 front and 255/45/18 rear, this matches the stock heights closer than your suggested setup

 

oh really? im confused now because while using the tire calc i put in the old tire size: 235/50/17 for the rear, and new tire size 255/45/18 and the difference was 2.9% which is a bit high for me.

but this leads me to another confusing turn. Am i putting in the RIGHT old tire size??

now im pretty sure i have a touring (04, leather[heated,power], bose, cruise) but when i bought from the dealer it came with these wheels:




so should i be putting in the old tire size 235/50/17 or the other touring size 245/45/18? or does it not matter?

 

there is a slight difference between the 17" OEM tire sizing and 18" OEM tire sizing. the 255/45/18 I suggested is closer to the 245/45/18 tire size than the 255/40/18, but if you are comparing to the 235/50/17 then the 255/40/18 is probably closer. Either should work, and the rear tire is still taller than the front which is good, up to you which one is best, neither is optimal.

 

hmm so what is optimal? a 265 in the rear?

 

Keep it simple… Instead of thinking in terms of width and aspect ratio, simply select tires that match the stock overall diameter:

Front: 25.9" (Overall Diameter)
Rear: 26.7" (Overall Diameter)

The width is important when matching the tire to the wheel, and the aspect ratio (second number) is important as it relates to the width (which determines the sidewall height and thus, with the wheel size, determines overall diameter).

--Spike

 

Just ordered 2 255/35/18 Gforce's for the front. Now Ill have 275/35/18 rear and 255/35/18 front. Thats a pretty good sidewall difference.

 

I just recently ordered some new wheels and tires, and this statement worries me. I have incoming some 19x8.5 19/35/245, 19x9.5 19/30/275 wheels & tires. Is this going to be an unsafe performance issue? I do drive my Z on mountain roads, and would hate to have some abnormal steering issues.

I haven't had the wheels installed yet, so if you get back to me ASAP, I could likely change the tire order to 19/35/245, 19/35/275. I only paid $530 for a set of Nexen 3000 tires, so got a pretty good deal.

 

change the rear to 275/35/19. This is the correct aspect ratio

 

Change out to the proper rears , and if you can, swap up to a better tire.

 

Perfect size for the Z IMO

 

I called my wheelshop. The wheels & tires are in, and I need them on my car badly... I'm parked on tire wire. They said Nexen doesn't make a 275/35/19. Will I be okay on Front 245/35/19, Rear 275/30/19. What issues might I expect with the slightly off tire size for the rear?

I'm sticking with Nexen because I can get them for so cheap... trying to save money on this first set of tires to counter the pocketbook weight of the wheels.

 

If you have VDC you screwed yourself. The front tire has a larger diameter than the rear! Get ready for FIAL.

If you don't have VDC the worst it will be is very ugly and handle weird.

Good luck!

JET

 

Use this calculator when determining your next tire size(s):
http://www.1010tires.com/tiresizecalculator.asp

 

Interesting thread...lol. I did some calculations for overal diameters in inches for grins and giggles

Stock (225/45/18F 245/45/18R)
25.9724409" front
26.6811024" Rear
R:F ratio is 1.027:1


Original Poster's specs:
25.7165354" front
25.5787402" rear
R:F ratio is 0.99:1 (EEK!)

Well, at least the problem was found quick and major disaster was avoided Hope you get the right size tires next time

 

Short answer: NO!

Again, you will be in the same boat as the original poster...your fronts will be larger than your rear! AAH..fail.

 

I have 245/35/20's on the fronts and 275/30/20's in the rear on my set of Iforged Sprints, while I don't have VDC/TCS, it definitely doesn't handle poorly or feel dangerous in the slightest (and I have 20's!).