Tire Gurus: Stock 17" Wheel/Tire Setup to 18" Wheel/Tire Setup
 

NOTE: This was posted in the G35Driver forum as well...

I've done a few searches on the topic but I haven't found and acceptable answer...

G35 Coupe 5AT:

I'm planning on changing my stock 17" wheels/tires to aftermarket 18" wheels/tires. The wheels (4) are 18X8.5 +24 OS. Is there a problem with the two options below? The percentages (speedometer) shown are from the miata.net calculator if you deviate from the stock setup. I thinking of staying with the setup for the stock 18" tires but also considering other two options.

STOCK 17
225/50-17 F
235/50-17 R

STOCK 18
225/45-18 F (-0.4%)
245/45-18 R (-1.6%)

OPTION 1
235/45-18 F (-1.8%)
255/45-18 R (-3.0%)

OPTION 2
235/40-18 F (+1.8%)
265/40-18 R (-0.4%)

Any advice/help is appreciated. Thanks.

Norb

Option 2+

245/40-18 F
265/40-18 R

Lou

Thanks. Some others have proposed (Option 3)

245/40-18 F
275/40-18 R

What would be the correct offset for the wheels in these cases (Option 2+ & Option 3 without any fender rolls, etc.?

8.5" rim is too narrow for a 275 tire. Offset should be something like +25 or so.

Sorry. I forgot to mention that the rear wheel will be 8X9.5 with undetermined offset for the 275 case.

In that case, the 275/40 is the correct size for a 9.5" wheel. What do you mean undetermined:confused: That's sort of important.

Thank you for the responses LOWRIDER.

Undetermined meaning I didn't know what the correct offset would be. However, I did run Solidworks to see how the setups below would look and checked my numbers with the marksink.com & miata.net numbers.

245/40-18, 18X8.5 +25 --- OK, tire will be flush with fender

265/40-18, 18X9.5 +24 --- OK, tire will be flush

275/40-18, 18X9.5 +24 --- OK, but tires may stick out a little bit from the fender by about 1/8".

The problem I see with the 265 setup is not so much the numbers but the availability of the tires. The only good tire available at that size at DTC is BFG. With the 275 setup, the availability increases with different brands.

Has anyone else done these setups and had any problems? Thank a bunch.

IMO -

1. The front offset you have listed is perfect for the wheel width and tire size.

2. Since you have an 9.5" wheel in back, go with a 275/40 tire. When this thread started, I didn't know the wheel was that wide. For the offset, with a 9.5" wheel, and if you want to retain the same look as the front, go with something like a 28 to 30mm offset. Don't push the rear wheel out more than the front, if it's wider.

And yes, I have this set-up on my Nismo wheels. +25mm Front, +30mm Rear. My current tires are Dunlop Sport Maxx, 245/40/18 and 275/40/18. I've had my wheels for better than three years now, and again, IMO, the offsets are just about perfect.

Lou

Thanks a bunch, Lou.

sorry if i hijack this, but i'm looking at track wheel options, and am considering 17x9.5. i'd prefer to run the same size all around, but am offset-retarded. can i run the same offset front and rear (ie, buy 4 of the exact same wheel - 17x9.5 +35)? this is not a looks thing, strictly for track use.

ahm