Widest tire possible on gen3 SHO?

[99V8SHO]

I am looking at purchasing 18" rims and Goodyear Eagle F1 tires. The problem is that the tires are 245/45R18. Will the 245 present a problem?

I could also go with 225/40R18. Will this throw the speedo off?

 

[stephen newberg]

It is certainly possible. It depends on the offset of the wheels. The two things that you can contact are the rims of the wheel well on the outside, particularly when turning, and the strut assembly on the inside. I have run 245/45x17 without contact problems. IIRC, the offset was 42mm. 18 inch rims are half an inch higher from the axle center and more likely to contact the strut system, so you might need a different offset.

As per the speedometer, you need to get a figure from the tire manufacturer for the circumference of the particular tire, since there is variance even for the same listed size due to differing tread depth and such. Again, IIRC the OEM tires produced about a 512 circumference ( think that number sounds right). If your new ones are close to that, your speedometer will still be close to correct.

pax, smn

 

[v8mod'99]

Originally posted by stephen newberg:
I copied this info from V8SHO.com
"In theory a 18x8" rim with a 32 mm offset should clear the brakes and struts (a wheel with 35 mm may fit but it would be very close to the strut). Will it clear the fenders? I don't know, I think so! Team Dynamics makes 3 rims in that size and with 30 mm offset. DTM, Monza, and the Qualifier."

SHO Shop reports very poor ride quality without improved performance when they tried 18" Rims(this is a cosmetic only mod.)

<small>[ July 29, 2003, 10:42 AM: Message edited by: v8mod'99 ]</small>

 

[Venom 800TT]

Quoted directly from V8SHO.com:
"As for offset from sizing. Through a great deal of research into what has worked for others, and my own experience, I've found that 38-40mm offset works best up 8" width and a 235 tire width works best, though wider will work up 255 if the fenders are rolled. My 18x8 40mm offset rims have been on the car for a couple years now, and not once have I rubbed the strut or the fender, and this includes some very spirited trips through the twisties of back roads and highway on/off ramps. I simply can't agree with your guide on your site. It's a fact that without changing outside diameter, I could easily run 235/35ZR19's on 19x8 rims. On the same note, with a bit of rubbing on occasion I know that you may run a 245/35ZR20 on a 20x8 rims, if you can find them. 19's and 20's have both been done on 3g's."

In other words, the 225/40ZR18's will work..they will be a tad short, but your much more likely to avoid the significant rubbing problems a 245/45 ZR18 would cause. And yes, that quote is mine that Tim Wright put onto the V8SHO FAQ's site.

 

[99V8SHO]

How far off would the speedo be with the shorter tires?
Shorter tires give slightly better acceleration, right?

 

[Venom 800TT]

Yes, a shorter tire would provide a slightly better accleration, though the weight of the wheel amy counteract this. As for speedo error:
http://www.miata.net/garage/tirecalc.html
Enjoy. wink

Venom

 

[Joshua]

I run 245 40 18's on mine and i have no problems at all..it's a close fit but no rubbing.

 

[NECGP]

I can say that 18's on an SHO does make for a rough ride but I like it.

<small>[ August 06, 2003, 11:15 AM: Message edited by: NECGP ]</small>

 

[Wess]

Man Garrett, she sure is purrty! hail

 

[wuzzzer]

If only I would have known that my SHO would end up as low as it is I would have bought 18s in a heartbeat instead of my 17s.