What's the optimal tire size with 18" rims?

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What's the optimal tire size with 18" rims?

Postby lobsternet1 » Wed Dec 14, 2011 6:53 pm

What tire size can be ran with 18" rims without having to fender flare and will accommodate a modest suspension lowering?
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Re: What's the optimal tire size with 18" rims?

Postby Brian » Wed Dec 14, 2011 9:27 pm

I will assume MX5....

The 215/40/18 is about 24.8 inches, just a little taller than stock MX5 and works in stock fenders even if mildly lowered. We have that size in two tires. We also have 215/35/18 in Proxes4 which is 24 inches, a little shorter than stock and will fit even if the MX5 is lowered 2 inches.
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Re: What's the optimal tire size with 18" rims?

Postby lobsternet1 » Thu Dec 15, 2011 5:47 pm

Brian wrote:I will assume MX5....



is there any other kind of car?? :D


I'm trying to decide between 225/40-18 or 235/40-17.

I really like how the 18" rims look even if it's a couple pounds more per corner. My MX5 is just a daily driver, so I'm not looking to shave tenths of a second off a track time, but I don't want to turn my sports cars nimble handling into that of a tank with excessive unsprung weight. I also don't want a really awful ride either and I think the 35's might be too short of a sidewall.

I was thinking specifically the Ultraleggerra's @ 18.4lbs (18x8 +48mm) or Enkei RPF1's @ 17.6lbs (18x7.5 +48mm). The Ultra's look cooler imo, but the Enkei's are almost a pound lighter and cheaper.

Hmmm...
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Re: What's the optimal tire size with 18" rims?

Postby Brian » Thu Dec 15, 2011 6:35 pm

If you don't want the ride quality going downhill, that makes killing the 18 inch idea easy. Going to 18 inch WILL hurt your ride. I run 18 for autocross because that's the only way to get 285mm wide tires on the ground with diameter that can still be fitted.
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Re: What's the optimal tire size with 18" rims?

Postby lobsternet1 » Thu Dec 15, 2011 6:39 pm

well in that case, from what I've read, the best choice is probably the 235/40-17's in +48mm.
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Re: What's the optimal tire size with 18" rims?

Postby Brian » Thu Dec 15, 2011 8:46 pm

lobsternet1 wrote:well in that case, from what I've read, the best choice is probably the 235/40-17's in +48mm.


That's right. That is max fitment for stock fenders and perfect offset to do it....

You can do that tire on 17x8. But for autocross and track in particular you can max the performance by using 17x9.

Shown below is our 17x9 and 235/40/17 R1R combo....great for STR class (click HERE for more info).

Image
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Re: What's the optimal tire size with 18" rims?

Postby lobsternet1 » Thu Dec 15, 2011 8:54 pm

so for that tire, both 17x8 AND 17x9 fit with completely stock fenders? this is just a daily driver, so which do you suggest?
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Re: What's the optimal tire size with 18" rims?

Postby Brian » Thu Dec 15, 2011 10:02 pm

Yes, that tire will fit stock fenders on 17x8 and 17x9....with 48mm to 50mm offset. As for which to pick, the 17x8 gives the rim a little more protection from curb rash. The 17x9 gives you a little more performance from the tire. Thus, for the daily driver that will autocross the weekends the 17x9 is the faster choice. For the 100% daily driver.... 17x8 may be the better choice.
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Re: What's the optimal tire size with 18" rims?

Postby Oz » Sat Dec 17, 2011 12:50 am

I'll second that!
I'm now running 17X8 et50 PF01 with the new 235/40/17 Toyo T1Sport.
The car is lowered about 15mm from std and there is not a hint of clearance problems.
The tyre looks absolutely perfect on the rim and does give that little extra protection for the daily drive.
Hard road use suffers little if at all from the wide section.

Couple of pics, last post this thread
viewtopic.php?f=12&t=23&start=315
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