Best tire width for performance on an 18x9
 

I've done some searching and can't find a good thread with an explanation...

I'm getting wider wheels and would like the most performance out of them. 18x9 all around with a 38mm offset. What is the best width as far as your experience goes, guys?

Thanks.

245x40 are generally considered the best all around, daily driver, performance width/ratio tires on stock rims, on up to 18x9.5 (so aok for your intended 18x9).

No one that I know of here or elsewhere has had any fender clearance (rubbing) issues with 245x40, given stock suspension height.

You can of course go a good deal wider, provided you go with a lower sidewall ratio and even wider rims, e.g. 275x35 18x9.5 +45 offset

https://www.rx8club.com/showthread.p...ght=Enkei+RPF1

Thank you, brother.

275/35/18 or 265
245 is too small for a 9" rim

...see, this is why I started this thread. People having freaking 275's on their 9-inch wheels. 'Cause it looks sweet, or 'cause that's what you SHOULD put on them?

like Huey's answer, I'm really interested in best daily driving and performance, tread life, etc.

245/40 is perfect for a 9" wheel. In my opinion 8" wide wheels don't provide enough sidewall support for a 245/40, which leads to sloppier handling than stock when using such a width on the stock wheels. The increase in tire width of 20mm corresponds pretty closely to the increase in wheel width by an inch, which is 25.4mm. A 265/35 or 275/35 on a 9" wheel would be akin to the 245/40 on an 8" wheel. People always try to stuff the widest tire possible onto a given wheel, but in terms of handling precision, feedback, and responsiveness, you actually want the opposite; put the widest wheel possible for a given tire width that doesn't go into the area of being unsafe.

Not to mention at 38 offset, a 275/35 has a good chance of rubbing.

There is 48mm and 38mm... I haven't bought the wheels yet, so would 48 be better?

Performance? What do you mean: dry highway comfort, wet roads, autocross, HPDE, drag? All of these things ask different things from a tire. Compound and construction are as/more important than size, imho.

Generally, for the best all around tire/road contact, the tread section on the road should be the same width as the wheel. For a 9" wheel, this converts to 228 mm. When they report tire sizes, they give the outer sectional width, ie 265 mm. This isn't the same as the tread width. Note also that there is a large variation between tire manufacturers between the section width and the tread width. For example, the snows on my Subaru are listed as 215mm width, and the tread is slightly wider than the stock RX-8 tires - go figure.

For speedo accuracy (to stock tires), 255 / 40 / 18 would be the best choice. (less than 0.2% difference according to miata.net)

Here are a couple of tire / wheel size calculators for you to play with:MIATA NET WHEELMASTER

Check out the 'will it fit' thread, for starters, BUT if you want to achieve something specific, try to buy from a place that will test fit on your car.

+1 for 255/40

But the slightly slower actual-to-indicated mph of 245x40's might save him a ticket. ;)

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/45-18 4.0in 13.0in 26.0in 81.6in 777 0.0%
245/40-18 3.9in 12.9in 25.7in 80.8in 784 -1.0%

A 255/40 would be good as well in my opinion, just that selection is more limited in that size. I personally would prefer the +48 offset to the +38 as the scrub radius and all the steering geometry is closer to factory. What wheels are you looking at?

check it

It was that or the enkei zr1; this one is about 40$ a wheel cheaper, though... plus ordering wheels and tires is an extra $100 off.

By the way, performance for me means DD and HPDE.

A 245 is perfect for a 9" rim, in my opinion best performance probably would be a 265/35. But I think that might rub with a 38mm offset. When I was trying to decide what wheels and tires to use for STX next year I was considering a 18X9 with a 35mm offset with a 265/35 tire and had decided that it would rub for sure and I would definitely need to roll the fender. I ended up choosing 17x9 wedssports that went on clearance at tirerack, http://www.tirerack.com/wheels/Wheel...d&showRear=yes for the better offset much lighter weight, and much lower cost. I haven't decided on which tire I want yet but it will for sure be a 255/40.

That is an amazing looking wheel :)

So first you said that 245 would be perfect; however your opinion is that 265's are best for performance. Then, though you said that you would for sure decide on a 255.

I'm confused :lol:

rub all depends on how much you have rolled, offset, and camber. +38 offset will look better.

Who ever said more tire is bad is wrong. I regularly track my car and can notice a big difference in 245 vs 225, I really dont think the tire can make that much of a difference.

You can run 245 on a 9" wheel if you want, but that'll give you a stretched look. I would run 275 or 265.

Sorry, what I ment was a 9" rim was perfect for a 245, not that a 245 was perfect for a 9" rim. And that was in response to some one saying the 245 was too small for 9" rim.

I went with the 255 because nobody makes a 265 in a 17 and the max tire I can run per the rules is 265, so that eliminates the 275, plus I think the 275 is a little bit big for a 9" rim, which is also the max I can run per the rules.

^your talking about 17's op is talking about 18. A lot more tire options are available in 265 and 275.

Actually I'm talking about both, thats why I said for him 265 and why I chose 255.

We are perhaps getting into a horses for courses argument. On the stock wheels, a 245/40 will deliver more grip than a 225/45 simply because there is more thread width. However, what will suffer is the transient dynamics as a 245/40 has less support and so flexes more than a 225/45; i.e. turn-in isn't as sharp, steering feedback is diminished, and response time is slower. This is of course assuming equal tires; I'm sure going from the stock 225/45 to a R compound 245/40 will mask the transients as R compounds are just that much stiffer and generally a better performance tire. If your application calls for pure grip, then a wider tire within reason is the way to go, but if what you need more feedback and transient characteristics, then go with a narrower tire for more sidewall support.

There is a certain point where you actually have too much tire and won't be able to run faster. For NA and NB Miatas, you generally won't be faster on a track going to a 225 from a 205. I'm not sure what the point is for the RX-8, but looking at the engine power I'd assume 275 would be somewhere close to the edge.

265/35-18

+1

245 is to narrow for a 9" rim.

If he wants to run 265s he will likely need a bigger offset. They might work fine on a stock alignment/suspension but if there's any plans on putting on springs that lower the car he's going to be cutting it awfully close. Nothing a more agressive alignment wouldn't cure (or rolling the fenders) but he should keep that in mind when purchasing. Also wider tires tend to be louder. I have 275s and they have to heat up a fair amount before I stop noticing the noise.

If you go with 265s then plan on getting the +45 offset. If you go with the +38 offset then play it safe with 255s. Personally I'd go with the bigger offset and bigger tire. Wait... I did! ;)

PS. Those are very nice looking wheels and they appear to be around the same weight as our stockers. Looks like they're around 23.5lbs per wheel. If you're really looking for performance then you might want to try to shave some of that weight off or go with the smaller offset and smaller tires.

http://www.3si.org/forum/f41/enkei-o...weapon-416264/

EDIT: use this to see all the differences. Should come up with stockers on the left and my configuration on the right. FWIW my wheels/tires are 1.2" wider than stock and was fine with stock suspension but would have rubbed the front fenders if it was dropped w/o an alignment. 265s on 18x9+38 will be another half-an-inch wider than mine.

http://www.wheelsmaster.com/rt_specs...&text1=&text2=

Thanks for the info, guys... I hate getting a wheel already heavier than stock, but the enkei zr1 (18x8, 20lb) is out of my budget.