DavidDeco

I've read the posts and have some implied conflicting answers (of course) on what's the best or biggest wheel I can get away with 9.5" rims (on 18" wheels).

In particular I was looking for going with the RE Amemiya's at 18" which are 8.5" front and 9.5" back.

Originally my plan was to go 285/30 in the back but I'm scared the 9.5" may not be good enough for 285. I'm assuming 245/35's are fine for the front too?

Johnny

yeah...9.5 is really not wide enough for 285's..you need 10's min

mako

iTrader: (5)

285's will fit fine on a 9.5 wheel if you are worried about it go with a 275 instead.

SleepR1

What's wrong with a 255/35-18 on a 9.5 x 18? 275's too tall for gearing and will jack up the rear end...

DavidDeco

I'd prefer the widest tire I can get for the back...What can I expect if I put 285's on a 9.5" rim?

ARD T2

iTrader: (22)

FYI, you can do a 285 on a 9.5" but it has to be a 35 series tire. Must remember that the smaller the profile number the less range of wheel widths you have.

Being that you have an FD you will not want to run a 285/35 as it is too tall. That's MUSTANG status.

I would suggest running the 275/35 as there really isn't that much difference in section width. Look at your tires' respective specs.

Good luck, Rishie

Follow Johnny and Sleep's advice they know what they're talking about. A 285/30 must be on a 10" width wheel minimum.

DavidDeco

Thanks. If I went with 275/35's I know that will be too tall but will I screw up teh gearing significantly with 275/30's? That should be a little shorter than the stock diameter but not too much (I think).

I'm kinda set on the RE Amem wheels which is why I'm limiting to 9.5" rms. If the tradeoff isn't too bad I really want to make the 275's work over 255's.

AnthonyNYC

iTrader: (3)

You should have no issues with 285's. I am running 275 35 18 on a 18*9inch wheel. If you are worried about how it will look, it will look great. Here is a closeup pic of the setup I just mentioned.

http://rx7s.com/sandy/rx7/imagepages/image5.htm

Anthony

DavidDeco

I got around to Tire Rack and looked up the P-Zero Asymetricos which I intended to use (Not sure there was much choice for what I needed).

Tire Rack says the range for 285/30R18's is
9.5" to 11" which would indicate that at least in this
case 9.5" IS OKAY.

Any comments? I would think Tire Rack would run conservative numbers.

ptrhahn

iTrader: (9)

It is DOABLE, but tires work best on the WIDEST rim within the range. I've had tire engineers tell me that you could actually get better performance out of a narrower tire on a properly sized wheel.

As far as looks go, a 285/30/18 is actually slightly SMALLER diameter than stock. They actually look sorta dorky.. you need the extra diameter to fill out the wheel wells better w/ 18's. Plus, unless you can find a 245/35/18 for the front (rare, asimetricos are about it... nice to have choices) you'll have a TALLER profile on the front. Super dorky. That gearing business is BS. its very slight.

Most folks use 275/40/17 rear, which is the same diameter as 275/35/18. Thats what i would go with on a 9.5" wheel.

DavidDeco

So if I go with:

275/35/18's on 9.5" rears
245/35/18's on 8.5" fronts

I'll be okay...Meaning my gearing won't be noticeably altered, handling will be fine, and it'll like good? How much understeer will I be introducing with the wider rear wheels?

ptrhahn

iTrader: (9)

Common sizes would be:

275/35/18 on 9.5, 235/40/18 on 8.5

Sometimes folks use a 255/35/18 front if they have a 9" front wheel.

245/35/18 will work if you can get it. It will look smaller than your rear.

If you're making more power, you'll enjoy the wider rears. I originally had 245/40/17 all around and had the worst power-on oversteer ever w/290rwhp. Balance is your taste: how hard do you wanna stand on it coming out of a corner? Seriously the 275/235 stagger is VERY commonly used and enjoyed.

SleepR1

265/35-18 on the 9.5 x 18 would bring you closer to the stock overall diameter and still give a wider tire in back. I like the 245/35-18 size with 8.5 x 18...should work nicely...

JSpecRZ

I'm running 18x9.5 w/ 285/35 with no problems..the only problem is how much tires are when their going to need to be replaced.. LOL

SleepR1

A 35-series tire provides more sidewall flex/stretch than a 30-series tire...That's illustrated by the overall tire diameters:

285/30-18s are 24.8 inches in OD
285/35-18s are 25.9 inches in OD

As you can see the 35-series is a full inch taller, and thus offers at least 0.5 inches of more sidewall "stretch". The additional sidewall height allows the tire to be compressed onto a narrower rim...

Note that your gearing will be off, as well as your speedometer readings.

The weight of such a tire/wheel combination probably weighs in the range of 50 to 55 lbs. The Yokohama AVS Sports are especially heavy tires!

As always, it's your money, and you should do whatever makes you happy, our opinions be damned

dclin

iTrader: (4)

The size width rim you can mount a given tires to is dependent on what the tire manufacturer designed it to mount to. They are all different, though generally they fall within a similar range for a given size.

Tirerack gives manufacturer specifications, not what Tirerack interprets or measures. I say stay within the specifications and you'll be fine.

FYI, the particular tire you looked at are the PZero Rosso series. This came out after the orginal P Zeros, and have a bit more 'comfort' built into them. As such, the Rossos generally run taller - in the case of the 285/30/18 Rossos, overall dia is 25.2", the tallest of any the 285/30s I've researched.

With a taller sidewall, you generally have a greater range of wheel widths to work with. That is why 285/35/18s can generally be mounted on narrower wheels compared to the 30 aspect ratio tires.

(Note: the regular PZero Assimetricals in 285/30/18s give an approved rim width starting at 9", but can only think that this is a typo - I had these on my 10" wheels and they where hanging over the lip, but perfect. 9.5" should be ok in this particular model. Any narrower width of wheel combined with such a short sidewall would not be good, IMHO.)

Sorry, not a good angle, but the only pic I have close up of the tire:



Again, 285/30/18 Pirelli PZero (regular) Assemtricals on 18X10. The regular Pzeros have a shorter sidewall with an overall dia of 24.9", so cannot see why one can mount this to a narrower wheel, given that the taller Rossos have an approved width range starting at 9.5".

One thing that has not been mentioned is that the larger in tire size you go, the heavier the tire will be. A 285/30/18 will weigh close to 30lbs, whereas a 265/35/18 will weigh around 25-26lbs. 4-5lb extra at the very edge of a tire/wheel will be noticeable, but only a concern if you drive 10/10ths like the track people here (which is what I assume you are).

If I was limited to 18X8.5 and 18X9.5, I personally would run 245/35/18s front and 265/35/18s (maybe even 255/35) on the back.

Best of luck.

dclin

iTrader: (4)

Oh wait, another angle:



Still not good, but....

Daniel

SleepR1

Yeah, what dclin posted

dclin

iTrader: (4)

Sleep beat me to it.... what he said.

DavidDeco

Nope, not racing at any track, at least not in the near future. I care about the best looking street setup I have without compromising performance. My car will likely put out 330-360 RWHP when I get it back so that's why I'm hung up on maxing the width.

I guess basically you're saying with the PZero Rosso's I'd be fine with 285/30s likely but not in your experience with the normal Asym's which you had on your 10"

I liked the fact the 285/30's and 245/35's in front are almost identical sizes and close to stock. If the performance hit is insignificant I'd prefer to go 285 over 275 or 265. I won't go 255.

SleepR1

Yeah, I agree with your setup, 285/30-18 rears, and 245/35-18 fronts. I guess you just have to be choosy with the tire brand to be sure a 9.5-inch wheel width will be ok to mount the 285/30s...Have fun with it!

ZoomZoom

iTrader: (2)

I have 285/30/18's on my FD in the rear. The Rim is a 9.5 inch wide. The tire is a Bridgestone S-03 and is 1/10 of an inch shorter than the stock 225/50/16's. Fit is fine. Looks good IMO. I posted pics here https://www.rx7club.com/forum/showth...threadid=94047

dclin

iTrader: (4)

Just for the record, Bridgestone gives an approve rim width of 10" to 11" for the S03 285/30/18 (If anything happens, Bridgestone/Firestone does not need any more lawsuits hehe).

I think it needs to kept in mind that when we are talking about fitment above, it is from the prospective of 10/10ths driving. Only track fiends like Sleep will be able to tell the difference in handling under track/racing conditions.

It probably is important to follow the manufacturers recommendation still (they have them for a reason), but likely the only penalty (for strictly road use) to mounting tires on a rim 1/2 size smaller then recommended is maybe slightly worse wear characteristics? Of course, if your tread seperates, make sure their lawyers do not know what width rim you had them on.