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Opinions on small diameter tires?

Old 01-22-2018, 02:56 PM
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Opinions on small diameter tires?

For those of you who've tried 17" wheels with 235-245/40 or similar diameter tire, what did you think? I can see plenty of advantages (weight, gearing, tire selection, lower center of gravity) but the obvious disadvantages (lower ground clearance, speedo and odo inaccuracy) don't seem too bad. I feel like I must be missing something or else I'd notice more people running smaller diameter tires.
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Old 01-22-2018, 05:10 PM
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There are many threads on this subject.
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Old 01-22-2018, 06:08 PM
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For track duty and winter tires the rubber is cheaper than 18". I don't know which people you have seen, so can't speak to why more people do or don't do something. But 9k is right this is a pretty common point of discussion over the years. You're right? Go for it?
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Old 01-23-2018, 08:15 AM
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I tried searching by tire size before posting but obviously the results were not what I was looking for.

Currently my right front corner seems to be maxed out at at a height of 13" with the suspension I just installed and that corner was bumped prior to my ownership. That tire (215/45/18) currently hits the front liner near full lock. I'm bringing the car by a pro driver/setup guy I know what see what he can do with the ride height. If it really can't go higher I'll likely go to a 235/40/17 (595 rs-rr is cheap!) and hope that does it, as the car will hopefully see some street driving and I'd like to keep the liner in. I actually wanted to keep a near OE diameter so the odometer would read correct for the rally portion of the targa events I will be going to but I can give that up if need be and use a gps phone app.
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Old 01-23-2018, 09:50 AM
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What offset is the wheel that's rubbing? I was down near 12.5" at one point, due to unfortunate circumstances, but with stock wheels and with my track wheels at offset around +42 there was no rubbing.
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Old 01-23-2018, 10:42 AM
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The stock 18x8, which I believe is +50. I was planning on going with a 17x9 +40. That does make sense that lowering the offset would pull the wheel away from the inner liner, but I was thinking a 1cm offset difference would not matter since the wheel was 2.54 cm wider, and would end up sitting 2.7 mm further inward if my math is correct. Though that's not accounting for the diameter difference.
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Old 01-23-2018, 04:48 PM
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215/45/18 should already be slightly smaller than stock OD. No way should it rub unless something's wrong. I wouldn't want to go even smaller.

When you said "that corner was bumped prior to my ownership", what did you mean?
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Old 01-24-2018, 09:01 AM
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you can add limiters to the steering rack inside the tie-rod boot at the steering rack

same thing works on our rack, you will lose a little max steering radius turning, but you shouldn't need much based on your description

https://www.rx7club.com/suspension-w...miter-1117648/



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Old 01-24-2018, 12:20 PM
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Originally Posted by IamFodi View Post
215/45/18 should already be slightly smaller than stock OD. No way should it rub unless something's wrong. I wouldn't want to go even smaller.

When you said "that corner was bumped prior to my ownership", what did you mean?
I mean it was bumped in a parking lot a couple days before I purchased it. And it had a rebuilt title prior to that. Oil cooler was pushed back. Front end had to be pulled a bit to get the bumper cover to fit right. So that corner is a limiting factor to a small degree. The important bits are in good shape.
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Old 01-24-2018, 03:19 PM
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Originally Posted by eyeguy View Post
I mean it was bumped in a parking lot a couple days before I purchased it. And it had a rebuilt title prior to that. Oil cooler was pushed back. Front end had to be pulled a bit to get the bumper cover to fit right. So that corner is a limiting factor to a small degree. The important bits are in good shape.
Then I strongly suspect something is messed up in there. At least out of alignment vs. factory. Best to have that fixed before throwing parts at it. Again, there's no way that tire on that wheel should rub even with some lowering.
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Old 01-25-2018, 06:58 AM
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I was thinking the same thing.

Relative to the original question/thread title, back when I was running in the STX street tire class I ran the Toyo R1R 235/35-17, which only has a 23.7" OD. As I recall it resulted in an effective 4.782" gear ratio even though the actual gear ratio is 4.444. Which of course is relative to the original tire size from the factory which is almost 2" larger OD.

Other than that that the speedo and odometers are off as the OP suggested and mileage goes down if you're driving it regular on the street, but you do get a nice gear ratio boost. I use to eat other RX8's up off the start line and could almost be even with AWD cars that would otherwise get a big jump off the start. Top speed in each gear goes down too, but having the rev limiter set at 10k kind of made up for that ...
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Old 01-25-2018, 08:03 PM
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The alignment on the stock suspension looked fine, though I never checked it. Nothing that I saw was obviously off other than the stuff behind the front bumper. And if something really is off, it's no big deal to me as the car was fantastic on track with the stock suspension. Easily faster than my previous well prepped miata, when the rx8 had skinny 300+ tw tires, crappy unknown brakes, unknown alignment, child seats, etc. It also drove great on the street and didn't make any funny noises.

The new suspension actually feels way more comfy than I was expecting as well, so I'll be happy as long as the liners can stay with no rubbing if I have to go to a smaller tire. But I am pissed that the targa is getting axed!
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Old 01-25-2018, 08:54 PM
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To be clear, when I said "out of alignment vs. factory", I was referring to the body parts, not the suspension.

Either way, it's entirely possible that there could be a problem big enough to cause your rubbing but not big enough to be eyeballed. In fact, given your description, I'd say it's almost certain.

Also, if you've lowered it, it no longer matters what the (suspension) alignment was like on the stock suspension; it needs to be re-checked and likely tweaked.

If you're happy with the car, enjoy it. But something is definitely not optimal.

Last edited by IamFodi; 01-26-2018 at 04:58 AM.
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Old 01-25-2018, 09:50 PM
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I know that, hence why I said it was bumped. The things been hit twice, it's definitely not perfect. Otherwise this thread wouldn't exist. After lots of pounding with a hammer and some cheap work by a body/frame guy it's close enough for me. This is an extra car for fun and track use, not a show car.
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Old 01-26-2018, 10:13 AM
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sooner or later you'll figure out who the myopic nitpickers are around here ...
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Old 01-27-2018, 07:02 PM
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Eyeguy,

I always try to lower gear with lower profile.

I have the dreaded 6spd auto, so it is geared higher.

Some dealer swapped for Enkei GF-1 with 7.5x18 et38, so I put 215/40r18 Michelin PSS on with 24.8" diameter or 5% gear down.

It drives and sticks like a dream, and stopped skittering across street ripples.
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Old 02-02-2018, 01:02 PM
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This morning I decided to go with 235/45/17 rs4, and nabbed the last set of k5r in a 17x9 +48.

And +1 for fortune auto, who will be sending me a set of longer bottom mounts so I can raise the car up.

I need to get out of the habit of relying on fender measurements for ride height, as they proved to be inaccurate.

Last edited by eyeguy; 02-04-2018 at 04:56 PM. Reason: left out important word
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Old 02-03-2018, 06:47 PM
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... or measure more accurately.

245 would afford a bit more grip, but the 235 on a 9” wheel should be quite responsive for turn-in etc.
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Old 02-04-2018, 05:01 PM
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Coming from a miata where 225s on a 9" wheel is the norm, a 235 seems like plenty of tire for a 9" wheel. If I decide I need more grip, I'll likely move to a 255 on a 9.5 or 10" wheel in the future.
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