AlwaysBroken

Option 1: 15x10 w/ 245/40/15
Option 2: 15x9 w/ 225/45/15

Assume RS-4s or something similar. Going to be running XIDA ACE GS with no drop spindles. This is mostly a street car.

Is it possible to run 15x10 with 245 width tires on an NA miata and actually drive the car like a miata? IE- drive over bumps and turn the steering wheel without rubbing. I realize that 245 requires a fender pull. I think 225 does too. I'm willing to do this, but I've heard rumors of people pulling the fenders on their NA and still rubbing, which seems to me like a huge pain in the ***.

How noticeable of a difference between 225 and 245 width tires in terms of:
-grip when accelerating
-cornering grip?
-aerodynamic drag?
-hassle

matrussell122

iTrader: (1)

Im running 15x9 245/40-15 RS-4's with a mild fender roll and I clear just fine. I removed the inner fenders too. Grip on the 245 RS4 is really good for a street tire and im happy with them. At full lock i barley rub on the sway bar but thats only when i pull out of my driveway.

doward

Define "fit"
At 949 Racing, if it won't clear a damper sweep with the spring removed, it doesn't "fit". 15x8" fits.
If it just touches the inner wells or fender at full bump, we'd call that a race fitment and accept the minor rubbing as a compromise.
The 9" is a race fitment, as it rubs the swaybar and fender liners on both NA and NB.
The 10" has the same inboard obstacles, but adds interference with the fender that is manageable on the NB with a flat roll and aggressive alignment. NA's need a very hefty pull to get the wheel to clear the fender under bump travel. I've only seen 1 or 2 examples that have proven clearance at near full bump travel. One was my own NA with 245 Maxxis and rear fenders I took a sledgehammer to from the back side, not pretty.

If it's just a street car, or you're a novice/casual track driver, or your 3 piece shocks are missing a bunch of bump travel when compared to Xidas, you may never have the serious interference/rubbing that is possible under extreme bump travel.

This gets even trickier as the control arms pull the wheel in as you lower the car. Xida ACE and XL ride height ranges put the control arms roughly parallel to the ground, making for the worst case scenario for fitting wide wheels inside the fenders. Going below 5.5" pinch starts to bring the control arms past parallel and creates easier wheel fitment by pulling the wheel inboard and adding more negative camber, both static and dynamic. The dynamic part is important to prevent serious outboard rubbing.

Things are tight enough that the specific alignment and model of tire become noteworthy. Maxxis 245s run narrow and are "easy" to fit. The Hankook RS4 is a bit wider than the Maxxis, the BFG Rival even wider again with it's giant shoulder blocks.

doward

Option 3: 15x9 w/245/40/15
Accelerates and brakes better than 225/9" because of bigger contact patch.
Easier to fit(hassle)
Is aerodynamic drag a serious concern?
More cornering grip than 225/9", less than 245/10". Either way, probably not noticeable on the street.

DeerHunter

I've heard arguments on both sides regarding contact patch size, but my understanding is that size/area mostly depends upon tires pressures and vehicle weight (the idea being that tires are imperfect balloons). In other words, a 205/50-15 will have a longer/narrower contact patch than a 245/45-15 (but total area is approx. the same). This will vary due to wheel width, tire construction and moon phase, but as a rule-of-thumb, it should hold true. If you accept this, consider that tire compound will play a far larger role in providing straight-line traction than going to gonzo wheel and tire widths. Of course, if you're going for track performance in a high-po Miata, it's proven that the widest wheel/tire combination you can stuff under the fenders is the ticket.

Anecdotally, I've run sticky 205/50-R15s for many a year and have no trouble putting the power down (my situation is helped by having longer gearing than stock). Changing out my OEM BBS rims for 15x8 6ULs was a great upgrade, as it provided more than enough cornering stability for the street and didn't cause any tramlining issues. For track use, I switched to 15x9s with 225/45-15s. Last summer I used the larger wheel/tires on the street and was less happy. Yes, cornering was more effortless but it came at the cost of noticeably more rotating mass and a predilection to follow ruts in the road. YMMV.

MrJon

I think the part you are missing is that you are probably going to run lower pressures on the wider tire.

DeerHunter

You can run lower pressures on a narrow tire (old drag racing trick). It's all a series of trade-offs. Do you want the best cornering ability? Run the wide tires and deal with the tramlining and reduced squirtability (the extra rotating mass makes the car less responsive). Do you want a car that's comfortable in the daily grind but still able to hold its own in the twisties? Run a narrower tire on a wide rim. My point is that the wider tire won't put down the power any better in a straight line - you'll have as much traction as your tire compound/pavement grip will allow.

AlwaysBroken

I don't really care about removing fender liners or rolling/pulling the fender. If that's what I need to do for a significant upgrade in traction, then I'll do it.

But is this enough? Googling the various forums on this subject reveals a range of experiences from "I run 275 hoosiers on 15x9 on my 90 with no problems" to "I rub with 205 width tires on 15x7 wheels in my 99" But it seems like some people are possibly bitching about rubbing against the stock fender liners and some people are "fine" because they've pulled fenders and learned to live with not going full lock to keep the swaybar happy (which is honestly not a huge problem, depending upon how much steering wheel travel I'm giving up).

I would be ok with this I think. Then again, I don't know how often I'm on the bumpstops. I would imagine fairly rarely during street driving, not sure about track use.

pdexta

iTrader: (17)

Height has a lot to do with rubbing as well, even to the point where you rub the top of the wheel well, where wheel fitment is basically irrelevant. I think that explains a lot of where the wide range of answers.

I've run a bunch of 225's on a 15x8 +25 on 2 NA's and 2 NB's with a light roll and I've been really happy with the setup for a street car. It's never rubbed at any reasonable height and until this recent cold front and some aging tires it hooked up in 2nd gear. I know 225's on a 8" wheel are a sin on here worthy of 400 neg cats, but anyone outside of the miata world thinks it's a completely reasonable option and I've been happy with it.

ridethecliche

iTrader: (2)

A few folks on here run 225's on 8's and 245's on 9's as well!