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Old 11-25-2011, 01:06 PM   #1
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Default why 225/45/15 RS3s and NT01s on 15 X 9 wheels

I would like to know why it is common practice to run tires this size on rims that are (according to the tire manufacturer) too wide? I'm wondering if there is any downside, and if they work so well on the wider rims why they don't recommend them. Don't get me wrong, I intend to buy some 15 X 8 or 15 X 9 6UL wheels to use with these 225/45/15s, since this seems to be the fast setup, but why do they work better on the wider rims?

Thanks!
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Old 11-25-2011, 01:22 PM   #2
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The closer you get the wheel width to the actual tire width, the more responsive the tire will be. You will have less sidewall flex, have much crisper feedback, and the car will be more responsive.

With the 225 they look the slightest bit stretched, but it works very well.
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Old 11-25-2011, 04:08 PM   #3
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Quote:
Originally Posted by rharris19 View Post
The closer you get the wheel width to the actual tire width, the more responsive the tire will be. You will have less sidewall flex, have much crisper feedback, and the car will be more responsive.

With the 225 they look the slightest bit stretched, but it works very well.
This.
And empirical data (testing) shows it is fastest on a 9.

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Originally Posted by emilio700 View Post
If you have any experience testing radials, you will already know that they will be fastest on a wheel roughly the same width as the casing, not tread. This does not change with sidewall stiffness. FWIW, the DOT is only slightly less stiff than the non DOT radial. I have mounted both on our 8's and 9's so I'm familiar with them.

I have spoken with Hoosier when developing both the 9" and 10" versions of the 6UL. This goes back before the 275 existed and I was talking to Jeff Speer about a 245/40. When they decided to do a 275 instead, he contacted me because he knew I was working on a 9" wheel. I think I was the first guy to post the 275 news on a forum. Anyway, I talked to an engineer there about the 275 and whether it needed an 10.5 or 11" wheel and he said that due to its cantilevered design, the 10.5 or 11 would not give it any more support than a 10" wheel. Thus, we made a 10" wheel.

The non DoT slick isn't cantilevered though so its needs a wider wheel relative to it's tread width.

If you have ever obtain any conclusive data under controlled conditions (same car/day/driver/track/weather/setup) that shows the 245/580R15 Hoosier is faster on a 9 than a 10" wheel, I'd like to see it.
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Old 11-25-2011, 04:53 PM   #4
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Kinda sorta on topic,

say I wanted a more "comfy" ride. softer overall, less jerky/etc.
would the opposite of this idea work just as effectively?

like putting a 225 on a 8" or 7"
or will it just take away response but not add comfort?

I know going from my 15x9 w/ 205/50 to 16x7 w/ 205/55 actually made the car a lot "mushier" and/or comfortable, but not sure if thats just in my head or if you guys' had similar experience
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Old 11-25-2011, 05:07 PM   #5
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Yeah if you want comfort then run a taller side wall. 55+ ive never run over a 50 on my car but ive test driven one on 195/65s and it handled horribly for my driving style.
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Old 11-25-2011, 05:17 PM   #6
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I have had a car with 225 on 15x7, 15x8, and 15x9. The difference between them was that the car felt sloppier and not more comfortable. It would make sense that if the sidewall was more rigid that it would give a somewhat harsher ride, but I don't think it was very discernible. I would think that a good alignment that is aimed toward what you want will give you a car that is less twitchy ride.

I do know when I had 195/60/14 star specs that the ride was softer, but you will get that with a taller sidewall if all else is held equal.
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Old 11-25-2011, 07:11 PM   #7
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Yeah that's the tricky part: I refuse to go higher than 50 for sidewall.

here's specifics:
tire is 225/50
I have the option of 7.5" or 8" rim.
Will the difference in ride harshness be insignificant with the less "stretched" tire?

sorry for threadjack OP, though it is kinda on topic lol
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Old 11-25-2011, 10:26 PM   #8
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I doubt you will feel any ride quality difference, especially since its only a half inch difference. Just do the 8.
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Old 11-25-2011, 10:30 PM   #9
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Quote:
Originally Posted by 18psi View Post
Yeah that's the tricky part: I refuse to go higher than 50 for sidewall.

here's specifics:
tire is 225/50
I have the option of 7.5" or 8" rim.
Will the difference in ride harshness be insignificant with the less "stretched" tire?

sorry for threadjack OP, though it is kinda on topic lol
the 205 RT615 felt great with the 7 inch ATS rims, so I'd assume the 225 on your 8 inch rim should feel fine also.
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Old 11-25-2011, 11:14 PM   #10
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I believe a stretched tire (small wheel, larger tire) will technically improve ride quality a bit, soften it up. With a bulged sidewall, its "cushier". This translate into less feel and responsiveness while cornering, but should be more ultimate grip.

225/50 looked ok on my 7", should be fine on 7.5", and obviously the 15x8 6ul used to be the wheel of choice for 225/45 until the 9 came out.

The bigger problem with 225/50s is the tire diameter, you'll have to go about .5-1" higher than most miatas around here so they don't rub, and that's with a fairly conservative offset.
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Old 11-26-2011, 12:05 AM   #11
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The only disadvantage I see from running a slight stretch on the tires (like 225 on 9" instead of 8") is you get more curb rash. Especially if you track the car and run up gators or anything of the sort, you will notice little nicks and scratches on the outside lip.

For a set of track rims, that shouldn't really matter. chalk it up to weight savings or whatever, but for a nice set of street wheels, I wouldn't stretch it much. If its dual purpose, you will need to make an appropriate decision factoring in the road quality in your area. I personally have shitty roads, track the car, and daily it to work and back for now.
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Old 11-27-2011, 11:05 PM   #12
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Another advantage of the wider wheels is optimal tire pressure tends to drop, making for a more compliant contact patch.
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Old 11-29-2011, 02:15 PM   #13
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I have 15X9 with the rs3's I have heard that the little bit of stretch gives the sidewall some preload and the rs3's are great tires...(when its nice, and warm out)
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Old 12-03-2011, 01:44 AM   #14
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Because I am feeling generous, I used the excellent search functionality built into this website for you.

225 on 9" wheel is unarguably faster than 225 on any smaller wheel. The slight stretch takes the squirm out of the tire and makes the contact patch more stable.

The only use case I can see for an 8" wheel being a better choice than a 9" wheel for a 225 tire is for mixed street/track use with the same wheels & tires, an 8" wheel will prevent curb rash on the rims.

https://www.miataturbo.net/showpost....5&postcount=22

Edit: as can be seen from my signature, I am running 225's on 8 inch wheels. I will put 205's on them when the 225's are done.
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Old 12-03-2011, 09:02 AM   #15
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Quote:
Originally Posted by Mobius View Post
Because I am feeling generous, I used the excellent search functionality built into this website for you.

225 on 9" wheel is unarguably faster than 225 on any smaller wheel. The slight stretch takes the squirm out of the tire and makes the contact patch more stable.

The only use case I can see for an 8" wheel being a better choice than a 9" wheel for a 225 tire is for mixed street/track use with the same wheels & tires, an 8" wheel will prevent curb rash on the rims.

https://www.miataturbo.net/showpost....5&postcount=22

Edit: as can be seen from my signature, I am running 225's on 8 inch wheels. I will put 205's on them when the 225's are done.
Mobius,

I knew they were faster. I was wondering why the manufacturers list them as too wide to use. If you go to Tire Rack or Nittos site, the range of rims they deem appropriate are smaller. I just wondered why they would leave out the "better" wider rims? Thanks for finding that post! Why are you going to narrower tires and not wider rims? More for street use? I also have a C6 and I will admit my Miata with 195s on 15 X 6 rims feels SO nimble at low speeds compared to those 245/285s!!

Thanks again!

Tom O
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Old 12-03-2011, 09:09 AM   #16
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Much more selection of 205s both in street and race rubber. With 8" rims you can have that great selection while still having the option of running sticky 225s. With 9" rims, you cant really run 205s, and you're limited to race rubber, or at least barely street able.
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Old 12-04-2011, 01:32 PM   #17
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Quote:
Originally Posted by curly View Post
Much more selection of 205s both in street and race rubber. With 8" rims you can have that great selection while still having the option of running sticky 225s. With 9" rims, you cant really run 205s, and you're limited to race rubber, or at least barely street able.
I noticed that. How much difference do you think lap times would be off running RS3s or NT01s on an 8" rim. I like the idea of having more choices.

By the way I am only 59
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Old 12-04-2011, 09:54 PM   #18
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I will move to 205's on my 8's instead of getting 9's for several reasons. I don't feel like justifying the expense to Ms Mobius to change the rims. 205's on 8's, treadwise, are almost indistinguishable from 225's on 8's once the tires are mounted, and will be more responsive. And, I don't actually want the ultimate 225 on 9 grip. My car has no aero in its future for years, so I wouldn't be able to make best use of it. My skill level is moderate as I haven't been able to arrange track time last couple of years, so I will progress more as a driver and have a more fun car with less grip. And the 205/50 tire selection is larger and somewhat less expensive.

I only use my 6UL/RS2 set for performance driving. When I first got them, I ran them during summer and commuted with them, and discovered I don't really like running them on the freeways around Portland. All of our limited access roadways around here have noticeable ruts from all of the snow tires. The wider wheel and tire causes significant, noticeable, annoying tramlining in those ruts. That's where the car wants to climb up and out of the side of the rut. With the stock alloys and 205/45R16 tires, the car still tracks true, and the ruts aren't noticeable. But with the 225's, the car is nervous and darty on the freeways, constantly trying to climb out of the ruts. Lane changes require more concentration and anticipatory driving corrections. Ms Mobius especially does not like that, and she sometimes borrows the car.
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Old 12-05-2011, 07:50 AM   #19
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Some very good points!
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Old 12-05-2011, 09:37 AM   #20
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Quote:
Originally Posted by Mobius View Post

I only use my 6UL/RS2 set for performance driving. When I first got them, I ran them during summer and commuted with them, and discovered I don't really like running them on the freeways around Portland. All of our limited access roadways around here have noticeable ruts from all of the snow tires. The wider wheel and tire causes significant, noticeable, annoying tramlining in those ruts. That's where the car wants to climb up and out of the side of the rut.
I found that the tramilining was more related to the RS2's than to the tire size.
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