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Tifun
11-18-2009, 07:38 PM
I'm looking at wheels with these specs.....trying to figure out if this is within that B5 tolerance. I had a link to a tire calculator but since I lost all my bookmarks from the last crash I have yet to find it again [:(] Any help on this one????

f 18x8.5" 215/40/18
r 18x10" 235/40/18

andyrew
11-18-2009, 07:57 PM
http://www.miata.net/garage/tirecalc.html

Google miata tire calculator

andyrew
11-18-2009, 07:59 PM
Go with 215/45/18's

.8% different 1/2 a mph at 60..! Less than the diff between new and old tires!

keeganhartman
11-18-2009, 08:01 PM
The difference is 2.5% i calculated. A 225/40 and a 215/40 would be closer, but a 215/40 and a 245/35 would be damn near perfect for you.

Tifun
11-18-2009, 09:35 PM
Yep, that's the one, thanks guys!

onemoremile
11-20-2009, 10:14 AM
There is a much better one here that lets you compare several sizes next to each other. It also shows you the tires available in each size.
http://www.1010tires.com/tiresizecalculator.asp

That site also has a wheel calculator that helps you calculate offsets and clearances with a graphical representation.
http://www.1010tires.com/WheelOffsetCalculator.asp

onemoremile
11-20-2009, 10:15 AM
I'll never understand staggered setups on a quattro car. Might as well run fat tire up front too. The handling will be better, there will be no issues with the diffs, and you can rotate them front to back and get longer life out of them.

keeganhartman
11-20-2009, 08:17 PM
Easier to fit the wider wheel in the rear with no turning. And you need to go wide where you can haha.

onemoremile
11-20-2009, 08:21 PM
Easier to fit the wider wheel in the rear with no turning. And you need to go wide where you can haha.

You can fit the same size tire up front and still turn. The rear actually has less clearance than the front due to the shape of the upright. A taller than stock tire is hard to fit in the rear. I've run 245/40-17 all around without issue.

keeganhartman
11-20-2009, 08:26 PM
I guess it all depends on what you're doing with the car.

jprice
11-21-2009, 11:30 AM
Skip. Wider in the rear means MORE understeer from a platform that give a lot of it to begin with.

onemoremile
11-21-2009, 09:50 PM
I guess it all depends on what you're doing with the car.

Driving. Stopping and turning are both better with a matched set. [rolleyes]

DND
11-22-2009, 09:20 AM
This site will give you a side by side graphical comparison of any size tire and rim combination and calculate the differences for you:
http://www.wheelsmaster.com/rt_specs.jsp

DND
11-22-2009, 09:25 AM
P.S. Unless you like stretch and poke those sizes don't make a lot of sense.
I'm running 245/35-18x8.5et38 matched front and rear and just barely clearing my uprights but it works with no rubbing with the tires I've got.

Tifun
11-22-2009, 03:23 PM
My car isn't a dedicated track car, I would prefer looks over handling sometimes. If I want super handling I'll swap out and put my track wheels on [:p] I would prefer not to run stag but for the wheels I have but don't have a lot of choice nor willing to spend and extra $2500 to get matching fronts from HRE.

Like Jim said the rears can't hold as wide a wheel. I run 9" all around with zero rubbing on a 225/40/18. It does have some stretch but the car still handles way better than stock so regardless it may not handle as well as a track setup it still outperforms stock and in the end is the best compromise for what I am looking for [drive]

Thanks for those links, nice to add more to my bookmarks hehe. I've started sending stuff to myself via PM so I can always have them if my ish ever crashed again [headbang]

-Keith

jprice
11-22-2009, 05:30 PM
I would prefer looks over handling sometimes.
Yes, it will look like the car is owned by someone who doesn't have a clue what they're doing with the platform.

Tifun
11-22-2009, 05:57 PM
Yes, it will look like the car is owned by someone who doesn't have a clue what they're doing with the platform.

I was going to type out a real response to this but I think you just need to stop being stuck on one look style and function and realize others don't share your taste nor opinion and realize this is a community not a dictatorship and understand that there will be different styles.
-Keith

keeganhartman
11-22-2009, 06:10 PM
Agreed. http://zilvia.net/f/chat/259260-tire-stretch-calculator-wheelwhores-tyrestretch.html This one isn't bad either.

JonAth4n
05-17-2016, 08:21 AM
Hey guys, I'm in need of 2 tires for my rears but I'm not sure which size i should get...

currently,
Fronts: 18x8.5 WITH 215/35/18
Rears: 18x9.5 WITH 215/35/18

I would like to get 225/35/18 for the rears since I don't like the crazy stretch it currently has but I'm not sure if that would be bad for the quattro system

Any help is greatly appreciated! Thanks in advance

ray4624
05-17-2016, 09:32 AM
Hey guys, I'm in need of 2 tires for my rears but I'm not sure which size i should get...

currently,
Fronts: 18x8.5 WITH 215/35/18
Rears: 18x9.5 WITH 215/35/18

I would like to get 225/35/18 for the rears since I don't like the crazy stretch it currently has but I'm not sure if that would be bad for the quattro system

Any help is greatly appreciated! Thanks in advance

did you read the 6 year old thread you bumped or nah?
dimensions within 3% and youre fine

DoesntCare
05-17-2016, 09:39 AM
did you read the 6 year old thread you bumped or nah?
dimensions within 3% and youre fine

Is it 3% diameter or circumference?

walky_talky20
05-17-2016, 10:56 AM
It is circumference. And I don't believe Audi actually published the 3% figure. The only figure I know that Audi published equates to about 1% difference, as is discussed below:


It is all about rolling radius, also known as circumference. Quattro doesn't really care about the width on it's own, BUT the circumference is a function of both the series *and* the width.

Even if you have 4 tires that are exactly the same, even the wear on the tread makes a difference. Audi's official recommendation is to stay within 4/32" of tread depth for all 4 tires. They don't give a specific recommendation for allowable circumference differences other than they must be "the same". I would take that to mean as close as possible.

You can, however, use their tread wear recommendation to extrapolate a circumference difference recommendation. Let's do some math. Here we go:

- Given the stock size of 205/60/15
- Diameter when new = 24.7"
- Circumference when new (diameter*pi) = 77.6"

Now factor in the tire wear:
- Wear of 4/32" changes diameter by 8/32" (4/32 each on the top and bottom)
- 8/32 = .25"
- Worn diameter (24.7 - .25) = 24.45"
- Worn circumference = (24.45*pi) = 76.8"
- Difference compared to new = .8"
- Difference percentage (.8/77.6) = 1%

A difference in circumference of about 3/4", or about 1%, given maximum allowable wear difference on the stock 15's. So you should stay within 1% in circumference.

For comparison: Subaru, who's AWD system is more sensitive than ours(uses variable locking clutches), recommends staying within 1/4" in circumference. I'd recommend staying closer to that if possible.

ray4624
05-17-2016, 11:22 AM
ah my mistake. Meant circumference