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Old 11-02-2007, 03:28 PM   #1
Slug71
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Default Wider back wheels AWD???

Can the rear wheels on a AWD car be wider than the fronts? I heard its bad for a AWD car but i thought it was just bad to have different size tires as in diameter??
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Old 11-02-2007, 03:53 PM   #2
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Its bad for the diffs to have tires different size diameter....good luck trying to find tires that are different widths and the exact same diameter.

It doesnt make any sense to put wider tires in the back anyway...some Auto-x guys in Evos and STis put wider wheels up front (with the same TIRE front and rear)...some people also experiment with staggered setups for competition use only...not for long term street use.
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Old 11-02-2007, 04:27 PM   #3
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So as long as its only the width that differs it should be ok? I was thinking going 225 Rear and 205/215 Front. Not a big difference.
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Old 11-02-2007, 04:32 PM   #4
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So, can someone explain to me how Porsches can run staggard?
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Old 11-02-2007, 04:53 PM   #5
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Most Modern Porshe's run a Mid Engine RWD or Rear Engine RWD layout.
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Old 11-02-2007, 05:01 PM   #6
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Quote:
Originally Posted by flukewrx View Post
Most Modern Porshe's run a Mid Engine RWD or Rear Engine RWD layout.
But the Carrera 4s are staggered too and to boot they aren't the same outer diameter. The fronts are 235/35-19 and the rears 305/30-19.
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Old 11-02-2007, 05:03 PM   #7
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^ True that
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Old 11-02-2007, 05:03 PM   #8
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Quote:
Originally Posted by flukewrx View Post
Most Modern Porshe's run a Mid Engine RWD or Rear Engine RWD layout.
Mhh hmm... so the 993/996/997 911s are RWD? and the Carerra 4s as stated above.

I think I could like a handful of modern AWD porsches running staggered.
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Old 11-02-2007, 05:15 PM   #9
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all 4wd porsches are staggered
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Old 11-02-2007, 05:24 PM   #10
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Just because porsche does it on a toally different platform doesn't mean you can do it on a subaru. And you need to calculate the outside diamater of the wheel/tire combinations before just looking at the wheels and saying, hey that's good!
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Old 11-02-2007, 05:34 PM   #11
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That's almost 3% difference. and I can't remember of the allowable tolerance is 2% or 5%.

Last edited by LastResort; 11-02-2007 at 07:23 PM.
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Old 11-02-2007, 07:23 PM   #12
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Yes the AWD turbo porsches run staggered because they have that engine hanging over the rear axle. They need as much grip in the rear as possible to keep you from spinning into a tree.

Why would you want to run wider tires in the back? You're not doing your handing or performance any favors by doing so anyway. If one thing, having wider tires in the front to help keep the front end gripping would at least have some sort of logic behind it.
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Old 11-02-2007, 08:09 PM   #13
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Quote:
Originally Posted by moss View Post
Mhh hmm... so the 993/996/997 911s are RWD? and the Carerra 4s as stated above.

I think I could like a handful of modern AWD porsches running staggered.
If you read what I said it says MOST Modern Porshes. I did not say ALL.

If you really want to know how they are able to do it, you probably will have to ask the Porsche Engineers. However, having the engine in the rear of the vehicle instead of in the front probably has something to do with why they are able to run a staggered fitment.

Just because it works on a Porsche does not mean it will be able to work on a Subaru, however, feel free to try for yourself.
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Old 11-02-2007, 08:39 PM   #14
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So as long as its only the width that differs it should be ok? I was thinking going 225 Rear and 205/215 Front. Not a big difference.
A 225/40 is not the same height as a 205/40 or 215/40. They need to be the same within .25" in circumference. The only combos I can think of off the top of my head are 255/40/17 with 225/45/17 or 275/40/17 with 245/45/17.

Go here and play around for yourself:
http://www.miata.net/garage/tirecalc.html
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Old 11-02-2007, 09:13 PM   #15
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Quote:
Originally Posted by rougeben83 View Post
Yes the AWD turbo porsches run staggered because they have that engine hanging over the rear axle. They need as much grip in the rear as possible to keep you from spinning into a tree.

Why would you want to run wider tires in the back? You're not doing your handing or performance any favors by doing so anyway. If one thing, having wider tires in the front to help keep the front end gripping would at least have some sort of logic behind it.

Yes there is no logic behind why i want to do it, But it looks good
Thats the only reason.
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Old 11-02-2007, 09:17 PM   #16
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Looks like 225/40/17 and 205/45/17 might work though!!
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Old 11-02-2007, 11:25 PM   #17
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....d00000000000000000d.....

the GD chassis is a pig and understeers as it is...why do ya wanna make it WORSE???

this is a really dumb idea...been discussed here before....more than once ....and the answers will not change, this time

ya better off putting the bigger tires on the FRONT
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Old 11-03-2007, 12:29 AM   #18
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Different width tires are almost NEVER going to be the same diameter/circumference...there are very few exceptions (like the 225/45-17 and 255/40-17 mentioned above)

Porsches can run staggered sizes because they are DESIGNED that way and the gearing is set up to accept it...if the Porsche owner put 4 of the same diameter tires on he would be in trouble.

The front 2 wheels and the back 2 wheels need to be traveling the same speed (most of the time)...by running different size tires you would have one set rotating faster than the other and the center diff would die a horrible death.

Its dumb when people do it on VWs, and its even dumber on a Subaru...and like Uncle mentioned above, you would be better off with bigger tires in the FRONT.
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Old 11-03-2007, 12:47 AM   #19
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Yes but if you go to this do-da http://www.miata.net/garage/tirecalc.html 225/40/17R and 205/45/17F is such a little difference that it should be within tolerance. And ill be doing it on the GC Wagon chassis not GD.
I dont know maybe it is a bad idea, thats why im asking.

Last edited by Slug71; 11-03-2007 at 12:48 AM. Reason: Forgot something
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Old 11-03-2007, 12:50 AM   #20
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Quote:
Originally Posted by Slug71 View Post
Looks like 225/40/17 and 205/45/17 might work though!!
No. the circumference is 75.7" vs 76.2". That's 1/2" difference. Too much. But hey, it's your car...
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Old 11-03-2007, 12:52 AM   #21
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Looks like ill be bagging that idea then.
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Old 11-03-2007, 10:29 AM   #22
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Originally Posted by austinpike View Post
No. the circumference is 75.7" vs 76.2". That's 1/2" difference. Too much. But hey, it's your car...
That's just a nominal difference. You'd have to go check the specs for individual brands/models of tires to figure out what the actual difference is.

And I thought the accepted difference was 1/4" diameter, not circumference. Unfortunately, I can't find my Owner's Manual (or any of the other stuff in my glove box - what did I do with all that at my last track event... ) to confirm that.

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Old 11-03-2007, 11:34 AM   #23
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That's just a nominal difference. You'd have to go check the specs for individual brands/models of tires to figure out what the actual difference is...
Yes that assumes mathematically "perfect" tires. I would rather start with a calculated difference of nearly zero, assuming they would still be within 1/4" tolerance in the real world. That may not hold true comparing one brand/model to another, but within one model I would expect it to be a pretty good indicator. (assuming the OP is at least planning on running the same kind of tire on all 4 corners.)

Quote:
Originally Posted by some Subaru tech document
All of the tires on your AWD Subaru must be within 1/4 of an inch of rolling circumference.
http://www.subaru.com/common/faq/tech_info.jsp#4
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Old 11-03-2007, 11:34 AM   #24
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Tirerack says 1/4" circumference, or 2/32 tread depth.
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Old 11-03-2007, 11:44 AM   #25
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Our AWD system is different. the Porsche has a more rear biased system. Also their suspension geometry is different. Not to mention the engine is in the back. Long story short if you put wider wheels and / or tires on the back your car will suck to drive compared to what it does now. Like a few have said so far wider up front would likely be a better choice.
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