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Old 11-27-2008, 10:36 PM   #1
wopdeeze
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Default 255 40 17 front 225 45 17 or 235 45 17 rear issues?

Looking into stuffing 255s up front and either 235s or 225s in the rear, has anybody run this setup for a while and have some issues to report? i know there is a bit of size difference between them but im looking more for traction in cornering on circuit/time attack. comparing front and rear tire temps on 225s all around fronts heat up much more and cause more understeer. any feedback would be appreciated. before anybody says it i know about differential problems could arise but not high on my priority list. thanks

Jarrett
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Old 11-28-2008, 12:16 AM   #2
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tires should all be the same size
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Old 11-28-2008, 12:18 AM   #3
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If you were FWD or RWD then go staggered but AWD...all wheels, should be the same size with the same size tires.
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Old 11-28-2008, 12:29 AM   #4
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Your center diff would not like that...if anything run slightly wider rims in the front with the same size tires.
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Old 11-28-2008, 04:09 AM   #5
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i understand running the same size tires, i plan on running the same tires all around for normal day to day driving but on the track stagered might be better for me for hard cornering and faster speeds through corners. this is not for drag or autocross use.
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Old 11-28-2008, 02:18 PM   #6
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I would think that there are much better ways to counter understeer. I have never seen or heard of a AWD car using bigger tires up front for a track. Tens of thousands of AWD cars are raced and I'm guessing that there is a reason why people don't do that. 235/45/17 would probably be tall enough to cause the center diff to overheat and lockup.
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Old 11-28-2008, 06:06 PM   #7
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yes, i could install a front diff, but the cost of the diff, plus install probably around 1500-2000 dollars.
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Old 11-29-2008, 01:29 PM   #8
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An inexpensive way to kill a little understeer is to use some small front wheel spacers to pooch out the track. Don't put them on the rear. That way you don't have to deal with two sizes and you can rotate your tyres for wear.

When I say small spacers I mean 3-5 mm with longer wheel studs all the time. For track use only you could get away with much thicker spacers. Big spacers are hell on wheel bearings running straight down the road, but when you vector in the cornering component, the forces are more balanced. Let your conscience be your guide.

(I'm not being hypocritical. It is a matter of applications. Parts for the track are not just for "looks".)
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Old 11-29-2008, 02:04 PM   #9
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Run the same size tires all around. Use driver technique, suspension tuning, and alignment to reduce understeer.

I run 255/40-17 R888's, 500/400 RCE T2's, Whiteline swaybars 27-29 Front (set on softer setting) & 24-26 rear (set on stiffest setting), Kartboy F&R endlinks, and an alignment at -3 front camber with 1/16 toe out & -1.5 rear camber with 0 toe. Car handles phenomally on the track. It's a little tail happy if anything.
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Old 11-29-2008, 06:07 PM   #10
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finally a little decent feedback, I am already running spacers, 7mm front and 3 mm rear it helped a little but not exactly what im looking for. when i say im getting understeer im not just saying it because it feels like it pushes a little, the reason im looking into this is to get that last bit out of the car before she pushes through or breaks loose. i would love to go 255 all around but im just worried for fittament in the rear. and when it comes to tires im cheap, i use re070s because i can get them cheap and im working on getting some 255 070s but they usually only come up in pairs. here is my current setup.

Camber -2.5 (3-3.5 for track)front and -2.5 rear
Caster 4
Toe front 0 rear 0
DMS 40mm Gold
DMS adjustable camber plates
helix 21mm FSB
Hotchkis 25mm RSB
Hotchkis rear endlinks
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Urethane control arm bushings
Cusco Front and rear strut bars
225 45 17 RE070
17x7.5 BBS RG-R

and im waiting on the WL roll center kit to arrive.
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Old 11-29-2008, 08:20 PM   #11
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First thing I'd try is to take out some of the rear camber. Like I said, I run -1.5 in the rear.

Running different size tires really isn't an option.
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Old 11-29-2008, 09:12 PM   #12
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but think about it
255 40 17
overall diameter 635.76mm

225 45 17
overall diameter 634.23mm

with the difference in overall diameter being 1.53mm its like having having 2 brand new tires and 2 used tires with 5000 miles on them. i would think that is still the the tolerance for the center diff. even taking into account drag from the wider front tire i think that it would be less of an impact as say a front lsd compared to wider tires and front open diff.
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Old 11-29-2008, 09:35 PM   #13
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Quote:
Originally Posted by mav1c View Post
First thing I'd try is to take out some of the rear camber. Like I said, I run -1.5 in the rear.

Running different size tires really isn't an option.
Yea for sure dial out some of that rear camber, ^like down to between -1 to -1.5 and add a tad bit of front toe

Also, when people talk about running wider wheels in front, you can use the same size tires all around, but the wider front wheels will cause the tires to have a wider contact patch. You can also run lower offset wheels in front...
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Old 11-29-2008, 09:57 PM   #14
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I noticed you said you are running a 21mm front and 25 mm rear swaybar. From everything I have read here it seems you want a bigger front swaybar to increase front end grip. McPherson strut suspension gains camber as the suspension compresses reducing grip in corners, bigger swaybar would reduce roll which would reduce suspension compression therefore reducing the amount of camber you gain. I am not sure if this still holds true with stiff coilovers as opposed to something more stock but this is what I get from what other people have said. You should go to the suspension forum and read the stickies.
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Old 11-29-2008, 10:30 PM   #15
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Quote:
Originally Posted by wopdeeze View Post
but think about it
255 40 17
overall diameter 635.76mm

225 45 17
overall diameter 634.23mm

with the difference in overall diameter being 1.53mm its like having having 2 brand new tires and 2 used tires with 5000 miles on them. i would think that is still the the tolerance for the center diff. even taking into account drag from the wider front tire i think that it would be less of an impact as say a front lsd compared to wider tires and front open diff.
You might want to look at these pages from TireRack:

http://www.tirerack.com/tires/Spec.j...e1=yes&place=1

This has the true tyre sizes. Not calculated.

http://www.tirerack.com/tires/tirete...currentpage=52

The wear allowance: "Subaru Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth. "
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Old 11-29-2008, 10:32 PM   #16
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Originally Posted by afviper View Post
I noticed you said you are running a 21mm front and 25 mm rear swaybar. From everything I have read here it seems you want a bigger front swaybar to increase front end grip. McPherson strut suspension gains camber as the suspension compresses reducing grip in corners, bigger swaybar would reduce roll which would reduce suspension compression therefore reducing the amount of camber you gain. I am not sure if this still holds true with stiff coilovers as opposed to something more stock but this is what I get from what other people have said. You should go to the suspension forum and read the stickies.
dont really have a problem with body roll or suspension camber gains. after 8 hot laps the front tires get greasy because of increase load for braking for corners, and cornering. after a pit an average tire temp for fronts is around 180F and rears 130F with a track tarmac temp of 100. If you increase the sway bars soo stiff that you completely eleminate body roll you will in turn decrease cornering ability. and actually make your suspension work harder with less effectevness (not a great speller) and can be sometimes dangerous because of less warning for breakaway.

i have actually seen this done before twice one on BOZZ Speeds 02 STI spec c and another 05 spec c but i dont speak japanese so it would have been difficult for me to ask questions about it.
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Old 11-29-2008, 10:45 PM   #17
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Originally Posted by Web Foot STi View Post
You might want to look at these pages from TireRack:

http://www.tirerack.com/tires/Spec.jsp?make=Bridgestone&model=Potenza+RE070&part num=245WR7RE070&vehicleSearch=true&fromCompare1=ye s&place=1

This has the true tyre sizes. Not calculated.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18&currentpage=52

The wear allowance: "Subaru Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth. "

within 1/4inch is 6.35mm so it is well within the wear allowance. but there is nothing about different section widths. so say i bought 4 brand new tires, 255 40 17 re070s and 225 40 17 re070s and had them shaved to match exactly the same circumference. theoretically that would be well with in the 1/4 in tire circumference.
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Old 11-29-2008, 11:27 PM   #18
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Quote:
Originally Posted by wopdeeze View Post
within 1/4inch is 6.35mm so it is well within the wear allowance. but there is nothing about different section widths. so say i bought 4 brand new tires, 255 40 17 re070s and 225 40 17 re070s and had them shaved to match exactly the same circumference. theoretically that would be well with in the 1/4 in tire circumference.
It's not quite that good.

The chart shows the two tyres within 0.1" OD. 4/32nds is the wear allowance on the OD. This says it's OK by 0.025", or less than 1/32nd".

Pi*OD=C
3.14*24.9"=78.2"
3.14*25.0=78.5"

Delta=0.3">1/4" Not quite within spec.

I feel that your front tyre wear would get rid of that 0.050" difference pritty fast at the track. But it is just an opinion. You should see what my Victoracers look like.
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Old 11-29-2008, 11:41 PM   #19
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Keep in mind that the tire sizes probably have a bit of a fudge factor, especially when considering that you may not be mounting them on the factory-spec wheel.

However, if the tires are shaved to match, i would think it'd work OK.



I don't think it's a very good solution to your problem though. Not saying i know a better way, but it is a curious way to go about it.
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Old 11-30-2008, 12:17 AM   #20
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Actually it's an elegant solution given the Subarus weight distribution. The down side, if the tyre OD's work out, is that us church mice can't rotate our tyres to equalize wear. Porsche did it with the 959, 235/45 fore and 255/40 aft, but that was a $225,000 homologation special 20 years ago.

For fun:
http://auto.howstuffworks.com/porsche-959-history.htm
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Old 11-30-2008, 07:14 AM   #21
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Actually it's an elegant solution given the Subarus weight distribution. The down side, if the tyre OD's work out, is that us church mice can't rotate our tyres to equalize wear. Porsche did it with the 959, 235/45 fore and 255/40 aft, but that was a $225,000 homologation special 20 years ago.

For fun:
http://auto.howstuffworks.com/porsche-959-history.htm
exactly, but thats why i go for used tires, they dont last long enough for me to have to rotate them.
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Old 11-30-2008, 07:26 AM   #22
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HKS konsai run 255/40 on front and 225/45 on rear wheels GRB 2008
i dont understand it
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Old 11-30-2008, 11:19 PM   #23
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HKS konsai run 255/40 on front and 225/45 on rear wheels GRB 2008
i dont understand it
Correct, here is a link
http://www.hkskansai.co.jp/democar/s...b_a/grb_a.html

only real difference from my car i think is the DCCD transmission and front diff. there is a huge difference between the 265 35 18 and 245 40 18 that they are running.
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Old 11-30-2008, 11:51 PM   #24
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I know of some autoX subarus that run a wider front than rear.

you can run a wider tire as long as over alll dim. is the same as you guys know
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