Tyres!

[RubyRS4]

A quick Q about tyre profiles.

With the AWD system, what happens if you run say 35 profile tyres on the front and 45 on the rear?

Or even if you have 35, 40, or 45 all round, but have an underinflated tyre?

How would that affect the AWD system?

Someone asked me last night, and I really didn't have a close enough/accurate answer.

[RubyRS4]

Just also thinking. If you're running 17" or 18" or 19" rims and you get a flat and fit the 16" spare, how does that affect things too?

[DaveB]

A quick Q about tyre profiles.

With the AWD system, what happens if you run say 35 profile tyres on the front and 45 on the rear?

Or even if you have 35, 40, or 45 all round, but have an underinflated tyre?

How would that affect the AWD system?

Someone asked me last night, and I really didn't have a close enough/accurate answer.

This has been covered before in detail somewhere; basically attesa does not like this, unless you can very closely match the rolling radius. Some people have been getting vibration through the s/wheel, 4wd lights coming on etc. from using mismatched rolling radius's. I believe it will handle a millimetre or two (ie. treadwear) but 16's on the front and 17's on the back for instance no good (ymmv)

Just also thinking. If you're running 17" or 18" or 19" rims and you get a flat and fit the 16" spare, how does that affect things too?

Again shouldn't drive very far like this, attesa (and your diff's I suppose) will not like this; only a 'limp home' solution.

[rb26stagea]

Attessa doesn't like variations like that: from what I understand, running odd sized wheels/tyres will cause damage in the long run.

[rb26stagea]

damn synchronised replies!

[RubyRS4]

Okay so thats obvious, mismatched rim sizes is BAD

What about 17" rims with 35 profile front and 40 profile rear?

Or even same profile all round, but spanking new 40 profile on the front and 50% worn 40 profile on the back?

[rb26stagea]

I've only had issues when there was a 50% or more difference in wear between the front and rear, and it showed itself as a steering shudder on light throttle corners, and even then, only intermittently. Personally, I wouldn't mess with different profiles, but different wear of the same profile shouldn't be too bad...

[RubyRS4]

Hmm,

Out of curiousity I just checked my tyres. I purchased two sets of rubber on Tuesday and didn't think about mismatching profiles. Never gave it a second thought. Seems I'm running 40 on the front and 45 on the rear on 18" rims. I'm not experiencing any shudder or side effects, but I guess I should grab another set of 45s today for the front.

I only fitted the rims last night, and drove a whole of 8.5kms to work in 50-60kph zones, so I should be safe for today.

I'm gunna buy my friend a beer for bringing up the discussion.

Still on another note: it seems pretty silly designing an AWD system where unevenly worn tyres will result in more wear/stress on the AWD system. There must be some 'slip' there somewhere?

Edited April 9, 2008 by RubyRS4

[yokotas13]

simple solution

take out front driveshaft

[RubyRS4]

simple solution

take out front driveshaft

I'd rather not.

[MRO]

simple solution

take out front driveshaft

Burnouts!

[webng]

Here's what I found. They don't have to be exactly the same tyres. As long as the rolling dimension is the same or within something like a 2% tolerance (don't quote me on the exact percentage) it's fine. This is to allow for uneven wear and tear. i have different profile tyres front and back but the rolling dim is nearly the same (R - 235/45/17, F - 215/50/17)

there are a few websites to calculate rolling dimension (tyre circumference) that are quite good, here's one i googled. some other ones give you the actual % too.

http://www.club80-90syncro.co.uk/Syncro_we...0calculator.htm

EDIT: Here's a better one

http://www.nitinchordia.com/upsizing.htm

Edited April 10, 2008 by webng

[yokotas13]

I'd rather not.

WHY?

yuo have a Stagea, yoru not going to be breaking traction any time soon taht coudl be dangerous, less parasitic drag on your drivetrain.....

i mean, unless you drive in snow on a regular basis, is there a reason not to?

[RubyRS4]

Here's what I found. They don't have to be exactly the same tyres. As long as the rolling dimension is the same or within something like a 2% tolerance (don't quote me on the exact percentage) it's fine. This is to allow for uneven wear and tear. i have different profile tyres front and back but the rolling dim is nearly the same (R - 235/45/17, F - 215/50/17)

there are a few websites to calculate rolling dimension (tyre circumference) that are quite good, here's one i googled. some other ones give you the actual % too.

http://www.club80-90syncro.co.uk/Syncro_we...0calculator.htm

Thanks for that

I've done the calculations and the F circum is 1968mm compared to the R circum at 2040mm. Thats a 3.6% difference in circumference. At 100kph thats a difference between the two of 0.2kph.

I'll still play it safe and get another 2 235/45 tyres

[RubyRS4]

WHY?

yuo have a Stagea, yoru not going to be breaking traction any time soon taht coudl be dangerous, less parasitic drag on your drivetrain.....

i mean, unless you drive in snow on a regular basis, is there a reason not to?

Because its my car not yours, and you are only speculating on how I drive now. So ... I'd rather not.

[webng]

When I first bought the car it had more then 2% difference on the circumference between front and rear which lead to a funny "farting/groaning" sound when I turned the engine off, and a strange shuddering at about 70kph. The Attessa reservoir dropped pretty quickly too but once i topped that up and got new tyres all was good.

re: rwd vs awd... I personally prefer awd, otherwise i would have bought the RS version wouldn't i. Much prefer the security of the awd, especially when wet.

[Sydneykid]

WHY?

yuo have a Stagea, yoru not going to be breaking traction any time soon taht coudl be dangerous, less parasitic drag on your drivetrain.....

i mean, unless you drive in snow on a regular basis, is there a reason not to?

Parasitic drag? In order for my Stagea to proceeed down the road the front wheels have to turn, whether that's by 4wd or via the rear wheels and the road. So all you are talking about is the small effort required to turn the drive shafts and the front diff, neither of which are excessively large (weight and drag). Especially in comparison to wheels, tyres, brake rotors etc. Lowering a Stagea too much soaks up more power than that.

Cheers

Gary

[yokotas13]

which is why its got a t04e going on it..

point?

[RubyRS4]

which is why its got a t04e going on it..

point?

He's still not making any sense.

[leetom]

He's still not making any sense.

i thought he went to iraq