HELP HELP...... S3 DIFF / SUSPENSION PROBLEM

[Tom Mineral Grey S3]

Hey,
Can someone help me please??
Its a bit of a long winded story but if you have the time to read this it would be greatly appreciated.

I have just fitted a set of Eibach lowering springs to my 2001 S3. At the same time as having it lowered i also fitted a set of BBS CH reps (8x18 front with 215 40 18, 9x18 rear with 235 40 18) Since fitting the springs i have started to hear/feel a rubbing coming from the car. I originally thought it was brakes as the only way to describe the sound is like a faint rubbing when your pads need replacing. I have been driving for several days and the noise seems to be getting worse. I can now feel the rub through the pedals(especially when braking at low speed) and also when the wheels are turned it seems to be worse.
Around 6 months ago i had the diff oil replaced (as it was grinding and making a similar noise) so im thinking its not that which needs to be replaced again.
I have been told that the rolling radius of wheels can be very important and can effect the diff quite badly if its not correct, as you can see above i have put the sizes of the wheels and tyres ive had fitted, can anyone tell me if this seems ok and if not how to fix it???

Basically ive got noise off the diff which i think may be caused by the wrong rolloing radius and the last thing i want to do is keep driving the car and blow the diff up.
Can anyone help???

Thanks a lot guys

Tom

 

[Mpathe]

when lowering these cars the anti roll bar touches the wishbones and people tend to replace it with a uprated different shape bar, ive been looking into this as ive just lowered mine and they are touching. as for the different sizes of tyres - its recommend to have the same tyres all round on a 4 wheel drive evo or imprezza but the s3 has a haldex and is not permenant 4x4 so i dont know if its ok or not tho

 

[jonny87]

as mpathe said the rubbing will most likely be your arbs, try looking under the car without jacking it up and see if they are or not

second the rolling radius is very important on these cars, the haldex can easily get confused by different tyre sizes

my mate was explaining the importance of rolling radii to me just yesterday, something like the aspect of the tire is a percentage of the tire width, i cant remember the exact sum to work it all out but my educated guess would be that you need 35 profile on your rears rather than 40, dont quote me on that, theres plenty of other people on here who understand this much better than me though and im sure they will correct me if wrong

 

[Tom Mineral Grey S3]

cheers guys,

ill have a look at the arbs in the morning to see if they are touching.
i might be completely wrong but i was thinking i would need larger profile on the rear to compensate for the streched side wall??
like you said ive been led to believe that the rolling radius is very important............. its a shame i no sod all about it.
more help needed please.

 

[jonny87]

im pretty sure larger the width, smaller the aspect, like i say its a percentage of tire width

i had 265 30 19s on the rear and 235 35 19 on the front

 

[Tom Mineral Grey S3]

okey dokey,
were those rims on an s3?? and what width were they??

 

[jonny87]

yer both rims were 19x9

 

[tompearson]

Try this - tyre size calculator - Stock would be 225/40/18 so you want the same, or near enough, to that in terms of rolling radius.

 

[Tom Mineral Grey S3]

ok, how does this sound................ 265-35-18 rear and 225-40-18 front??

thinking if i go for the same rear size as yourself (as she wheels are the same width) and go slightly smaller on the front as they are 8 wide rather than 9.

Cheers