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      11-29-2012, 04:05 PM   #1
dreamweaver
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tyre size different on front than rear

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Was having a look round the car today and never noticed but the rear tyres looked smaller than the front ones, upon closer inspection the rears are a smaller size, is this how it should be?.

4 Weeks old today and I have a brake squele at low speed when stopping, she sounds like a dust cart,.
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      11-29-2012, 04:40 PM   #2
ovekvam
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If the tire size is different, the wider tires are supposed to be at the back.
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      11-29-2012, 04:59 PM   #3
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Originally Posted by ovekvam View Post
If the tire size is different, the wider tires are supposed to be at the back.
That.
But you can drift easier with smaller rear tires
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      11-29-2012, 05:43 PM   #4
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Yup the rears are 245 35, fronts 225 40
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      11-29-2012, 05:57 PM   #5
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For the brake squeal noise, that is due to parking brake. My dealer finds it normal but I do not agree. If you park without parking brake, e.g. With 1st gear engaged, the noise will disappear. In any case the noise lasts only few brakes and then it is gone, at least in my case...
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      11-30-2012, 01:32 AM   #6
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Originally Posted by XavVD View Post
For the brake squeal noise, that is due to parking brake. My dealer finds it normal but I do not agree. If you park without parking brake, e.g. With 1st gear engaged, the noise will disappear. In any case the noise lasts only few brakes and then it is gone, at least in my case...
How can the parking brake be involved in making any noise when you are stopping? You don't apply the parking brake until you are stationary.
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      11-30-2012, 02:25 AM   #7
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Quote:
Originally Posted by ovekvam
Quote:
Originally Posted by XavVD View Post
For the brake squeal noise, that is due to parking brake. My dealer finds it normal but I do not agree. If you park without parking brake, e.g. With 1st gear engaged, the noise will disappear. In any case the noise lasts only few brakes and then it is gone, at least in my case...
How can the parking brake be involved in making any noise when you are stopping? You don't apply the parking brake until you are stationary.
From my understanding, parking brakes generally use the rear caliper but activate them mechanically and not hydraulically. Then how the noise potentially occurs, no clear idea but I would suspect that caliper can get a bit of free play that generates some squeal noise (under low force braking) and after a few braking actions caliper has absorbed this free play (centering of shim in a pin/piston, shim getting perfectly perpendicular to pin/piston ???). Perhaps as parking brake is applied mechanically (in parallel to normal hydraulic brake system) force to caliper is applied at different location and not perfectly in uniform way that generates some shim slanting that is corrected after a few brake actions. Any brake specialist to confirm???
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      11-30-2012, 02:31 AM   #8
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Quote:
Originally Posted by dreamweaver View Post
Was having a look round the car today and never noticed but the rear tyres looked smaller than the front ones, upon closer inspection the rears are a smaller size, is this how it should be?.

4 Weeks old today and I have a brake squele at low speed when stopping, she sounds like a dust cart,.


Rears should 245 35 and fronts 225 35/40 depending on brand
It is possible that the car came with freight wheels fitted and your dealer's tyre fitter mixed them up before delivery. They need to be swapped as it will change the tracking on the car and effect the handling
Whilst there, get them to look at your hand brake adjustment.
The Brake noise is probably due to the hand brake pads (seperate from the disc pads) slightly rubbing whilst they seat in.

If you cannot stand the noise
You can fix it by driving your car slowly for a few hundred metres.
With the hand brake engauged to the take up point (nearly stopping the car) You simply drive along and release/pull on and off for a about 10 seconds at a time for a minute or two (this will 'seat' the pads). When you have released it and the noise disappears it should be OK from then on. If this does not fix it, take the car back to your dealer.
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      11-30-2012, 03:04 AM   #9
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Quote:
Originally Posted by XavVD View Post
From my understanding, parking brakes generally use the rear caliper but activate them mechanically and not hydraulically. Then how the noise potentially occurs, no clear idea but I would suspect that caliper can get a bit of free play that generates some squeal noise (under low force braking) and after a few braking actions caliper has absorbed this free play (centering of shim in a pin/piston, shim getting perfectly perpendicular to pin/piston ???). Perhaps as parking brake is applied mechanically (in parallel to normal hydraulic brake system) force to caliper is applied at different location and not perfectly in uniform way that generates some shim slanting that is corrected after a few brake actions. Any brake specialist to confirm???
On BMWs the parking brake is usually a drum brake integrated in the rear brake rotor. It is a completely separate system from the regular brakes.
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      11-30-2012, 04:35 PM   #10
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Quote:
Originally Posted by dreamweaver View Post
Was having a look round the car today and never noticed but the rear tyres looked smaller than the front ones, upon closer inspection the rears are a smaller size, is this how it should be?.

4 Weeks old today and I have a brake squele at low speed when stopping, she sounds like a dust cart,.
I see you have the M-sport model, which will have a 'staggered' wheel set, with wider rims on the rear. Rear tyres are not smaller, but have a lower aspect ratio which keep the RC to very similar figures, front and rear.

Brochure shows:
17" wheel set are: 225/45 R17 front and 245/40 R17 rear
18" wheel set are: 225/40 R18 front and 245/35 R18 rear

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      11-30-2012, 04:53 PM   #11
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Some of the staggered wheel sets have 255-tires in the back.
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