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Offline silverstripes

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Warped Disk Rotors
« on: March 21, 2015, 10:13:59 am »
HI chappies

I have not got warped disks nor never had on any of my bikes  :046: But there have been many posts about this and even one about 10k service and the possibility of one disc being warped due to the linked brakes.

So I have a theory and it's only that so lets open the debate. For those who have suffered with this, when you brake and come to a stop at traffic lights and junctions, do you sit with the front or back brake applied ?. My theory is that the heat soaks out of the disk through the pads and the calipers, thus cooling the disc unevenly. I accept on an incline there is no option, but I always try to not apply any brake when stopped front or rear.

Ok that's my theory  :112: what to the experts think  :028:
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Offline Coconut

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Re: Warped Disk Rotors
« Reply #1 on: March 21, 2015, 10:58:14 am »
UK "Discs" = US "Rotors" .....

I'm no expert but it is a good theory and one I have both heard of before, and experienced -
albeit on a car with Auto transmission when the foot brake was always kept applied after stopping
at Lights etc, rather than engaging the Parking Brake or setting the Gearbox to "Park".

What seems to happen is that the brake pads -
which have been heated up from the friction of braking,
remain in contact with a small area of the disc after stopping. 

The longer and harder the braking was before stopping,
the hotter the discs and pads will be.
As the discs get hot they expand slightly.

After stopping the discs begin to cool down, and contract slightly,
but the portion in contact with the hot brake pad does not cool down as quickly
as it is somewhat insulated by the hot pads surrounding it,
and that section therefore does not contract as much, or as quickly
as the rest of the disc in free air, and this can lead to warping.

By releasing the brake after coming to a stop,
the pads will not be in such tight contact wth the disc.
The effect will still be present, but to a lesser degree.

It might be good practice, depending on individual circumstances, to stop slightly short,
and then every few seconds roll forward ( or back ) slightly so that one area of the disc
is not left constantly under the pads, thus allowing more even cooling to take place  :084:

« Last Edit: March 21, 2015, 11:02:53 am by Coconut »

Offline Trophy Tom

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Re: Warped Disk Rotors
« Reply #2 on: March 21, 2015, 11:03:36 am »
 :460: Never had any problem myself but I think what you say makes a lot of sence
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Offline cropbiker

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Re: Warped Disk Rotors
« Reply #3 on: March 21, 2015, 11:15:03 am »
It is certainly a theory with a lot of logic.

I have not had any issue with my discs and I can't say that I consciously sit at lights with brakes on unless on a slope.

I do drive an automatic car and never put the handbrake on and only if I am stopping for more than a minute or so will I put the car in park. But there too I have never had a problem with the discs on my automatic cars either..
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Offline Coconut

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Re: Warped Disk Rotors
« Reply #4 on: March 21, 2015, 11:24:25 am »
I had it hppen on a Volvo XC90 - heavy car, heavy braking = lots of heat.

Being an Auto, and being too lazy to take my foot off the pedal
when I probably should have done I ended up with warped front discs.

New discs fitted and modified my driving style ( used "P" more ) = no further problems.


Offline Gordon3xBBB

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Re: Warped Disk Rotors
« Reply #5 on: March 21, 2015, 02:06:54 pm »
It being my bike that has the Warped Front Discs (Rotors) a bit more explanation might be required....

I've only done 1600 Miles on it and the Tech thought they were warped shortly after I took delivery - why didn't they spot it earlier on the PDI ? - so 8,500 miles were done by the Previous Owner.

I obviously can't speak for the P.O. but I live in a hilly area (The Cotswolds) and stops at Traffic Lights, Junctions etc are frequent so application of either brake but usually the Rear is often a requirement.

As stated in the previous post by me (10K Service...) the Disc Run-Out Service Limit is only 0.15 mm which is not very much at all in the grand scheme of things. The "Pulsing" doesn't really bother me as I can make it go away by braking harder on the Front.
When I get a new attachment bracket for my DTI I will measure the run-out of both front discs and report back..
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Offline malcolm

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Re: Warped Disk Rotors
« Reply #6 on: March 21, 2015, 03:33:32 pm »
If that theory was correct most warped discs would be on the rear as most people use the rear brake when stopped. The reports of warped discs I have read about on bikes and car forums are usually on the front discs.
The theory I think is most lightly is manufactures are making discs thinner to save weight and this is leading to more warped discs

Offline Gordon3xBBB

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Re: Warped Disk Rotors
« Reply #7 on: March 21, 2015, 03:47:46 pm »
I've just noticed that the Run-Out Service Limit for the Rear Disc (Rotor) is 0.5 mm, compared to the 0.15 mm Run-Out on the Front Discs.
The Rear Disc is also a "solid" disc as opposed to the Fronts which are "Floating" type with Bobbins...
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1997 Trophy 900 MkII (aka My Lady Sharon)
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