Front brake effort fluctuation

[Otley77]

Hi all, here's the thing: my R1200RS has slight fluctuation of brake effort, its an advisory on the mot. Braking is fine, I can feel slight fluctuation, more noticeable when coming to a full stop, for the last few rotations of the wheel.
It's not a serious problem, annoying and spoils the ride a little.
Any thoughts on a straightforward and not expensive fix?

[runnerhiker]

Is the front tire cupped?

I am not quite sure what you mean by fluctuation. If you apply the front brake and you feel a pulsing fluctuation at the lever, then tire cupping is probably the reason. If by fluctuation you mean the amount of effort (force) applied to the brake lever (sometimes needs lots of effort, sometimes needs little effort), the cupping is not something to look at.

[Otley77]

Hi, the front tyre is new Metz Roadtec.
The fluctuation is most noticeable on the last few rotations as the bike comes to a halt. It feels like a binding then release. Often caused by warped discs, but mine look good.

[Grumpy Goat]

Hi all, here's the thing: my R1200RS has slight fluctuation of brake effort, its an advisory on the mot.

What is this advisory on the MOT? Do you mean that during your MOT inspection they passed it with a note that there was this slight fluctuation of braking effort?

Did this start after the new front tire was installed? Could be warped disc (have to do a runout test, not just a visual).

[Mark]

Hi all, here's the thing: my R1200RS has slight fluctuation of brake effort, its an advisory on the mot. Braking is fine, I can feel slight fluctuation, more noticeable when coming to a full stop, for the last few rotations of the wheel.
It's not a serious problem, annoying and spoils the ride a little.
Any thoughts on a straightforward and not expensive fix?

I had a similar situation as well with my front brakes, turns out it the front wheel bearings were the problem.

Mark

[Duckbubbles]

I'll relate a problem a couple of friends had while changing a tire on a Coates machine. When they broke the bead on one side, they didn't pay enough attention to the wheel placement and put pressure on the edge of the front brake disc when breaking the bead bending the disc slightly- enough that it was very evident on the "test" ride.

Frank

[Otley77]

The problem was present before the new tyre was fitted.
There is no vibration from the front wheel at speed, so it's balanced ok. The wheel bearings seem good, no play is apparent.
I'm going to check the run out on the discs. What are the limits on run out?
Thanks all for your ideas ?

[Chris216]

You might try cleaning or scuffing the surface of the discs with scotchbrite or something similar. The pads actually leave a deposit on the discs and if it becomes uneven it will feel similar to warped discs.
Chris

[Otley77]

Disc run out is 0.10mm on r/h disc, 0.12mm on the l/h disc. The Haynes manual gives a service limit of 0.15mm. So the run out us within limits, but I think this is the issue. Ho hum, looks like new discs ...