lunge when braking over bumps

[BobSut]

Hello!

 

I got my 2003 (built 12/2002) twin-spark R1150RTP only last May, and I've only put 19500 freeway commuting miles on it, so I'm still finding new things to ask questions about.

 

I have (fully integrated) Integral ABS, which the Clymer book says I must take the latter to the dealer for even simple service like fluid replacement and bleeding. Really?

 

When I'm braking on an uneven surface, the ABS intervention seems both too sensitive and too severe. When the suspension unloads or the pavement is damaged, the bike will seem to lunge forward momentarily, then braking will resume. This happens whether I'm using only the front brake lever (as usual) or both front and rear together. I have never seen a warning light after the pull-away test. I have checked both front and rear sensor triggers for location relative to the sensor wheel.

 

Is this normal behavior, or a common problem, or something unique to my bike?

 

(As with any such persistent behavior, I'm used to it and have learned to anticipate it, but my lovely Favorite Passenger finds it disconcerting. And I'm all about relieving her disquiet.)

 

Thanks for any insights!

[Tri750]

The braking release under uneven surfaces is pretty normal.

Some things that can effect its severity are, SOME aftermarket pads having too much or not enough initial bite, worn or hard tires, wrong tire pressures.

Check to see what pads you have but to a certain extent, they do that under rough pavement conditions and heavy braking.

If it happens often, why all the heavy braking?

 

But the 1100 ABS was maybe a bit worse as it was even less advanced.

 

As far as "too sensitive or too severe" in relation to what?

 

Unless you have a typo, 19500 miles would allow you the time to get used to a bikes tendencies no matter what they were.

 

The brake flush can be done at home with YouTube videos and a weird funnel you can buy from BeemerBoneyard .

 

 

 

[dirtrider]

Afternoon Bob

 

That ABS jump is pretty common on the early 1150Rt's -- some riders (like myself) got it pretty regularly as I am a fast rider with aggressive braking habits & ride on somewhat rough roads surfaces.

 

The problem stems from the rear wheel anti-lift algorithm calibrated into the ABS system.

 

What happens is: the rear wheel starts to decel at a rate that the ABS system thinks is too fast of a spin-down rate so thinks the rear wheel is lifting. It then quickly counters that by releasing the front brake to bring the rear wheel back down. (on rough road surfaces, or gravel-on-the-road surfaces, the rear tire loses traction during hard braking)

 

Overly aggressive rear brake pads or sticking caliper pins on the rear brake caliper can make the problem worse.

 

On my old (personal) early 1150RT's I would install the organic rear brake pads as the organic's were less aggressive & while that didn't totally eliminate the "jump" it did significantly reduce the brake jump during hard braking on rough pavement.

 

Added: the 1150R (not RT) used the organic rear brake pads.

 

 

[BobSut]

The braking release under uneven surfaces is pretty normal.

Some things that can effect its severity are, SOME aftermarket pads having too much or not enough initial bite, worn or hard tires, wrong tire pressures.

Check to see what pads you have but to a certain extent, they do that under rough pavement conditions and heavy braking.

I installed EBC HH pads shortly after I got the bike, because I like their bite and firm feel.

If it happens often, why all the heavy braking?

I don't often brake hard when I'm commuting, but when I need the stopping authority, I'm glad it's there.

As far as "too sensitive or too severe" in relation to what?

Just seems like it's kicking in on too little provocation, and the release is more complete than I would like.

Unless you have a typo, 19500 miles would allow you the time to get used to a bikes tendencies no matter what they were.

No typo. I live in San Jose and work in San Francisco, so yeah, I spend a lot of time on I-280. The RT is well suited to this purpose.

I've gotten used to this behavior, but that doesn't mean I'm satisfied with it :-)

The brake flush can be done at home with YouTube videos and a weird funnel you can buy from BeemerBoneyard .

Thanks for the pointer to the funnel - that should get me headed in the right direction.

 

 

That ABS jump is pretty common on the early 1150Rt's ...

The problem stems from the rear wheel anti-lift algorithm calibrated into the ABS system...

What happens is: the rear wheel starts to decel at a rate that the ABS system thinks is too fast of a spin-down rate so thinks the rear wheel is lifting. It then quickly counters that by releasing the front brake to bring the rear wheel back down. (on rough road surfaces, or gravel-on-the-road surfaces, the rear tire loses traction during hard braking)

That's plausible, and that describes my symptoms.

Overly aggressive rear brake pads or sticking caliper pins on the rear brake caliper can make the problem worse...

I would install the organic rear brake pads as the organic's were less aggressive & while that didn't totally eliminate the "jump" it did significantly reduce the brake jump during hard braking on rough pavement.

That's a good suggestion - thanks! I still have the stock(?) pads that came in the bike, so I'll try putting those rears back in.