Strange feel when emergency braking

[JayGee]

Had bit of a scarey moment today when a Volvo pulled out in front of me when I was doing about 60 . I grabbed a handful of brake lever and just squeezed like hell. After a very impressive initial retardation the brakes seemed to let go for a bit before working again when I say a bit it seemed like ages. I actually released the lever a touch and re-applied as I thought about ABS and trusting it to sort things out. The brakes did work incredibly well but the sensation was a bit unnerving so when I calmed down and got home I went to brake test the bike on a deserted straight road and noticed the same effect. Just using the bar ("front") lever I grabbed it as tight as I dare at around 80 and again I got a lot of braking followed by slighly reduced braking for quite a bit before I got full braking again. The roads are dry, the tyres A1, the surface very grippy and if I'd done it on any other bike it would have been a BIG stoppie. If it was the ABS I would have expected a more regular pulsing and not such a long reduced breaking period. Anyone else noticed this effect, is it normal (I did wonder whether it was the rear wheel lifting but whatever it is I'm not sure I like it). Having said that such lunatic behaviour on a non ABS bike would have seen me on the floor. I've heard some of you guys extolling the virtues of the servoed ABS brakes and how you can use them for ultra late braking on track days etc but they just seem a bit unpredictable for that sort of thing. I don't think I have a fault so I'd suggest anyone who hasn't felt the effect of emergancy braking should go and try it cos it's awfully tempting to let some of the pressure off the lever as the bike veers about and feels like the front is going to lock-up at any moment. Any advice/thoughts/comments would be appreciated.

 

[Deleted account 211025001]

They all do that sir, well, at least, mine does

It is a strange feeling though, isn't it? Seems to work though!

Andres

 

[Deleted account 210609001]

Before getting a GS, I had a K1200RS with ABS. When the ABS kicked in on that, it was exactly as I had expected based upon experience of ABS on cars, i.e. a high frequency pulsing through the brake lever and/or brake pedal.

On the GSes - 1150 and 1200 - there does seem to be a definite "brakes on - brakes off - brakes on" cycle. It feels to me like the ABS is cutting in too harshly, so rather than letting the brakes off a bit, there is a complete withdrawal of braking.

Just using the back brake to "test" the ABS, though, and it seems to be as I would expect - quick pulsing and modulated braking rather than no braking. So it must be something to do with the front.

I've read the same thing (about ABS cutting in too harshly) in magazine reviews, which reassured me that it wasn't just my bike. And I take this all in context - the ABS is still way better than I am at sensing a lock-up and reacting accordingly. And on the couple of occasions when I've needed to do emergency stops, one of which was on a very wet road surface, I just pulled as hard as I could and let the ABS take care of everything. With a happy outcome.

The emergency stop on a dry surface was a revelation. You can't "fake" an emergency stop so when a car pulled out in front of me whiel I was doing 50-odd, my first thought was genuinely that I was going to T-bone the car and probably die. Hauled on the brakes, a couple of those jumps as described above, but came to a halt well short of the car. In fact the bigger risk turned out to be being bashed by the traffic behind me.

Finally, I had a collision earlier this year that required me to brake and swerve at the same time. I'm convinced that on a non-ABS bike I'd have fallen off, but was able to steer past a U-turning car and just clip the front rather than have a full impact.

So all in all, I'm a massive fan of ABS brakes, but I don't think the set-up on servoed GS's matches the set-up on th eun-servoed RS I had before.

Robin.

 

[JayGee]

The overall braking is very impressive and I'm sure it saved me from being painfully spead occross a Volvo today it's just the brakes off/reduced phase seems to last quite a while. I can't see how the ABS would be kicking in (too much grip today) and if it was it feels like no other ABS I've ever come accross. It could maybe be the linked brakes transfering braking off the front as the rear wheel approaches lift off.
I've tried locking the rear and the ABS gives a very slow pulsing with a small amount of wheel lock but the front should be much finer as there is no ABS ring on the back so the control is coarser (I think).

 

[ianm00]

I wanted to test the ABS on my bike as its the first bike that Ive had with ABS. I found the best place to test the ABS was "Weston Beach". On sand you onlt need to be doing 10-20mph pulling the leaver sharply activates the ABS. On the front this does feel like a car ABS ie a pulsing feeling. However using just the rear barke shows that the rear wheel has a much coarser ABS feel. I thought that the back wheel was been shaken off!

Ian

 

[plasmatron]

I had a similar reaction from the ABS system during emergency braking... The front locked mementarily, the release and no pulsing as I'd expected to fell but a longish delay before hauling to a stop... perhaps the actual duration of the lag in braking is exaggerated by the "d-a-m-m-i-t... I-'m g-o-i-n-g t-o c-r-a-s-h..." slow motion sensation one gets in these situations... also even during 1/10th of a second at 60mph you've already covered 2.7meters so maybe it's the sensation that you're still travelling forwards in a hurry that also contributes to the delayed braking feeling?

I'd guess that pulsing as per car ABS might now allow the front wheel of a bike enough time to recover from being locked and more importantly enough "off time" to prevent doing a stoppie/flipping the bike... I guess the ABS sensors are waiting for the front and rear wheel speeds to be equal again before re-applying the brakes...

I think an important point is that I noticed on the handout from a recent "you and your ABS" seminar the local dealer put the many first time riders getting BMW bikes here, that BMW emphsize that during emergency braking you should not release or reduce the pressure on the lever once the ABS system kicks in, but keep the braking input as constant as possible until it's safe to release the brakes... at least I'm 95% sure that's what it said, since the handout was written in Chinese...