Servo ABS question

[JayGee]

I have an 04 1200GS with the servo brakes and ABS. When practising emergency stops I have never been happy with the way the brakes release as the rear wheel begins to loose traction and the brakes do not come back on for quite some time.

The following is a quote from the BMW Sport Touring Forum
"having the front brakes release cause the rear brake locked up is STUPID. The mid-type ABS systems did this "

Is this what happens with the servod ABS? It would explain what seems to happen when trying out an e-stop and has once happened to me as a car pulled out in front of me and I attempet to use max braking. I guess it would also explain why a similar thing can happen when braking on rumble strips. surely the front shouldn't release just because the rear is lifting/skidding.

Does this happen on the later non servo ABS bikes?

 

[Ali-bear]

I can't believe it does.

Also, that guy on the BMW S T F (ahem) may have been talking through his arse in any case.

 

[Brian ROSEN]

"......I have an 04 1200GS with the servo brakes and ABS." So have I and I have never had any problems - but braking on rumble strips or on poor road surfaces still requires caution. I have to admit however that, after three years plus, I have not tried an emergency stop, either in practice or for real. I don't see why the servo would make matters worse -

 

[Deleted account 210609001]

I don't know for sure, but don't non-GS BMWs have fully linked brakes (i.e. the "back" brake pedal works both front and rear brakes. Maybe this makes a difference?

I'm not aware that my front brake releases if/when only the back wheel locks when using the "front" brake lever, but to be honest I don't think I'm good enough to know whether such a situation hads ever arisen. In fact I don't think I'd trust anyone who claimed that.

I've only had my ABS working in anger a couple of times and both times i was too busy worrying about crashing and dying to consider the complexities of what might be going on with the technology...

 

[karnevil]

I don't know for sure, but don't non-GS BMWs have fully linked brakes (i.e. the "back" brake pedal works both front and rear brakes. Maybe this makes a difference?

My first GS,which I got in Jan 05 had linked brakes.this second one does not.
I think you will find that the ABS works more often than we realise.
Try riding along and stamping on the rear brake,one will just slow down.Switch yer ignition off,switch on the ignition again whilst holding the ABS button then try stamping on the back brake!BUT BE READY FOR IT TO LOCK INSTANTLY,and dont blame me if ya fall off

 

[Deleted account 210609001]

I don't know for sure, but don't non-GS BMWs have fully linked brakes (i.e. the "back" brake pedal works both front and rear brakes. Maybe this makes a difference?

My first GS,which I got in Jan 05 had linked brakes.this second one does not.
I think you will find that the ABS works more often than we realise.
Try riding along and stamping on the rear brake,one will just slow down.Switch yer ignition off,switch on the ignition again whilst holding the ABS button then try stamping on the back brake!BUT BE READY FOR IT TO LOCK INSTANTLY,and dont blame me if ya fall off

I've deliberately triggered the ABS enough times to know what it feels like when it kicks in, thanks. And I still think it's only ever worked, front or rear, on a few real emergencies. Stamping on the back brake isn't the copybook method of slowing down, ABS or not., but even doing this you can sense the ABS working.

My point about linked brakes was that (as far as I'm aware) the GSs with linked brakes have only ever had semi-linked: the front brake lever works both brakes but the brake pedal only works the rear. Other BMWs with linked brakes (and relevant Hondas, I think) have fully linked brakes - brake lever and pedal each operate both front and rear brakes to one degree or another.

I still think that to differentiate between the front brake being released by the ABS because the back wheel had triggered the ABS on one hand, and the front brake being released because the front wheel had triggered the ABS on the other hand would take a very experienced and skilled rider or some sort of electronic diagnostics. I find it highly unlikely that there would be just one ABS circuit so that both wheels stopped braking if either wheel locked.

I will try it out next time I'm out on the bike - see if I can lock the rear wheel through over-enthusiastic back brake use while maintaining braking from the front wheel.

 

[Brian ROSEN]

Linked brakes and ABS etc;

If you ride in a reasonable manner you may, with luck, never need your ABS. I have tried out those on my car by intentionally braking hard going down my fairly steep drive when it is snow covered & they work extraordinarily well & I don't know which wheels are being braked more or less than the others. On those few days a year I am afraid that the bike stays IN the garage.

 

[JayGee]

I read that many bike accidents could have been avoided if the rider had braked harder so I went out to practice a few e-stops. I rode at about 60mph, sqeezed the lever with increasing force. I was on a dry road and before the rear wheel left the ground (i.e. before I did a stoppie) the brakes released and didn't come back on for a frighteningly long time (even though I kept the lever squeezed hard). I think this could be explained by the ABS sensing the rear wheel is turning at a different rate to the front and releasing the front for a while and I wondered if the newer non-servo ABS did this as well (cos I want a new bike and I don't like this effect).

Sorry but I can't believe anybody triggers the ABS without knowing it, especially the rear where there is no ABS ring and the on/off ABS cycle is very crude.

 

[GSmonkey]

I've triggered the ABS a few times. It does feel as thought the bike is surging forward and it does feel like an awfully long time. Never noticed a rear wheel lockup at the same time though.

ABS will activate when braking over any surface that leads to either wheel leaving the road. For some reason my '04 12GS did it all the time, whereas my '07 12GSA (non-servo) virtually never does it - although I've put this down to the additional weight.

 

[ahutcheon]

My experience is with a servo/ABS 1150, but I have heard that it and the 1200 share similar "anti-stoppie" software in the ABS: the front brakes are released if the rear stops turning on the assumption/possibility that the rear has lifted.

Uneven surfaces downhill (a particular tarmac repair on my regular route, corrugations on gravel roads) are prone to show up the behaviour: temporay loss of all braking, often when slowing gently. I'm pretty sure it's a front/rear issue, since turning off the ABS on gravel roads removes the effect and gives more effective braking on uneven surfaces going downhill (without reaching the point of having to modulate the front brake myself to manage lockups).

I'm pretty sure the ABS has saved me once or twice (cold, wet mornings when a car driver did something stupid). It may not be perfect the rest of the time, but the behaviour is predictable and I can turn it off.

 

[Ali-bear]

(cos I want a new bike and I don't like this effect).

My new GS has ABS and I am very pleased with it. I had been put off getting a GS because of the earlier servo system but when I heard they'd changed it I knew it was time to buy.

I've provoked it deliberately on the rear wheel and it comes in very smoothly and effectively. You could almost not know about it working in a marginal situation where it only just kicks in.

Why not get a test ride and spend half an hour putting the ABS through its paces?