ABS, although not intended as a comedic device, it still seems funny to me

[joeb]

Can anyone explain the thinking behind the 09 r1200 gs abs deactivation process ? According to the riders manual, while switching it off , ONLY the front wheels abs is deactivated . Integral braking for BOTH wheels is still in effect  ( when using just the hand lever ) until the foot brake is engaged.  What possible scenario could occur that would make me want to lock the front wheel while the rear continues to have ABS functioning ?

[dirtrider]

1 hour ago, joeb said:

Can anyone explain the thinking behind the 09 r1200 gs abs deactivation process ? According to the riders manual, while switching it off , ONLY the front wheels abs is deactivated . Integral braking for BOTH wheels is still in effect  ( when using just the hand lever ) until the foot brake is engaged.  What possible scenario could occur that would make me want to lock the front wheel while the rear continues to have ABS functioning ?

Afternoon joeb

 

That is a strange system. With the ABS system turned off the rear ABS function should be deactivated if using the rear brake pedal. 

 

One place having no front ABS but having rear ABS active would be in descending a very long very steep loose substrate hills (like loose sand or loose gravel) you want no front ABS to allow a lot front wheel braking as with ABS active it will not allow enough front wheel lockup to pile up sand or gravel in front of the front tire (with ABS active it will allow way too little front braking is this situation so you can get a runaway speed increase). With the rear ABS still active that will prevent rear wheel lockup with engine stalling, if you get an engine stall on that loose steep downhill  you probably won't have enough rear wheel traction in the lower gear range used for hill decent to get a rolling restart & probably won't be able to stop completely due to the steep loose substrate. You could do a clutch lever pull in then push the starter button but when descending a very steep loose surface hill with nearly crashing every inch that is difficult to pull off for most riders. That also leaves you with no engine braking & no rear braking during the attempted restart. 

 

 

[joeb]

I knew there had to be a reason. That makes sense. Thank you. Now I can sleep better tonight. I just won't be laughing myself to sleep

[dirtrider]

1 hour ago, joeb said:

I knew there had to be a reason. That makes sense. Thank you. Now I can sleep better tonight. I just won't be laughing myself to sleep

Afternoon joeb

 

What I posted above was more to answer your question on "What possible scenario could occur". 

 

I don't believe that BMW designed the ABS deactivation based on that, might be some of it but that would be a real outlier to design around.

 

My guess (just a somewhat educated guess here) is that the rear ABS deactivation was more based on road safety. With the ABS turned off you still have the front to rear brake linking using the front brake lever only, with the front/rear braking bias based on either a fixed percentage, or it possibly still using the learned front/rear braking bias based on your last few braking events stored in the ABS module (the automatic  front/rear brake bias learning based on wheel spin down vs braking pressures. 

 

With that front/rear linking, no ABS front or rear, & front lever braking only, you could easily have a  braking event where you could use more, or needed more, or could sustain more front braking pressure but you might already be getting rear wheel lock-up as the weight was transferring to the front tire (rear ABS "only" could prevent this).  Locking a rear brake at speed can actually be worse than short time locking the front brake.

You can release the front brake to stop front lock-up but (if) the rear is locked up & the rear wheel is sliding sideways (they usually do that pretty darn quickly at speed) then the motorcycle (and rider) can go high side in a nano second when the rear brake is released & starts spinning again. 

 

Without the brake linking (conventional braking)  then you have rear foot pedal control of the rear brake so the rider can independently control rear wheel lock up. But when you deactivate the ABS on a front/rear linked system it is a whole different ball game as one lever can activate both front & rear brakes with no independent control of the rear brake pressure. 

 

But BMW did design in the option to use the rear brake pedal so that would THEN deactivate the rear ABS & stop the front/rear linking.