1150GS ABS performance

[The Fabricator]

I recently returned from a vacation.  My 2000 R1150GS was fully loaded with camping gear and wife.  I was curious to know how much weight I was dealing with.  I was on the look out for any truck scales.  I found a 'public' truck scale in Oregon, next to a cafe, at a remote cross roads  location.  The unvarnished truth is the unit weighs 750 lbs.   8 gallons of fuel and 3.5 gallons of water, food, tent, etc.    [Without rider or passenger].

 

I digress.

 

This vacation entailed miles of very good dirt roads.  These were traveled by the locals.  The road had developed acceleration riffles about one inch high about 4 inches apart. [I confess I did not measure.]

 

On down hills, I wanted to limit my speed, so naturally applied the brakes.  I was traveling 20 to 25 mph. The ABS was activated.  I applied moderate force [according to me] on the front brake lever.  Apparently that was enough braking force that the wheel slipped and the ABS was activated.  As per previous ABS experience, the lever moved 1/2 way to the grip, which was expected.  However, the braking force was AMPLIFIED to the extent that the braking effect was on the order of 3x more than the applied force on the lever [according to my estimate].

 

I freaked but did not manifest any symptoms [according to me] so as not to alarm the wife.  Let's just say she is not as 'risk averse' as I.  AND she didn't notice.  I though it was somehow to my injudicious efforts, so I repeated the operation again, just creeping up on the lever force.  Repeat.

 

My thoughts are that the riffles and the ABS pump cycles were matched in frequency such that the brake released on the downside of a riffle and brake applied on the up side of the riffle, were the same cadence.   AND, because the up side of the riffle will have increased traction than the down side, due to weight transfer, the slide threshold will be higher on the riffle up side than on the down side; hence the increased braking effect.

 

So my questions are;

Does  my explanation explain it?

Has any one experienced this?

If I were to hold the brake on, would the front wheel eventually slide out?; slow the bike down to a speed where the ABS and riffles are not in cadence and so the ABS does not amplify the braking effort?

Is this a phenomenon not present with more modern ABS systems?

Any comments?

 

I AM INTICIPATED COMMENTS SUCH AS "ABS SHOULD BE TURNED OFF ON DIRT ROADS"  AND VARIATIONS OF SUCH.

THAT IS THE ANSWER TO THE QUESTION "WHAT WOULD YOU  DO?" , "WHAT SHOULD I DO?", WHICH IS NOT A QUESTION I AM ASKING.

SO DON'T BOTHER.

 

 

 

[dirtrider]

18 hours ago, The Fabricator said:

I recently returned from a vacation.  My 2000 R1150GS was fully loaded with camping gear and wife.  I was curious to know how much weight I was dealing with.  I was on the look out for any truck scales.  I found a 'public' truck scale in Oregon, next to a cafe, at a remote cross roads  location.  The unvarnished truth is the unit weighs 750 lbs.   8 gallons of fuel and 3.5 gallons of water, food, tent, etc.    [Without rider or passenger].

 

I digress.

 

This vacation entailed miles of very good dirt roads.  These were traveled by the locals.  The road had developed acceleration riffles about one inch high about 4 inches apart. [I confess I did not measure.]

 

On down hills, I wanted to limit my speed, so naturally applied the brakes.  I was traveling 20 to 25 mph. The ABS was activated.  I applied moderate force [according to me] on the front brake lever.  Apparently that was enough braking force that the wheel slipped and the ABS was activated.  As per previous ABS experience, the lever moved 1/2 way to the grip, which was expected.  However, the braking force was AMPLIFIED to the extent that the braking effect was on the order of 3x more than the applied force on the lever [according to my estimate].

 

I freaked but did not manifest any symptoms [according to me] so as not to alarm the wife.  Let's just say she is not as 'risk averse' as I.  AND she didn't notice.  I though it was somehow to my injudicious efforts, so I repeated the operation again, just creeping up on the lever force.  Repeat.

 

My thoughts are that the riffles and the ABS pump cycles were matched in frequency such that the brake released on the downside of a riffle and brake applied on the up side of the riffle, were the same cadence.   AND, because the up side of the riffle will have increased traction than the down side, due to weight transfer, the slide threshold will be higher on the riffle up side than on the down side; hence the increased braking effect.

 

So my questions are;

Does  my explanation explain it?

Has any one experienced this?

If I were to hold the brake on, would the front wheel eventually slide out?; slow the bike down to a speed where the ABS and riffles are not in cadence and so the ABS does not amplify the braking effort?

Is this a phenomenon not present with more modern ABS systems?

Any comments?

 

I AM INTICIPATED COMMENTS SUCH AS "ABS SHOULD BE TURNED OFF ON DIRT ROADS"  AND VARIATIONS OF SUCH.

THAT IS THE ANSWER TO THE QUESTION "WHAT WOULD YOU  DO?" , "WHAT SHOULD I DO?", WHICH IS NOT A QUESTION I AM ASKING.

SO DON'T BOTHER.

 

Morning Fabricator

 

I am not familiar with the early non-USA 1150GS but I presume that your early 1150GS has the ABS II braking system not the later I-ABS (wizzy) braking system? 

 

The ABS II ABS braking system is pretty slow response & antiquated by todays standards plus it has some quirks (you found one of them). The ABS II system uses a spinning shaft with clutches and displacement pistons. This means that once the ABS (anti-lock) part of the system is activated it takes total control of the braking apply so basically disregards any rider brake lever or foot pedal input until the ABS event is over & the tires regain decent traction, OR the rider releases braking pressure on the foot lever and/or hand lever. 

 

What happed to your downhill ripple braking can even happen on a level road with ripples (we call those chatter bumps) or in some cases even happen on a paved road with ripples or even on paved roads with gravel on it. 

 

It really has nothing to due with the matching  ABS apply rate to ripple frequency but has all to due with the slow ABS response coupled with the intermittent tire slippage over those ripples. 

 

Some of the issues on those ABS II systems is inherent with the type of ABS system itself & other is due to the ABS programing that is programmed to prevent rear wheel lift under heavy braking. If that ABS II system thinks the rear wheel is lifting off the road (based on front to rear wheel spin down rates) it slightly releases the front brake to bring the rear wheel back down)__ Problem is,  In a lot of cases that slow antique ABS II system can't tell rear wheel lift from a rear wheel lock-up braking on ripples or chatter bumps (especially when going down hill with the transmission in gear & clutch engaged adding in engine drag)  

 

You can try different things to help reduce the problem, like pulling the clutch in to remove engine drag on the rear wheel. And/or greatly reducing the rear brake apply in that type braking condition.    

 

Or just live with it as it is still braking to the traction limits it THINKS  are available even though it feels like no braking.

 

I know you didn't want to hear it but turning the ABS off is an option in those conditions as it is a low speed event & there are some advantages to not having the ABS totally releasing the wheel at each ripple gap. With the ABS active you never get a pile of dirt building in front of the tires on dirt or loose gravel surfaces so you can loose a lot of braking performance due to never getting that small pile of dirt in front of the tires. 

 

The trade off with leaving the ABS II turned on is longer braking distances on loose surfaces & very reduced rider brake control input once the ABS  part is activated & takes full control. This needs to be balanced against the ABS turned off where the rider has more actual braking control throughout the braking event that allows dirt or gravel build up in front of the tires with continuous brake apply even across the ripple gaps. But with ABS off that does increase the risk of brake lockup if the rider is not well practiced in loose surface near lock-up braking.

 

The next generation of BMW I-ABS (wizzy) power servo assist was much better at handling braking on ripples, as due to the servo pumps, the response time was greatly improved & the anti-lift calibration was much improved. The ripple (chatter bump) braking was still somewhat unpredictable (especially at speed going downhill) but it was more predictable anyhow. 

 

The later I-ABS gen2  was even better as that system used an accumulator for front make-up fluid with very quick valve response  (allowed much better lever input control in an ABS event). The rear still used a servo pump though but the calibrations were much improved (especially on loose dirt & gravel road conditions). 

 

 

 

 

 

[9Mary7]

Excellent explanation D.R.

Just wanted to point out that this ABS issue was experienced regularly by 1100RT-P riders while braking hard on asphalt at the bottom of fwy off ramps where the trucks have caused those damn ripples..........simply breathtaking the first time I experienced it!!!