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ABS performance


The Fabricator

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The Fabricator

I have a 2000 R1150GS with ABS brakes. I decided to test the ABS performance. I have tested the rear brake to activate the ABS occasionally in dirt. It performed as expected. I decided to test the front. I found a dirt area [gravel actually, this may have bearing on what happened], and, because I am old and apprehensive, was going slow. I would say about 5mph. I confess I don't actually know how fast [slow] as I did not look at the speedometer, which is probably not accurate at that speed anyway. I would say it was a trotting speed. I squeezed the front brake lever only, the wheel locked and skidded. I released the brake, foot down for strong jab, saved it. Now what?

 

I tried it again. Same except I went down. On the way down, with hand on lever, the lever traveled most of the distance to the grip. I kind of expect that.

 

Why didn't the ABS release the wheel [in time?]? My thinking was I was going too slow for the computer to process the wheel speed differential AND the processor chip speed was too slow AND the surface was very slippery so the wheel 'resume wheel turning rate' was too slow. Or some combo. I know there are improvements to technology and things are better [faster] now.

 

Anyway, is this what I can expect from this system? Does anyone have any data that translates to user experience? Anyway to up date?

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Or, being linked, both wheels locked on the gravel, so no speed differential F to R, so ABS was not activated? Just guessing.

 

Newer bikes have inertia sensors that might know bike is still moving when wheels are not. Earlier systems only detect wheel rotation.

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I have a 2000 R1150GS with ABS brakes. I decided to test the ABS performance. I have tested the rear brake to activate the ABS occasionally in dirt. It performed as expected. I decided to test the front. I found a dirt area [gravel actually, this may have bearing on what happened], and, because I am old and apprehensive, was going slow. I would say about 5mph. I confess I don't actually know how fast [slow] as I did not look at the speedometer, which is probably not accurate at that speed anyway. I would say it was a trotting speed. I squeezed the front brake lever only, the wheel locked and skidded. I released the brake, foot down for strong jab, saved it. Now what?

 

I tried it again. Same except I went down. On the way down, with hand on lever, the lever traveled most of the distance to the grip. I kind of expect that.

 

Why didn't the ABS release the wheel [in time?]? My thinking was I was going too slow for the computer to process the wheel speed differential AND the processor chip speed was too slow AND the surface was very slippery so the wheel 'resume wheel turning rate' was too slow. Or some combo. I know there are improvements to technology and things are better [faster] now.

 

Anyway, is this what I can expect from this system? Does anyone have any data that translates to user experience? Anyway to up date?

 

Afternoon Tom

 

You were probably going too slow. I'm not sure what the low speed cut-off speed is for the very early 1150 GS with ABS-II but probably somewhere between 4-6 mph.

 

If the ABS didn't have a low speed cut off the bike could never stop as the wheel brakes would keep releasing as the wheels slowed down to near 0 rolling speed.

 

Those old non servo ABS-II systems were slower than honey in mid winter as they used a rotating shaft, chains, & displacement pistons. They had virtually no read ahead (reaction only) & were slow to release so wheel spin-up on low traction surfaces was also quite slow.

 

Wait until you descend a steep sand or gravel hill without turning the ABS off, it will be almost total brake release as you keep gaining speed even with the brakes clamped on tight.

 

Same of icy roads, virtually no wheel spin up once you get a near wheel lock.

 

 

 

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My old boss, the dealership owner was an incredible dirt rider on a GS. He would always suggest turning off the ABS when going off road to insure one could use the rear wheel to steer when needed. Grabbing the front on an ABS bike or not on gravel is almost a guaranteed flop though isn't it ?

I'm no dirt guy.

I stepped in some once. Didn't care for it at all.

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Morning Tri750

 

My old boss, the dealership owner was an incredible dirt rider on a GS. He would always suggest turning off the ABS when going off road to insure one could use the rear wheel to steer when needed. --Some dirt riders do turn off the ABS & some don't. There are a LOT of depends in answering this one. I seldom turn it off on hard pack dirt or worn gravel roads but almost always turn it off in soft sugar sand or on loose gravel and when riding fast on loose surfaces with steep down down-grades. There is some rear brake steering used at times but mostly I use power and/or engine braking to rear wheel to steer off road. A good "practiced" off road rider is usually much better off with the ABS turned off (or on newer bikes at least set to set to off-road or pro mode). New dirt riders might be better off leaving the ABS on until they develop good loose surface braking abilities.

 

Grabbing the front on an ABS bike or not on gravel is almost a guaranteed flop though isn't it ? -- First GRABBING needs to be defined. If the front brake is used correctly when off-roading a rider can use a tremendous amount of front brake & still remain upright, stopping straight, & under control. Now just grabbing a hand full of front brake lever with no control or modulation IS asking for disaster. Personally, I use a LOT of front brake off road, way more front than rear brake, & can usually use it to my advantage as I can ride much deeper into a corner or curve than more timid rear-brake-only users. It still needs to be balanced & the rider needs a good feel for impending front wheel lock up. Max braking on gravel & soft dirt is achieved when the front wheel is building a pile of material in front of the tire contact area BUT still spinning enough for stabilization (a very narrow window on this one). Now on loose rocks & tennis ball sizes loose rocks on hard pack, all bets are off, as braking on something like that is a constant battle no matter how it's done.

 

Bottom line on this: to go fast off-road a rider needs to use both brakes in a balanced (& constantly changing) continually modulated way. The more upright the bike is during hard braking the less chance of going down or of going off-line or off-path.

 

It's fairly easy to understand & practice good loose surface braking habits (with or without ABS), to me the difficult part is in how a rider saves his butt when things don't go as planned during hard braking on a loose or changing surface. Or unintentionally entering a loose surface curve or corner at speed, or entering a decreasing radius very loose surface turn that the rider enters W-A-Y too fast for straight up braking. (over the years I have gained a number of permanent scars from practicing the last part of the above).

 

 

 

 

 

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The Fabricator

Dr sez.

You were probably going too slow. I'm not sure what the low speed cut-off speed is for the very early 1150 GS with ABS-II but probably somewhere between 4-6 mph.

 

If the ABS didn't have a low speed cut off the bike could never stop as the wheel brakes would keep releasing as the wheels slowed down to near 0 rolling speed.

 

Those old non servo ABS-II systems were slower than honey in mid winter as they used a rotating shaft, chains, & displacent pistons. They had virtually no read ahead (reaction only) & were slow to release so wheel spin-up on low traction surfaces was also quite slow.

I think that is what's happening, the wheel speed was too slow. Can you steer me to a tutorial about used a rotating shaft, chains, & displacent pistons?

Thanks for your reply.

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Isn't there a tip over sensor already in the tank? See upper right corner near hose clamps #2. Not sure how it works.

 

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Dr sez.

You were probably going too slow. I'm not sure what the low speed cut-off speed is for the very early 1150 GS with ABS-II but probably somewhere between 4-6 mph.

 

If the ABS didn't have a low speed cut off the bike could never stop as the wheel brakes would keep releasing as the wheels slowed down to near 0 rolling speed.

 

Those old non servo ABS-II systems were slower than honey in mid winter as they used a rotating shaft, chains, & displacent pistons. They had virtually no read ahead (reaction only) & were slow to release so wheel spin-up on low traction surfaces was also quite slow.

I think that is what's happening, the wheel speed was too slow. Can you steer me to a tutorial about used a rotating shaft, chains, & displacent pistons?

Thanks for your reply.

 

Afternoon Tom

 

I would be reluctant to point to any online source of CREDIBLE info on the internal workings of the old ABS-II systems as there is as much bad info as good info on those old systems. I'll take a look when I get back to my shop as at one time I had a BMW white sheet on basic control & operation. They are basically designed as a non-serviceable controller so there really isn't a repair manual on them (that I know of anyhow). I do believe there are some online disassembly info as far as unsticking pistons & internal clean out.

 

Best way to learn them is first handed by disassembling & inspecting each part & how it relates to ABS operation.

 

Quick summery is: during ABS event the motor spins cross shaft, clutches engage & pull on chains attached to displacement pistons. The bad part is the system is slow to respond & the valving in slow to open & close. I suppose the good part is that they don't need an additional accumulator. That rrrrupppp you hear at first ride off then occasionally during a ride off from a stop is the system calibrating the piston position.

 

The BMW ABS-II system was pretty crude but did allow a functioning ABS system on a motorcycle that worked as both an ABS system & an "anti stoppy" system (anti-rear wheel lift). It did work as a rear wheel anti-lift but at the expense of front braking performance on a rough or chatter bump road surface. (the ABS-II systems had a habit of suddenly releasing some front braking under a hard stop on rough roads surfaces, or if gravel on the road surface, so the bike would take big jump forward while stopping even with the front brake lever held on hard). The work-around we used on this was to use very little rear braking pressure on those types of road surfaces. It feels like the bike suddenly jumps 10' forward all by itself & that you lost the brake function but in reality it only jumps a foot or two then regains the braking back.

 

First time it happens it will scare the poop out of you, by the 20th time it's annoying but not bothersome. If you are a non aggressive rider or light early braker then you might never see it, that is until you need to clamp down hard quickly on a changing red light or fi someone pulls out on front of you. (this ISN'T the time to experience it for the first time)

 

Next ABS iteration (The I-ABS) wizzy system addressed most all of the ABS-II shortcomings with a very very fast cyclic rate & a front/rear learning brake proportioning (learned the wheel spin downs & adjusted the front/rear bias to compensate. With the servo pumps it also didn't need accumulation as it had unlimited make-up fluid capacity. Great system UNTIL a servo quit then they had virtually no brakes at all, NaDa.

 

The later 1200 series I-ABS-gen2 had the best ABS of all the boxers, up to it's time frame anyhow, as it used no front servo & special quick response valving. It did use accumulation for the front (no servo pump on the front channel) & used a servo pump on the rear for rear braking from the front lever and while in ABS mode, but used an either/or shuttle valve to allow a stand alone rear brake direct from rear pedal to the rear caliper.

 

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Isn't there a tip over sensor already in the tank? See upper right corner near hose clamps #2. Not sure how it works.

 

Afternoon TheOtherLee

 

That isn't a sensor it is a tip over valve (basically a little ball over a hole). It's not there to shut off the engine it is there to prevent fuel from running out into the tank vent system in a tip over.

 

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