Understanding the ABS system on the R1150RT

[twelve]

 

Hi Guys,

 

I am trying to understand the rear ABS behaviour on my R1150RT and hope to find some answers.

 

I hear of ppl locking up the rear wheels and the ABS systems springing into action. I always thought one can lock up the rear wheels only if the clutch is disengaged but if the bike is in gear, would this be possible? I mean the drive line and pistons would all stop moving and would there be engine stalling and damage resulting?

 

I hope someone can explain what actually happens or can happen assuming if travelling at 50 km/h on a slippery surface, I step on the rear pedal hard hard enough to lock the rear wheel, what will the ABS be doing?

 

It is easier to understand for the front wheel as there is no drive and the wheel is spinning independently.

 

I am not technically inclined so explanation in layman terms much appreciated.

 

Thanks Guys.

 

Tay

[dirtrider]

----

 

I hope someone can explain what actually happens or can happen assuming if travelling at 50 km/h on a slippery surface, I step on the rear pedal hard hard enough to lock the rear wheel, what will the ABS be doing?

 

 

Morning Tay

 

The 1150RT has the I-ABS (wizzy) ABS system.

 

That ABS system monitors the front to rear wheel slip rate difference & adjusts the braking front/rear bias based on that. This is assuming you only use the front brake lever to stop.

 

On your question above: Seeing as the ABS system is monitoring both the front & rear wheel speed & their decel rate, if you step on the REAR brake (only) & hard enough to lock the rear brake the ABS will intervene & release the rear brake pressure to the point of the rear wheel not locking up due to the BRAKES. That includes trying to include the engine & drive train drag.

 

Obviously once the rear brake is fully released & if engine & drive train drag is still present the rear wheel can still slide a bit if you are traveling faster than the engine can increase speed to catch back up. But as long as the engine is spinning the wheel shouldn't completely stop turning.

 

The BMW I-ABS system isn't the fastest cycling system so under certain conditions you might be able to stall the engine with a very quick & heavy rear brake only apply. On a good traction surface the engine should light off again as the rear wheel brake is released by the ABS & traction starts spinning the rear wheel again

 

If on a real slippery surface then the remaining engine drag can still allow the rear end to slide sideways even with the ABS completely releasing the rear brake. So on slippery surfaces you really should de-clutch as soon as you can to allow the rear ABS to function to it's best ability.

 

[philbytx]

Just to add to DR's comments. If you hit the rear brake hard, it will also add braking pressure to the FRONT brake calipers as well!

 

They are integrated brakes, meaning that pressure applied to EITHER front or rear brakes will add braking pressure to the other wheel.

 

i.e. Front will add braking pressure to rears and rears will add braking pressure to front .

[PAS]

Is there any easy, cheap way to eliminate the power assist? I personally dont like it.

[dirtrider]

Is there any easy, cheap way to eliminate the power assist? I personally dont like it.

 

Afternoon PAS

 

Not really. You need the power assist to have the ABS function.

 

IF, you can live without ABS then you can remove the entire ABS controller. That will require adding a relay for the brake lights to work properly & adding a couple of loops of brake line or buying the non ABS front junction block & adding a new rear brake line.

 

The good part is the 1150RT without the ABS controller has wonderful feeling & working brakes. The bad news is you no longer have ABS brakes available.

 

Not that big of a job but the job does require a bit of mechanical ability & bit of electrical ability.

 

[PAS]

Morning D.R.

I guess I'm still a bit confused. It's the touchy whizzy front brake that I dont care for. Am I correct in saying that not all ABS brakes have this servo option?

 

The 03 1150RT has been a learning experience for sure.

[dirtrider]

Morning PAS

 

 

You are correct in that not all ABS systems have power servos. Not even all BMW motorcycles have the power servo ABS system.

 

Problem is: your 03 bike has the power servo system as well as all the other 1150RT's with I-ABS brakes.

 

Unfortunately your 03 RT needs the power assist or power servos to function as an ABS system. You eliminate the power servos you also eliminate the ABS ability.

 

That servo system your 03 RT was an interim system that was designed to get faster ABS cyclic rates & faster pressure build for shorter stops & better ABS brake re-apply recovery. And it does as that system is a very good ABS system at high speeds on marginal road surfaces.

 

The ABS-2 system of the BMW 1100 era was pretty crude & used moving pistons & chains to re-apply the brakes during an ABS event. That system worked as far as keeping the brakes from locking but had a slow cyclic rate, not very precise, was slow at building re-apply pressure. (in a nut shell you didn't fall down but it added distance to the ABS controlled stop & would release braking pressure even in non ABS stopping when stopping hard on rough roads or over square edged bumps )

 

When the BMW 1150's came out BMW wanted a better ABS system with a learning function for balanced braking, rear wheel anti-lift, very quick response time, also able to do ABS event brake reapplies many times without running out of apply fluid.

 

About that time some of the auto companies were fooling with valve type ABS systems (a very good ABS system) but apparently none were suitable for motorcycle usage so BMW went with the FAG Kugelfischer servo system that was very fast & very responsive as it used servos & pumps.

 

The BMW I-ABS Integral braking system has a suggested release response time of around 80 milliseconds with a response time that can be as as low as 50 milliseconds under certain (dry road high traction) conditions (you can’t even come close there modulating the brakes yourself). The system can also vary the response frequency from around .6Hz to as slow as 5 Hz on really slick or gravel roads. With a non servo system you can’t get close to the pressure build times of the Integral braking system either as it not only uses motor/pump pressure assist but also uses a very short lever stroke so you get a very fast pressure build for a very short stroke & it can move massive amounts of fluid very quickly.

 

The BMW I-ABS system was a very good ABS braking system for a motorcycle during it's time of introduction. The big drawback was in the aggressive braking characteristics it exhibited during low speed or parking lot slow speed normal braking events. (in a word grabby)

 

 

By the end of 2006 BMW got the I-ABS-2nd generation fast response valve type ABS system to function properly on a motorcycle. That system has a very fast response time. Only uses a pump & servo on the rear brake from front lever apply (rear brake from rear pedal is non servo if apply pressure is higher than front pressure.

 

This system seems to be a much better received braking system than the older I-ABS system as few riders find fault with it's braking smoothness at low speeds. It is linked from the front lever but stand alone from the rear brake pedal.

 

[PAS]

Thanks D.R. That was a very appreciated explanation! I'm just having a problem when I go from the 81 R100RT and then ride the 03 R1150RT. Hard to reprogram my aging habits.

 

The slow speed parking lot whizzy brakes are scary!

 

I did find a page on how to eliminate those brakes on a GS if someone was inclined to do so for financial parts replacement reasons. No cost removal of servo ABS brakes

 

Thanks again for you time and detailed explanation.

[dirtrider]

 

The slow speed parking lot whizzy brakes are scary!

 

 

Morning PAS

 

Yes, the low speed parking lot or garage braking can be a bit of an issue if you ride different bikes.

 

-You could remove the ABS system but then you have no ABS available. Personally that wouldn't bother me as I ride a lot of bikes without ABS. Your 03 with the ABS system removed actually would have very nice feeling brakes (just no ABS protection)

 

-One thing I did on the I-ABS (wizzy) systems I owned was to use the 1150R (not RT) organic rear brake pads. That took a bit of the aggressiveness out of the rear brake at low speeds.

 

-The thing to remember on the I-ABS (wizzy) systems it to try & not use the front brake lever at low parking lot or garage speeds with the handle bars turned. If you remember this it make the brakes almost a non issue at low speeds. Most issues with those I-ABS brakes happen with the bars turned at low speeds.

 

[ragtoplvr]

After setting the bike down for a nap a couple of times, I have made my peace with the servo system.

 

1. In a parking lot, use only one finger, and carefully. 2 is plenty on the street.

 

2. It is sensitive to the speed the lever is pressed, if you stab at it the brake acts as if you are going 80 and a car pulled out in front of you, it slams on the brakes. This is true even if you moved thru the free play quickly and never applied much pressure. Get the habit of moving the lever slowly. Slowly means 1 second.

 

3. When you do need them, you will absolutely be impressed at how fast you can stop.

 

Rod

 

 

[philbytx]

If you find the rear brakes too touchy, I recommend going for a ride and ONLY use your rear brakes for stopping. This will give you a goodly amount of body memory learning and will help you finesse the brakes a lot better.

 

Of course, you do this on quiet roads and use your front if you DO need it LOL!

 

[Gaston]

If you find the rear brakes too touchy, I recommend going for a ride and ONLY use your rear brakes for stopping.

Phil,

 

How do you do this on a pre-2006 1150RT?

[philbytx]

The iABS is a LINKED system. If you put sufficient pressure on the rear brake pedal it will bring in the fronts! Try it and you will see what I mean.

 

BMW changed the iABS system rear to front bias in early 2002 (IIRC!) as the early system brake pedal was VERY touchy. You will find that on the later systems you have some pedal travel where it just applies rear brake pressure BEFORE it brings in the front circuits.

 

It also helps to only use the rears in low speed manouevres BUT if you are a little heavy on the rear brake pedal, the fronts will be applied as well and if your front wheel is at an angle you could end up dumping the bike.

[dirtrider]

Afternoons Phil

 

The I-ABS controller was changed on the 1150RT around VIN ZE 87455. That also involved using a larger diameter rear master cylinder piston size 14.29mm vs the earlier 13mm size. The M/C size increase was mainly to allow the new revised ABS controller to have enough reserve braking from the rear pedal but that also had the side effect of taming down the rear brake apply a bit. The new ABS controller also has a different calibration that allowed the rear servo to shut down with an idling engine & sitting still as a power saving function.

 

[philbytx]

I knew there was a more technical explanation around somewhere

 

Thanks DR

[MAT2CHI]

Morning D.R.

It's the touchy whizzy front brake that I dont care for

 

When I bought my new '04 R1150RT the front brake was great. After one of the services it started acting all grabby. On my 6,000 mile service I had the brakes flushed and now it's back to normal and the grabbiness is gone. Have you flushed your brakes lately?

[Boulder Dave]

Morning D.R.

It's the touchy whizzy front brake that I dont care for

 

When I bought my new '04 R1150RT the front brake was great. After one of the services it started acting all grabby. On my 6,000 mile service I had the brakes flushed and now it's back to normal and the grabbiness is gone. Have you flushed your brakes lately?

 

I noticed the same effect after a flush. Brakes are very powerful, but that initial grab is gone.

[Gaston]

BMW changed the iABS system rear to front bias in early 2002 (IIRC!) as the early system brake pedal was VERY touchy. You will find that on the later systems you have some pedal travel where it just applies rear brake pressure BEFORE it brings in the front circuits.

 

Mine was built in April of 2002, and any touch of the foot pedal seems to activate both the front and rear brakes. At least I have not been able to feel the rear brake only being applied...

[Gaston]

The I-ABS controller was changed on the 1150RT around VIN ZE 87455. That also involved using a larger diameter rear master cylinder piston size 14.29mm vs the earlier 13mm size. The M/C size increase was mainly to allow the new revised ABS controller to have enough reserve braking from the rear pedal but that also had the side effect of taming down the rear brake apply a bit. The new ABS controller also has a different calibration that allowed the rear servo to shut down with an idling engine & sitting still as a power saving function.

My VIN is higher numerically than ZE 87455, therefore built later. So, I should have a tamed down rear brake?

[philbytx]

Yes.....!

[PAS]

Morning D.R.

It's the touchy whizzy front brake that I dont care for

 

When I bought my new '04 R1150RT the front brake was great. After one of the services it started acting all grabby. On my 6,000 mile service I had the brakes flushed and now it's back to normal and the grabbiness is gone. Have you flushed your brakes lately?

 

I did a complete system flush (wheel and control circuits) two weeks ago. Bike has approx. 13,600 miles on it. Just the nature of the beast it seems. Slow speed is the issue just have to try and be more cautious.

[AndyS]

As an aside. When I removed the i-ABS from my 2003 RT, I then found the rear brake to lack 'bite' because it had the larger rear master cylinder fitted., So I swapped my rear master cylinder for the smaller unit and got all the punch back that I needed.

 

The nice thing about not having the iABS is that it now behaves in a much more linear way. But as has been posted above. The powererful Servo Assisted Brakes are 'the nature of the beast', and to be perfectly frank, once you have come to terms with that, it is just a case of riding with it, just like it is haveing a powerful motorcycle instead of a small one. You learn to love its strengths and live with its weaknesses.

Andy

[Alfred02]

Here, here

I "like" my iABS brakes.

Had them on the 04/1150RT and have them now on the 05/1200RT.

Very slow speed is a re-learning that's all.

Higher speed and they are just magical. I can pull up my R1200RT in an amazing short distance using two fingers on the front brake.

 

[Urban Surfer]

I have the 03 RT with the linked ABS system. One of the reasons I chose this bike is the amazing brakes. I believe they saved me from a spill once coming of the road on to a gravel shoulder too fast and heavily loaded.

Since then the ABS has never activated. How can I be certain the still work properly?

[dirtrider]

Afternoon Urban Surfer

 

 

If the ABS general & warning lights are working & they go out as you ride off then your ABS system is more than likely functioning OK.

 

 

But, to be sure you have ABS available you can have your dealer or someone with GS-911 see if there are any stored failure codes. Then do a system bleed down test. If no problems found then again you more than likely have ABS available.

 

The other way & the way I do it is to ride the bike on a dirt road or well worn in gravel road at about 15-20 mph then stop hard enough to get the ABS to kick in. If you can't lock a wheel then the ABS is working. If you lock & slide the front wheel or the rear locks up & slides then your ABS isn't doing it's job.

 

If you are not comfortable doing the above braking test yourself then either have a trusted friend or a dealer tec do it for you.

 

On my personal cars, trucks & ABS equipped motorcycles I intentionally initiate a low speed ABS brake stop every few drives/or/rides or so just to verify the system is operational & I am familiar with it's behavior at wheel lock/unlock.

 

Remember, you don't went the first time you get your vehicle into an ABS event to be in a real emergency situation. Force the ABS operation once in a while just so you know what to expect & how it reacts as far as vehicle handling reaction & braking disruption.

 

[Urban Surfer]

That makes sense thanks. I'll do the dirt road test.

[Boffin]

That makes sense thanks. I'll do the dirt road test.

 

Every month or so I carry out a paved road test from about 30mph. It usually takes two or sometimes three, attempts before I brake hard enough to activate the ABS. It is useful to know not only how the ABS feels in operation on your usual riding surface but also just how darned hard it is possible to brake. In the UK at least, it is reckoned that quite a few bike/car interactions could have been avoided if the rider had braked hard enough but had been to scared of locking the front to do so.

 

Andy

[twelve]

 

 

Morning Tay

 

The 1150RT has the I-ABS (wizzy) ABS system.

 

That ABS system monitors the front to rear wheel slip rate difference & adjusts the braking front/rear bias based on that. This is assuming you only use the front brake lever to stop.

 

On your question above: Seeing as the ABS system is monitoring both the front & rear wheel speed & their decel rate, if you step on the REAR brake (only) & hard enough to lock the rear brake the ABS will intervene & release the rear brake pressure to the point of the rear wheel not locking up due to the BRAKES. That includes trying to include the engine & drive train drag.

 

Obviously once the rear brake is fully released & if engine & drive train drag is still present the rear wheel can still slide a bit if you are traveling faster than the engine can increase speed to catch back up. But as long as the engine is spinning the wheel shouldn't completely stop turning.

 

The BMW I-ABS system isn't the fastest cycling system so under certain conditions you might be able to stall the engine with a very quick & heavy rear brake only apply. On a good traction surface the engine should light off again as the rear wheel brake is released by the ABS & traction starts spinning the rear wheel again

 

If on a real slippery surface then the remaining engine drag can still allow the rear end to slide sideways even with the ABS completely releasing the rear brake. So on slippery surfaces you really should de-clutch as soon as you can to allow the rear ABS to function to it's best ability.

 

Hi dirtrider,

 

Thanks for the explanation, however it can be rather unnerving to hear chattering sound from the rear when the ABS kicks in.

 

 

 

 

[dirtrider]

----Thanks for the explanation, however it can be rather unnerving to hear chattering sound from the rear when the ABS kicks in.

 

 

Morning Twelve

 

Better to hear & feel the ABS involvement when practicing and get used to it than have the first time you feel & hear it be in an emergency situation.

 

After it does it's thing for you a few times & you know what's coming it's a non issue when it happens unexpectedly & for real.

 

 

You can get rid of most of that chattering sound if you pull the clutch lever in as the thing enters ABS as that disconnects the engine from the rear brake application.

[Mr. Frank]

In a number of these posts it is implied that with the integrated brakes it matters which brake lever (front or back) you apply as to the balance of front/back braking balance. Could someone expand on that? I was under the impression that you get both brakes whether you use the hand lever or foot pedal, but I have heard that the balance of power is affected by which one you use. True?

[dirtrider]

Morning Mr. Frank

 

Sort of, it depends on the brake system you are talking about as there are some basic differences between the ABS-2,, I-ABS,, I-ABS authority,, I-ABS-II.

 

Too much typing to explain all & their differences here. I see you are riding a 2004 RT so we'll address that one. I assume you have a regular 1150RT & not the police model? That bike has the I-ABS servo system.

 

Basically under heavy braking or in ABS mode the I-ABS controller controls the front to rear braking bias. The ABS controller on your 1150RT has a learning ability that monitors wheel decel slippage & both front & rear braking apply pressures to pretty well keep the front/rear braking balanced regardless of the load you have on the bike & no matter if you use the front lever or rear pedal (or both). That is pretty straight forward for an adaptable ABS system.

 

But, due to the way the front lever & rear pedal apply hydraulic pressure to the opposite end control pistons (through the crossover passages) inside the ABS controller, when braking at very light braking pressures the front lever applies just a bit more front braking at light braking & the rear pedal applies just a bit more rear braking at very light rear pedal apply.

 

So at low speeds and light braking input (like parking lot turning speeds) if using only the rear brake pedal the rear bake is providing a bit more stopping than the front is. The front is sill working just less powerful than the rear.

 

On your later (04) I-ABS system at a standstill & light brake input pressure the rear brake servo should actually shut down until moving again or increasing brake pressure.

 

 

[Mr. Frank]

Thanks, D R. Yes I have the regular 2004 R1150RT. Can I conclude that when mashing the brakes in a panic stop I will get the same amount of braking whichever brake I hit? With light trail braking in a curve would there be a bias to the rear if using the foot pedal?

[dirtrider]

Thanks, D R. Yes I have the regular 2004 R1150RT. Can I conclude that when mashing the brakes in a panic stop I will get the same amount of braking whichever brake I hit? With light trail braking in a curve would there be a bias to the rear if using the foot pedal?

 

 

Morning Mr. Frank

 

 

 

Can I conclude that when mashing the brakes in a panic stop I will get the same amount of braking whichever brake I hit? >>>>>>

 

Yes, within reason anyhow. That is where the ABS learned braking bias is at it's best.

The downside is (IF) the I-ABS system perceives enough rear wheel slippage vs pressure it will automatically release a bit of front brake to prevent excessive rear wheel lift.

 

 

 

With light trail braking in a curve would there be a bias to the rear if using the foot pedal?>>>>>>

 

Yes, but that is at very light rear brake input only & you will still get some front apply.

 

[azccj]

On your later (04) I-ABS system at a standstill & light brake input pressure the rear brake servo should actually shut down until moving again or increasing brake pressure.

 

 

Are you saying that when stopped at a light and just the rear pedal is depressed slightly, that there should be no whizzing sound coming from the brakes?

[Alfred02]

Are you saying that when stopped at a light and just the rear pedal is depressed slightly, that there should be no whizzing sound coming from the brakes?

 

No

What you are hearing is the "servo assisted" part.

So you will be hearing the servo(s) no matter if you are moving or standing, while the engine is running and any or both brakes are applied.

That is on a properly working system.

[dirtrider]

Are you saying that when stopped at a light and just the rear pedal is depressed slightly, that there should be no whizzing sound coming from the brakes?

 

Evening Azccj

 

 

 

Basically as a power conserving measure on the later BMW I-ABS systems BMW implicated a rear ABS pump shut down to help elevate excess power drain at engine idle.

 

At engine idle & sitting still the rear I-ABS modulator

pump shuts down. This occurs only below a certain brake pressure in the rear wheel circuit.

 

The rear servo pump shutting down should be somewhat audible when the engine is idling, sitting still, & very light brake pedal or lever pressure applied.

 

 

The front servo pump will remain running as long as either the front lever or rear pedal is depressed.