How to disable rear abs only?

mondrage · May 8, 2022

I’ve been taking my R1200GS more off-road lately. Even got a 21” front wheel.
How do you disable the rear wheel abs only?
It’s a 2008 K25.

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theoneandonly · May 8, 2022

you don't .

abs takes readings from BOTH wheels , compares them , and when they give a big enough difference ....the abs kicks in.

botus · May 9, 2022

theoneandonly said:
abs takes readings from BOTH wheels , compares them , and when they give a big enough difference ....the abs kicks in.

I thought you could have the rear skid and leave on the front but the manual says NOT

don't agree on the second point - that is exactly how ASC functions (and entirely from the info of both of the ABS sensors). Whilst the brakes are linked, the ABS is and must always be totally independent

On what happens when turning OFF the ABS.
Switch off with handle bar button and ONLY use the front brake lever then ABS at the back says on, but off at the front.... ABS at the back only goes off if you use the brake pedal

Doofus · May 12, 2022

theoneandonly said:
you don't .

abs takes readings from BOTH wheels , compares them , and when they give a big enough difference ....the abs kicks in.

Typically ABS doesn’t look at the difference between wheels, but looks at each wheel independently. The computer knows how quickly the wheels slow down under maximum braking in normal riding, and if a wheel slows down significantly more quickly than this, then it suggests it has (or is about to) lock - or you’ve hit a wall.

Even if the ABS were looking at differences between wheels, the ABS module could in any event only apply the ABS to the front circuit and not the rear circuit.

theoneandonly · May 13, 2022

FFS .
2 sensors , 1 front 1 rear , ecu reads both , when they go far enough apart , and the brakes are being applied , the abs will kick in on the wheel that is turning the slowest .
the abs will work on both wheels , to bring their speed back to acceptable limits .

do a stoppie , without touching the rear brake , abs won't work . touch the rear brake and it kicks in.

my brakes aren't linked.

botus · May 13, 2022

all GS's with ABS have linked brakes - a really simple test go for a 10 min ride, braking like a crazy person but NEVER touching the rear brake pedal - then get off and hold the rear disc - u will burn your fingers...

your description of how abs works is incorrect - two others said it correctly

gazza12adv · May 13, 2022

botus said:
all GS's with ABS have linked brakes - a really simple test go for a 10 min ride, braking like a crazy person but NEVER touching the rear brake pedal - then get off and hold the rear disc - u will burn your fingers...

your description of how abs works is incorrect - two others said it correctly

Slightly easier to put it on the mainstand. Put it in gear let the rear wheel spin then apply the front brake. And you won't burn your fingers.

DrFarkoff · May 13, 2022

theoneandonly said:
FFS .
2 sensors , 1 front 1 rear , ecu reads both , when they go far enough apart , and the brakes are being applied , the abs will kick in on the wheel that is turning the slowest ..

Where did you find that Bullshit!?

When the rate of deceleration of a wheel, falls below a threshold the ABS will kick in until the rate moves about that "line" and it is ON THAT WHEEL ONLY as it has reached the "theoretical" point of wheel locking ON THAT WHEEL ONLY AND FUCK ALL TO DO WITH WHAT THE OTHER WHEEL IS DOING !!!

Brakes are "linked" But the ABS ECU runs constant algorithms to calculate which is close to lock up and it will only modulate the circuit pressure only on the wheel

Doofus · May 14, 2022

theoneandonly said:
FFS .
2 sensors , 1 front 1 rear , ecu reads both , when they go far enough apart , and the brakes are being applied , the abs will kick in on the wheel that is turning the slowest .
the abs will work on both wheels , to bring their speed back to acceptable limits .

do a stoppie , without touching the rear brake , abs won't work . touch the rear brake and it kicks in.

my brakes aren't linked.

If it’s only detecting the difference, how does it distinguish between tearing down the motorway at 80mph with both wheels locked and waiting patiently at traffic lights (FFS)?

theoneandonly · May 14, 2022

i might not have been clear , it works on the wheel that is close to locking up . not both at the same time.

if both wheels are locked at 80 mph , i would be amazed , but at some point 1 will have locked up first , therefore the abs would have acted on that wheel . what do you think happens when both wheels are on ice , and both are locked ? the abs will not react cos it thinks you have stopped.

what it can do is switch from front to rear and back again, as each one is modulated by the abs .

some seem to be missing a bit . abs works whilst brake is applied not when they aren't.

my 1150 will work on the rear only , if i leave the front brake alone , i tried it on the way to work today . it works on the circuit being applied.

Doofus · May 14, 2022

theoneandonly said:
i might not have been clear , it works on the wheel that is close to locking up . not both at the same time.

if both wheels are locked at 80 mph , i would be amazed , but at some point 1 will have locked up first , therefore the abs would have acted on that wheel . what do you think happens when both wheels are on ice , and both are locked ? the abs will not react cos it thinks you have stopped.

what it can do is switch from front to rear and back again, as each one is modulated by the abs .

some seem to be missing a bit . abs works whilst brake is applied not when they aren't.

my 1150 will work on the rear only , if i leave the front brake alone , i tried it on the way to work today . it works on the circuit being applied.

ABS will work the same on ice. It will not think you have stopped because it will know the wheels went from rotating to not rotating too quickly. Here’s how the good folk of Carole Nash summarise it:

****
How does ABS actually work?

Motorcycle ABS works to stop the wheels locking thanks to wheel speed sensors that detect the rate the wheels are spinning. These sensors relay the rotational speed of the wheel and detect if the wheel has stopped rotating, sending a signal to the bike’s ECU.

The ECU determines if the wheel deceleration falls outside of predetermined limits, and if this is leading to a locked wheel. The ECU then tells the ABS control unit to ‘pulse’ and reduce the hydraulic pressure of the braking system.
******

In reality I suspect the system will take account of all of the individual wheel deceleration, the speed before sudden wheel deceleration and the difference to decide what to do, but it can be detected and applied to both wheels independently- can be applied to one or other or both.

theoneandonly · May 14, 2022

if both wheels are locked at 80 mph , i would be amazed , but at some point 1 will have locked up first , therefore the abs would have acted on that wheel . what do you think happens when both wheels are on ice , and both are locked ? the abs will not react cos it thinks you have stopped.

did you read this bit ^^^ ?

unless your speedo is driven by gps ? it comes from wheel or drivetrain . both wheels locked , speedo goes to zero ,bike thinks you've stopped.

most abs's stop working at approx 8mph .

Doofus · May 14, 2022

theoneandonly said:
if both wheels are locked at 80 mph , i would be amazed , but at some point 1 will have locked up first , therefore the abs would have acted on that wheel . what do you think happens when both wheels are on ice , and both are locked ? the abs will not react cos it thinks you have stopped.

did you read this bit ^^^ ?

unless your speedo is driven by gps ? it comes from wheel or drivetrain . both wheels locked , speedo goes to zero ,bike thinks you've stopped.

most abs's stop working at approx 8mph .

Yes I read it all.

If both wheels lock at 80 mph, then ABS will operate on both wheels. The ABS will know the bike has not stopped because the ABS knows the bike cannot go from 80 mph to stopped in a fraction of a second. That is the whole point of measuring the rate of deceleration of the wheels and comparing it with a threshold. This does not require GPS. Do you really think that if the ABS kicks in for the front wheel and in panic I stamp on the back brake that the ABS will just let the rear wheel lock because it’s only willing to apply ABS to the first wheel to lock?

mondrage · May 18, 2022

I’ll do a test and take the rear ABS connector after the self test have passed to see what happens.

If this works, it’d be a matter of having a switch to interrupt the rear wheel ABS signal.

I’ll find the time to do this.

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Doofus · May 18, 2022

mondrage said:
I’ll do a test and take the rear ABS connector after the self test have passed to see what happens.

If this works, it’d be a matter of having a switch to interrupt the rear wheel ABS signal.

I’ll find the time to do this.

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Possibly a simpler switch option and perhaps less likely to throw an error (e.g. mess up your speedo or cause the ABS to decide it cannot trust what it is seeing and give up for the front too) is to interrupt the wiring at the rear brake cylinder / lever that triggers the brake light - assuming the ABS will only kick in if it thinks you are pressing the brake, it seems likely, or at least possible, it will pick this up from the brake switch (this would not work if it instead uses a hydraulic switch in the ABS unit to decide if you are pressing the brake)

mondrage · May 18, 2022

Doofus said:
Possibly a simpler switch option and perhaps less likely to throw an error (e.g. mess up your speedo or cause the ABS to decide it cannot trust what it is seeing and give up for the front too) is to interrupt the wiring at the rear brake cylinder / lever that triggers the brake light - assuming the ABS will only kick in if it thinks you are pressing the brake, it seems likely, or at least possible, it will pick this up from the brake switch (this would not work if it instead uses a hydraulic switch in the ABS unit to decide if you are pressing the brake)

Actually, starting from 2008, the ABS system does not use switches for the brake levers, but rather pressure inside the ABS module itself.
The front levers, actually have the room for the switch (same as the clutch switch) but no switch. Same for the rear brake lever.
The Conti Téves ABS system does not use switches.

I can't believe BMW wouldn't know that disabling the front ABS off-road on big adv bike is not the best... and somehow they saw the light in the K50s almost a decade and a half later...
Anyways...

dirty_t · May 19, 2022

Interesting thread. I wonder what JVB might know about this...

Apart from that, if in fact the system works by comparing wheel speed between front and rear to decide if one is turning slower than the other (eg, in the case of an impending front lock up), what hapapens, I wonder, if you switch out your front wheel from a 19" to a 21"? Wouldn't that mess up the computer's ability to accurately guage wheel speed difference?

mondrage · May 19, 2022

It’s a two channel ABS system.
It’s doesn’t compare the two wheels. The ASC does that not ABS.
ABS only looks at the rate of turning speed of each wheel independently.

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botus · May 21, 2022

dirty_t said:
if in fact the system works by comparing wheel speed between front and rear to decide if one is turning slower than the other (eg, in the case of an impending front lock up), what happens, I wonder, if you switch out your front wheel from a 19" to a 21"? Wouldn't that mess up the computer's ability to accurately gauge wheel speed difference?

the bike gets an operating window set in software for each wheel's distance travelled per revolution ( the idea to cope with a new tyre vs worn, diff brands etc.), if you fit a set up that usually >11% outside the parameters the ABS gets muddled. Its a well know fight Harley chopper boys have when fitting a 21" wheel (even the factory took a while to understand it ...of course brakes were never really a consideration for this brand).

There are ways in software to alter the ref points... to cope with different set ups

How to disable rear abs only?

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