Servo brakes .. are they that unreliable?
- Thread starter Bryn
- Start date
DutchBryn
Registered user
"That's not how mine work "
I know they are a servo and not literally like Merc's Emergency Brake Assist, (whereby the driver becomes a passenger as far braking is concerned.)
My point was that the system is intended to do more braking sooner. The ABS
then regulates the braking force.
The degee of servoeing(?) is deliberately very high - to begin heavy braking
as soon as mechanically possible and not as soon as the rider thinks it prudent. That was what I intended by ref. to EBA
As others have said, heavier bikes than ours do not require (or have) servo assisted brakes merely to stop (in perfect conditions).
But they weren't fitted to provide simple assistance. Their role was to save the rider from himself(ie, by underestimating the bikes true braking ability) by braking harder sooner.
With BM's servos, if you were to graph braking force against time, the line would be nearly vertical, then horizontal in a saw-tooth pattern(ABS working).
It is therefore the steepness of that initial 'curve' that BMW were after.
If everything's working and you have abs/servos, I believe you have a safer bike than (say) an ABSII equiped machine.
I do accept the concept as a good one. But it has to have car-levels of reliability.
I know they are a servo and not literally like Merc's Emergency Brake Assist, (whereby the driver becomes a passenger as far braking is concerned.)
My point was that the system is intended to do more braking sooner. The ABS
then regulates the braking force.
The degee of servoeing(?) is deliberately very high - to begin heavy braking
as soon as mechanically possible and not as soon as the rider thinks it prudent. That was what I intended by ref. to EBA
As others have said, heavier bikes than ours do not require (or have) servo assisted brakes merely to stop (in perfect conditions).
But they weren't fitted to provide simple assistance. Their role was to save the rider from himself(ie, by underestimating the bikes true braking ability) by braking harder sooner.
With BM's servos, if you were to graph braking force against time, the line would be nearly vertical, then horizontal in a saw-tooth pattern(ABS working).
It is therefore the steepness of that initial 'curve' that BMW were after.
If everything's working and you have abs/servos, I believe you have a safer bike than (say) an ABSII equiped machine.
I do accept the concept as a good one. But it has to have car-levels of reliability.
I don't know what makes you think that BMW intended servo-abs to be some sort of "emergency brake assist" system. They never marketed it as that and I have never seen any mention of such an intention.
Emergency brake assist on cars is designed to detect heavy braking and to push retardation to the limit of grip using additional power assistance and abs and stability systems to keep it under control. But the BMW bike servo system works all the time (like a normal car servo does) and makes no distinction between light or heavy braking.
Another point - ultimate braking performance is achieved by progressive brake application to first achieve weight transfer onto the front tyre, followed by harder braking to make use of the additional grip that the weight transfer provides. Applying the brakes hard, instantly (the near vertical line for brake force against time that you mention) will serve only to overwhelm the grip and trigger the abs, thus actually increasing braking distance. No one in their right mind, least of all a major bike manufacturer, would actually set out to design a bike braking system that works in this way.
Emergency brake assist on cars is designed to detect heavy braking and to push retardation to the limit of grip using additional power assistance and abs and stability systems to keep it under control. But the BMW bike servo system works all the time (like a normal car servo does) and makes no distinction between light or heavy braking.
Another point - ultimate braking performance is achieved by progressive brake application to first achieve weight transfer onto the front tyre, followed by harder braking to make use of the additional grip that the weight transfer provides. Applying the brakes hard, instantly (the near vertical line for brake force against time that you mention) will serve only to overwhelm the grip and trigger the abs, thus actually increasing braking distance. No one in their right mind, least of all a major bike manufacturer, would actually set out to design a bike braking system that works in this way.
How do you ride ?
You regulate the braking force, the ABS is for unexpected emergencies.
DutchBryn
Registered user
Hi Sproggy,
I can't say what the marketers said.
What I wrote here is not original to me, though. I picked it up from a tech article I read, on the system.
I first mentioned, rather annecdotally, how many riders react in a real emergency situation. Many riders simply do not apply their brakes effectively.
What to do? 'Simple' ABS, allows the rider to brake less cautiously than without it.
But it needs the rider to apply the brakes and to hold them on.
In many accidents, riders didn't brake at all(!) or only used the rear brake.
Hence linked brakes.
Adding servoes is a further development. Harder braking, sooner.
Graphing braking force: I said 'nearly vertical'. It's force vs time time
so it's clearly a diagonal line, but steep (using the same scale) relative to an average rider, sans servoes.
The latest and best quick cycling ABS systems are in fact 'programmed'
to limit their braking performance to prevent the rear wheel lifting.
Neil. This whole thing is about braking in emergencies. I know..
It may well be that you and many others here possess the reactions of a mongoose and the foresight of a minor prophet.
Increasingly, though, the bike / car is going to be making the decisions. Whether we agree (about anything) or not, the manufactures view the rider / driver as the weakest link and are using their technology to 'rescue' him from himself. Doubtless, you'd never open a throttle too violently.
With throttle-by-wire, you couldn't even if you wanted to. The stepper motor
does what computer thought you meant.
So far, cars have much more of this stuff than bikes. For now.
Honda's new braking system is 'by wire'. Not sure when it'll be developed
further with (giros / yaw detectors), to enable abs braking into corners. But it'll come. The manufactures, mindful of how bad we make them look, in accidents / deaths relative to miles covered, are protecting their investment.
Remember Peter Bottomly? He nearly succeeded.
How do I ride? After leaving my bike to warm-up for half an hour (or so),
I set off, making sure I don't ride in the red-zone. No, I rev. past that asap.
etc..
I can't say what the marketers said.
What I wrote here is not original to me, though. I picked it up from a tech article I read, on the system.
I first mentioned, rather annecdotally, how many riders react in a real emergency situation. Many riders simply do not apply their brakes effectively.
What to do? 'Simple' ABS, allows the rider to brake less cautiously than without it.
But it needs the rider to apply the brakes and to hold them on.
In many accidents, riders didn't brake at all(!) or only used the rear brake.
Hence linked brakes.
Adding servoes is a further development. Harder braking, sooner.
Graphing braking force: I said 'nearly vertical'. It's force vs time time
so it's clearly a diagonal line, but steep (using the same scale) relative to an average rider, sans servoes.
The latest and best quick cycling ABS systems are in fact 'programmed'
to limit their braking performance to prevent the rear wheel lifting.
Neil. This whole thing is about braking in emergencies. I know..
It may well be that you and many others here possess the reactions of a mongoose and the foresight of a minor prophet.
Increasingly, though, the bike / car is going to be making the decisions. Whether we agree (about anything) or not, the manufactures view the rider / driver as the weakest link and are using their technology to 'rescue' him from himself. Doubtless, you'd never open a throttle too violently.
With throttle-by-wire, you couldn't even if you wanted to. The stepper motor
does what computer thought you meant.
So far, cars have much more of this stuff than bikes. For now.
Honda's new braking system is 'by wire'. Not sure when it'll be developed
further with (giros / yaw detectors), to enable abs braking into corners. But it'll come. The manufactures, mindful of how bad we make them look, in accidents / deaths relative to miles covered, are protecting their investment.
Remember Peter Bottomly? He nearly succeeded.
How do I ride? After leaving my bike to warm-up for half an hour (or so),
I set off, making sure I don't ride in the red-zone. No, I rev. past that asap.
etc..
motobiker
Registered user
I'm so glad i don't have to worry about ANY of this rubbish...
Neil. This whole thing is about braking in emergencies. I know..
It may well be that you and many others here possess the reactions of a mongoose and the foresight of a minor prophet.
.
Your too focussed on certain points - re-read what i said.
ABS is for the emergencies. So it's nothing to do with what you keep harping on about, reactions of a mongoose, riding gods etc etc
in fact completely the opposite. And applies to me when i have my nap while riding.
DutchBryn
Registered user
We agree on what ABS is for.
I attempted to make a case that servoed braked (necesarily linked to ABS)
had a function beyond reducing input / effort at the controls.
No one 'bought' it.
Oh well.
Just for clarity, my ref. to perceived need for ABS yes / no, was not aimed at
anyone as a question, per se. I meant, "what does Honda, BMW etc think we need"(?) ie regardless off whether anyone else agrees or not.
So,
Here's to motorcycles. One of the last great freedoms.
I attempted to make a case that servoed braked (necesarily linked to ABS)
had a function beyond reducing input / effort at the controls.
No one 'bought' it.
Oh well.
Just for clarity, my ref. to perceived need for ABS yes / no, was not aimed at
anyone as a question, per se. I meant, "what does Honda, BMW etc think we need"(?) ie regardless off whether anyone else agrees or not.
So,
Here's to motorcycles. One of the last great freedoms.
ExpatinIstanbul
Registered user
If I had the technical knowledge I'd have 'em off in a jiffy. They locked up on me a while back, only while pushing the bike though (yes, it's a 12 so enough of the cracks). For no apparent reason the brakes seized on and wouldn't release. But the main reason for wanting to ditch 'em is the horrible whine they make. Whine, whine bloody whine.
ahutcheon
Registered user
I suspect that any Japanese sportsbike built in the last decade or so can develop very high braking forces almost instantly with a relatively modest pull on the lever. I've even heard some people say that they are aware of the servo start up delay with BMW servos (I'm not one of them).
OK, on my 1970s Moto Guzzi it took a moment to build up the death grip required to stop hard with the old Brembos. If that's what BMW were trying to overcome, I don't understand why they went to servos. If they wanted front-rear linking with reactive proportioning then maybe the servo is no worse than the Honda setup with lots of pipes, valves and different pistons in the same caliper operated by front and rear brake (I don't follow the reliability of those Honda models).
There's no complex component in a Honda CBS system that might fail and leave you with almost no brakes in the same way that a dead BMW servo might. Sure, there are more pipes, but technically it's very simple. IMO the Honda setup is a far superior method of linking brakes....if you really want linked brakes.
I've fun a few Blackbirds and not had, or heard of, problems with CBS. It's a matter of taste (some people prefer to have absolute control over which brakes come on and when) but you get used to it and it is reliable.
Incidentally it's much more expensive to de-link the CBS brakes on a Blackbird (or, presumably, any CBS Honda) than it is to de-servo a BMW. Useless fact for the day
No one "bought" it because any time someone offered an opinion you dismissed it with frivilous remarks about "riding gods" etc..
Incidentally it's much more expensive to de-link the CBS brakes on a Blackbird (or, presumably, any CBS Honda) than it is to de-servo a BMW. Useless fact for the day
Jaws does a kit for £99.90, which is a third of the price of a new set of 10 braided hoses to keep the CBS. I Know cos Ive just done my Blackbird this summer, 10 hoses that is. I actually like the CBS system, it works and as you've said its a lot simpler than the servo system and has virtually nothing that will cause the dangerous failures that can happen with BMW's Servo's.
So true.
I ride my R850GS with standard BMW non servo brakes back to back with my Blackbird, and I can barely tell any diference between them. I just get on and ride, I never think the BMWs brakes are heavy and don't work very well, or that they require extra effort to stop.
DollyRocket
Registered user
My Servo/ABS system has started buggering about this weekend again, occasionally i get the flashing lights on the ABS (4Hz) with the Gen Light on - I assume it is a sticky back brake switch since there is no perceived braking effort from the rear but a continual whine from the servo - I also had a continual whine from the wife on the back but I don't think that is related to the ABS system. Turn off/on ignition it all comes up trumps again for another few hours. Probably get steptoe to take it out on the next service (which is likely to be quite soon) unless i can track down the fault.
STUBBS
undead
on my last bike it was removed when it packed up
Ed209
Registered user
My brakes do a weird thing from time to time. A couple of times on my route I have a road downhill to a junction of a main road. The road surface is a bit uneven and not sure if this has anything to do with it, but when I hit the bumps downhill and brake at the same time the ABS or servo seem to kick in and I almost feel like I am losing brakes. Ive also had to park facing uphill a couple of times then forgotten about the lose of brake effect as it starts to roll backwards. 
Ive also had to park facing uphill a couple of times then forgotten about the lose of brake effect as it starts to roll backwards.
This is another occasion when they're particularly shite offroad, parked in gear, climb on the bike on a steep hill, pull the clutch in and ........."feckin thing"
Ed209
Registered user
This is another occasion when they're particularly shite offroad, parked in gear, climb on the bike on a steep hill, pull the clutch in and ........."feckin thing"
Yeah I nearly caved in the side of a transit as well, just managed to dump the clutch and stop it.
This is another occasion when they're particularly shite offroad, parked in gear, climb on the bike on a steep hill, pull the clutch in and ........."feckin thing"
Ever thought of switching on the ignition, allowing the check circuit to do its thing and then having full braking assistance, pull on the brakes?
Jeez. It ain't rocket-science.
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