Servo thoughts

[nleader]

I spent yesterday working with a Met Trafpol who wants to convert from cars to bikes. He was talking about the police R1150RTs with servo brakes. They seem to believe that the servos are more likely to fail because they can 'burn out' (his words). This happens when Met riders are stationary (happens quite a bit in London traffic) and keep the rear or front brake applied as they've been taught.

Does that sound likely, anyone? I don't think the servo needs to assisting braking effort once the bike is no longer moving, surely?

Anyone who knows what they're talking about care to comment? What happens in a car? Or are they just better built because there's more room for a more robust unit in a car?

Norman

 

[Mouse]

Car servo brakes aren't electrical like those on the R1200GS (and I presume the earlier bikes use the same system). The braking assist is provided by using the vacuum from the inlet manifold to move a diaphragm that provides the extra "push" on the brakes.

I assume this type of assist isn't used on a bike because the manifold and the engine are that much smaller, that there's not enough vacuum, or something.

As for keeping the brakes on when you're stopped - on my 1200, the whining noise from the servos does stop after a few seconds if I leave my foot on the brake pedal with constant pressure (while stationary). So it would appear to be the case that the servos don't run continuously. Can't say I've noticed the front one doing the same, maybe it takes more time to build up enough pressure to make it stop, in the larger hydraulic system (assuming it's pressure that makes it stop). Lot of assumptions there

 

[MikeP]

Mouse,

My 1150 does the same ie the servo whines when the brake (front or rear) is first applied and then stops. There is no loss of braking effect or increased lever movement when the noise stops.

I think you are correct about the reasons for the servo system as applied to bikes v cars.

I've read and re-read everything posted plus all the links. I'm still not sure what the fault is. Some talk of ABS failure and some of an intermittent servo failure.

 

[Spout]

It doesn't really matter whether the servo is mechanical, electrical or even nuclear. Servo brakes are completely unnecessary on a 200kg motorcycle.

 

[Mouse]

I've read and re-read everything posted plus all the links. I'm still not sure what the fault is. Some talk of ABS failure and some of an intermittent servo failure.

I think part of the problem with getting accurate information on this, is that a lot of people seem to confuse the servo system with the ABS. For example, we all know that next year the 1200GS will be available without ABS. But will it have servo assist or not? Many people assume not, but is this true?

ALso, assuming you are unlucky enough to have some sort of failure ... you lose braking ... how do you know if the servos have failed or the ABS has activated? Both would feel pretty similar when your mind is occupied with stopping, I reckon.

We all know the ABS can activate if the wheel skips over a bump in the road, for example. How would you distinguish this from a momentary servo failure?

 

[ahutcheon]

It doesn't really matter whether the servo is mechanical, electrical or even nuclear. Servo brakes are completely unnecessary on a 200kg motorcycle.

That was certainly true for my last few Hondas. The brakes on the non-ABS 1150GS demo bike I test rode were somewhat underwhelming in comparison; not the gentle two-finger squeeze I was used to. I'd have suspected BMW of doing it to make the ABS/servo option seem attractive if I didn't see so many airhead riders debating the relative merits of anchor vs parachute. They're fixing a problem other bike manufacturers don't seem to have. And we (at least I) are buying their bikes because the whole riding experience is much greater than the sum of the specs.

 

[littleredrooster]

The brakes on the non-ABS 1150GS demo bike I test rode were somewhat underwhelming

Must have been summat drastically wrong with the bike, then, 'cos the brakes on both the demo bike I tried and my own bike (2001 ABS non-evo-thingies) are just devastating compared to anything else I have ridden. This includes stuff like 'Blades, GSXRs, R1s, by the way. More feel and more power, no fade and lots of confidence in them. Best brakes on any bike I have ridden in the last 34 years. One or two fingers to get the front tyre smoking into roundabouts, if you're that way inclined!

Try another one!

 

[ahutcheon]

Must have been summat drastically wrong with the bike, then, 'cos the brakes on both the demo bike I tried and my own bike (2001 ABS non-evo-thingies) are just devastating compared to anything else I have ridden. This includes stuff like 'Blades, GSXRs, R1s, by the way. More feel and more power, no fade and lots of confidence in them. Best brakes on any bike I have ridden in the last 34 years. One or two fingers to get the front tyre smoking into roundabouts, if you're that way inclined!

Try another one!

I bought an ABS one (I wanted the feature anyway). Just observing that without the servo, the non-ABS (on a dealer demo bike, so presumably OK) needed a much harder pull at the lever than the Firestorm I was getting rid of. Stopped the bike plenty effectively, rather like the Brembos on my old Guzzi now I think back. I'd have adjusted to them; it wasn't the scary "brakes" I remember from a mid-seventies 550/4 Honda!

Seems to me (comparing the 2003 options) that BMW were using servos to get the light pull at the lever that Honda achieved without them half a decade or more earlier.

Has anybody noticed whether the the brake effort increased between the Brembo and non-ABS "BMW" calipers? I'm curious, not concerned: did BMW add servo to get a perceived low-effort lever that others had anyway, or was it needed to get a clever front-rear split from the ABS electronics (rather than the primitive Guzzi linked setup or the complex plumbing that Honda use)?

 

[Dave Barrett]

I've how had 1150GS's both with and without servo brakes. At the beginning, I was also reluctant to have a servo-brake equipped bike, especially after experience of the 1150RS with the same braking system. Sure, there are downsides, but I can honestly say that braking from high speed (180 km/h) on the autobahn, fully loaded, is just so easy on the servo version, especially if you have to panic brake.

I can also say that once you get used to them, they do not grab, they are not difficult to use in traffic, they are not insensitive.

It's the same old "horses for courses" argument. At the end of the day, my bike spends (unfortunately) most of its life on autobahns, which for the most part have no speed limit. The advantages of servo brakes at these sort of speeds far outweighs the negative points.

For the noise part - I wear earplugs, and when possible, don't hold the brakes on when stationary.

 

[GSmonkey]

The brakes on the 1200GS are just fantastic. Much better than on by CBR6. When the shit hits the fan and you've got to scrub off speed quick, the 12GS's brakes are just the ticket. I've never been so happy with a braking system on any other bike I've owned.

The only downside is the brakes are that good, you do things you wouldn't normally do on other bikes, in weather conditions you wouldn't normally do them in

 

[Spout]

Dave and GSMonkey,

you've both mentioned how superb the servo brakes are.

"......but I can honestly say that braking from high speed (180 km/h) on the autobahn, fully loaded, is just so easy on the servo version, especially if you have to panic brake."

So what happens in this situation when the electrics decide to switch off the servos just before?

"When the shit hits the fan and you've got to scrub off speed quick, the 12GS's brakes are just the ticket."

But only when they are working!

The worry for me is that over 25 years of motorcycling I've had plenty of blown bulbs. If they can't get those right how can I trust any electrical feature on a bike?
Bulbs, ignition, fuel pumps going wrong ain't going to kill me. Brakes 'switching off' might.

 

[Spanish Bob]

It doesn't really matter whether the servo is mechanical, electrical or even nuclear. Servo brakes are completely unnecessary on a 200kg motorcycle.

thank goodness my adventure weighs considerably more than that eh!

Ive been reading everything on the servos and to be honest (no offense intended to anyone) this thread is about as genuinely informative as all the others.

 

[Mouse]

Bob has a point All these threads are a micture of speculation and peoples' opinions on the servo brakes ("I like them", "I don't like them" ...)

I would point out though, that I imagine an ignition failure could kill you, if you were half way through a manouvre like an overtake, and suddenly you lost power and couldn't reach safety. Unlikely, yes, but possible.

 

[mikeh501]

thank goodness my adventure weighs considerably more than that eh!

Exactly. Totalled up with ride, luggage and pillion your talking seriously more weight than that.

On my Aprilia RST1000, the non-servo brembos goldline brakes were getting overwhelmed when pillion and luggaged up. Servos are good IMO.

And in any case the brakes still work when the servo is off, you just have to pull a lot harder. I would jam it back to the bar if the servos died and I'm sure it would pull up ok.

and I'm sure this bs was done to death when cars first got it.