Braking question for RTP Riders

[Modie]

1150 RTP to be exact. I ride an '05 (yes '05) 1150RTP. It's my work bike. Today during our monthly training day, I decided to see how quickly I could get my bike stopped at 45. Actually the test pattern is a 40 mph decel within, I think it's 80 feet, then do a few turns. Anyway I was trying to get stopped within that distance at 45 mph as opposed to 40.

Now, I do not depend on anti-lock. I try to 7-8-9 brake and prefer not to get to anti-lock due to the extended braking distance. To my point, I was squeezing harder and fast harder than usual for the stated reasons. I kept getting it into anti-lock and as soon as I hit anti-lock, I could not increase my braking power. Again I don't regularly get into anti-lock but I thought the system went into a pulsating mode similar to the type in autos. It was as if the system sensed maximum braking pressure and would not allow any more pressure to be put into the brakes, no matter how much harder I squeezed.

Could someone educated me please.

[UA342]

I'll bump this for you.

 

I am not a motor officer nor do I ride a RTP. I have an 05 R1200RT. I can trip the ABS doing emergency stops without a terrible amount of trouble.

 

I did a little breaking drill last Saturday. I've been remiss in my drills lately so I went to my favorite deserted industrial park. I didn't have the top case or the panniers on so the rear was lighter. I was able to loft the rear tire under braking. It was just a quick bounce at the very end. The last time the ABS kicked in before the back lifted. I need to go practice with the bags on again.

[upflying]

It sounds like your brakes are working correctly. After you reach the point of ABS engagement, it's the computer that decides how the bike stops, not the strength of your squeeze.

[KER]

possible tire problem? I noticed for the short amount of time that i had the stock tires on my bike (dunlops) the braking system went into abs a lot easier. With better gripping tires it seems that i can brake harder and stop sooner without going into abs. Most in service police bikes use dunlops/dunlops runflats and their standard tire, i have found these are a hardered rubber and do not grip that well. So, just a thought that the tires are loosing grip and tripping the abs to kick in. It would be an intresting test to take two of the same bikes and run a control test using two different tires.

[ShovelStrokeEd]

The brakes are operating within their parameters.

 

The ABS goal is to keep the wheels turning with some minimal amount of differential in speed between front and rear wheels. It will modulate the pressure applied to the calipers to attain that. On an 1150, with the ABS working normally, all the braking force is actually provided by the ABS pumps. The hand or foot lever pressure just acts as a signal source for these pumps and is modified and sometimes amplified, sometimes attenuated by the computer depending on available traction.

 

That word, "traction", is the key. Tires provide the traction to exert stopping force. If your tires are worn, or of a harder compound, they will provide less traction and thus, trigger the ABS response earlier. Since you probably don't have any input into what tires are fitted to your work bike, you should just practice with that level to help you make decisions about whether you can get stopped/slowed in time or use other means of avoiding whatever it was that caused you to get on the brakes.

[Joe Frickin' Friday]

On an 1150, with the ABS working normally, all the braking force is actually provided by the ABS pumps. The hand or foot lever pressure just acts as a signal source for these pumps and is modified and sometimes amplified, sometimes attenuated by the computer depending on available traction.

 

From a user perspective, the difference between BMW's motorcycle ABS and the typical automotive ABS is in lever/pedal feel. On most cars, when you get into the ABS the pumps take over, and you get feedback at the pedal (that nice, crunchy-grindy foot massage) that actually backs the pedal away from the floor, no matter how hard you press on it. On BMW's bikes, the lever is simply locked out: you get no feedback, no finger massage, the lever simply is not allowed to move any closer to the bar (I guess if you're paying close attention, that lever freeze-up is your feedback).

[motorman587]

First, is your question that you are going into ABS mode too much?? Second as a motor instuctor you should not exceed the 40 mph in the 40 mph decel exercise, just for the reason if you got hurt or crash it could bit you in the rear. If you know what I mean. In our training I have seen that the rear will almost always go into ABS because of the weight shift. So we pratice not to get either tire into ABS mode.

[UA342]

First, is your question that you are going into ABS mode too much?? Second as a motor instuctor you should not exceed the 40 mph in the 40 mph decel exercise, just for the reason if you got hurt or crash it could bit you in the rear. If you know what I mean. In our training I have seen that the rear will almost always go into ABS because of the weight shift. So we pratice not to get either tire into ABS mode.

 

There's the rub.

 

The linked brakes provide a preset balance of braking force. An emergency braking manuver will naturally lighten up the rear tire from the weight shift. Why is it desired to limit front braking force before the rear abs kicks in?

 

I always just thought the rear brake of my 12RT went into ABS mode as a regular occurance during hard stops. Otherwise the braking system pressure couldn't be at a static 70/30 or 80/20 ratio.

 

I would assume the front tire has significantly more traction available at the time the rear reaches it's ABS limit.

[leikam]

I kept getting it into anti-lock and as soon as I hit anti-lock, I could not increase my braking power.

...

It was as if the system sensed maximum braking pressure and would not allow any more pressure to be put into the brakes, no matter how much harder I squeezed.

I'm wondering what you expected. What would "increasing braking power" do at this point since you are already at the point of wheel lockup? The ABS isn't going to let you lock up the wheels, so adding more pressure to the brake lines can't make a difference to your stopping performance. On other bikes you have ridden, if you lock up your wheels, does applying more braking pressure help you stop sooner?

[Shaun]

The linked brakes provide a preset balance of braking force. An emergency braking manuver will naturally lighten up the rear tire from the weight shift. Why is it desired to limit front braking force before the rear abs kicks in?

 

I always just thought the rear brake of my 12RT went into ABS mode as a regular occurance during hard stops. Otherwise the braking system pressure couldn't be at a static 70/30 or 80/20 ratio.

 

I would assume the front tire has significantly more traction available at the time the rear reaches it's ABS limit.

The following is strictly my conception of the braking system on BMW's, such as the '05 RTP, based on experience and responses to vague questions posed to equally perplexed (but supposedly knowledgable) manufacturers representatives. Leaving the technicality of residual braking aside, for whatever it's worth:

 

The factor of focus is traction, at either end, between the road surface and the tire ... be it limited to a greater or lesser degree by surface contaminants (either way) or quality (either way). Barring the bizarre, when ABS activates the tire in question is sliding. It isn't a question of limiting braking force for the sake of convenience.

 

While the brakes may be linked there are two independent systems monitoring traction (ABS front and back). The action of one does not influence the action of the other. In other words, ABS dealing with a locking rear does not restrict additional braking still available at the front even though the rider is implementing both through one control, say, the lever.

 

If circumstances activate ABS at the front and the rider is braking with the lever it may seem to freeze but this is only a perception. The ABS cycle of brake/slip/release has an upper limit which no extra effort at the control can overcome, therefore the feeling of loss. When the bike is 'on' and the servo active the travel/feel at the lever or pedal is what you get irrespective of ABS. Hydraulic pressure from the control is applied to the Controller, not the actual braking system where ABS resides.

 

The distribution of braking front/back is both dynamic and static. The first few hard stops give the computer an idea about weight distribution (dynamic) from which it determines an appropriate ratio (static). Could be 70/30 for one stint with two-up and full bags and 80/20 for the next with single rider and no gear.

 

Could be right, could be wrong, but some Bavarian Elf knows for sure.

[motorman587]

First, is your question that you are going into ABS mode too much?? Second as a motor instuctor you should not exceed the 40 mph in the 40 mph decel exercise, just for the reason if you got hurt or crash it could bit you in the rear. If you know what I mean. In our training I have seen that the rear will almost always go into ABS because of the weight shift. So we pratice not to get either tire into ABS mode.

 

 

I was not saying you were doing anything wrong or attempting throw you under the bus, but here is a good article about the braking exericses in motor training and liability.

 

http://www.motorcops.com/

[Baba_ORiley]

... On most cars, when you get into the ABS the pumps take over, and you get feedback at the pedal (that nice, crunchy-grindy foot massage) that actually backs the pedal away from the floor, no matter how hard you press on it.

Its the opposite on ABS-equipped cars with some form of Brake Assist. When the system senses a full-on panic stop, it pulls the pedal to the floor under your foot. It was very freaky for me the first time I experienced on a rental Peugeot. Apparently, a panic stop is recognized by a very quick transition from throttle to brake pedal, and the amount of force applied to the brakes.

... On BMW's bikes, the lever is simply locked out: you get no feedback, no finger massage, the lever simply is not allowed to move any closer to the bar (I guess if you're paying close attention, that lever freeze-up is your feedback).

Is that true for the older bikes such as the 1100, too? (this is a reminder I need to practice stopping on my RT-P)

 

 

 

.

[Modie]

Prior to this day, I had not put the bike into the antilock consistantly. Occassionally put not over and over. My only experience in anti-locks brakes is in cars. I thought I would get the vibration that I get when I put a car into anti-lock. On the 1150 I felt no vibration. Just the inabilty to provide more braking power through harder lever squeeze. As was replied, the BMW does not give the 'crunchy' vibration that one feels in a car. So, I was uncertain, was I in anti-lock being that I could not provide additional braking force? It appears I was.

[Joe Frickin' Friday]

... On BMW's bikes, the lever is simply locked out: you get no feedback, no finger massage, the lever simply is not allowed to move any closer to the bar (I guess if you're paying close attention, that lever freeze-up is your feedback).

Is that true for the older bikes such as the 1100, too? (this is a reminder I need to practice stopping on my RT-P)

 

I've only personally observed it on my 1100RT, but as Modie now reports, the same is true of the 1150's. Can't speak for the hexheads, but I suspect the same is also true there.

[Boffin]

... On BMW's bikes, the lever is simply locked out: you get no feedback, no finger massage, the lever simply is not allowed to move any closer to the bar (I guess if you're paying close attention, that lever freeze-up is your feedback).

Is that true for the older bikes such as the 1100, too? (this is a reminder I need to practice stopping on my RT-P)

 

I've only personally observed it on my 1100RT, but as Modie now reports, the same is true of the 1150's. Can't speak for the hexheads, but I suspect the same is also true there.

 

I suspect it is not true for the latest generation of BMWs. Up until the latest non-servo ABS brakes came along BME bikes used an unique method of achieving brake fluid pressure control for ABS. In the standard system (and the newest BMW bikes) the ABS unit uses rapidly switching valves and a pump to modulate pressure. The system dumps pressure with a valve, then re-instates via another valve from a pumped supply. This leads to the familliar pedal modulation. BMW always felt that this was too coarse for good ABS on a bike until now, when computing power allows more subtlety.

The system used up until now on the BMW bikes uses a piston in a cylnder to control pressure, - on the generation 1 brakes the large cylinder is obvious. As you apply more pressure on the brakes it cancels your input leading to a smooth, pulse-less ABS action.

 

Andy

[MotorinLA]

Could be right, could be wrong, but some Bavarian Elf knows for sure.