ABS equipped bike: Proportioned brake system question

[AV8R]

Assume an ABS equipped bike...

If you hit only the front brake lever, do the rear brakes engage also?
If yes, to what extent, same as if you apply both front and back manually?

What about the reverse case...

If you only use the rear brake pedal, do the front brakes engage?
(My experience says no)

Reason I ask, is a veteran motor says he never uses the rear brake on his modern BMW R1200RT-P cop bike.
Im wondering if its proportioning system is different than the ST-1300PA or he just learned habits from the old school days.

 

[ST Gui]

Yes
Yes
Yes

In either using the front or rear brake only a percentage of the other is used.

 

[AV8R]

I’ve learned it’s better at low speeds to use only the rear brake, like coming to a stop; else risk the nose diving into the forks and not a stable stop. Is that as expected, or is my proportion slave not working?

 

[ST Gui]

a veteran motor says he never uses the rear brake on his modern BMW R1200RT-P cop bike.

That's true of a lot of motor guys. My Wing buddy prior to retirement was a motor instructor for the local SO. He'd go down to Santa Barbara (IIRC) to be rectified. He taught all his guys to run patterns with no rear brake. Riding like that seem to have some affect on riding his 'Wing and he rarely uses his brakes in any turns. The 'Wings brakes are linked I believe.

Other motor schools may teach trail braking- I dunno. He's never mentioned it. He preflights his guys before they go to motor school in SoCal and they can run patterns tighter than what the school requires.

 

[AV8R]

I don’t think trail braking has to do with the rear brake, as much as it has to do with keeping some braking throughout the turn to keep a longer wheel base profile and a bigger traction footprint or patch, yes?

As for my practicing uturn and figure-8s in parking lots, basically tight turns, I only use rear brakes. Plus a constant throttle and modulate the clutch. Don’t know how one uses front brakes in slow maneuvers while controlling the throttle.

Forgive me if I misinterpreted the comments ST GUI.

 

[ST Gui]

I’ve learned it’s better at low speeds to use only the rear brake, like coming to a stop; else risk the nose diving into the forks and not a stable stop.

I generally use most/only the front brake for low speed stops. I get a small amount of weight shift with either brake. If you're getting front end dive maybe a little too much initial brake? More spring in the tubes? At low speeds it may not be necessary to use the front brake. That's mostly habit on my part. I do use use enging braking though there are those who'll tell you that's a no-no. I don't care.

 

[ST Gui]

Don’t know how one uses front brakes in slow maneuvers while controlling the throttle.

Yeah no that's not a thing. Unless maybe you're a trials rider I'd think front braking only or maybe even at all in a low speed turn is petitioning membership to the Tip Over Club.

 

[Larry Fine]

I don’t think trail braking has to do with the rear brake, as much as it has to do with keeping some braking throughout the turn to keep a longer wheel base profile and a bigger traction footprint or patch, yes?

Trail-braking is actually gentle front-brake application while in tight turns, which steepens the front fork angle and quickens steering response (effective while trail-braking), as does raising the rear suspension (effective all the time).

If anything, front braking would reduce the wheelbase slightly, because of compression of the tilted forks.

 

[ST Gui]

Trail-braking is actually gentle front-brake application while in tight turns,

Maybe that's true for tight turns but it seems to me trail braking is any of the two or combination of the to depending on the circumstances. Maybe on a track it's always front brake. That may be a more efficient manner or the hallmark of a better rider but I think that makes for a very narrow margin of error.

 

[AV8R]

Trail-braking is actually gentle front-brake application while in tight turns, which steepens the front fork angle and quickens steering response (effective while trail-braking), as does raising the rear suspension (effective all the time).

If anything, front braking would reduce the wheelbase slightly, because of compression of the tilted forks.

That’s right, shorter wheel base for the sport profile which is more turn response. Remembered that aspect backwards. Did get the traction part right. More pointsmof traction when the front wheel is pushed more into the road, hence a bigger patch.

 

[mortenk]

Yes
Yes
Yes

In either using the front or rear brake only a percentage of the other is used.

True as long as bike is moving forward. Some people tried this in the garage and were confused that rear wheel would spin freely when front brake lever was pressed. The bike must be moving for the rear brake to engage as a result of applying the front brake lever. Of course, rear brake pedal always works, regardless of speed...

 

[T_C]

Don’t know how one uses front brakes in slow maneuvers while controlling the throttle.

I'd think front braking only or maybe even at all in a low speed turn is petitioning membership to the Tip Over Club.

I'm with you, only touch the rear brake on quick sudden stops. Downshift and front is my normal, might light touch the rear pedal for activating lights before I slow.

It's a learned technique. Often done in mountain biking, apply power to rear and push front end against front brake, you can go slow or even standstill. Yes, be ready for bars to be pulled as you jam back of bike towards front.

Using just 2 fingers on brake, other two fingers, palm and thumb are wrapped around holding throttle. You can engage brake and control throttle. Similar to rolling a throttlemeister, couple of fingers hold throttle and some roll bar end.

 

[AV8R]

Cutting out all of the detail - A quick overview (that is slightly wrong)
When moving, the front brake will cause the all 3 calipers to apply braking force - using only 2 pistons in each caliper.
The rear pedal will cause braking force to all 3 pistons in the rear caliper, and some braking force to just the centre pistons in both of the two front calipers.


Now for the detailed explanation - (come on, you didn't really think I was going to stop at a short answer, did you ?)



If the bike is stationary, no. Squeezing the front brake lever applies the front brakes only - by pushing out the two outer pistons of the front calipers - both equally and at the same time.

If the bike is moving, yes. The result of the left hand caliper grabbing hold of the spinning rotor is that the left hand caliper bracket rocks forward. This activates the Secondary Master Cylinder which applies pressure to the two outer pistons of the rear caliper.
Because this may otherwise create too much braking force on the rear wheel, and induce a skid (especially since the braking force at the front will make the rear end lighter), the brake lines to the rear outer piston pass through a proportional control valve (located in front of the right hand side ignition coil). When the pressure increases, it overcomes the strength of a spring in the PCV, which moves a spool or piston inside, which acts as a valve to reduce the pressure to the rear brake caliper outer pistons.



When moving, applying the front brake levers results in just the 2 outer pistons of all 3 calipers being applied. The centre pistons do not move. So using just the front lever will apply 6 out of 9 pistons - 4 directly, 2 indirectly.



If the bike is NOT moving. If you use the rear brake pedal, then the centre piston is activated on the rear caliper - unrestricted.
The rear brake master cylinder also activates the two centre pistons in both front calipers. So applying the rear brake pedal activates all 3 centre pistons....

BUT - there is no anti-dive feature on the front forks. Instead, the braking force to the front calipers is limited INITIALLY to just the centre piston in the front left caliper
UNTIL - the pressure from the brake pedal increases to a point where it overcomes the pressure of a spring in the delay valve (at the rear of the front right fork). When it does, the pressure from the rear brake pedal operates the centre piston in the front right caliper as well. This helps to prevent the front forks from diving when controlling the bike with the brake pedal during slow manoeuvres.
Also - when stationary, the SMC on the front left caliper will not operate. Nevertheless, the fluid is able to move past the rear of the primary seal inside the SMC and apply the rear outer pistons (subject to the limits allowed by the Proportional Control Valve).


If the bike is moving. Then the same thing happens - more or less. But now, because the front left centre piston is grabbing the disc/rotor, the SMC moves and it applies the rear caliper outer pistons (again subject to the proportional control valve). So when moving, pressing the rear pedal hard will apply 5 out of 9 pistons - 3 directly (1 delayed), 2 indirectly.

Whether or not the bike has ABS makes no difference to these scenarios. They both have the identical set up. It is just that if the bike has ABS, it is there to repeatedly remove and reapply pressure in a rapid cycle, should the front or rear brakes lock up. But the balance is so good, I find that very rarely happens.



I hardly ever use the rear brake either, except to give it a bit of exercise every now and then. It certainly improves the retardation when I use both together.

hot damn! A great answer that revives memory cells back when IGOFAR tried to ‘splain this to me over his white support phone. Written, it’s much clearer to me. Thank you. Although I’ve not seen “retardation” used in this context before. Usually only with timing.

Boiling down the aforementioned detailed explanation:
- “the front lever will apply 6 out of 9 pistons - 4 directly, 2 indirectly.” 66.7% Of total braking power
- “the rear pedal hard will apply 5 out of 9 pistons - 3 directly (1 delayed), 2 indirectly.”. 55.6% Of total braking power

with proportional braking taken into account,
- using only either the front or rear brake provides roughly two thirds (~60%) of the total available braking power
- the majority (~60%) of the braking force will come from the wheel that the brake was applied to exclusively.

At the end of the day... (in summary), the take always for me are:
- Using one brake only provides 60% of available braking power
- The greater braking force will be biased by 60% towards the front or back, acording to the one brake lever used
- The best emergency braking is attained with both front and rear brakes being applied together and with ABS pulsing.
- At very slow and rolling to a stop speeds where too much front brake can cause nose tip overs if the steering isn’t perfectly straight; more rear brake than front makes sense. Hence using the rear brake when coming to a rolling stop could be better in that the focus of the braking power is biased to the rear.
- Going through turns and using the “trail braking” technique, judicious application of only the front brake is sufficient to effectively using the proportional amounts of front and back brake together.

 

[dduelin]

Assume an ABS equipped bike...

If you hit only the front brake lever, do the rear brakes engage also?
If yes, to what extent, same as if you apply both front and back manually?

What about the reverse case...

If you only use the rear brake pedal, do the front brakes engage?
(My experience says no)

Reason I ask, is a veteran motor says he never uses the rear brake on his modern BMW R1200RT-P cop bike.
Im wondering if its proportioning system is different than the ST-1300PA or he just learned habits from the old school days.

The BMW system on the RTP is different from the Honda linked system. BMW links some front lever to the rear brake but the rear brake is not linked to the front at all. Instead of Honda’s pivoting secondary master cylinder for pressure distribution BMW enlists the ABS modulator computer to distribute hydraulic pressure front to rear. The rear ABS will engage quickly due to both hand and foot pressure so a really light foot is needed. This might be why he’s trained himself never to use the rear. FWIW I use the rear alone when called for.

FWIW I use front alone or rear alone (knowing they are combined transparently) or combined hand and foot as needed. The Honda system is quite good at keeping much front pressure from reaching the calipers when lightly applying rear brake both in corners and during slow speed maneuvering.

 

[AV8R]

The BMW system on the RTP is different from the Honda linked system. BMW links some front lever to the rear brake but the rear brake is not linked to the front at all. Instead of Honda’s pivoting secondary master cylinder for pressure distribution BMW enlists the ABS modulator computer to distribute hydraulic pressure front to rear. The rear ABS will engage quickly due to both hand and foot pressure so a really light foot is needed. This might be why he’s trained himself never to use the rear. FWIW I use the rear alone when called for.

FWIW I use front alone or rear alone (knowing they are combined transparently) or combined hand and foot as needed. The Honda system is quite good at keeping much front pressure from reaching the calipers when lightly applying rear brake both in corners and during slow speed maneuvering.

perfect!
insignt from someone that has both systems

 

[AV8R]

Retardation - oh yes, I'd forgotten about doing that and then having to readjust the contact breaker gaps, and then having to adjust the retardation again ………..



Yes - that is more or less right. I avoided putting percentages on it because the centre pistons are smaller than the outer ones and so the braking effort is different. Applying the rear brake pedal doesn't provide nearly as much braking power as applying the front brake lever. Those two centre pistons on the front pads just can't hack it by themselves.

Then as pointed out earlier, as the transfer of weight to the front increases, the front stopping power is massive compared to the bit of stopping power as the back wheel gets lighter.
I did start to wonder about working all of that out, but then my brain started hurting.

you’re right again...
70% of the braking comes from the front brakes typically and generically.
So the percentage math has to take this into account for front /back brake forces.
Im sure the Honda engineers did all their homework to come out with the systems and components
So my math is a rough first order pass to get a feel as to what and why to use which and when

 

[SMSW]

hot damn! A great answer

- The best emergency braking is attained with both front and rear brakes being applied together and with ABS pulsing.

John sure knows his brake system AND he can explain it in a way that make sense to all of the rest of us!

Depends what you mean by "best". The most braking force you can make is by applying the brakes just short of locking up the wheels and keeping them there. Pro racers can do this and very experienced riders can too. This is why grabbing a handful of brake and letting the ABS cycle the brakes on and off yields longer stopping distances. This has been discussed in Motorcycle Consumer News a number of times, and as mentioned there, even their experienced tester sometimes is bested by the ABS. So, for most of us, your 'best' is correct. I remember years ago driving in my SAAB (before ABS), when some guy stopped suddenly in the middle of the intersection (I had no stop sign). I hit the brakes and steered to the right. My car stopped behind him just beyond his midline. Had I locked the brakes*, I would have hit him (no steering). I know I don't have the ability to slow the bike just above wheel lockup, so ABS would be best for me, and allow steering as well.

*This was probably either luck or lousy brakes on that car, I probably did not have the skill to brake my car just short of skidding back then.

 

[dduelin]

The shortest stopping distance is when the front brake is squeezed linearly to maximum, allowing maximum weight transfer onto the front contact patch concurrent with applying rear brake. This applies to ABS and non ABS systems. Just grabbing a handful of front brake locks up the front tire before it can generate maximum friction coefficient. The non ABS rider loses the front and goes down while the ABS rider loses precious time and distance as the front brake cycles on and off and saves his bacon while adding stopping distance. If ABS firmly squeezed "one two", building pressure, the weight transfers onto the contact developing far greater friction and the ABS cycles less.

 

[AV8R]

The shortest stopping distance is when the front brake is squeezed linearly to maximum, allowing maximum weight transfer onto the front contact patch concurrent with applying rear brake. This applies to ABS and non ABS systems. Just grabbing a handful of front brake locks up the front tire before it can generate maximum friction coefficient. The non ABS rider loses the front and goes down while the ABS rider loses precious time and distance as the front brake cycles on and off and saves his bacon while adding stopping distance. If ABS firmly squeezed "one two", building pressure, the weight transfers onto the contact developing far greater friction and the ABS cycles less.

well said

which is why emergency braking and swerving into a plan B path is a constant calculation when avoiding collisions

 

[ad.hom]

John's excellent posts (as always) have clarified good the system works.

Don’t know how one uses front brakes in slow maneuvers while controlling the throttle.

I do, all the time. Especially while filtering/splitting. It's a learned habit, motorcycle instructors have always drilled the use of the back brake... but I still automatically use the front.

Supermoto riders use large doses of front brake & throttle to spin the rear tyre up for drifting. Spent a fair few years destroying rear tyres that way...

trials rider

Used to be one - riding on wet mud teaches fine muscle control on the front brakes.

Don't get me wrong, I'll drag back brake if I go into a corner too hot, occasionally use the back brake when slowing etc, and both brakes in an emergency, but my habit it to use the front brake by preference in most situations.