ABS Question

[Knifemaker]

Someone had mentioned that they did not like the idea of a linked brake system, and gave the example of how , when they are riding down a steep gravel road they usualy drag the rear brake abit, but know that they should not touch the front brake , as it would invite the front tire to wash out and likely cause them to dump the bike. With a linked system, the front brake would be applied to some degree when the brake pedal is used.

My thinking on this is .. the reason the front would wash out using the front brake, is because the tire looses traction and locks up. Well , if the ABS system is working, this would not happen.

My question here is..Is there some point that the ABS "turns off" ?

It seems logical that at some point it should , otherwise you would not be able to lock the brake while sitting on a hill waiting for the light to change. So there must be some cut off velocity that triggers the system to disengage. I can see it being something fairly slow...like 1 foot per second..or even zero...or even being as high as 10 mph.

Anyone have any info here?

Knifemaker

 

[ionbeam]

In a previous post I wrote:

In automotive ABS applications the trigger point for ABS is typically defined as when wheel slip angle becomes greater than 87% This is the critical point between a rolling wheel and a skidding wheel. [translator] When vehicle speed and wheel speed vary by more than 13% (impending lockup) ABS will engage until vehicle and wheel speed come closer to balancing. With a slip angle of 86% the wheel is already beginning to skid. [/translator]

To which the (ig)noble Radman added:

Most ABS systems work by comparing the speed of the wheels, using the toothed reluctor wheels. The Feej system adds chassis speed into the equation. Since the Yamanual doesn't break down the ECU/ABS control unit, one has to assume there is an decelerometer built in for this function. But in any case, from what I can see, front/rear wheel speed differential AND chassis deceleration are all taken into account. Sophisticated, by neccessity. Automotive systems work somewhat differently, and due to wheelbase and much more weight (any idea how hard it is to lock up fronts on a late model car on good pavement these days?) Rears lock readily-fronts not so easily. Now, most of my knowledge of automotive systems is somewhat dated, so this is not gospel by any means. Automotive may very well use chassis dynamics for ECM info now.

Alan

 

[rodantking]

All I know is that like or hate link brakes, start saving your change. Steel lines are going to be a petty investment.

 

[Colin24]

You've got two separate issues here. Linked brakes and ABS. They are different features, but are often used together.

Linked Brakes -- The front and rear brakes are linked together so that applying the front also applies the back, or vice versa, or both. The exact way its done varies by implementation

ABS - An hydraulic-electromechinical system that monitors wheel speed and senses if a wheel is about to lock. When it senses this it backs off the brakes to allow the wheel to keep spinning.

2004-2005 FJR's do NOT have linked brakes

2004-2005 FJR's have ABS as an option

As for the 2006 this is what the website says

All new unified braking system with computer controlled ABS. When the front brake is applied, all 4 - LHS front caliper pistons are activated, while only the "upper" two pistons on the RHS front caliper are activated. When applying the rear brake, both rear caliper pistons are activated plus the two lower pistons on the front RHS caliper are activated. Brake feeling is the same as previous versions.

In short. Front brake stops mostly (75%) front wheel, Rear brake stops rear wheel and partial (25%) front. And all backed up with ABS. So on the 2006 FJR the condition that your friend worried about (dirt road and using front brakes) simply wont happen. The ABS will take care of it.

------------------------------------------------------------------------

The issue of locking the front wheel with linked brakes on the 2006 FJR is moot, the bike has ABS and wont allow them to lock.

Now. I have a 2005 FJR with ABS. I recently spent some time on the back lawn (very wet grass) and a slightly muddy dirt road. Here's what I found. The ABS just flat out works! Every time I used the ABS the bike just plain stopped. No muss no fuss. And thats all due to the ABS. It truely is a cool feeling to be travelling down a dirt road at 55 mph and be able to hammer the brakes and just stop. Like when some dipshit comes over a hill on the wrong side of the road (dont ask :angry: ).

The only time I had an issue was on the wet grass when I wasn't paying attention and the momentary locking of the front wheel caused the wheel to start to flop over. The ABS caught it and the wheel straightened back up. But because I was already travelling extremely slowly and an extremely slippery surface it took a moment for the wheel to respin once the ABS released the brakes. But please note, even though I wasn't paying attention the wheel _did_ respin and straightened up even though I wasn't paying enough attention. Which of course is exactly what it should do.

Okay, now its time for Stupid FeeJeR Tricks.

Take your 2005 FJR with ABS and get the bike sitting so that the front wheel is on wet slippery grass and the back wheel is on a dry pavement surface. Apply the front brakes full on while you are sitting there. Now feed in some gas and clutch like your going to do a burn out. The ABS will activate and the front wheel will start to turn and the bike will move forward even though you have the front brake on full. Very cool.... ABS activates even from a dead stop.

The very interesting thing about this was the pulsing coming through the lever felt like a high speed vibration, not the usual lower speed pulsing I feel from the ABS when I am moving. This I realized was a clear indication that the ABS on the FJR does have a fairly high cycle rate in the ABS pump (ability lock/release fluid pressure). You normally dont feel it on the road because the computer waits for the wheel to respin before reapplying the brakes. In my little test I was going so slow there was virtually no respin time, so the ABS was cycling at full speed. Very cool.

And finally onto your original question

My question here is..Is there some point that the ABS "turns off" ?

Nope, its pretty much always on. But its not so much that its always on as it is always monitoring. It only activates and releases the brakes when it senses that the vehicle is moving.

If your sitting on a hill, the brakes will hold. Even a slippery hill. But if it senses the bike is moving, it will allow the brakes to operate, but not to the point of lockup.

The point is that its trying to ensure the front wheel and rear wheel decelerate at the same rate. It determines lockup by sensing a speed difference. In my example above the rear wheel was moving and the front brake was fully applied and the front wheel was not moving. so the ABS computer sensed this and released the front brake enough to allow the front wheel to spin at the same rate as the rear wheel.

In theory you could achieve the same thing on a dirt road or even dry pavement. Hold the brake on to the point of lockup but keep the engine screaming and feeding power with the clutch to the rear wheel causing it to spin and the ABS to release the front wheel. But you would be on your own for repairs after that kind of abusive riding!

----------------------------

I wouldn't sweat these kind of details. The ABS just plain works. You grab the brakes, you stop. The harder you squeeze the faster you stop. Its that simple and it works.

- Colin

 

[Knifemaker]

Thanks Colin.

This means then the ABS works even at zero velocity , so coupling that with the linked systen, the arguement against the new brakes on the 06 FJR as making it "more dangerous" going down a gravel road would be utter nonsence. I can see the point if there was no ABS system , but the brakes were still linked.

I for one never had much problem on gravel roads , but then again I never tried going down one on a 600lb bike.

The 06 I am waiting for will cover a few firsts for me , It will be the first bike I have owned that :

Displaces more than 750cc

Has EFI

Has ABS

Has Linked Brakes

and is blue.

My viewpoint on ABS is that it is the MOST intelligent thing they have added to a motorcycle since it's creation. I was a bit perplexed why they went with the Linked Brakes however , as most of what I have read singled the (pre 2006) ABS system on the FJR as the best one out there. I doubt the addition of having them "linked" will really matter that much to me , and I can see the distinct advantages of this anyway.

I have seen a few posts with some other "examples" of why linked brakes can be bad..but for the life of me can't understand them. I remember some comment about using the rear brake in a turn to "set" the suspension ..but I guess I was taught incorrectly...as I never brake in a turn, always before one.

About 90% of the time I only use the front brake anyway. so I still unsure of what the complaints are about when it comes to linked brakes. In a panic stop or just hard braking I do use both front and rear..so the fact that they are linked does not matter. However the advantages of ABS seem to me to make them a must have for any street bike. ...but I can understand why you might not want them on a race bike.

About half of my riding on my new FJR will be with a passenger..so the added security of both systems is very welcome.

Knifemaker

 

[rdfrantz]

Despite the behavior Colin mentions (The Burnout), the FJR ABS does Deactivate, doing so upon decelration from faster than, and then down to about 6 mph.

There is no "decerarometer" called out in any description or schematic of the braking system. Consequently "Chassis speed" is inferred from the velocity of either non-locking wheel's sensor ring (times Pi, times it's distance to the tire contact patch, etc).

ABS will not prevent either wheel from sliding laterally -- it only prevents "too fast a deceration for the current road speed", the "87% velocity" computation mentioned the earlier post. With the pre-06 non-linked systems It is quite possible to apply enough brake pressure to the rear brake -- while leaned over -- that does not cause it to "under-rotate", but which traction requirement, uses up the ability of the tire to track in the direction of travel (slide out). This can be accomplished, independently, at the front as well.

Finally, following that line of facts, the upcoming liniked brake system, having rear pedal pressure applied, applies some braking force to the front tire -- although I belive we will discover it is infact a minimal, and thus useless amount vis a vis the "stop rear brake stompers from killing themselves" direction. None the less, on very low traction surfaces, such as deep, soft sand, or sand upon pavement, that braking force could use up all the tractive force of the tire, and any turning moment would cause the front tire to slide laterally: You'll fall.

Best wishes.

 

[06FJRAEPILOT]

Ignition off. ABS off.

Why would anyone drag their brakes under any conditions?? I have had the FJR on a lot of dirt and gravel road for a lot of miles and I haven't ever felt the need to drag the brakes yet.