Rear brake torque arm, frame mount vs. swing arm mount.

[SkyFive]

Can a brake torque arm be chassis mounted? This doesn't make sense! The caliper mount has to be stationary...right? As an example, on a car when the front suspension travels the tie rods get longer or shorter throughout the arc of travel, this is called bump steer. Seems like the same principal would apply to a frame mounted brake torque arm. I vote for the swingarm mounted torque arm.

[Travis398]

Don't some of the Kawi's mount to the frame too?

[andyb]

Looks frame mounted to me.  Couldn't find a good shot that showed the attachment, but the early 90's ZXR7 looked similar.

[SkyFive]

I see now, the caliper mount pivots and the caliper stays centered on the rotor. What will they think of next...a man on the moon? 

[fj1289]

... What will they think of next...a man on the moon? 

Metal covered wings!   

[SkyFive]

... What will they think of next...a man on the moon?  

Metal covered wings!  

Are you referring to my Super Cub avatar? That is Sky 5, a plane I flew aerial advertising (banners) in Myrtle Beach. She weighs 950 lbs empty, 160 hp, a Borer prop and pulls like a FJ1100, literally. If you look closely you can see the tow rope running from the tail up to the wing strut along the bottom of the fuselage.

[RACER111V]

 I am with "CARSICK" on this one,I also don't use the rear brake on a street bike.But I do know the effect of a linked brake.I used this system on my yz400 mx bike for a while.

http://www.oldrice.com/Preston_Petty_No_Dive.jpg

After installing it there was no reaction to the suspension when applying the brakes.That was when I realized that some fork dive is a good thing.The bike was hard to steer without some dive.I do use a lot of rear brake off road and I like a floating rear brake,but they are to easy to damage.

[SlowOldGuy]

It DOES matter where it is attached. It makes a HUGE difference.

If the brake reaction arm is mounted to the swing arm then the torque reaction is ultimately transferred through the suspension and results in rear wheel squat.

When the arm is mounted to the frame the 100% of the torque reaction is no longer transferred through the suspension ...

How can you say the above then give an example that's opposite below???

To demonstrate this, there was a 1970's experiment on Barry Sheen's grand prix Suzuki whereby the FRONT calipers were mounted on floating radial mounts and the torque reaction arms went vertically to mount on/under the lower triple tree. Therefore upon suspension compression the calipers rotated freely and were in effect suspended unsprung weight - one of the reasons they tried it. When heavy front braking force was applied the front of the bike didn't dive - it actually ROSE UP because as the calipers tried to rotate, the torque reaction was transferred vertically and converted to suspension movement according to the forces now at play.

You say "it actually ROSE UP because as the calipers tried to rotate, the torque reaction was transferred vertically and converted to suspension movement according to the forces now at play."

How is this NOT transferring the braking force into the suspension?  Am I misunderstanding the semantics?  By not transferring force to the suspension, I'm assuming that the braking force does not transfer any force directly into suspension action.  It INdirectly transfers force due to weight transfer, but the braking moment torque is NOT directly coupled into suspension action.

What you describe above is a direct coupling of the braking torque moment into the chassis and it's effect on the suspension action.

So lets transpose that experiment to the rear and to demonstrate the potential, imagine a hypothetical where a true floating rear caliper that (let's say) sat in the 9 o'clock position and the reaction arm were to mount vertically upwards to the rear subframe.... The caliper would become (to some degree) unsprung mass as it's now supported and the braking force would raise the back of the bike upwards actually creating artificial mass and therefore increasing traction.
It makes a HUGE difference where it's mounted - it's all about directing that force...

Again, by mounting the torque arm on the chassis/frame, you are directly affecting suspension action.  With the arm attached to the swingarm, all the forces are contained within the swingarm and there is no direct coupling of the force into the suspension (again, weight transfer is an indirect coupling).

DavidR.

[Pat Conlon]

........ by mounting the torque arm on the chassis/frame, you are directly affecting suspension action. 

DavidR.

David, I think we all agree (?) that a frame mounted torque arm will affect the rear suspension, but what Oz is saying,  it's in a good way.

I can visualize what Oz is talking about.

I think we all agree (?) that applying the rear brake can cause the rear end to squat. True, not by much, but it's still there.

With a bottom mounted caliper on a floating arm, when the brake is activated the torque arm applies tension (pulling force) to the frame mounts.
Because this tension line is below the axle to swing arm pivot line, this tension helps by holding the rear end up, counteracting the squat.

Yea, I can see this....

[WestOzFJ]

Hey David, WOTEVER!

read what I wrote and quote that, not what you've made my words into....

There's a big difference between some of the words I wrote and the ones you're throwing back at me....

Semantics or not, a dictionary is all that's required.

I'm not going to argue with you, think what you will, everyone else pretty well seems to get it....

[SlowOldGuy]

Oz, I wasn't trying to pick a fight.  There are 3 pages of information on this subject so there's quite a mixture of opinion and fact.  I'm just trying to sort it out.  If you want to be part of the discussion try not to instantly turn into a dickhead when you get a question.

Pat, yeah, I can picture what's going on.  It was a very good description and exactly what I imagine is going on with the suspension.  I can see where it would prevent potentially unwanted suspension action on either end of the bike.  

It wasn't intended to be an attack, I'm just trying to clarify the concepts.  I appear to be on a different page with the description of the process and what is (or is not) being "transferred through the suspension."

That description confuses me.  I keep trying to picture it as what affects the suspension action, which appears to be the opposite of a force being transferred in this discussion.  

We all appear to know that feeding the force from the caliper arm into the chassis will jack with the suspension.  I consider a force that directly prevents the suspension from compressing or rebounding to be "jacking with the suspension."

So, in a "conventional" rear brake arrangement, why does the rear end squat when the rear brakes are applied?  It's NOT because the caliper torque arm is tied to the swingarm.  It's because the braking force of the rear tire is forcing the weight transfer to pivot around the swingarm axis.  The front end dives when the front brakes are applied because the weight transfer is pivoting around the front contact patch.  

I know brake dive is generally considered bad, but it seems to me that if you try to prevent either of these actions from happening you're kind of artifically stiffening the suspension.  I would think better suspension is the better answer.

DavidR.

[Pat Conlon]

When I think of "jacking the suspension" I think of pinion creep on a old BMW or Guzzi, jacking up the rear end and worse, letting the rear end down when rolling off the throttle. Remember this suspension action we're talking about is in proportion to the use of the rear brake, i.e. smooth is good.
I can imagine that if you're abrupt, stabbing the rear brake, you could jack the rear end.

[SlowOldGuy]

Hey Pat.

Okay, I'm also guilty of using confusing descriptions.  Sorry about that.  :-)

How about "influencing" the suspension action.  We all know how bad brake peer pressure can be.  I'd hate for my suspensionm to take up smoking.

I should be out riding, but it still raining.  :-(

Maybe I'll go out and polish on my rear wheel some more.
(Hey, 4 more posts and I'll catch up with you)

DavidR.

[Pat Conlon]

Yea, we are having a bit of a early fall heat wave here in the desert, gonna be 110* today.
I'm leaving now for a ride in the mountains, up to Julian for lunch.  Cheers amigo!

(oh yea, sorry about your Long Horns, those UCLA Bruins can be a pesky lot)

[andyb]

Damn, right to the cheap shots Pat.. that's mean!