brake caliper location

[Damien]

Check out this link on race-dezert.com its pretty much the same question. I'm D.Mavis on that site. needless to say there were a few different ideas.

But beind the spindle is better, strengthwise, if you have the choice.

Brake caliper placement versus brake torque effect - race-dezert.com

[nutz4sand]

Originally Posted by Damien

Check out this link on race-dezert.com its pretty much the same question. I'm D.Mavis on that site. needless to say there were a few different ideas.

But beind the spindle is better, strengthwise, if you have the choice.

Brake caliper placement versus brake torque effect - race-dezert.com

Can you elaborate as to why is supposed to be stronger BEHIND VS anywhere else? I am going to go read the thread you posted in the link but curious as to why you say that?

[nutz4sand]

I went and read the other link and I can see why it would be eaiser on the spindle itself and the wheel bearings due to the force the rotor itself enacts towards the spindle when the caliper tries to stop it.

Never thought of that before. Good-un.

[jumpin jellybean]

oww now my head hurts after reading that, good info lots of stuff happening out there, it was just like a icee first it was like mmmm good then ow ow ow no more but after a few minutes you have to have moreis there any such thing as to much information? not in my opion! thanks guys

[K-fab]

Interesting read on Race-Dez.

I can see how the placement (especially on a trailing arm) of the caliper can cause suspension reaction.

Take a look at a trailing arm set up from the side.

First - the caliper will induce torque around the center of the axle. The rotational force from the brake rotor being slowed by the caliper will be the same to the system regardless of where the caliper is located - in front, behind, above, below. Torque is torque and it's always around a given point.

Where the change comes is the location of the input of the caliper in relation to the pivot point of the arm.

Let's say (for simplicities sake) we have a 3' long trailing arm from pivot point line to center of the axle.
We have a caliper that has the centerline of the brake pads set 6" out from the axle.

Therefore we can have a lever arm that is either 3'6" long (caliper hanging off end of trailing arm) or 2'6" long (caliper leading).

The caliper out back is able to produce a lever arm (around the pivot of the trailing arm) that is a full foot farther out than the forward mounted setup. That's a fairly large change in the overall lever's length.

A really easy way to experiment with this is go find a lathe that has jaws that can be removed from the chuck. (after reading the race-dez thread and this one, this example came to me and made the entire discussion crystal clear)

I use an 8" chuck on mine. When I take the jaws off to change them out, I always make sure that the t-handle wrench is inserted so that the wrench goes towards the center of the chuck, not out extended from the center of the chuck. This would make the lever arm pivoting around 6" out from the center of the chuck, but the input (where I whack the wrench with my palm to break the bolt free) is pretty much right in the middle of the chuck.

I can give the wrench a fairly hard, quick snap with the palm of my hand to break the bolts free and the chuck won't rotate much at all.

If I position the wrench so that it's sticking out away from the center, the same quick snap of the palm will result in a rotating chuck and a still tight bolt. The input on the wrench (lever arm) is now about 12" out from the center of the chuck.

We just went from what is effectively a 0" long input in relation to the center of the chuck to 12". Big change!

The torque amount applied to the bolt is the same in either setup (think of the bolt being in the same position as brake pads), and the torque is being applied to the same place in relation to the center of the chuck. The difference is where this torque is coming from in relation to the lever arm's position. The longer lever (caliper out back) will produce more input on the system than the short lever arm.

Pretty cool, eh?

[jumpin jellybean]

thanks K-FAB great laymans terms that made it clearer to me I had the concept but that helped me visulize it. now I need to rethink my caliper placement might just stick them inboard now and rely on front brakes if axles break

[Damien]

K-fab-- I think there is a flaw in your example. The caliper creates a force on your trailing arm at some point ( this is your force pushing on your lathe jaw bolt wrench). The thing that you are forgetting is that there is an equal and opposite reaction force that the spindle is producing on the trailing arm. (in your lathe analogy this would be like supporting the bot or the wrench at the bolt with a bock of wood. if you did this then I think you'd find that there was no difference in the amount of torque that was trying to spin the lathe, if you did this it would be the same as useing an impact gun to remove the bolts--with an impact it shouldnt matter where the bolt is it will impart the same torque on the lathe) It really should not matter where the caliper is placed on the upright as far as the forces on the suspension.

Any engineering students out there?---
Its been a while since I took a statics class (15yrs) so maybe someone can verify this, but I believe the caliper force and the reaction force cancel them selves out when you sum the forces but they create a couple which can be resolved as a moment and a moment can be moved anywhere on a ridgid body without any effect. Right?

[evan]

I'm no engineering student but I have to agree that the lathe analogy isn't apples for apples. As stated, torque is the same. The only diff as described in the above link is whether the equal and opposite force induced into the hub bearings counters the weight placed on it (dynamic wheel load) or places an additional load (force).

[LiveWire]

I don't buy it on the trailing arm since the caliper and stub axle do not change in location to each other, therefore there is only rotational force applied to the trailing arm. The rotational force is centered around the axle.

I do see that it would affect load on the bearings.

[Damien]

it does work the same as on the front. instead of the "spindle" in front you have the stub axle, or micro stub unit bearing.