Rear brake caliper mountings?

[gavinnz]

I have a rear caliper mounted with a torque arm coming forward to the frame
on my Gilera.
For weight reasons I am thinking of mounting it on the plate that is attached
to the swinging arm.

I have done as much reading on this as I can on the net the last two days
and looked at a heap of newer bikes set ups.

Was the advantage of mounting the caliper to be able to rotate with a torque
arm from the frame an idea that was a good solution to a problem that was
not large enough to worry about??

None of the modern sport machines I looked at seem to do it now.
It was all the rage in the late 1980's and early 90's going by my very
limited reseach.

Thoughts?

Regards
Gavin
"Supperleggera Gilera 588 Saturno project"

[vifferman]

I can't see what difference it would make - the arm's only there to stop the caliper rotating, so if your bracket does the same thing, it should be OK.

[F5 Dave]

Question before you get started. Is this for a roadbike? If so you will need an LVV cert if you modify the brakes, . . in virtually any fashion.

[gavinnz]

I can't see what difference it would make - the arm's only there to stop the caliper rotating, so if your bracket does the same thing, it should be OK.
Thats what I though also at first.
It has the effect of ultering the point where the force of the braking caliper trying to move is applied to the bike
Which in turn does have a small effect on suspension/wheel movement.
It is the degree of that small effect I am questioning.

I have a feeling it was a great solution to a problem that was not really worth solving.

I am looking to get the skinny on it BEFORE I go and modify it... then find out why they did it!

Regards
Gavin

[gavinnz]

Question before you get started. Is this for a roadbike? If so you will need an LVV cert if you modify the brakes, . . in virtually any fashion.
Road bike. No WOF guy I go to would know what the brake set up looked like on a 1991 Gilera Saturno... so I am happy to mod it and not worry about the cert.
Just to get in first....I am 41 with an engeneering background and have been riding and modifying bikes since I was 15. So I am not a 17 year old bunny with a death wish playing with brakes! lol

Regards
Gavin

[vifferman]

Thats what I though also at first.
It has the effect of ultering the point where the force of the braking caliper trying to move is applied to the bike
Which in turn does have a small effect on suspension/wheel movement.
It is the degree of that small effect I am questioning.
It must be fairly insignificant, or all bikes would either have them, or at least similar designs.
Is it an underslung caliper, or on top of the swingarm? The VFR's rear caliper is underslung, and has no torque arm.

[gavinnz]

It must be fairly insignificant, or all bikes would either have them, or at least similar designs.
Is it an underslung caliper, or on top of the swingarm? The VFR's rear caliper is underslung, and has no torque arm.
A chap on my "chassis design" news group made this interesting observation....

"I expect that the era of wider and wider tires have ushered out torque arms since the arm would need to run outboard of the wheel"

That makes sence as to why they have all but gone.
His reason for their use was.... "it helps reduce wheel hop"

The orginal caliper is mounted straight down underneath.
I am tossing up if I should mount it on the top of bottom of the swinging arm.

Top makes sence as the braking force is trying to push the caliper into the swinging arm hence I can make lighter mounts.

But under the swinging arm mounting keeps the weight lower....

I think over all top would work out better for me. I have a very neat looking tiny UK made MotoGP super light caliper to fit it the 190mm disc I have had made... so it would also be nice to see it!

Regards
Gavin
Superleggera Gilera Satuno project.

[F5 Dave]

Cool, worth asking, just if it doesn't 'look factory' it will likely get picked up. One of my bike's runs R1 calipers after a minor mod. They weren't std but they sure look as if they were. The WOF guy can pick it but he's fair & can see there is no drama, but a VINZ guy told me that they look to see & even if it had a non std master cylinder they would fail it. Mine did but it was a dif diameter with the same form so you couldn't tell. I bet there is an issue with people buying Radial master cylinders for their bikes. Mind you some of those Chinese 'Brembo marked' ones are pretty suss.

On the same bike I was making a rear mount (for smaller caliper) but never finished it as it was getting a little hard to make it look as factory (& I lost interest). One of my earlier bikes had ally plates to fit modern calipers, I wonder how they are getting on for WOF these days? (wasn't a prob when I did it).

I'd agree that the feed it back to the frame torque arm (though some just go to the SW so it is redundant anyway) was an MX idea in the 80s. someone described it as a problem that didn't need solving. As long as it is strong enough with a short load path it should be fine. Higher slung calipers have an advantage of being out of the way & picking up less road crud. Ease of adjusting chain has to be considered.

On a racebike I move one above & used a top mounted short torque arm so the muffler had space & could use a race stand.

[gavinnz]

Good stuff Dave, thanks.
quote... "was an MX idea in the 80s. someone described it as a problem that didn't need solving. "

Now it makes more sence... if you had a motocross bike with soft long travel suspension then the torque from the braking action would be a much larger factor..... then they used it on road bikes with short travel harder suspension and I would say most of the benefit was gone.

At least thats how I am going to justify binning it for less weight.... ! :)

I take your point about it looking factory, and I will make sure it does.
Thanks.

Regards
Gavin
"Supperleggera Gilera 588 Saturno project"

[Kickaha]

I'd agree that the feed it back to the frame torque arm (though some just go to the SW so it is redundant anyway) was an MX idea in the 80s. someone described it as a problem that didn't need solving.

Yet Honda on their RS125 had the torque arm to the chassis and probably still do

[F5 Dave]

Yes my RS did, but it doesn't now. Can't say I've noticed any change.

[gavinnz]

One thing I WILL need to be aware of is that the swinging arm structure is not designed to take the braking forces applied at a mid span point near the wheel end of the arm... I can design this in as I am seriously looking at making a new swinging arm anyway from light weight steel tube. One made by a Swiss company who do lots of tuning work on Saturnos say their steel twin tube arm is 1.2 kg less than factory which is a damn good saving!
Regards
Gavin

[pete376403]

How much braking do you do with the rear brake anyway? Most of the brake effect happens on the front wheel.