Rear brake caliper mod - why no direct to swingarm mount?

[highlander]

I have been thinking about a wee weight saving mod to replace the chunky rear brake caliper with a smaller brembo one and it struck me that I have never seen a caliper mounted directly on to the swingarm, the bracket is always based on

either a loop for the spindle and key to swingarm


or TRX style loop to spindle and torque arm to frame.


It seems to me that the simplest would be a bracket bolted/welded directly to and above the swingarm to ensure wheel can drop out, so why is this not done? There must be something about the dynamics/physics I am missing that requires them to not be completely fixed to each other ....

My best option seems to be go the first standard option : Drill&tap and fix a bolt to the inside of the swingarm using the bolt head for the key. Or find someone to weld a nut on. Should be able to find a nice alloy bracket with minimal mods to fit.

[cobbadiggabuddyblooo]

DT 230 uses the same bolt pattern as the trx and it's a 220mm disc. Thinner and lighter than the 5mm / 245mm trx disc.
The photo shows the caliper mount I looked into. Even if I removed more material from the mount on the RHS it's still around the same weight as the std set up.
I had a bush made to accomidate a 20mm axle and a Tee piece made to weld to the swing arm.
But I scraped this idea. ( but still have the smaller disc fitted )

You gain more by Kayla's set up with a thin alloy disc. ( I don't use the rear brake anyhow unless at lights)
Less rotating mass and you make a yoke to take a small calliper and suspend under like the Std set up.
As I found out later, you need to find out the grade of aluminium used on the trx swing arm otherwise the strength and integrity of your swing arm could be compromised if you weld.
I'm still tracking down that info to brace the Std swing arm.

Problem solved, 2001 gsxr rear caliper and mount are under hung and 220mm..

[Snod Blatter]

It seems to me that the simplest would be a bracket bolted/welded directly to and above the swingarm to ensure wheel can drop out, so why is this not done? There must be something about the dynamics/physics I am missing that requires them to not be completely fixed to each other ....

Uhhh, is it not just so that the caliper always moves back/forward with the rear wheel and disc during chain tensioning? Are you suggesting lining the caliper up yourself with slots?

[highlander]

Uhhh, is it not just so that the caliper always moves back/forward with the rear wheel and disc during chain tensioning? Are you suggesting lining the caliper up yourself with slots?

Ah, of course! I knew I was missing something.
Hard to imagine more than a few mm of chain adjustment could be accommodated by a "fixed position" caliper even if you positioned it to be tolerant at approx 1pm when looking at the brake disc

[Mincehead]

Yep, the caliper must be able to move to accommodate chain adjustment. That said, there are all kinds of ways you could use a custom caliper mount.
I have a very good friend (Colin) who runs Bespoke-Bits http://www.bespoke-bits.co.uk/
He`s in Dundee, lovely bloke, biker and damn good engineer, if you want something special he may be able to help you out. Ring and chat to him, visit and have a cuppa. Tell him Geoff Paige recommended him to you.

[highlander]

I have a very good friend (Colin) who runs Bespoke-Bits http://www.bespoke-bits.co.uk/
He`s in Dundee, lovely bloke, biker and damn good engineer, if you want something special he may be able to help you out. Ring and chat to him, visit and have a cuppa. Tell him Geoff Paige recommended him to you.

Cheers, I just might do that. He's close enough I can take parts down to have a look at. Which is one of the main difficulties living up here. I envy central England for all the local resources there are to hand!

[dandywarhol]

Many rear calipers are designed to "float" to eliminate rear wheel hop and stop the rear brake act as an additional "friction damper"