bottom mounted rear disk brakes, why do we still have them.

[epz]

ive seen several bikes with the rear brake caliper mounted above the swingarm so it requires less parts to fit and doesnt get hit with so much crap off the road, anyone know why plenty of new expensive bikes havent followed this idea.

[california_rookie]

Lower center of gravity?
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[Claud 14.7 to 1]

Which bikes?

Most bikes now have followed this idea. Honda had them from early on, even my one has it.

ZX-R and GSXR used to have it, now they've changed to the "above and held on via the swingarm" option. It's lighter, uses less parts and looks better.

[mchaggis]

The reaction arm is easier to set up with the calliper underneath the swingarm. It only has to be in tension like that, whereas if it is above the swingarm, it is in compression. Struts resisting compression are more difficult to design than those in tension.

Mind you, if you can get away with mounting it directly on the swingarm, I think you could get away with a fair deal less other structure.

https://www.ibike.com.hk/01_bike_report/local/bmw/r1150r/brake_rear.jpg
Under swingarm


https://www.bmw-motorrad.co.uk/com/_common/img/services/vis_techniquedetail_paralever.gif
Paralever above swingarm

https://www.cmgonline.com/articles/CMG03/bikes/Yamaha/WR450/TestRide/BigP/WR_rear_wheel_bg.jpg
On swingarm.

See the difference in the reaction arms between the under and over the swingarm.
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[Kickstart]

Hi

Can think of a few reasons.

With the disk mounted under the arm the mount is under tension and is not attempting to bend the swinging arm. Also if you do mount the caliper off the swinging arm on the top then the mount will be attempting to twist the caliper. Mounted under the arm with a mount under tension, it is easy to have the mount coming back to the centre line of the caliper so greatly reduce the tendency for it to twist.

Also results in a lower centre of gravity (slightly).

There are also down sides. Caliper gets covered in crud and it is difficult to bleed.

All the best

Keith
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[iCraig]

It can't be down to cost really as the GS500 (a really cheap bike) has it mounted above the swing arm.

https://www.craiggiles2.f2s.com/brksuz.JPG

[Kris]

Also steel is crap in compression but very good in tension so the 'pulling' effect by placing the caliper underneath allows easier design.
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