Oversizing brakes

[ac3_snow]

Can you explain why a smaller bore on the master cylinder would work better? I'm still trying to learn all this stuff

Apparently that is what I have inadvertently put on my bike, a larger diameter bore, twin disc master cylinder with a single disc front. It makes the brake lever ridiculously hard, and needs very little pressure and movement to apply the brakes hard.

edit; you end up with twice the required pressure/fluid going through one caliper.

[ducatilover]

Apparently that is what I have inadvertently put on my bike, a larger diameter bore, twin disc master cylinder with a single disc front. It makes the brake lever ridiculously hard, and needs very little pressure and movement to apply the brakes hard.

edit; you end up with twice the required pressure/fluid going through one caliper.

Personally I don't think it's going to be an issue and neither the caliper or master are renowned for being exceptionally powerful. They work well, but I do very much doubt this is going to be a problem If nathanwhite wants I can always unbolt one line from my splitter on my ZX6 (same brakes) and try it, if I lock up/flip/die, then it's awesome

[nathanwhite]

Apparently that is what I have inadvertently put on my bike, a larger diameter bore, twin disc master cylinder with a single disc front. It makes the brake lever ridiculously hard, and needs very little pressure and movement to apply the brakes hard.

edit; you end up with twice the required pressure/fluid going through one caliper.

Ok that makes sense.

Personally I don't think it's going to be an issue and neither the caliper or master are renowned for being exceptionally powerful. They work well, but I do very much doubt this is going to be a problem If nathanwhite wants I can always unbolt one line from my splitter on my ZX6 (same brakes) and try it, if I lock up/flip/die, then it's awesome

Yea but you have the weight and speed of a 600. My 125 would do 1/3 the speed and probably weigh 1/2 as much.

[nathanwhite]

Break out the Dremel, make a hole in the pin on the inner side and keep it place with either a split pin, R clip or lock wire?

Now this idea, I like. I might even try it too.

[FastFred]

Personally I don't think it's going to be an issue and neither the caliper or master are renowned for being exceptionally powerful. I can always unbolt one line from my splitter on my ZX6 (same brakes) and try it, if I lock up/flip/die, then it's awesome

The piston on a dual caliper master cylinder is a bigger diameter (area) than on a single caliper master cylinder unit.

If you use a dual caliper master cylinder on a single caliper because of the laws of hydraulics it is likely to feel hard and wooden and have less breaking effect for the amount of squeeze you apply at the handle bar.

Master cylinder piston to caliper piston size is like gear ratios the smaller the driving gear (or Master cyl piston area) compared to the driven gear (total caliper piston area) the greater the torque amplification of the gears or hydraulic squeezing amplification of your hand pressure between the brake pads.

[ducatilover]

Ok that makes sense.



Yea but you have the weight and speed of a 600. My 125 would do 1/3 the speed and probably weigh 1/2 as much.

I've only got 200kg wet
And I don't ride that fast

The piston on a dual caliper master cylinder is a bigger diameter (area) than on a single caliper master cylinder unit.

If you use a dual caliper master cylinder on a single caliper because of the laws of hydraulics it is likely to feel hard and wooden and have less breaking effect for the amount of squeeze you apply at the handle bar.

Master cylinder piston to caliper piston size is like gear ratios the smaller the driving gear (or Master cyl piston area) compared to the driven gear (total caliper piston area) the greater the torque amplification of the gears or hydraulic squeezing amplification of your hand pressure between the brake pads.

I am very much aware of the theory/physics. But I'm very, very familiar with ZZR brakes. The set that's on mine now had 6 seized pistons out of a total eight, effectively making it a dual caliper master running a smaller twin piston unit and from what that was like, I'd be willing to say it'll perform okay solely because the master is not a big ginormous grunty one,

There's a reason people throw the calipers/master way from them
Thankfully mine work pretty well, but mine's also 200kg wet.

[F5 Dave]

. . .Can you explain why a smaller bore on the master cylinder would work better? I'm still trying to learn all this stuff
. . .

Fred has it mostly covered, but think of it as 'leverage'.

The reason a bigger disc works well is there is more leverage on the wheel, a tiny disc has considerably less.

Similarly the lever ratio of a drum brake, the longer lever at the hand & at the drum will have more 'advantage'. Only trade off is that you need to move the lever longer, but it is much easier, just as a longer ratchet handle undoing a bolt is easier.

Hydraulic system is same principle. A larger ratio (so small lever piston to big calliper piston area) will give huge 'advantage'. the trade off is more lever travel.

This is where people get it wrong. They know a knackered line feels soggy & mistake the travel for weak. Too big a master cylinder makes the ratio less & thus feels wooden. But you have to use more pressure to do the same work. If the brake is powerful enough it can still lock the wheel of course.

Somewhere in the middle there is a sweet-spot of ample power & enough travel for 'feel' but not too much so it comes to the bar.

I like to minimise air in the system, maximise rigidity (braided helps here) & maximise lever travel (some master cylinders need a lever mod to get a another cm travel + adjust so only 1mm clearance, yet still fit a human hand). Then you can run a smaller cylinder than often possible.

[F5 Dave]

RG50 brakes aren't up to it on a faster bucket on a faster track. A good mod is to fit a NZ250 disc if you can find one. It has the same bolt pattern as an RG50 and the same offset. Then you just need to extend the caliper mounting plate. I still found the Vesrah redback pads overheated and cracked all over and lost chunks. The red paint also got scorched off at places like Wanganui. Even the bigger disc turned blue but at least it kept working.
. . .

Those redbacks (NR5) aren't available any longer, but where the only pad that worked on the RG50 discs & were great. But as you found out you could over stress them away from Kart tracks.