Rear master cylinder drilling out

[StuNVA]

The rear brake on the Tuono is shit.
In an attempt to fix it I have used a master cylinder off a K5 GSXR1000.
It is better but not as good as a jap bike.

I was wondering if I was to drill out the hole to let more fluid through would this increase the braking capacity or would it be limited by the size of the hole in the banjo bolt ?.... Or do I just turf the caliper and find a replacement. I use the rear brake to help launch at the drags any hardly ever at any other time, that is the only reason I wont it to work very well.

[Redmohawk]

How do you want to improve it mate ? More braking force I assume loading up the rear before launch ? Braking force is controlled by the amount of force induced onto the disk by the pad. Make pad bigger or push harder to increase the static drag on the disk.

So caliper with bigger pad area is one move, and or one with less flex or give alowing extra force to be transfered into disk instead of bending caliper . Changing the MC is another but will only improve to the limit of the caliper. Larger disk diam will make the force of the caliper more effective, but will increase weight of your wheel.

Drilling a bigger hole wont improve the braking as it will only improve fluid flow at high flow rates (brake runs at low flow high pressure)

[StuNVA]

Makes sense, someone said to drill it out from 3mm to 4.5mm, but as you say that would only impact on flow rate not force / sq cm. Thanks. I'll look at some different types of pads for starters.

Yeah, I just let the clutch out until it grabs, stand on the back brake and give it another 500rpm or so, then use the back brake to launch, I found it stopped me doing wheelies (as much) off the line.

[Dynomutt]

You can increase the braking force by increasing the mean braking radius. Currently the mean braking radius is the halfway point between the inner and outer diameters of the pad track, so if you have a disc of 240mm diameter, and a pad track of 30mm your mean radius will be 225mm, to increase this without adding a larger disc you remove pad material from the inside half of the pad, this means you now have a 240mm disc with a pad track of 15mm which puts your mean radius at 232.5mm. Your pads will wear twice as quickly due to the reduction in material, but your braking force will be increased.

[BANDITROD]

Fuck me you are awesome

[StuNVA]

So your saying the same force over a smaller area will make it grip harder ?

[xa-mont]

yeah i'm with StuNVA on this one...

If you have the full pad on there the largest diameter is still the same, but you also have it working all the way to the inside... surely that is better?

[BANDITROD]

..... it makes sense to me.... Thats why rim discs are so good yeah ....because the the further out from the centre of the wheel the disc is the more effective it will be

[wackyrider]

Seems to make sense. The further you are from the pivot point = less force needed to be exerted to equal the same torque. Therefore same force loaded at a point further away from the pivot point would equal to more braking force applied.

However this only makes sense to me when you are stationary (which is what you need). When the bike is rolling you will have less of a contact surface area creating friction. So what is better? Having the larger surface area on the smaller diameter or the smaller surface area on the larger diameter. All that would have to be factored in depending on the surface area and the diameter.

My opinion anyway. You would really need to do some calculations to be able to prove which would work out better

[wackyrider]

quote:Originally posted by BANDITROD

..... it makes sense to me.... Thats why rim discs are so good yeah ....because the the further out from the centre of the wheel the disc is the more effective it will be


True, the larger diameter improves the braking, however the distance of the disc brake on rim discs is not directly proportional to the reduction in the size of the pads.


[:I] I'll go back to my corner now [:o)]

[BANDITROD]

Ahh very wise words there mr miaggi

[StuNVA]

My gixer brakes were way better than my Buell brakes, but I assume that is the theory Mr Buell was executing.

I'll look into this a little further, maybe I have a set of old pads kicking around I can grind up and play with.

[BANDITROD]

Sounds like a plan let us know how you get on

[Redmohawk]

Decreasing the size of the pad will increse the effect of the force increaseing friction, making the pad area left over on the outside is logical as the force has more leverage on the outer part of the disk. Negitives are the piston is designed to push from the middle of the pad causing the pad to wear at an angle reducing pad life far faster the expected, and reducing desired force as it starts to cant sideways. Also pad jaming is a possability so if you aim to try this idea keep a close eye on pad.

One full size pad on piston side of caliper and a half pad on clamp side would give simmilar effect with less likelyhood of pad jamming.

[pappas]

Surface area has no effect on the amount of friction. The formula for friction force is coefficent of friction x Force applied. Smaller pads will only generate more heat and wear quicker. Using Dynomutt's example you would only increase your braking tourque by about 3%, so I doubt it would be worthwhile.

[Redmohawk]

Yes your right friction is F= C times force BUT

Not quite true as , force applyed over a smaller area INCREASES (half area double C quater area quadrouple C But once moving heat will distroy pads very fast) coefficent of friction thats why it increases over all braking.

Ie 40 kg weight on concrete floor with steel surface area of .25 square meter is easy enough to push around by hand and does no damage to the floor, but shrink that steel surface area down to 2mm square and your grinding into the concrete and its hard work to push it.

Thats why a comp brass button 4 puck clutch plate that has more gap than button and is a grippy as hell (and hard to slip from a stand still) compared to a fiber full clutch plate with the same pressure plate.

The grinding of the pad effects the coefficent of friction is why it works , its just more logical to use the outside of a disk to its advantage is all. I wouldn't go below 50% in pad side on one side only, But then again I wouldnt go that route I would still get a better caliper say a 4 pot front (for better pad size and less caliper bending and different MC so you can just stop on it a bit harder) and still have great brakes when your on the road.

[pappas]

The coefficient of friction is a constant when you are using the same materials under the same conditions. It does not change with surface area. If the brake pad had coefficient = 0.8 it would always be 0.8 regardless of surface area. The 40kg concrete weight may damage the floor but it will take exactly the same force to move it with the smaller surface area.

[Redmohawk]

I stand corrected, your right pappas as pressure to friction would counter offset each other assuming pressure was the same.

So a the same size pad with more pressure or a larger pad with even more pressure will increase static friction.