Discussion in 'Norton Commando Motorcycles (Classic)' started by jsnorton, Jun 8, 2019.
They’ll work even better with a 11mm master cylinder.
Maybe, but you are into personal preference territory. Feel would be good and progressive, but for me the lever would be coming too far back to the bar and as Jim says, you may get it too hot and you may then have a problem.
On my commando I have a 320mm disc and a nissin 4 pot caliper with a 12mm master cylinder
I honestly cannot fault this setup,it gives superb braking with plenty of feel
By contrast my t160 has twin 300mm discs and ap racing calipers and a magura MC
I'm pretty confident the Norton would out brake the triumph
Of course the trident is a much heavier bike
The size of the best master cylinder/caliper size is determined by physics, not personal preference. As far as lever coming too far back, my personal experience says not so. That’s with a 2 piston, 41mm caliper and a 11mm master cylinder. What you are saying as for excessive heat is to have a master cylinder that creates less force rather than a better caliper and rotor combination.
There is probably no person with more practical knowledge of early motorcycle disc brakes than Michael Morris of Vintage Brake. I’ll stick with his recommendation.
And it is a recommendation, and the guy at Vintage Brake you mention himself says that there is an element of personal preference! He says his preference is a ratio of around 27, which is bang on your 11mm for 41mm twin pot, if it works for you, fine. But he accepts that others have a different preference! If you are going to adopt his 'advice', don't do it blindly, try to read all of it and understand how he develops his argument and apply it to your situation.
It may be physics, actually riding a motorcycle is all physics, but when it comes to it, it also has to work for you as a human. We all differ in physique and the performance of our senses! So different things work for different riders. Throughout the '70s riders used Lockheed 5/8" master cylinders with Lockheed 41mm calipers, the ratio (13) delivered totally lacked feel and no one would choose that ratio today. Same master cylinder with twin 41mm calipers is 26 ish!
But it also has to be true that for a smaller bore master to pump sufficient fluid, it has to travel further to create movement at the caliper (physics), ergo the lever has to move further. It is down to your own comfort and control set up how far is too far. With a rapid action throttle you can get the lever touching the throttle before it touches the bar.....not helpful....you can play with the set on teh bars to improve it, but best not to have more movement than you are comfortable with.
Of course this has to fit within a range of parameters, and clearly when you go way off from the physics recommendations you will run into problems. He quotes the main issue with too low a ratio is that you aren't getting adequate feedback to your braking effort, so you apply more force, until you eventually lock up the wheel and lose control, without knowing why!
I am not sure I fully understand your last sentence, I don't think it relates to what I did say. Read what Jim said earlier regarding heat and fade in mountains. He is saying that continual heavy braking will generate a lot of heat, at some point more than the pad/disc and fluid can cope with. Having set pads on fire in the Italian mountains on a heavy 4x4 I think I concur. You may not have stressed it all that far yet.
Some of us are also limited by race regs as to what we can choose as rotor size and design.
Going smaller and smaller bore is not a universal solution. Why? Physics. That is, physics of the whole package including rider.
Why the long winded response? You go ahead and use what ever size master cylinder you want. I and anyone who has tried it will testify a 27:1 ratio performs better than a 20:1 ratio, personal preference notwithstanding.
You conviently left out this from Vintage Brake: “For a firmer lever, use 23:1. I think ratios lower than 23:1 produce a lever feel so "wooden" as to have little, if any feel.“ BTW, a 13mm master paired with a 41mm caliper has a ratio lower than 20:1.
Your argument has no merit other than obstinacy. Reminds me of years ago, on this forum, when those ignorant of physics would not accept that a good reed valve was necessary to depressurize the Norton crankcase. Many were looking for a crankcase seal made of unobtainium. Those who tried a proper reed valve reported oil then stayed INSIDE the crankcase.
As for Jim Comstock’s report of cooking the brake with a 11mm master and a 41mm caliper, I have no doubt as to it’s validity. I doubt, very seriously, he went to a larger master. I would bet money he added another disc.
JimC , you are obsessed with this 27:1 ratio .
I believe lever length should be part of the equation.
Brembo also knows a thing or two about brakes.
Their recommendation for a single disk is 15 or 16 mm dia. radial mc .
I use a 16x18 radial mc, in combination with a 4 piston caliper.
Surface ratio is nowhere near 27:1 .
Braking power and feel is awesome .
Six apples do not equal six oranges.
The Vintage Brake chart shows a 41mm, 4 piston caliper with a 16mm master having a ratio of 26.27:1. I’d say that is pretty near 27:1.
Maybe there is something to this 27:1 ratio. After all, you said braking power and feel is awesome.
The pistons in that caliper are probably around 2 x 30 mm and 2 x 34 mm.
The Vintage brake chart as good as it might be is veryyyyyyyyyyyy old.
Like Time Warp correctly guessed, pistons are 2x 34 and 30 mm.
Surface ratio is 16 :1
Lever ratio is equally important.
On a16 x18 radial mc, distance from fulcrum to load point (piston axis) is 18 mm.
Std Lockheed Norton mc is around 22 mm.
Plus: with an axial mc, the applied force has to change direction 90°, with loss of power and feel.
I suggest you ( and others ?) change that 11 - 12 -13 ..mm axial mc you speak so highly off for a 15 or16 mm radial and report back ..
I used that radial Brembo master on a Suzuki GSXR750SRAD with six pot Nissins, Galfer discs and Bendix race pads. It was the best motorcycle brake I have ever used. They make the lever adjustable, to suit your preference!
I would love to use one of those Masters on my race bikes, but.....regs don't allow.
They also come in an alternative ratio of 16 x 20, apparently for Superbike/MotoGP use!
I think I could take lessons in obstinacy from you! My responses will have as much wind as I care to expend.
...read your chosen quote... I didn't leave it out, because I didn't 'quote'.... 'I think' in other words..... he has stated an opinion!
I have tried various masters, my personal preferance for ratio works out around 20! It does not seem to limit my personal 'feel' for wheel locking, I don't do that often on two wheels on tarmac.
I have been racing various vehicles for 45 years, I have done some braking, the vast majority of it 'successful' on a variety of surfaces and conditions.
In circuit racing the majority of overtakes are on the brakes at corner entry!
I was also an engineer with a 46 year career, not 'ignorant of physics' (and I have a 'proper reed valve fitted'), I am also human with all of the physical variations to my fellow humans that implies.
There is never only one solution. There is normally a range of successful solutions and a plethora of opinions regarding the best. Such is the lifeblood of forums.
The lever ratio is often forgotten. Some seem to think only one ratio is used for levers, both clutch and brake. I learnt a bit about this relatively recently, one trying to get a good set up for my Norman White belt drive/clutch combined with TTi gearbox clutch operating mechanism (Triumph part). To avoid drag I needed more lift. At first I looked at a small amount of wear in the Triumph 3 ball operating mechanism and this gave a small improvement, but I only achieved the lift needed with an expensive Tomasseli race part with a suitable lever ratio.
But the other was on an AJS 500 single I bought a 3 years ago. The old single leader drum front brake is never going to be up to our expectations, but this seemed particularly bad, and the previous owner admitted he had been very uncomfortable with it, but just assumed that was how it was in the '50s. Basic alignment set up improved it a little. But it was only when I changed the levers from the nice modern style alloy ones that were fitted to the original 7/8" pivot, chrome steel style that it began to stop passably well, if I could get a better made set with a more stable pivot it would be even better.
I do like a bit of thread creep
I think the original question has been adequately covered, but I'll add my experience...
I fitted an RGM re-sleeved Master cylinder and braided hose to my standard front caliper/disc and the brake was transformed from being (a) inadequate, and (b) having no more feel than gripping a plank, to being entirely adequate and having lots of feel, so yes, it's a huge improvement, and changed my riding style on the bike massively. Yes I could squeal the tyre if I was minded to. Never tried a burnout with it though
As I was doing a bit of 2-up work (neither of us are lightweights...) I fitted an AP racing CP2696 caliper and RGM floating disc and this brought the brake up to modern standards. Although I never went canyon racing on it I felt totally confident hooning around on our local back roads.
There's still a lot to be said for improving a Commando whilst keeping it original looking IMHO.
That said, an early Fastback with a Fontana 4LS would look beyond cool