Optimal master cyl size for AP caliper

linker48x said:
If the question is, has anyone used an 11 mm master cylinder with a 41 mm two piston Lockheed, the answer is, I used that combination on my AHRMA 750 sportsman Triumph 750 in a Redline frame for nearly 25 years, and on my AHRMA F500 RD 430 for 10 years, and then I stopped racing or I would still use that combination on the track. I still use it on the street these days on my Norton Commando with a 12 inch floating disc, and on my Triumph T140D with floating disc. They have all worked really well. My usual answer to this question is to include the link to the Vintage Brake table, so you can see what an expert recommends, but that appears up above--Michael Morse knows brakes and knows what he is talking about. The lever is a little soft, with a woven stainless line, if you are used to old fashioned British disc brakes with a large master cylinder, the feel is about like my R-1 race bike, but I have many times picked up these bikes on the front wheel with the brakes, so the braking power is high, and the feel is also very good. You should use whatever you have tried and like, and if that is a 5/8, or 12mm, or 13 mm, whatever, you should use it. Use what works for you, change it only if you are displeased with what you have, but that is what I have used for many years. But one thing---if the lever is going to the bar with the 11mm, or any combination, there is something wrong, and you need to fix it--with stainless braided line, and careful bleeding, this should not be happening.
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Thank you, that’s super informative. I was concerned that although 11mm is right ‘in theory’ … it might not work in practice. Obviously it does !
 
Yooz boyz !

I have a 13mm Brembo on the shelf, but now I’ve just ‘had to’ buy an 11mm as well. Will see which turns out best.

Next question: is there a similar chart available for rear brake application ?

I have a bike with a poor rear brake and I’m pretty convinced it’s a piston sizing issue.
 
Fast Eddie said:
That’s kinda my fear also.

FYI this job doesn’t involve a radial MC.

I have a 13mm Brembo on the shelf, and I know that worked superbly with a 4 pot caliper. Based on your calculations comparing a 4 pot to a bigger piston AP twin pot, it should work well, so I’m thinking I’ll try that first.

Steve Borland also reported a 13mm working well with a single AP.

I’m just not looking forward to bleeding it, I seem to recall that being something of PITA…
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Whatever an early 2000s Triumph Daytona 955i ratio is, it works perfectly with my twin AP calipers on my T160.
 
Fast Eddie said:
Next question: is there a similar chart available for rear brake application ?
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Its the same but it really depends on the weight of your foot and your ability to control that. As the effect of braking is to move weight forward then the rear brake, if too efficient, will lock the back wheel. Hence why drum brakes lasted so long on the rear both on cars and bikes. So chart is same but the 27:1 may not be the best result if you have a lead boot.
 
Fast Eddie said:
Yooz boyz !

I have a 13mm Brembo on the shelf, but now I’ve just ‘had to’ buy an 11mm as well. Will see which turns out best.

Next question: is there a similar chart available for rear brake application ?

I have a bike with a poor rear brake and I’m pretty convinced it’s a piston sizing issue.
Click to expand...
Nigel,
The increase in lever travel with the rear is really a PITA. Something to consider.
 
On my Himalayan I fitted a second hand Nissin 11mm master cylinder from a Honda ANC125. They are pretty cheap, so maybe give one a try and see how it feels?

One example here…

www.ebay.co.uk

2017 HONDA ANC 125 Brake Master Cylinder | eBay UK

This item has been removed from a: 2017 HONDA ANC 125. Year: 2017. Model: ANC 125. Engine Size: 125. Part Type: Brake Master Cylinder. Make: HONDA. All parts are stamped & removal of the marks will invalidate your warranty.
www.ebay.co.uk

You can also get a longer lever for it if you find you need one.
 
The optimum size master cylinder for the front brake depends on how you use the bike. If you want safety a bigger bore is better, if you tend to over-react. If you ride more systematically and don't rely much on reflexes a small-bore master cylinder can give one-finger operation. The only person who rode my Seeley 850 other than myself was a friend who was very experienced. The only time I use the rear brake is when I get into a corner too hot and need to lose speed before I can accelerate to get around the corner. I hold the bike as vertical as possible - then I just wait until I judge the tyres will stay stuck, then accelerate - when the rear of the bike goes down the bike will turn. If I was ever really in the shit, I would use the rear brake to put the bike on the ground, before it could hit anything. There is usually one corner on any circuit where I tend to run wide - I find it by riding progressively faster. The rest of the speeds on the circuit relate to the slowest corner. - Does that sound like idiocy ? - I have crashed more than a few times.
 
This is the chart I use when matching up un-stock parts. Look for a ratio in the 27:1 area for 2 finger braking. I use a 12mm M/C on my MKIII with the AP caliper. Works great!



Optimal master cyl size for AP caliper
 
Re the question concerning rear brakes—i know of no similar table similar to the Vintage brake front brake hydraulic ratio table for rear brakes. If it’s any help, as noted you are trying to balance and render controllable the mechanical advantage of what is usually a relatively long brake pedal, plus the additional muscle advantage of your foot and calf muscles, against (in a road race setting) the very limited rear wheel traction when you are hard on the brakes, so I’ve always used a big (5/8) rear master cylinder and a small caliper (the little triangular Brembo and not a Lockheed) to sort of reverse the hydraulic ratio of the front brake setup, to be less effective and have less hydraulic advantage, plus using a littler disc and a caliper with small brake pucks. I never used much rear brake on a track so it worked okay for me. Again, you should experiment with caliper annd m/c sizes annd pedal lengths and use only what works for you.
 
My method was to shorten the rear brake lever. When that didn't seem enough I shortened the lever on the
back plate. Got there in the end.
 
I copied the overall leverage ratio, both hydraulic and mechanical, when doing my FF Commando rear brake, basing it on the rear Mk3 Commando as baseline, since I liked the feel of that one. (I ended up with a Honda Blackbird caliper, KTM master cylinder for the hardware). It worked out very well.
 
Holmeslice said:
Edward Rapido,

13mm Brembo is magic with a single CP2696. Proof is in the eating. They are the easiest to bleed of any M/C if you ask me. And if you want to get really punk rock you a get a lever with an adjustable ratio, and change it during the race, as I do.
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The 13mm Brembo is perfecto Kenny 👌

Thanks again.

Optimal master cyl size for AP caliper
Optimal master cyl size for AP caliper
 
Last edited:
Fast Eddie said:
The 13mm Brembo is perfecto Kenny 👌

Thanks again.
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Apparently Joey Dunlop used to adjust his hydraulic steering damper as he raced. If he had the adjustable damper on the left and the adjustable brake lever on the right, the bike might faster on the straights, when there was a tail-wind.
 
12.7mm Brembo works pretty well. Or 'half inch' to you.

Some Brembo '13mms' actually measure 12.7mm
 
I keep both hands on the bars while racing - not off twiddling knobs. I keep my mind on the job. It takes concentration and feel.
 

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