Vintage brake's (now interactive) ratio chart

[bikeboy]

Seen a bit of discussion regarding brake and master upgrades, and thought this might be useful. While I was upgrading the bol d'or, I came across the chart mentioned earlier at vintagebrake.com, and thought "I could probably do something with that". So I did. I made an Excel document using the info and put it in a more user-friendly format. Mainly because it didn't include the set-up I was working with.

Anyway, you can grab it here: Vintage brake interactive chart. (Or I think I can attach a zip version?) At the bottom it explains that ratios in the 27:1 range-2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum-firm. Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks. So the ratios to shoot for are around 27:1 mark.

To use it, you put in the diameter of the pistons in col. A, (total) number of pistons in B, then read across the line to your master cylinder diameter to find the ratio. I've filled it with vintagebrakes data, but you can change any row and it will re-calculate. You can therefore use it to find the optimum ratio by finding the closest fit to 27.

Oh, I should also put in some sort of disclaimer that this is a guide only, put together by a graphic designer, and I take no responsibility for anything

Someone else might find it useful?

cheers
ian

 

[scm]

Nice chart and really helpful for 2 and 4 piston brakes!

There's just one mistake in it, and that's the calculation for a single piston caliper.
In this case all values have to be exactly the same as the ones with 2 (opposed)
pistons.

I.e. if an 11mm master cylinder works fine with a lockhheed caliper (two opposed
d41 pistons), it'll do the same with a 41mm single piston floating caliper.

Best regards
Sven

 

[bikeboy]

Nice chart and really helpful for 2 and 4 piston brakes!

But you can change the number of pistons, and it will re-calculate?

There's just one mistake in it, and that's the calculation for a single piston caliper.
In this case all values have to be exactly the same as the ones with 2 (opposed)
pistons.

I.e. if an 11mm master cylinder works fine with a lockhheed caliper (two opposed
d41 pistons), it'll do the same with a 41mm single piston floating caliper.

Best regards
Sven

Thanks for the heads-up Sven. I just copied the info in the original chart, but I'll try and get my head around that and change it.

cheersian

 

[scm]

Yeah, the original chart is a bit strange in this point, it calculates the ratios for the single piston
to half of that of the 2piston calipers, but then recommends ratios from 14:1 to 12:1, which is,
you guessed, quite precisely half of the recommendation for the 2piston brakes ... so after all
you'll find the same mcs fit both 1 and 2piston calipers.

Best regards
Sven

 

[bikeboy]

... so after all
you'll find the same mcs fit both 1 and 2piston calipers.

Best regards
Sven

I'm not sure I follow you Sven? Isn't the basic premis that the ratio (and consequently the 'feel') will change when the surface area increases? If you add another piston, you've increased the surface area, so the ratio *must* change? I have no experience with the set-up you've highlighted, but surely the feel at the lever will be different if you change from single to double piston calipers and retain the same master? This is what the whole discussion seems to be about? trying to 'quantify' the 'right' feel?

Then again, I'm a graphic designer, so this right-brain/left-brain stuff leaves me with a headache

Happy to make any changes you think might improve the document.

cheers
ian

 

[scm]

Isn't the basic premis that the ratio (and consequently the 'feel') will change when the surface area increases?

Yes, e.g. for a given caliper the feel will get softer with decreasing mc-diameter
(and the brake will get stronger in a sense that less force on the lever is needed
for the same clamping force of the caliper).
On the other hand, enlarged caliper pistons will lead to a similar result, as like in
the first case the ratio caliper:mc is increased.

If you add another piston, you've increased the surface area, so the ratio *must* change?

That's true, but only if the additional piston occurs on the same side as the existing one.
If e.g. you have a single piston caliper and you add a second, same sized piston on the
opposite side, nothing will change, the ratio remains the same.
Imagine you take your personal scales, hold it to the wall and push as hard as you can.
Let's say you achieve 150lbs. That's the single piston floating caliper.
Then you ask a friend who is as strong as you to help you. Now with two men pushing
the scales from one side against the wall obviously the force on the scales is doubled,
hence 300lbs. That's the 2piston-floating-caliper.
To simulate the 2 piston-non-floating-caliper the scale is now being pushed by one of you
on each side. Although two are engaged, the result will be the same as in the first case:
150lbs. (That's just Newton's third axiom: actio equals reactio).

O.k., we know now that it doesn't make a difference whether one or two opposed pistons
of the same size work, if only the same force is applied to each of them. This is the case if
both times the same mc is actuated with the same force (creates equal pressure hence equal
force on piston).

Though the area of piston is doubled with the 2piston caliper, this doesn't change anything
compared to the 1piston device.

Let me quote the vintage brakes website:

For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1. ... Single piston calipers are much happier in the 14:1 to 12:1 range.

Though both calipers mentioned act the same, vintage brakes calculates half the ratio for the single piston caliper,
only to recommend half the value of the 2 piston caliper as the proper range.

any changes you think might improve the document.

I'd suggest either to add the notice about the 14:1 - 12:1 for the
single piston calipers or to leave away the their rows and just mention
they act like the 2 opposed piston calipers.

Best regards
Sven

 

[bikeboy]

That's true, but only if the additional piston occurs on the same side as the existing one.
If e.g. you have a single piston caliper and you add a second, same sized piston on the
opposite side, nothing will change, the ratio remains the same.
Imagine you take your personal scales, hold it to the wall and push as hard as you can.
Let's say you achieve 150lbs. That's the single piston floating caliper.
Then you ask a friend who is as strong as you to help you. Now with two men pushing
the scales from one side against the wall obviously the force on the scales is doubled,
hence 300lbs. That's the 2piston-floating-caliper.
To simulate the 2 piston-non-floating-caliper the scale is now being pushed by one of you
on each side. Although two are engaged, the result will be the same as in the first case:
150lbs. (That's just Newton's third axiom: actio equals reactio).

O.k., we know now that it doesn't make a difference whether one or two opposed pistons
of the same size work, if only the same force is applied to each of them. This is the case if
both times the same mc is actuated with the same force (creates equal pressure hence equal
force on piston).

Though the area of piston is doubled with the 2piston caliper, this doesn't change anything
compared to the 1piston device.

I'd suggest either to add the notice about the 14:1 - 12:1 for the
single piston calipers or to leave away the their rows and just mention
they act like the 2 opposed piston calipers.

Best regards
Sven

That's a great explanation Sven. Thank you very much for that. I'll put that note in the file.

cheers
ian

 

[teazer]

And don't forget that a larger diameter disk will create a stronger braking action (torque) for the same amount of force - or less effort ofr teh same brake action.

Light bikes need less brake torque to slow that heavy ones, so dumping weight will make for more effective brakes - all other things being equal.

Kevin Cameron had a version of all of that in his book. You can adapt that to take those ratios a huge step further. I use a clamping force (hand) to generate 1G of stopping power as a guideline and that takes the ratios, disk size, pad friction levels and machine mass into consideration. All of the calculations are just a starting pint to understand why the brakes are like they are and as a guide to modify them and in the final analysis you have to try them on the street or track and try different sizes until you get what works for you.

Rider preferences are different, so for example, an 11mm might be perfect for you and a 1/2" might work for me because we like a different feel.