lever being 1 to 4 leverage.....
H: Hubs, Wheels and Tyres Eight inch brake ?
- Thread starter Julian R.
- Start date
Yes. 10 pounds with a spring scale pulling at the tip of the lever. On my twin I get about 20 pounds when the handle bar lever is pulled up tight. This is with the spares heavy cable and alloy backing plates. My brakes are reasonably good.
When you pull on the handle bar lever you are using a long lever pulling a short lever thru the pivot pin fulcrum, which shortens the pull and increases the power, based on the lever lengths from the fulcrum. It is exact ratio of the lengths. If the lever is 7/8 from the fulcrum to the cable and the spring scale is 31/2 inches from the fulcrum to the point on the hand lever where the scale is attach, you will get 1/4 the travel and 4 times the force. In your case (if indeed those are the correct measurements) this would show that you are pulling a 40lb load on the cable end and producing 20 lbs at each brake, exactly what you would expect from a twin pull cable setup.
Nice one MSVH. That is a very useful and instructive test.
Thank you for the work, I find it instructive also.
Just for reference:
In Neville's article he called "d2" above "N" and found the stock pivot to be .906" or 29/32" and most other pivots 1.125".
I realized a while ago I would have to do the same experiment on my machines, so I ordered several spring balances. There are so many variations with levers, brake arms cables and balance beams that I realized I needed more specific information to figure out how to make the brakes work better. With luck I may learn something about the why the brakes tend to be so ineffective.
I have both the stock bike set-up as well as the twin cable set-up, so I should be able to do a direct comparison.
Just as a note, I was talking with another racer today who said he ordered a balance beam from the club and when he went to sand the paint he noticed it was a bronze casting under the paint. He was unhappy with the rigidity and replaced it with the 4130 casting done by Mike Breeding. This might be something to check.
Thanks again for your help.
David
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So to be clear you were not getting 40lb on each brake you were getting 20lbs so the gentlemen quoted by David in the statement below were wrong:
This came up in MPH during a discussion of brake levers and their effects by Neville Higgins. He and George Spence, among others, assert this as true. That is, the Vincent balance beam and cables are designed in a way that the force transmitted by the cables is doubled when they reach the brake arms on the drums. Thus, if you use a stock Vincent cable and balance beam and you tied concrete blocks to the cable ends instead of the brake arms, you would be able to pick up two 100 lbs. blocks with the Vincent while the dual cables could only hoist two 50 lbs. blocks.
To be fair, In the case pictured and quoted, we do not know the lever lengths on the handlebar lever, if for instance if it is a 1 1/8 centre lever and the handle length is not 3 1/2 inches and the pull was applied at some other than 90 degrees to the line from the pivot then the results of the pull would be different.
Pivot centers 1 1/8. I put a spring scale at 4 inches, on the handlebar lever, from the pivot bolt of the perch. I preloaded the other two spring scales to 15 pounds each. The scale at the lever took 7 pounds to start the other two scales to move. I tried to keep things at right angles.This is just a lash up so I am sure there are some anomalies.
I remember talking to John McDougal about this. He had installed Speet brakes and had elected to retain the balance beam. He preferred the look of this system, and it can have some advantages when it comes to quickly removing the wheel. In order for this to work right he had to shorten the levers on the brake plates quite a bit (theoretically by half) I told him about how I understood how the balance beam worked. He said I was probably one of very few people who understood it. None of these mechanisms will give you something for nothing. If a lever is twice as long it will double the torque with the same force applied, but to have the same torque and angular movement the distance the force is applied will be doubled so nothing is really gained. It is the same thing with the balance beam. It does apply the same force to each side of the brake and that force is the same as the force in the cable that comes from the handlebar, the trouble is that both ends of the beam move only half as far as the cable where it leaves the handlebar lever. To operate the brake you really need force times distance not just force. If is so simple I can't believe people are still arguing about it after 60 years.
I have Speet brakes on my bike. I used the twin cable system that came with it. To get that to work properly you need to have brake levers with 7/8" distance between the pivot and the cable. I had to modify my lever because I am using Amal racing type levers and they have 1 1/8" centers. The Speet brake is pretty good even for two up touring with luggage.
I have Speet brakes on my bike. I used the twin cable system that came with it. To get that to work properly you need to have brake levers with 7/8" distance between the pivot and the cable. I had to modify my lever because I am using Amal racing type levers and they have 1 1/8" centers. The Speet brake is pretty good even for two up touring with luggage.
Hi,
Using your setup try pulling the 10 Lb ON THE END OF THE CABLE not the lever - then I predict (with the certainty of Archimedes ) that the SUM of the pull on as many spring scales you care to attach to the other end of the cable will also be 10 Lb.
Now do the same thing but this time pull on the lever with the spring attached to the lever close to the pivot point - You will get more than 10Lb total, but not much more; Now move the spring attached to the very end of the hand lever and again apply a 10 Lb pull - this time, as a result ONLY of the leverage from the hand lever, the total pull at the other end will be much more than 10 LB ., though the lever will travel a much greater distance.
Nothing to do with balance beams!
The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. 'Give me a place to stand, and I shall move the Earth with it' is a remark of Archimedes who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).
Baaa