Can we see the other side please?
H: Hubs, Wheels and Tyres Eight inch brake ?
- Thread starter Julian R.
- Start date
I think there is a simple way to summarize the balance bar debate that bypasses lever ratio complications.
With the original Vincent set up (with the cable from the handlebars attached to the END of the balance bar) the force in EACH cable at the brake is the same as the force in the cable at the handlebar lever. This is ignoring friction.
With a balance bar fitted at the handlebars so that the cable from the lever is attached to the CENTRE of the balance bar, the force in each cable at the brake is half the force in the cable at the handlebar lever. Again this is ignoring friction.
So the standard balance beam does not double the force, but it does apply twice as much force as a centre-pull balance beam.
The test rigs are interesting, as they should give an idea of friction levels. My guess is friction could be perhaps 5lbs, so a test force of 10lbs could be very misleading as an attempt to establish basic principles. 5lbs friction would be much less significant at cable forces of around 100lbs.
Could I suggest to all the fans of the extra bracing of balance bar pivot that they measure the deflection present before making changes?
By my admittedly crude measurement it is very small.
95% of the flex in the standard system is in the steel brake backplates.
After I fitted the 8" brakes, the vastly better rigidity and accuracy of the backplates meant I was able to use rear brake levers for a substantial increase in braking pressure. This is with the standard balance bar, and the brakes are still firmer than the originals, in spite of the extra leverage and no pivot point bracing. With so much leverage, I do need to keep the brake closely adjusted of course.
However, I have concluded that the 8" brake is perhaps overkill for a solo bike and adds unsprung weight.
Even when I did consecutive brake tests (approaching 1g stopping from 70mph) it was still quite cool.
If I had the money and energy, I would try either the Speet brake or the VOC spares company 7" alloy backplates with the rear brake levers.
With the original Vincent set up (with the cable from the handlebars attached to the END of the balance bar) the force in EACH cable at the brake is the same as the force in the cable at the handlebar lever. This is ignoring friction.
With a balance bar fitted at the handlebars so that the cable from the lever is attached to the CENTRE of the balance bar, the force in each cable at the brake is half the force in the cable at the handlebar lever. Again this is ignoring friction.
So the standard balance beam does not double the force, but it does apply twice as much force as a centre-pull balance beam.
The test rigs are interesting, as they should give an idea of friction levels. My guess is friction could be perhaps 5lbs, so a test force of 10lbs could be very misleading as an attempt to establish basic principles. 5lbs friction would be much less significant at cable forces of around 100lbs.
Could I suggest to all the fans of the extra bracing of balance bar pivot that they measure the deflection present before making changes?
By my admittedly crude measurement it is very small.
95% of the flex in the standard system is in the steel brake backplates.
After I fitted the 8" brakes, the vastly better rigidity and accuracy of the backplates meant I was able to use rear brake levers for a substantial increase in braking pressure. This is with the standard balance bar, and the brakes are still firmer than the originals, in spite of the extra leverage and no pivot point bracing. With so much leverage, I do need to keep the brake closely adjusted of course.
However, I have concluded that the 8" brake is perhaps overkill for a solo bike and adds unsprung weight.
Even when I did consecutive brake tests (approaching 1g stopping from 70mph) it was still quite cool.
If I had the money and energy, I would try either the Speet brake or the VOC spares company 7" alloy backplates with the rear brake levers.
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I fitted this Brace because I think it looks nice, Not sure it does anything. Cheers Bill.
100% of the flex in the system is the shoe bending.
Why should a steel plate flex when the load is applied at one edge ?
well 100? thats boud
I would say 97......
In short: it all Flexes to a degree, maybe even one of us might make a mock-up.
In the end even the thoughest Lathe is one big spring
I would think that steel might have been a better solution for shoes at the time. If you look at the difference between the 7" and 8" shoes it is fairly dramatic:
The presumption is that Rob is finding that the shoes at a minimum are more resistant to flex. Trevor's mock up for flex shows that the shoes themselves are the culprit.
I posted a video of Mike Hawthorn recently and I noticed that he has several mods on his brakes. The bridge plate is much thicker and he has not only drilled holes in the balance beam, but brazed some rods on underneath to reinforce it. Then, he has placed a stop under each end of the balance beam so it is rigid and run twin cables, one to each side of the now faux balance beam.
Additionally, he has run a longer lever on the brake arms. I see he is using Magura levers, probably because they make a nice twin cable lever for the brakes.
David
It seems that the 8" brake is stuck with fixed pivots and the poor braking associated with the uneven wear between the leading and trailing shoes. Cheers, Stu.