speedyxjs
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| posted on 24/10/08 at 09:32 AM |
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Calculating brake pedal effort
How would you calculate the amount of effort you put on the brake pedal?
I have shortened mine and would like to calculate how much more effort i would need.
How long can i resist the temptation to drop a V8 in?
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daviep
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| posted on 24/10/08 at 10:06 AM |
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I would say you can't, too many unknown variables.
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nick205
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| posted on 24/10/08 at 10:12 AM |
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Difficult to quantify in terms of outright effort as it will depend on you leg strength, seated position, pedal travel and the rest of the braking
system.
What you can do is calculate the leverage ratio or change in ratio by shortening the pedal.
IIRC the generally accepted wisdom says you should aim for a leverage ratio of around 5:1 for a non-servo system (I stand to be corrected here
though).
In other words the distance between pedal pivot point and where you press the pedal wants to be about 5 times the distance between the pedal pivot
point and the pushrod pivot point (I think!!!)
[Edited on 24/10/08 by nick205]
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wicket
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| posted on 24/10/08 at 10:41 AM |
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According to Des Hammill's book "How to build & Modify Sportscar & Kit Car Suspension & Brakes" the ratio should be
between 5:1 min & 7:1 max
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speedyxjs
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| posted on 24/10/08 at 10:50 AM |
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Looking at some pics earlier, i think i saw one with the brake mc almost on the pedal.
Would that be SVA fail then?
How long can i resist the temptation to drop a V8 in?
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daviep
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| posted on 24/10/08 at 10:58 AM |
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Pedal effort is affected not only by the mechanical advantage of the pedal but also the ratio of master cylinder to slave cylinder. If you had very
little mechanical advantage from your pedal you could make up for it with a smaller master cylinder or larger slave.
There is no reason why a short pedal or short pivot would be an SVA fail providing the brakes still work correctly.
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speedyxjs
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| posted on 24/10/08 at 11:10 AM |
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^^^ that sounds good but what is the difference between slave and master cylinder?
How long can i resist the temptation to drop a V8 in?
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daviep
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| posted on 24/10/08 at 11:18 AM |
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The master is the one that the pedal is attached to, it generates the pressure in the system. The slave cylinder is what operates the brakes whether
it be a calpier or a wheel cylinder.
A smaller master cylinder will generate a higher pressure for the same pedal effort and a larger slave will produce more stopping power for any given
pressure.
Simple
Davie
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britishtrident
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| posted on 24/10/08 at 12:40 PM |
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Term slave cylinder in automotive use should really be restricted to clutch slave cylinders.
Your jag donor would have a pedal leverage of a bit over 9 to 1 with a Locost style chassis it is difficult to get a pedal leverage of much more than
4.5:1
On the Jag the servo provided between 40 and 60% of the braking effort.
Assuming your car ways just half of the jags weigh ---
Then without a servo you will need to push the pedal about twice as hard as the jag to stop at 1g.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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JC
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| posted on 24/10/08 at 03:14 PM |
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I found a spreadsheet on tinternet to calculate brake pedal force. You needed info like master/slave cylinder bores, pedal ratios, disc size, pad
size etc. It came out with the pedal force and decel force. You can find it
here:Linky
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daviep
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| posted on 25/10/08 at 09:42 AM |
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quote:
Originally posted by britishtrident
Term slave cylinder in automotive use should really be restricted to clutch slave cylinders.
Why? I don't understand the difference.
Davie
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daviep
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| posted on 25/10/08 at 09:55 AM |
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Quote from the collins dictionary:
Slave cylinder
A small cylinder containing a piston which, under hydraulic pressure from a master cylinder, operates the brake shoes or pads in hydraulic brakes or
the working part in any other hydraulically operated system.
Davie
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