smart51
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| posted on 15/6/10 at 11:30 AM |
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how much brake pedal pressure is OK?
Correction
The front piston diameter I had was wrong. Redoing the calculations gives me a 30.3 kg pedal force with a 4:1 pedal in order to get 100% braking
effort at the front and 60% at the rear. A 5:1 pedal needs 24.2kg to achieve the same.
Original Text
I've just done the brake calcs for my 3 wheeler and with a 4:1 pedal ratio, 48.3kg of brake pedal force gives 100% brake effort on the front
wheels and 95% on the rear wheel. A 5:1 pedal needs 38.6kg to do the same. (thats 67 and 53 lbs in old money). Is this OK?
By 100 percent brake effort, I mean the stopping force applied by the tyre to the road is equal to the weight of the vehicle on the tyre. This is
assuming a 0.3 coefficient of friction for the brake pads and 100% tyre grip.
How much pedal force is about right?
[Edited on 15-6-2010 by smart51]
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turbodisplay
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| posted on 15/6/10 at 12:19 PM |
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A bit subjective, best way of looking at it is what is the weakest person to use the vehicle. Ie a femle would be 40 - 70 % of the effort of a man.
Pedal effort realy is what is within your best control range, ie you can be progrssive. For me i guess 20 - 30 kg, more or less than that there is
less feel.
You do what i did and put a pressure gauge in the brake line and work out what is comforatble. I produces 80 bar standing as hard as I could, no
servo, slightly lower pedal ratio than donor tin top.
Darren
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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hughpinder
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| posted on 15/6/10 at 12:50 PM |
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sounds high to me - I have in my mid about 50lbs for a road car and 80 for a track car as being recommended maximums ( but I can't think where
from - maybe a guide on rally design or burton power?)
Regards
Hugh
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Fred W B
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| posted on 15/6/10 at 01:55 PM |
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Sit across a passage with a bathroom scale between your foot and the wall. Push on the scale and by reading the scale you can get a feel for it.
I seem to recall reading that you can design for 70 kg for a panic stop.
cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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britishtrident
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| posted on 15/6/10 at 02:23 PM |
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If above about 70 lbf (310 Newtons) is required for a 1g stop it is a bit unpleasant.
Then you have to allow for fade, if after 3 stops in quick succesion from 60 mph more than 90 lbf (400 Newtons) is required it would be difficult to
have much faith in the brakes.
[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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smart51
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| posted on 15/6/10 at 02:29 PM |
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quote:
Originally posted by britishtrident
If above about 70 lbf (310 Newtons) is required for a 1g stop it is a bit unpleasant.
Then you have to allow for fade, if after 3 stops in quick succesion from 60 mph more than 90 lbf (400 Newtons) is required it would be difficult to
have much faith in the brakes.
So with the 5:1 pedal ratio, 53 lbs force, rising to 68 with fade, would probably be acceptable.
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britishtrident
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| posted on 15/6/10 at 02:29 PM |
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A Mu of O.3 is very low for road pads a teeny bit over 0.4 is nearer the mark.
[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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smart51
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| posted on 15/6/10 at 02:44 PM |
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Mu of 0.4 gives me 22.7kg (60lbs) for a 4:1 pedal and 18.2kg(50lbs) for a 5:1 pedal. The 4:1 option might be the best bet then.
[Edited on 15-6-2010 by smart51]
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NS Dev
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| posted on 15/6/10 at 03:10 PM |
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Yea its very easy to get caught up in too much detail on this one.
On a light car built for driving pleasure rather than a daily half asleep commute, I would definitely go for the 4:1 pedal.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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