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]
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
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
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
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.
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.
A Mu of O.3 is very low for road pads a teeny bit over 0.4 is nearer the mark.
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]
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.