Hornet
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 posted on 13/4/05 at 02:28 PM |
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Front rear brake bias
Hi chaps
Setting car up for SVA test and was wondering what I set front to rear brake bias? I have m16 calipers on front (assuming 100% eff) and 9"
drums on the rear with one of those fiat uno thingies 
what should the rear be set at 50% 60% ?? Rollin road in next few days so any pointers would be great.
J
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locoboy
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| posted on 13/4/05 at 02:37 PM |
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many people have not needed to 'fiddle' with the natural balance when using this set up.
On my car i had same set up with sierra MC and i dont think i managed to get the rear to lock up .......ever.
It stopped on a dime too.
ATB
Locoboy
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alister667
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| posted on 13/4/05 at 04:28 PM |
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I've got standard Sierra M/C, drums at the back and standar Sierra Calipers at teh front. I fitted a Bias Valve, but I just leave it fully open
to get as much braking pushed to the rear as possible, and the back brakes have never locked.
I'd leave it open or near open.
http://members.lycos.co.uk/alister667/
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smart51
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| posted on 13/4/05 at 04:33 PM |
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you should never have more brake force on the rear than the front unless you want to spin round.
Most ordinary cars go for 50% - 70% front bias but then most ordinary cars are FWD
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rayward
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| posted on 13/4/05 at 04:58 PM |
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Got mine set to 80% front, 20% rear.
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alister667
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| posted on 13/4/05 at 05:49 PM |
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My point was that even with the back brakes getting the same pressure as the front the drums at the back won't be as effecient as the disks at
the front, and won't cause the rear brakes to be too strong.
quote:
Originally posted by smart51
you should never have more brake force on the rear than the front unless you want to spin round.
Most ordinary cars go for 50% - 70% front bias but then most ordinary cars are FWD
http://members.lycos.co.uk/alister667/
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smart51
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| posted on 13/4/05 at 08:56 PM |
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for the same pad (or shoe) area, drum brakes produce the same stopping force as disk brakes, despite what public opinion says.
Disc brakes fade less and dry out quicker than drums.
Drum brakes make for better hand brakes.
Ideally, the front / rear brake force distribution should match the front / rear weight distribution UNDER HEAVY BRAKING where the weight is shifted
as far forward as it's going to go, provided that the front brake force is always higher than the rear.
You DON'T want the rears to lock up before the fronts.
too little brake force at the rear and you have less stopping effect. to much at the rear and you crash and die. A bit.
[Edited on 13-4-2005 by smart51]
[Edited on 13-4-2005 by smart51]
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Avoneer
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| posted on 13/4/05 at 10:22 PM |
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I passed SVA with M16's up front, drums up back and a Sierra bias thing. I have since removed the bias thing and my braking is much better and I
have still never locked the backs.
My friend passed SVA with just M16's up front, drums at back and no bias valve.
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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britishtrident
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| posted on 14/4/05 at 07:05 AM |
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Because of weight transfer it is almost impossible to set up the front/rear distribution on rollers. Only satifactory way is very careful road
testing on a good dry tarmac. But your current setup shouldn't cause any problems without any kind of bias valve.
The weight transfer varies depending on the decceleration, the most weight transfer occurring in an emmergency stop on a high friction dry surface. In
this situation(say a 1g stop) the brake effort distribution on a Locost. is 67% front 33% rear. In wet weather for an emmergency stop would this
be nearer 60% front 40% rear.
For a road car using discs on the front and drums on the rear works in our favour and actually helps to compensate for this.
Drum brakes have a self servoing action and respond differently to hydraulic line pressure to disc brakes.
With Disc brakes the relationship between hydraulic/pedal pressure and braking effort is almost linear at low pressures although it starts to fall
off as the pedal/hydrualic pressure isincreased.
Drum brakes with a leading shoe are self servoing -- this means that at low pedal pressures they are more "efficient" at connverting pedal
presure to braking effort, but because of mechanical stiffness reasons thet become much less efficient at converting hydraulic/pedal pressure to
braking effort at high hydraulic pedal pressures.
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marc n
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| posted on 14/4/05 at 07:18 AM |
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In dry conditions i would run a car with very low braking effort perhaps 25% roadcar and if on the track more likely 15 %
for wet conditions i would up this to 35% and on tack up to 45%
The way we have setup brake bias for many years in competition cars is as follows
get a helper to sit in the car and apply the brake pedal gradually to the point that you can only just turn the front wheel, make sure your helper
holds the pressure on the pedal at this point and move to the rear you should be able to spin the rear wheel
this we have found over the years gives you a good base setting to improve on by driving the car down the road and adjusting small increments at a
time
hope this helps
best regards
marc
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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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