Bias Pedal Box / 4 Pot Brake Issues

[Dj_mini 7]

Not tryed it with this new rear set up but it use to yes do you think i have mc issue then? Im using mintex 1155's if that changes it alot?

 

Thanks for your efforts

[Cloverleaf 1]

Changing the pads matters obviously, but if you are using the same pads front and back then the it won't make any difference.

 

What set-up did you have on the rear before?

 

If they were locking first before and you've upgraded them then it'll be worse. I don't think the std m/cyls that are available will give you back enough front bias.

Edited January 27, 2010 by Cloverleaf

[oonip 4]

1.4:1 = 0.7 front, 0.3 rear. or 70% and 30%

 

Now, assuming a weight distribution of 60:40 (front:back) and the ability to do a 1g stop you'll need ratio more like 8:1

 

Do you mean pedal Ratio as 8:1? What pedal load are you basing that on?

 

Also what have you used for C of G, mass, rolling radius and Mue between tyres and road?

 

I will have a proper look tommorrow but i dont think that set up looks to bad at all (although maybe a little over braked all round considering the wieght of your car...)

Edited January 27, 2010 by oonip

[Cloverleaf 1]

1.4:1 = 0.7 front, 0.3 rear. or 70% and 30%

 

 

 

Do you mean pedal Ratio as 8:1? What pedal load are you basing that on?

 

Also what have you used for C of G, mass, rolling radius and Mue between tyres and road?

 

I will have a proper look tommorrow but i dont think that set up looks to bad at all (although maybe a little over braked all round considering the wieght of your car...)

 

No, brake force ratio of 8:1 (front:back). I can't find where I wrote it down now but I'm sure that's what I calculated. It's only a rough guide I used for designing my system. I can't remember what I used for CoG height (something like 0.7m rings a bell). 60:40 static weight distribution, and a 1g stop (probably pretty acurate with sticky tyres). For max braking you're going to end up with little weight on the back so don't need much by the way of braking force.

Edited January 28, 2010 by Cloverleaf

[Cloverleaf 1]

1.4:1 = 0.7 front, 0.3 rear. or 70% and 30%

 

Actually,

 

1.4:1

58:42

 

If you just consider the static state of a std (ish) 205 with a weight dist of 60:40 you need a ratio of 1.5:1.

[Dj_mini 7]

So to get as near as i can to 1.5:1. what mc sizes do you think ill need?

Thanks

[oonip 4]

Ok ive had a good look at this and had made some silly mistakes, Your brake force ratio IS 1.4:1, this equates to 58% bias towards the front of your car. (i got this conversion wrong yesterday as i rushed thorugh it sorry)

 

If you give me you tyre size i could find out your theoretical ideal brake force ratio, this takes into account your weight distribution and all four wheels at the point of locking simultaneously i.e maximum braking capability. and compare it to what you have. You are already within any noticable difference from 1.5:1 (60% front) this could be tweaked with your balance bar. The thought of running an 8:1 balance ratio is ridiculous (88% front bias).

 

With that info i could give you the force at the pedal required to achieve a desired deceleration, i.e. 1g. maybe a bit OTT but it will give you something to compare how your car is actually behaving in real life.

 

So if you want me to have a look just let me know your tyre size. Are they full slicks or road tyres?

[Dj_mini 7]

Blimey this is much more involved than i expected

 

Im using toyo r888 med front soft rear or yoko 048's 195/50/15

[Cloverleaf 1]

Ok ive had a good look at this and had made some silly mistakes, Your brake force ratio IS 1.4:1, this equates to 58% bias towards the front of your car. (i got this conversion wrong yesterday as i rushed thorugh it sorry)

 

If you give me you tyre size i could find out your theoretical ideal brake force ratio, this takes into account your weight distribution and all four wheels at the point of locking simultaneously i.e maximum braking capability. and compare it to what you have. You are already within any noticable difference from 1.5:1 (60% front) this could be tweaked with your balance bar. The thought of running an 8:1 balance ratio is ridiculous (88% front bias).

 

With that info i could give you the force at the pedal required to achieve a desired deceleration, i.e. 1g. maybe a bit OTT but it will give you something to compare how your car is actually behaving in real life.

 

So if you want me to have a look just let me know your tyre size. Are they full slicks or road tyres?

 

This is basically exactly what I said yest including the calculation of dynamic weight transfer. My assumptions used to get 8:1 may not be perfect but they will give you a ball park figure. Don't underestimate the effect of weight transfer in a hot hatch, I think you'll be surprised how much weight transfer you can get with a 1g stop (which isn't OTT with sticky tyres on a track)

 

Then you have the balance bar to adjust your bias to suit conditions and you should be able to get it right most of the time. Most balance bars will give you twice as much force on one m/cyl than the other at the extremes of adjustment.

 

Dan, by running different tyres your calculation will be a bit more complex, but I still think it's a fair assumption.

 

If someone has an accurate CoG position for a 205 (as I guesstimated it!) I'll happily do the calculation again.

Edited January 28, 2010 by Cloverleaf

[oonip 4]

Yea it would be cool to compare results if we are both using the same data, with any luck it wont be too far out... I would imagine it to be closer to 500mm?

 

Oh and by the way i didnt mean a 1G stop was OTT i meant calculating pedal forces etc being OTT.

Edited January 29, 2010 by oonip