Sizing wilwood brake systems

[eke_zetec_RWD]

I'm going to replace the brakes on my lotus all round. Will use all wilwood stuff from the states.

Does anyone know if I can run the same 4 pot caliper and rotor on all 4 corners and then just use a 3/4 cylinder for the rear and a 5/8 for the front?

Has a tilton pedal box in it.

I will make floating disc hats.

I was thinking discs

http://r.ebay.com/uUOrne

Calipers

http://r.ebay.com/XKdHZn

I

[e30-323ti]

If you match the piston sectional area to the calipers you are replacing, you won't need to mess with the master cylinder sizing.

If you like the balance how it is, keep the piston proportions as they are (calipers & MC's).

 

Wilwood do the the 'same' calipers with various piston sizes, so you should be able to find something that suits.

[eke_zetec_RWD]

I got drums on the rear ATM. And princess 4 pots on the front with 260mm BMW discs.

[Rhyscar]

Hey jase you get anywhere with this? Had an issue with brakes on a rally car last week so sat down and worked out the master sizes/front rear brake balance - similar to but reverse to what your wanting to figure out..

Ill do some calcs after work and explain when i have 5mins.

[eke_zetec_RWD]

I just winged it a. 4 pots all round. Ordered small pistons for the back and bigger ones for the front. Should be here this week.

[Rhyscar]

Sweet what size master cylinders you got for?

[e30-323ti]

Just for reference For my E30 with 4pots all round, Tilton Sized the below for a 5.5:1 floor mounted pedal box (unboosted of course).

 

323mm rotors, Front Calipers run 40/36, and a 7/10" MC (75 series)

312mm rotors, Rear Calipers run 30/28, and a 3/4" MC (75 series)

 

Was previously running the same rotors / calipers on a 1" (MC Boosted, ~4:1 pedal ratio IIRC)

[Rhyscar]

So you need to decide on a front/rear balance you are aiming for. most rwd/4wd use about 65-35 front-rear split although I think you could get away with a bit more rear considering your car has a lot of weight back in the car and you have very little weight transfer/suspsension travel.

 

This doesn't take into account the efficiencies of front/rear rotors and calipers and assumes both front and rear friction coefficients/disc conditions are constant.

 

Work backwards through the equations below, keep in mind the larger the master cylinder, the more travel and force required but it gives a more direct pedal feel, of course this can be offset by changing the pedal ratio if needed but easiest to keep it simple. It is always best to set up the pedal box so balance bar is centred so you have adjustment each way depending on tyres, fuel loads, conditions etc etc. 

 

 

Hope this helps. worked well for rally car and will be setting up the pedal box MC's on the ae82 using this method.. also very easy to work backwards and compare front/rear balance of other cars. i.e. wanted to set rally car up with same brake balance as a late model evo and it worked awesomely.

 

 

[xsspeed]

Didnt look at maths but doesnt larger master cyl give you less travel but more force vs smaller bore which requires less force but more travel? (iirc of course)

[Rhyscar]

yeah I always get mixed up as well but you got to remember 

 

Force = Pressure x Area

 

in a hydraulic system pressure throughout the system stays constant, meaning the ratio between the area of the master cylinder piston size and the caliper piston size is equal to the ratio the force is increased by. 

[Brock-Lee]

larger area = larger volume of oil moved for the same piston displacement so smaller travel but as the area of the master piston is increased to create the same pressure in the system(so the same braking force at the wheels) a greater force is required.

 

Larger master = shorter harder pedal

 

smaller master = longer softer pedal

 

Assuming you leave everything else as is of course.

 

I will throw up an IIRC just to be sure haha

[xsspeed]

same reason I threw up an iirc lol

[xsspeed]

 

 

keep in mind the larger the master cylinder, the more travel and force required but it gives a more direct pedal feel, 

 

 

 

This is what I was questioning btw - I think its less travel (due to fluid displacement) but more force (from your leg) required due to larger bore to generate pressure

[Brock-Lee]

me tooo

[FuzzayD]

Well not always a shorter pedal more like less force required to apply with a large increase ration for example if you have a 50mm piston in the master cylinder and 100mm piston in the caliper the manual pedal effort you use is multiplied so if you used 3000newtons of force  on the pedal the force being applied by the caliper piston is 6000 newtons. if you have different sized pistons in front to rear calipers they would move at different rates so a biased adjuster would be needed to time them to apply how you would want

[eke_zetec_RWD]

That's a big sentence! And very wrong maths but you have the idea.

[Rhyscar]

ah yeah dammit somewhere in that spiel I got mixed up mybad! maths works though just haven't figured out a way of calculating pedal feel yet without going too deep into pedal ratios etc which can sometimes be an endless loop of simultaneous equations trying to get travel and force to work out. better to keep it simple. plus I suck at simultaneous equations since I stopped doing calculus at uni.. 

 

hope it helps anyway..