30 replies to this topic

[Winstar]

I have the AP four pots and personally i dont think the breaking itself is any better. Maybe they will last better without overheating/brake fade but actual braking force doesn't seem any better.

in fact on the std ferrod pads I found it worse than on my NA with mintex 1144's only really imporved when I swopped to pagids.

one thing I didn't like about them was the increase in pedle travel required due to the increased volume of fluid to move the pad. IIRC Chris_uk run 4 pots up front and 2 pot on a bracket at the rear and was looking to change the master cylinder as again adding the 2 pots increases the fluid volume needed to move the pads.

Edited by Winstar, 04 September 2011 - 08:21 AM.

[Dave E]

Apparently the bigger master cylinder from a Subaru Impreza or Forester fits with slight modification. .

[bunsenburner]

I have the AP four pots and personally i dont think the breaking itself is any better. Maybe they will last better without overheating/brake fade but actual braking force doesn't seem any better.

I could be wrong here, but I believe for the same pedal force you would get less clamping pressure with 4pots compared to the 2 pots due to the fluid having to move an extra pair of pistons which could have a bigger volume than the 2pots.

That aside, even with the same pad force as the 2pots the only thing the 4pots gain you is a bigger pad area to reduce the wear rate.

A pad the size of a pin head would give the same stopping 'power' as a pad the size of the disc (assuming both had the same leverage point. Just the pin head size pad would last milliseconds and the disc size pad would last longer than stonehenge

I would have thought a larger pad surface area would have more grip, therefore more stopping power. The extra pressure required to apply the larger pad makes sense however.

The basic calculation for friction dosent require Area to be included.
http://www.physlink....perts/ae140.cfm

But that assumes the same amount of pressure is divided over the larger area. If you push harder on the pedal you can compensate for that.

[slindborg]

I have the AP four pots and personally i dont think the breaking itself is any better. Maybe they will last better without overheating/brake fade but actual braking force doesn't seem any better.

I could be wrong here, but I believe for the same pedal force you would get less clamping pressure with 4pots compared to the 2 pots due to the fluid having to move an extra pair of pistons which could have a bigger volume than the 2pots.

That aside, even with the same pad force as the 2pots the only thing the 4pots gain you is a bigger pad area to reduce the wear rate.

A pad the size of a pin head would give the same stopping 'power' as a pad the size of the disc (assuming both had the same leverage point. Just the pin head size pad would last milliseconds and the disc size pad would last longer than stonehenge

I would have thought a larger pad surface area would have more grip, therefore more stopping power. The extra pressure required to apply the larger pad makes sense however.

The basic calculation for friction dosent require Area to be included.
http://www.physlink....perts/ae140.cfm

But that assumes the same amount of pressure is divided over the larger area. If you push harder on the pedal you can compensate for that.

I guess, but then you arent comparing equal experiments so to speak.

ie Lets assume the pedal travel vs pressure seen at the caliper is linear. With the 2pot you will always have greater pressure per area on the pad compared to the 4pot (unless the 4pot pistons total area was less than the 2pot ones).

Fundamentally the 4pot change is for longer pad life and thats almost it

[joshua]

Pressure in the caliper is not divided by a greater piston area but remains constant across the entire piston, hence why it's measured in psi etc. Twice the piston size gives twice the clamping pressure for the same pedal pressure.

[slindborg]

Ah yes, just re read some hydraulics stuff. The fluid flow/volume of fluid needed to move it increases, this giving shitty pedal with larger pistons.

[bunsenburner]

In that case perhaps the advantage is in the efficiency of the pads depending on temperature. A greater pad surface area would be cooler therefore having more grip (or rather not losing grip when they get too hot). So the larger brakes don't grip more they just do a better job of keeping everything at a lower temperature so they can grip more

[cicastol]

A question to those that have the four pot fronts and two pot (front calipers on rear) on rear set up.

thanks

I've put the 4 pot caliper on front first,no more stopping power but absolutly no fade even on road/track that push really hard on brakes,after i moved with the 2 pot caliper on rear 308mm ali belled disc with ap biasing valve and abs removed.
Now the stopping power is really improved over the standard setup, no comparison!

[Aerodynamic]

A question to those that have the four pot fronts and two pot (front calipers on rear) on rear set up.

thanks

I've put the 4 pot caliper on front first,no more stopping power but absolutly no fade even on road/track that push really hard on brakes,after i moved with the 2 pot caliper on rear 308mm ali belled disc with ap biasing valve and abs removed.
Now the stopping power is really improved over the standard setup, no comparison!

Regarding the 4 pot calipers usually fitted on Elises, you have every piston is slightly smaler then on std 2 pot caliper,tho the total area is a little bit larger.

But do you feel much difference in pedel movement, just changing front calipers?

Where do I find 308mm ali belled brake disc?

[cicastol]

I've taken the 308 ali belled disc from CTF (http://www.centertecnofreno.it/) pedal travel is no more than 1cm longer due to the piston larger area.

[chris_uk]

I never bothered with the different master cylinder as i purchased the exige 4pots instead. Originally i had 4pot front with 330mm alibelled discs and the brakes were fine i think i could remember locking the wheels up a couple of times trying them out, i then put the 2pots on the rears and still could lock the wheels on the front up, whether they helped in actually stopping quicker i never tested, it didnt feel much if any better tbh. After having the 2 pots fitted to the back i started to get long pedal travel this was ok when the pads were new but when they were about 1/2 way down i could get my foot all the way to the floor which was horrible tbh but you could live with it. i then upgraded to the ap racing ones (that joe had in that pic, although they have 4 pistons they have 2 tiny ones that accompany the 2 large ones) and the pedal travel issue has gone (i am using new pads tho so might come back) i also had new fluid put in and CL5+'s but since using 16" wheels ive had to downsize the discs to 308mm (probably could use 312mm if you could find some to fit) the braking now is far far superior to what i had before and interestingly its very rare i lock up the wheels even under very hard braking from 120mph. the brakes are much more progressive than they were before and feel a lot nicer to actually use. at both anglesey trackdays ive done i never got any fade or any negative feelings it juat felt superb every lap. I can't break it all down into formulas or equasions etc only opinion and how it feels. DW1 touched on it in his post, the braking is down to your tyres, but its also down to the pads you use. Ferodo 2500 pads were ok but they are nothing like the CL5+'s i now have. Everyone ive taken out or have driven it on track (JJJ) have all commented on the brakes and how well they feel. as far as the rear handbrake caliper goes, i agree its too big and heavy but i just cant be bothered to change it now.