UKC

Hello again all,

After a bit of information regarding Brake Kits.

Can anyone offer a decent explaination of why the greater "pot" a brake kit is, the greater stopping power/less brake fade. Or perhaps why bigger pistons are more important than more.

My guess is that it all boils down to Pounds Per Square Inch of pressure (PPSI). Meaning that the less pistons (pots) the higher amount of PPSI which then means greater stopping power. However the greater the amount of pistons, the greater amount of cooling and thus less brake fade. Also, the greater the amount of pistons, the greater the amount of surface area of the caliper in contact with the disk. But surely larger pistons can do the same job whilst keeping a higher PPSI?

Cheers for any info from the racers and mechanics out there!

In reply to Richiehill: Hydraulic pressure is equal in a closed system. Therefore the pressure applied at the pedal is the same as that applied at the pads. The differences are the amount of area this force is being applied with at the brake pad. Brake pistons are almost always circular as this is the easiest configuration to seal. Therefore more pots make it easier to apply more pressure as this has to be spread over an area of disc. This is as opposed to it being applied in one location as would be the case with a single large piston which would be less ideal. Also with the disc caliper design it's possible to have a more progressive brake feel through multiple pistons.

In reply to Richiehill:

Frank's done the force bit.

More pots = more metal as a heat sink and, probably, more surface area for cooling = less brake fade.

Then you get onto things like cross-drilled and grooved disks that are needed for larger brake pads to let the gases generated escape, etc

In reply to LastBoyScout:

Racing brakes tend to use stainless (or other exotic alloy) cylinders 'inside out' with the pot wall rather than the face pushing the pad to minimise heat transfer into the fluid. Ideally brake heat is transfered into the air flowing through the disk, heat flow into the caliper and hub is minimised.

Large diameter 'single pot' floating calipers are cheap as they minimise the amount of precision machining and finishing required. They are also heavy, tall (radially) and lack rigidity.

Non-floating calipers can gain rigidity and lose weight as the slider mechanism is eliminated. Multi (4+) pot calipers are radially shorter (same effective piston area from smaller pistons) putting more pad at the outer edge of the disk enhancing brake torque (for a given pedal pressure) and feel. It also allows the center of the disk to be lighter (typically replaced with an alloy carrier). Smaller diameter pistons have less 'overhang' (radially inwards) from the supporting outer edge of the caliper increasing effective stiffness of the structure and enhancing brake feel. Alternatively stiffness can be maintained while material weight is lost from the caliper by using multiple small cylinders close to the supporting backbone of the caliper. Pads supported by multiple pistons require lighter backing plates. Multi-cylinder calipers are generally designed so the pads can be replaced quickly and without removing the caliper (usually a simple set of pins or a clip retains them) which is important for endurance racing.

Mostly on a road car: They look great!

jk

In reply to jkarran:

All backed up by the fact that 4 pot calipers and even 6 pots have been used on motorbikes (where weight, size and inertia are even greater considerations than on cars) for the past 20 years.

They do look great, especially the machined from solid billet ones. :0)

http://www.google.co.uk/imgres?imgurl=http://www.4hd.net/images/products_fu...

In reply to teflonpete:

"All backed up by the fact that 4 pot calipers and even 6 pots have been used on motorbikes"

You can get 6 pot MTB brakes, slightly overkill for most people.

In reply to Richiehill:

Cheers for your answers so far; it's pretty much what I expected in that, the more pistons you have, the faster the heat dissipation.

So is there, and if so where does it lie, an advantage when comparing the following big brake kits:

http://www.awesomegti.com/car/vw/scirocco/vw-scirocco-ii-front-330x26-tarox...

http://www.awesomegti.com/car/vw/scirocco/brembo-gran-turismo-brake-kit-sci...

http://www.awesomegti.com/car/vw/scirocco/forge-big-brake-kit-330mm-17-or-l...

Cheers.

In reply to jkarran: hehehe VAG....

In reply to Richiehill:


The caliper design has not got a right lot to do with heat dissipation, it's mostly a stiffness/weight/pedal-feel/packaging issue.

Big disks increase braking torque, heat sinking (short term) and heat dissipation.


Why do you think you need big brakes for your Scirocco, are you racing it or caning it so hard they're getting unreliable? Assuming it's a road car I'd go for the one (if any) that has proper dust/moisture seals and reliable service parts availability.

To be honest assuming you do have overheating problems I'd look first at the driving then make sure the fluid is in tip top condition then probably start by changing the stock pads for something a little more able to handle the heat while remaining civilized and predictable for road use. Much cheaper and you maintain the reliability of the stock VAG set-up.

If you're dead set on the big brake kit as your only option I don't know which one I'd go for, they can be a bit of a minefield in terms of fit, quality and reliability. Is there a VAG forum where you can actually find some longer term user reviews?

jk

In reply to Richiehill: Don't go with the Tarox, they have strange ideas about piston sealing and you will have a devil of a time with pad knock off as they have decided for some reason not to use square section seals. They also 'know' something every other manufacturer of calipers doesn't with respect to the position and size of the pistons Quirky calipers. Their discs are OK but you will be stuck with using their friction material

EBC pads are definitely the budget option, I'd ask for those to be traded out and get Mintex, Performance friction, Pagid or Ferodo supplied

In reply to jkarran: I'm a mod on my Forum. I was just having a discussion with another mod who thought it was about the size of the piston rather than the amount. I was trying to get the actual facts rather than best guess info.

My car wont be receiving any upgraded brakes. I'm skint as it is! I'll be getting new pads in the next 12 months so any recommendations for these will be welcomed! .

Cheers for your brains JK! I chuffing love UKC sometimes.... Want to find out something completely random? Ask on UKC! There's bound to be someone that will know!