Originally Posted by Bram

Cool. I mis read your previous post and measurements. So that previous reply i made, didnt make any sense, hence why i deleted it. You must have already read it when you typed up this post ive quoted.

I appreciate your measurements. Always good to have the data there.

Further to the discussion. Pad size/area makes absolutely zero difference to braking torque. (It does however make a difference to pad life and heat handling capabilities and weight)

And caliper size/length material and weight etc also makes bugger all difference to braking torque. It does however affect things like caliper rigidity, which influences pad wear characteristics. Aswell as heat handling, and also the weight.

With braking. The important factors that effect the effectiveness of the system are :

Pedal ratio (or lever ratio in the case of the hydro handbrake) this is the mechanical force multiplication to the master cylinder by way of the pedal (lever) mechanism.

Master cylinder bore. The area of the master cylinder coupled with the force applied to it will result in the hydraulic pressure generated. Pressure = force / area. Hence SMALLER master cylinders generate MORE pressure for a same given force input. But the trade off is longer pedal travel and worse pedal feel because they move less volume.

Brake caliper piston area. The LARGER the pistons, the GREATER the braking force, because a larger piston has more area for the hydraulic pressure to act on. Its interesting to note that opposed piston calipers dont make any more braking force than sliding calipers with half as many pistons, given the same piston size. But opposed piston calipers do usually give better rigidity and weight savings, dont have the same issues with sliding mechanism, And look way better too.

Radius that the brake caliper/pads are acting on. This is effectively the disc diameter. Bigger diameter means more braking torque. More importantly with racing, it gives better heat handling due to bigger/heavier disc and more surface area to dissipate the heat away. With the trade off being more rotating mass.

And lastly. Brake pad friction co-efficient. Also called 'mu'. This is effectively how grippy the pads are. This gets pretty complex with various pad compounds and is greatly effected by heat etc.


In my quest to do a wicked skid in a Subaru. Ive tried playing with the lever ratio. With both the first twin cylinder arrangement i had, and also on the STi tandem cylinder.

Ive tried changing the master cylinder bore. (By going from a twin side by side arangement with 0.625" bores, to a tandem arrangement with a slightly larger 0.7" bore.) Even though the STi tandem is bigger bore than the twins. Its inline design does not double its surface area like the twins do.

I havent tried changing the rear calipers yet. Its a fair bit of added expense due to probably changing pads, discs rotors, and lines at the same time. But its not something im inpartial to, if i cant fix it other ways. Im hoping that maybe the Nissan calipers discussed before would be a straight swap onto my existing rotors, lines and even maybe pads. (Fingers crossed) i dont paricularily want to change rotors as i currently have 3 piece Biot rear rotors. And they cost a pretty penny. And they are sexy as.

A cheaper alternative could be trying a more aggressive rear pad. I currently have Cosworth street pads.




Oh yeah. While we are talking about brakes. These came in the mail yesterday. 355mm front Wilwood rotors. Straight swap onto my existing rotor hats. (With new bolts for safety) Still waiting on the hardware to space the calipers mounts out to suit. i opted for the slotted Spec 37 instead of the wanky electro coated, SRP drilled and slotted rotors. The drilled rotors are for 'show' and are considered a bad choice for track work. Unlike the old days of racing. The drill holes are purely an aesthetic thing now with advances in pad compounds that do not require drill holes to help with out gassing.

Check out how big they are compared to a stock standard Forester rear disc. If they were a few MM bigger, i could fit the entire Forester rotor INSIDE the Wilwood rotor.