1500 fnt discs & 944 rear discs

[Shad Laws]

Hello-

hey Shad cheers for all the help
got a few more questions for you if you dont mind

No problem!


-what is the optimum in terms of braking bias ratio???

Good question. I dunno! :-)

As you can imagine, it depends on a billion things. And, depending on how accurate you want to be, it'll eventually include a contribution due to caliper rigidity and whatnot, too (1-pot calipers are behind on this one).

The way I estimated what would be correct is by looking at comparable, proven setups. A good example is an early 911, which has 48mm front calipers, 38mm rears, and a 19.06mm MC. So, the overall F/R ratio is 1.60:1. The T1 front disc and CB rear is also another proven combo, with 1.38:1. So, as a good starting point, I'd try to get somewhere in between here. Too high of a ratio and the rears become useless. Too low and your rears lock first and your car is out of control. Too low of a ratio can be helped by a proportioning valve; too high can't. Just some considerations.

The 944 NA setup, as intended with the correct MC, gives 1.44:1.


-theres a guy i found running the following setup
a second hand (23mm/19mm) 944 master cylinder,
At the front: VW T1 calipers - 40mm diameter
At the back: Sierra calipers - 43mm diameter
I'll be running the master cylinder 'backwards' with the 23mm section running the rear calipers.
now ive had a go at the maths and ive got a ratio of 1.26:1
back 43mm dia/23 mc (43/23)^2 = 3.495
front 40mm dia/19 mc (40/19)^2 = 4.432
therefore 4.432/3.495 = 1.26:1

Note that the MC sizes are actually in 1/16"s of an inch, hence the use of sizes like 17.46mm, 19.06mm, 20.64mm, 22.23mm, and 23.81mm. That "23" is actually closer to 24... that makes the ratio seem a little higher :-).


i dont know the optimum ratio

There isn't one :-).

The perfect braking system is the one that just *barely* locks the front wheels before the rear ones in every single situation possible.

One danger with really low ratios (high rear bias) is that it may work for *most* situations, but when you really push it in a funny situation (rain, turning, over a bump, heat-soaked pads, cold pads, etc.), it won't.

Take care,