Brake cylinder setup

Hi All

I'm looking at changing up my cylinders on my pedal box in the car as I have a long pedal and it doesn't fill me with confidence on the track. I've watched the brake coarse and got some really good information, I'm now going through the spreadsheet that was attached to see what a good starting setup would be and how it compares to my current setup.

I have an evo 6 and have a set of Ksport 356mm 8pot up front and the standard 2 pot brembos on the rear, both running EBC yellow stuff pads. As I have 8 pots on front and the spreadsheet only had 6 pots I modified the sheet for the extra pistons as well as updating the calculations throughout. Here is a picture of the setup.

when I change the various cylinder options I'm having difficulty in getting the graph to align in the green when the 4 feedback blocks are also green as below.

I've changed several of the values and can see how it effects the results but I'm struggling to seem what would be the best compromise if I have to make one. It also seems like I potentially need to run a proportioning value to help with the graph?

I'm not sure what you're puzzled by - the spreadsheet you're using clearly shows you need a larger rear master cylinder, which will limit the pressure and also reduce travel of that cylinder and so reduce pedal travel.

I'd also suggest checking the pedal ratio, 4.5 seems a little low for an un-assisted pedal?

Depending on your physical strength, if you can apply a bit more force - 45 kg is little more than the load of an average person standing on both feet - you can run larger master cylinders, on top of the increase mentioned above - and that will also reduce pedal travel.

Other factors are checking you have a rigid mounting for the pedal box, the discs are freely floating and/or flat (those cause 'knock back'), the calipers aren't flexing, the pads aren't compressing, you're using a good brand of braided hoses? Oh, what brake fluid are you using, that may be a factor?

Hi Gord, thanks for the reply. I previously change the cylinder size to a larger one but I get the "DIFFERENCE IN MASTER CYLINDER STROKE MAY LEAD TO BIAS MIGRATION" so I thought that was a bad thing as I'm guessing it means inconsistent front to rear braking??

I re-measured the pedal and yes you were right the ratio is more like 5:1.

These are the results with changing to 5:1 and increasing the force to 55kg.

I have braided lines through out and am using RBF600 brake fluid.

If the "BIAS MIGRATION" is not too much to worry about then I'll probably try this setup as see how it goes.

this is my current setup with the cylinders I have for comparison

Hi Andrew,

The difference in master cylinder travel isn't ideal, but in my experience it doesn't make as much difference as the other factors, so that's usually where I would make the compromise if it was 8mm difference like you're case. I probably wouldn't want much more though.

I'd try moving up a size or 2 in the rear cylinder and see how you go. This should decrease pressure the the rear for the same input, helping your bias and also make the pedal shorter.

"Bias migration", as such and in context, would appear to reference the potential change in the pedal balance beam, and push/pull rods geometry during the travel.

Normal practice is to try and have the balance beam centred in the available adjustment range, and have approximately equal master cylinder travel, and normal practice is to change the master cylinder(s) bore sizes, the caliper piston area, the mean swept radius of the discs and/or the co-efficient of the brake pads.