Following a recent thread I thought it would be a good idea to write up a basic thread that may be useful to anyone who wants to consider changing calipers, going from 2 rotors to 1 etc.

I specialise in hydraulics so work with these concepts all the time. Personally, I have not changed my brake set up, and I wouldn't either - but equally so I understand why some people may wish to do this. I am in no way advocating either way, and certainly I do not intend recommending parts or options as, frankly, I have not investigated any of these products. This is intended as an explanation of the underlying principles rather than a "sales" perspective. These principles will apply equally to anybody's products.

To try and simplify the concepts I have made certain assumptions. I understand things are far more complex in the real world, but these assumptions and concepts are perfectly adequate for comparison purposes - i.e what can I expect as a braking effort if I do a certain modification.

Concept 1 : Piston force
The key formula for this is Force = Pressure x Area

Where area is the cross sectional area of the caliper piston. This is calculated using the formula for a circle (pi*(diam)^2)/4

The key things to not about this is as follows:

The force is proportional to the square of the diameter, in other words a small increase in piston diameter makes a big difference.

Where multiple pots are present in the caliper you calculate each piston area and simply sum the areas.

So if you want to change from a 6 piston pot to a 4 piston pot or vice versa, simply calculate the total area.

If you have a reduction in the area (for example go from 2 calipers to 1), the top formula tells you that you need to increase the pressure to compensate for the reduction in area. This means that higher loads are placed on the caliper, caliper mount and seals. It is not possible to say what the impact of this will be without analysing each specific example but should be considered.

To get the higher pressure you will have to change your master cylinder.

This is the first part of the calculation.

The second part is to calculate your brake torque.

Torque = Force x rotor radius
where force is as calcuated above

So, if you remove one caliper, you "should" double the pressure to get the same brake force. If you keep the same master cylinder (and hence pressure) you could double the diameter of the rotor and end up with the same braking force.

The above concepts are fairly straightforward to understand. One difficulty is figuring out what the pressure in the system is. You do not need to know this if you are simply comparing one system to another, but if you do intend changing master cylinders then you really do need to find out what the system pressures are for the original vs the new.

One final thing which I think is really important. I am not privvy to the exact algorithms that are used in the ABS control system but what I do know is that it works by modulating the system pressure. From the first part of this post it is clear that changing the total area of the pistons on the caliper(s) leads to a change in the pressure requirement to achieve the same brake force. If the ABS system has not been tuned for this you could get some very "interesting" results. I am sure there are those out there that have done this and will argue that everything works perfectly - that may well be true but I, for one, would certainly never contemplate taking THAT risk!