School me on disc brakes

[teledan]

So I understand the basic concept of the disc brake but I am a bit unclear on a few things and was wondering if someone could enlighten me. I know there are floating calipers and fixed calipers and there are floating discs and fixed discs but when would you use one and not the other? Would a floating caliper always be used with a fixed rotor and a fixed caliper with a floating rotor? Or could you use a fixed caliper with a fixed rotor? Or a floating caliper with a floating rotor? Also, is there such a thing as a floating caliper that has opposed pistons? Or do they always just have pistons on one side? Please pardon my ignorance.

 

[xb33bsa]

calipers ALWAYS have friction pads on both sides,pinching da disc,except some simple airplane lashes
you want the pads to wear evenly so below is pretty much written in stone:
a caliper with a piston/pistons on only one side MUST have a floating mount lashup
a caliper with a piston/pistons on both sides does not need to be floating mount lashup and almost never is
some most all new stuff front and even rear discs are floating to help avoid heat warpage,solid mount front disc setups are pretty much obsolete
floating or non floating discs are suitable for most any caliper lash doesn't really care

 

[teledan]

Ok thanks. So a fixed rotor would be fine with a fixed caliper (opposed pistons), but I imagine I would just want to make sure the rotor is as centered between the pads as possible? I am curious because I am researching options for a rear disc brake on my Yamaha XT500. I am leaning towards running a disc rear wheel from an SR500 (fixed rotor) and I'll probably use a caliper off of some type of sport bike. It sounds like either type of caliper (fixed or floating) would work with fixed rotors. What are the pros/cons of each type of caliper (floating vs fixed)? I have heard that floating calipers can stick and that can cause problems, anything else? Does one design provide more braking power over the other? Or are they pretty comparable? I imagine it mainly depends on the number/size of pistons.

 

[xb33bsa]

I wuld just use what fits yes center the caliper
a fixed caliper is much wider on the inside so it may cause clearance ishoes

 

[teledan]

Yeah, that is one thing I was worried about with a fixed caliper. I am thinking either an opposed piston fixed caliper off of a katana/sv650 (if it will clear the wheel) or a single piston floating caliper off of a CBR or an R6/R1.

 

[o1marc]

I use to get this argument when I worked the brake caliper department at Rebco Racing Enterprises on how closely centered the fixed caliper had to be on an opposing piston caliper. They said it had to be absolutely centered. I don't think it does. They claimed if it wasn't it would put more pressure on the closer side than the other. I thought OMG how dumb are these engineers. Once you put pressure to the system the closer pistons will come out and make contact with the rotor and put no more pressure on the rotor than the pressure needed to overcome the friction of the seals on the opposing pistons until they touch the rotor and then evenly distribute the pressure to both sides. Once the pressure is on the pistons and rotor the system doesn't care where the caliper is. Yes the pistons on one side will protrude more than the other side but seldom can you actually run out of pad enough to pop a piston from it's bore. As long as the caliper is shimmed close to center and misses the spokes you should be good. The purpose of floating rotors is to have lighter rotor carriers so help eliminate expansion rate of the whole rotor during heat up and cool down and has no bearing on whether the caliper is floating or fixed. Keep in mind this offset is only an issue the first time you put pressure to the system. Once you put pressure to the system the 2, 4, or 6 pistons will retract equally centering the rotor.
Not all fixed calipers are wider on the inside, depends on the calipers. My calipers are for a narrow front end and are actually thinner on the inside than the outside and run a shorter piston.

 

[teledan]

That definitely makes sense, thanks. What front calipers are you running?

 

[o1marc]

I'm running a completely custom fabbed set up of Hawg Halter 4 piston calipers (HawgHalters.com). I had to take the calipers and split them and make a bracket that sandwiches in bewteen the halves to make the caliper locate properly on my Kimtab/Ceriani set up. With the standard Hawg Halter caliper the inside hit my spokes so I was going to have them machine enough off the back side at an angle just enough material to clear the spokes. It's was when I asked Mark Thompson, the owner to do this that he remembered he had done a run of "narrow" calipers for some custom orders and had some left over NOS calipers. He pulled a set off the shelf and gave me the inside halves and it solved my issue without anymore customizing needed. You can see in the pic how the piston bores on the back side don't stick out as far as the front. I know you are probably looking for a stock type caliper to solve your issue but my application shows that when you converting to different things where there is a will there is a way. Fortunately Hawg Halters is 12 miles from my shop and I have been affiliated with them since the original owner started the business after making the caliper bodies for Rebco when I worked there. HHI is a sponsor on my XR1327 Sportster. On my set up due the 1/8" thick rotor I use I opted for the standard depth piston and not the narrow as you can see in the pic.

 

[Karlloss]

I use to get this argument when I worked the brake caliper department at Rebco Racing Enterprises on how closely centered the fixed caliper had to be on an opposing piston caliper. They said it had to be absolutely centered. I don't think it does. They claimed if it wasn't it would put more pressure on the closer side than the other. I thought OMG how dumb are these engineers. Once you put pressure to the system the closer pistons will come out and make contact with the rotor and put no more pressure on the rotor than the pressure needed to overcome the friction of the seals on the opposing pistons until they touch the rotor and then evenly distribute the pressure to both sides. Once the pressure is on the pistons and rotor the system doesn't care where the caliper is. Yes the pistons on one side will protrude more than the other side but seldom can you actually run out of pad enough to pop a piston from it's bore. As long as the caliper is shimmed close to center and misses the spokes you should be good. The purpose of floating rotors is to have lighter rotor carriers so help eliminate expansion rate of the whole rotor during heat up and cool down and has no bearing on whether the caliper is floating or fixed. Keep in mind this offset is only an issue the first time you put pressure to the system. Once you put pressure to the system the 2, 4, or 6 pistons will retract equally centering the rotor.
Not all fixed calipers are wider on the inside, depends on the calipers. My calipers are for a narrow front end and are actually thinner on the inside than the outside and run a shorter piston.

Absolutely bang on. My Speed Triple has Brembo radial mount calipers and they are definitely not centred, in fact one side of the caliper body is so close to the disc that I'm surprised it didn't rub on the disc. Although it has floating discs, this is not only for the heat reduction, it also allows for slight warping of the disc due to heat build up and tolerances in manufacturing. One of the quickest ways to warp a disc is to hold it on the brake when stationary when the discs are very hot after hard braking, as the pads also hold heat and the pads 'mask' the section of disc from the air, thus cooling at a different rate.