2001CamaroGuy

iTrader: (6)

After working out all the numbers, it looks like one can actually get more clamping force out of most 4 piston calipers than one could out of 6 piston versions.

The reason being that (use Wilwood calipers for example) the effective piston area of a 6 piston is limited by it's staggered bore vs. a standard 4 piston having symmetrical bore.

ex:

Wilwood SL6R bores are 1.62"/1.12"/1.12" which gives an effective area of 4.03"

vs.

Wilwood SL4R bores are 1.75"/1.75" which gives an effective area of 4.81"


Now when one runs the numbers of line pressure, rotor size, pad compound, etc., the differences are quite a bit.


As I understand it, the entire idea behind having the staggered bore of the 6 piston is to help with pad wear under extreme conditions but how serious is this? At what point does the 6 piston actually become better than the 4 because based on numbers only, the 4 would result in a much higher clamp load at the same pedal pressure.

mitchntx

iTrader: (14)

I can lock the tires up with my 2 piston calipers.

How much more clamping force do I need?

2001CamaroGuy

iTrader: (6)

and I can't, I don't have power brakes.....but that wasn't the question....

so thanks for the pointless post....

trackbird

iTrader: (4)

Wow. You ask for help, leave out very important information and get smart when you get an answer that would apply to 99% of the cars out there with this question, but not as much your one specific car with the condition that was critically omitted in the first place.

Well, it might have also been helpful if you had mentioned that you were running manual brakes on this car in your first post. It would have made your first post just a bit more useful to anyone who was trying to help solve problem. That little fact changes the question considerably. I was originally going to explain that the 4 piston kits could pull the bias forward a good bit (unless the rotor size was adjusted to keep things balanced), however, you probably need outright clamp load more than a power brake car. But we wouldn't know that unless you considered it important enough to tell us in the first place.

This is one of those rare cases where I'd suggest getting Wilwood on the phone, telling them what master cylinder bore size you have and what car, etc. They will probably ask for a bunch of information and try to guide you towards something for your application.

If this is a drag car, you might also look up Aerospace brakes. However, if it's a street car as well, be careful which brakes you buy from them. Make sure they know that it's driven, how far and how often.

chicane

Your next question should be about clamping force vs pad surface area. Then, pad surface area vs swept area... keeping the PVR in mind.

Clamping load isnt the 'tell all' about how your system is going to perform. Just because your numbers show the posibility of a higer clamping load, doesnt mean that the caliper is going to be stiff enough to harness that pressure/force.

Anyway, how serious is pad taper ?? Well, it can happen at street level braking, all the way up to professional track racing.

The six piston calipers have inhearent props from many different view points. Reduced taper, larger pads for better PSA to SA and their natural ability to use a larger rotor. Just the mere fact that the load can be spread over a greater area by splitting up the force, to the pad itself, from mulitiple pistons brings more light on how pad surface area to swept area lends much more to your question than that of simple clamping force alone.

trackbird

iTrader: (4)

For the second part of your question.

I'm running Wilwood SL6 calipers on my car. For autocross use, the pad wear was decent, but as I switched to more aggressive pad compounds and did more street driving, I found that the "grip" of the pads would still pull them towards the rotor and they can still wind up heavily tapered. With harder use, the differential bores will help keep the pads wearing even, with light use, or brake pads with high friction coefficients, you can still see considerable pad taper. The differential bore essentially a "best guess" at what will keep "pad a" wearing well under "condition b". If you fall outside that range, as I did, you'll still see pad taper. So, my experience says that you shouldn't get too hung up on 6 piston vs 4 piston for a car that sees street use. For all out racing when every stop is nearly max effort, it can work better. But on the street an aggressive pad will "work" well enough at very light pressures that the main benefit of the staggered bores is lost.

2001CamaroGuy

iTrader: (6)

But you see, nowhere did I even mention a car. The information I'm looking for is not vehicle specific. The question was entirely caliper dynamics, clamp force, and (then as others pointed out) pad area.

Not only was his reply not helpful in answering the question (it didn't even attempt to) but was pretty much a "why change anything" answer.

see...this is helpful....

I never stopped to think about the fact that a 6piston caliper has a larger pad which can thus have more area to grab the rotor.......hmmmm....


the reason I didn't go into specifics about MY car was because I was looking for WHY and HOW different calipers (specifically piston number comparison) perform differently and their advantages.....I knew if I started putting all this info in about my car, people would be more likely to just give "advice" vs. "information"....


Do you think the differential bore helped at all in your case?

We are talking about the leading edge of the pad "digging into the rotor" and thus wearing faster correct? SOMEWHERE (way back in time) I seem to remember reading something about some race teams actually "cutting/machining" their pads to have less "area" on the leading edge to help prevent this "digging effect."

2001CamaroGuy

iTrader: (6)

I guess since it has come up (and will come up again), AT CURRENT, I'm working up the brakes for my Camaro. It will be a road race vehicle (with the ability to still daily drive on NICE days).

I'm currently fabbing up a 3-link 12bolt (extended LCAs and a centrally located UCA off the center section). The pedal assembly is a Wilwood triple master setup with a 6.25:1 pedal ratio, a 7/8" bore clutch master, and then was THINKING 1" masters for the brakes (though that is still to be finalized). As far as the shocks/springs, I'm currently running LGs Coilovers but once I really get into it, I MIGHT play with the spring/valve rates (time will tell).

trackbird

iTrader: (4)

Well, Mitch, Chicane, Foxxtron and many others try to get to the root of the problem. Sometimes it's an effort to protect people from themselves. When someone starts asking about clamp load, it's easy to think they are looking for better braking on one of these cars. So, we get to the lecture about rotors and heat sink area and repeated stops being more important than outright clamp load (in most cases). Without knowing that you have manual brakes, it's pretty easy to start down that path. So, it's helpful to know why you're looking for increased clamping load. It helps put the question in perspective.


I'm not sure about that. We now have the information about your car and we are still trying to give you information.

With the friction level of the pads I was running, the pedal pressure in normal driving was minimal. So, even if there is a 50% gain of clamping force on the larger bore (as an example), it doesn't make much difference when you're running something really low like 1 lb of pressure (as an example, it will be higher as you know, but consider low pressure operation). In my experience, the pressures seemed so low that the difference in bore sizes had minimal impact on pad wear in actual operation. However, I've changed pads and this set seems to be wearing better (they are less aggressive, but still work well). So, if you stick to less aggressive pad compounds for street use, they seem to wear better. If you go racing, you might be able to use the more aggressive pads and keep the wear in check.

Again, this is just my experience, others may have different results.

trackbird

iTrader: (4)

The AV8SS car that I crew chief for is running 4 piston wilwoods with a wilwood triple maste cylinder setup. I forget what bore sizes we have in there though. On the other hand, we've always had brake issues with that car as well.....

2001CamaroGuy

iTrader: (6)

IF I understand what you are saying, at the "typical" lower pedal pressures and less aggressive pad compounds found on "street vehicles", the differential bore does not seem to make much difference as pad taper (and overall pad wear) are quite low.

HOWEVER under heavy load/aggressive compound conditions, the staggered bore tends to help the pad "live" a bit longer (not taper as fast).

Am I fallowing correctly?


PS. I guess I was a bit "blunt" on my first reply but it felt like his reply was more of a "cut/changing brakes is stupid" reply vs. an attempt to actually answer a question (I get very pissed off when I see people just post "crap" when others are honestly looking for info/help).

Carlos01SS

iTrader: (4)

I don't know if this helps or not, but I contacted http://www.revolutionbrake.com/index.html formally known as precision brakes and spoke with someone there, he compared the 6-piston setup as brakes an endurance racer would choose vs. the 4 piston for a sprint race, if that makes sense...He said that and endurance racer requires brakes that can really clamp down hard yet be somewhat more gentle on the pads as the 6-piston will wear the pads more evenly...

mitchntx

iTrader: (14)

Your first post dealt simply with clamping force and how to get more.

My response was an attempt to get you to think that there more to braking performance than just clamping force.

You shouldn't get so worked up over insignificant things like the internet.

trackbird

iTrader: (4)

What I was trying to say is that using a less aggressive pad on the street will require more pedal pressure (clamp load) to achieve the desired stopping force. This will help balance the pad wear by making the differential bore sizes work properly (or closer to properly). If you use a really grippy pad, you don't use much pressure (those pads stop well with "light" contact) and they will grab and taper. If you are on track and using high pressures to stop quickly, you can also use the more aggressive pads since you'll be using enough pedal pressure.

Did that help?

2001CamaroGuy

iTrader: (6)

NOW I GET IT!!!!!!!!!

lol...thanks...

trackbird

iTrader: (4)

No problem. Glad to help.

93Polo

iTrader: (5)

Clamping force is only a small part of the equation. Larger rotors and more pistons offer more leverage on the rotor and better control of the force resulting better threshold braking and in return shorter distances.

2001CamaroGuy

iTrader: (6)

so as I'm seeing it:

4 pistons have more "clamp force" (actual conversion of hydraulic pressure to mechanical pressure)

6 (or 8) pistons have more pad area (more friction surface to act against the rotor) and better modulation/feel

so in the end, while one might "loose" some clamp force with more pistons, they gain more contact with the rotor and also a heightened ability to control the application of the pressure


I think I'm getting the idea here....

trackbird

iTrader: (4)

That fact isn't lost on Mitch (or many others). In response to the original question that seemed to deal specifically with clamping force, his simple point was that we can generate enough brute force already. Originally nothing was asked about anything more than clamping force, we got into that as other details emerged. However, you are correct that most upgraded brake kits will offer increased threshold braking. However to say that "larger rotors and more pistons offer more leverage" is not exactly correct. Most kits that use a larger rotor use less piston area to compensate and keep brake bias from shifting towards the front wheels. For example, the 98-02 F-body has 11.8" rotors and 2 44mm pistons on the calipers. The C5 Corvette has 12.8" rotors and 2 40.5mm pistons. The reduction in area reduces the clamping force of the caliper for a given hydraulic line pressure. This helps to keep the effective brake bias even between both of those kits. Likewise, my 6 piston Wilwood kit has virtually the same total effective piston area of the C5 setup.

An explanation. "Effective Piston Area" is calculated on a 2 piston "slider" type caliper (like the F-body and C5) by doubling the piston area measurements. Meaning, you'd calculate the Corvette caliper as 4 pistons at 40.5mm each. This is because the pistons on one side pull the opposite side into the rotor, this causes those pistons to use twice the travel and use the front of the piston and the rear of the bore (equal and opposite reaction). So, you count them twice. The Wilwoods are more straight forward, you just add up the piston area of all of the 4 or 6 pistons.


Again, clamp force is directly related to piston size. What you are saying generally applies to the Wilwood calipers, but may not apply to the Porsche (and others) calipers. So, this is where generalizations are bad and someone may read this thread and get confused by not seeing that your statement is caliper specific.

Also, the pad area isn't figured into the braking calculations. However, more area can help to control peak temperatures seen by the pad/rotor interface. This can also help modulation and fade resistance, etc. So, though it doesn't specifically figure into the math, it can have a very real impact on performance. This is also why many prefer "tall" pads that sweep a lot of area (from the hub to the edge), they spread the heat out on the rotors surface since rotors do not "wick" heat into the center quickly (instantly?) enough to cool in real time while stopping. This is not to say that the center of the rotors won't get hot, just that the most effective part of the rotor (as a heat sink) is the part that comes directly in contact with the pads.

Also, the 6 pistons can often use a series of staggered bore sizes to reduce pad taper under hard use. As we stated, this isn't as useful under light brake applications, but can be a great benefit under track conditions.