I was looking at M3's and some (maybe all?) have single piston calipers. Whereas G35 have multi piston Brembo calipers. Why did M3's decide not to have multi pistons?

Also, why is piston abbreviated as pot?

Jae

 

where you looking at pics or specs?

 

pot is kind of like a cylindrical container, pistons are similar to them like that i guess.

multiple pistons supposedly spread out the pressure more evenly over the pad so you get a more uniform pressure pattern across it. BMW can do this without crazy amounts of pistons because they're both german and awesome.

honestly all of this extra piston crap is mostly just to satisfy customers IMO, it looks cooler and sounds cooler although you can get very similar performance with a caliper with less pistons.

also i'm pretty sure the M3 would have a dual piston sliding caliper up front like the M5. sliding calipers effectively double the number of pistons in a way as the pistons instead of just pushing one pad against the disc squeeze against a bracket that pushes the pad on the other side against it as well... so each piston is pressing both pads against the caliper. 2 piston sliding front and 1 piston sliding rear is pretty much the same as having a 4 piston front and 2 piston rear caliper (just doesn't look as cool)

 

its called a pot because it looks like one. they are hollow. bmw prolly has some big pots. 4th gen has OEM 1 piston too.

 

Simply put, multiple pistons not only help apply equal pressure on the pads to the rotor, it also helps make sure they're in proper contact.

In extreme cases, the pads tend to bend a little, so you're losing some pressure on those areas.

Although, it's not as obvious, here's a simple illustration that might help describe the above. (certain parts are exagerrated to clarify the point).

Some set-ups are better as a single piston. There are a lot of factors involved, but one of those could be because the piston area is as large as the pad itself - negating the need for more pistons.

 

http://www.car-stuff.com/mmparts/bmw...e_caliper.html

I don't see any websites listing multi-pot calipers for any year m3.

Jae

 

Cool, so, if more pistons = better, why don't m3's have more? Are they using some kinda trickery, maybe different master cyl technology, or some kinda brake assist?

I'm gonna look into the piston surface area theory.

Jae

 

for one they use a larger piston and MC size than alot of comparably-sized cars (maxima....), I'm pretty sure

for two....the M3s, from everything I've ever read on road-racing forums, are very seceptable (sp?) to excessive brake fade during hot-lapping.....there is alot of talk about the M3 (at least the E46 and before) being too heavy for their brakes (hmm...sounds like another car we know well). Several guys I've talked to at autocrosses said the first thing they upgraded on their E36/E46s were the brakes, before anything else.

not talking from firsthand experience, but just relaying what I've heard/read.

for three....believe it or not, the M3 is not "awesome" at everything. Quoted one-time "stop distances" are meaningless in a track environment, where battling fade is more important....but "fade resistance" isn't really a measurable stat for Car and Driver or Road&Track to do, ya know?



noteworthy that the new BMW 135 has multi-piston calipers up front? perhaps....

 

E36 and E46 m3's are way too overrated. true m3's were the E30's not these fat pigs in hands of the stunnas

 

Another advantage of multi piston calipers is brake feel. A fixed multi piston caliper will have less flex when you stand on the brakes VS a sliding type caliper. BMW kind of cheats a little, they use very aggressive pads to make up for the more basic caliper setup. If you want to look at factory brakes with function over cost, just look at Porsche.

 

irish44j, yeah I googled the 1 and noticed the multi-pistons. Should be a nice combo w/the engine/chassis.

With the exception of VIP Maxima, I thank everybody for their helpful replies.

Jae

 

Is this the cool thing to say now? It's amazing how many people spout this BS...

 

I wouldn't say the E46 and E36 are "overrated" necessarily. They are what they are, a high-performance luxury sedan/coupe (particularly the E46 M3).

What they are NOT is the purpose-built ETC race car that the E30 M3 originally was (after all, the race version of the E30M3 came BEFORE the street-legal version).

The E30 M3 was built as a track car
The E36/46/etc were not....

that's a fact. as to the "overrated" part.....it's all in the eye of the beholder. Personally, I have no love for the E46 M3, though I love the E36 (which has always been seen as a "poser" because of its limited success in road racing, as opposed to the E30 M3, which was HUGELY successful).

It's like a little brother trying to live up to a big brother who was the captain of the football team and dated the head cheerleader. High expectations are hard to match.

 

To the OP:

More pistons means more even pressure on the pads for better bite, modulation, and pedal feel. It also looks a hell of a lot cooler because people always think more is better.

Fewer pistons means less cost and less unsprung mass. Having fewer pistons also usually means a smaller caliper, which means heat is more localized, which means the pads get up to temp faster and stay there longer. Those are big reasons why BMW does it that way (single-piston on the M3, two-piston on the M5).

Keep in mind that those statements are assuming all else is equal. For example, it is possible to have 4-pot calipers that are lighter than single-pot calipers. They'll just be really expensive.

Overall heat handling is a function of the mass of the brake components, what they're made of (iron vs. aluminum vs. ceramic), and how well everything is ventillated. Number of pistons isn't really a factor in and of itself; sometimes calipers with lots of pistons handle heat better, but that's really only because they tend to be bigger.

It's all a design choice.


A note about the M3's one-pot calipers: those single pistons are HUGE, and the brake pads are relatively square so the piston ends up covering most of the pad. That's how they (mostly) get around the pad flex issue.

BMW also uses sliding calipers wherever possible. That way, the pistons are always on the inside, which gives a lot more freedom in terms of wheel fitment because you don't have to worry as much about whether the wheels will clear the brakes.

 

irish44j, I agree 100%, and obviously so do quite a lot of enthusiasts. It just seems that people seem to hear that reasoning and want to repeat it without actually knowing anything about the topic, and I'd be willing to bet it's because it touches a nerve with people who wish they had a newer/faster/more upscale/more popular car...

 

jealousy's a *****. When guys I work with buy new/expensive cars and brag about them, after congratulating them I always tell them one little problem that particular car is known for, just to bring them back down to earth

That said, autocrossing against E46s I've lost a measure of respect for their abilities in small courses....the E36s consistently whoop the E46s at autocross....plus for some reason BMW made the E46 M3 with wheels that weigh about 30-35lbs. WTF?!?! And they have the worst sounding stock exhaust of any car that I can think of....

I love me some E36M3 though (one of the best-handling cars ever)....and I love me some E30M3