is there a big difference between 4-piston vs. 6-piston brakes?
12-07-2004, 07:04 AM
#2
Member
Join Date: Feb 2003
Posts: 8,646
Likes: 0
Received 0 Likes
on
0 Posts
Depends on a lot of stuff.
Depends on who makes it, how it works with the car, etc. The stock M3 caliper (single piston) is probably nearly as good as many 4 piston aftermarket calipers.
To answer your question, I wouldn't pay a premium for a 6 pot caliper over any other caliper unless performance was dramatically better.
To answer your question, I wouldn't pay a premium for a 6 pot caliper over any other caliper unless performance was dramatically better.
12-07-2004, 08:40 AM
#4
there are advantages...
...As you inrease the number of pistons, you get the following:
1. You get less pad taper since you are dividing the duties among more pistons. Pad taper will start to **** the pistons in the bores which will start to grind away at the bores and eventually cause issue. The more pistons, the less taper, the less piston cocking, the less bore grinding, so you could say better reliability all things being equal
2. You can differentially size the pistons when you add more to accomodate the increased heat on the trailing edge of the pad so you can design a more even distribution to the pad which reduces taper.
3. Pad surface area. As part of calculating brake force, the surface area of the pad is part of the calculation. The larger you can make the pad, the more force you will get. So instead of making the pad "taller" like OEM does on a tall disc size (typically like 64mm vs 54mm for racing discs) by increasing hte number of pistons you can make the pad very long on the disc. Check out calipers from IRL/Cart or F1 cars, they are very long. I'm not sure if these people use multiple pads per side, but you get the idea. More pistons mean a longer pad which has more surface area and will get you more force.
4. The more pistons means each piston is smaller relative to a 4 or 2 or 1 piston caliper. Since they are smaller, you can move them further outboard on the disc to take advantage of more leverage, though this is minor.
I'm not sure if you could say that since more pistons mean each one is smaller, you are managing a smaller piece of mass during pedal modulation, and therefore you're getting better pedal feel. This might be a stretch.
1. You get less pad taper since you are dividing the duties among more pistons. Pad taper will start to **** the pistons in the bores which will start to grind away at the bores and eventually cause issue. The more pistons, the less taper, the less piston cocking, the less bore grinding, so you could say better reliability all things being equal
2. You can differentially size the pistons when you add more to accomodate the increased heat on the trailing edge of the pad so you can design a more even distribution to the pad which reduces taper.
3. Pad surface area. As part of calculating brake force, the surface area of the pad is part of the calculation. The larger you can make the pad, the more force you will get. So instead of making the pad "taller" like OEM does on a tall disc size (typically like 64mm vs 54mm for racing discs) by increasing hte number of pistons you can make the pad very long on the disc. Check out calipers from IRL/Cart or F1 cars, they are very long. I'm not sure if these people use multiple pads per side, but you get the idea. More pistons mean a longer pad which has more surface area and will get you more force.
4. The more pistons means each piston is smaller relative to a 4 or 2 or 1 piston caliper. Since they are smaller, you can move them further outboard on the disc to take advantage of more leverage, though this is minor.
I'm not sure if you could say that since more pistons mean each one is smaller, you are managing a smaller piece of mass during pedal modulation, and therefore you're getting better pedal feel. This might be a stretch.
12-07-2004, 08:56 AM
#5
AudiWorld Super User
Join Date: Feb 2001
Posts: 11,579
Likes: 0
Received 0 Likes
on
0 Posts
One thought
Even though you're talking about smaller pistons (smaller pistons, but more of them), what is the change in volume needed to move the pistons? How does that effect pedal travel/feel/modulation?
Total pad area is definitely part of the force calculation, but by increasing the volume needed to move the pistons and by increasing pad area aren't you going to be taking a lot out of the pedal feel and modulation?
The only reason for me to move into a 6 piston brake caliper would be for pad wear and heat dissapation. Maybe not the same for others. Maybe some people are more motivated by the glamour of a 6 piston caliper?
Total pad area is definitely part of the force calculation, but by increasing the volume needed to move the pistons and by increasing pad area aren't you going to be taking a lot out of the pedal feel and modulation?
The only reason for me to move into a 6 piston brake caliper would be for pad wear and heat dissapation. Maybe not the same for others. Maybe some people are more motivated by the glamour of a 6 piston caliper?
12-07-2004, 09:08 AM
#6
hmmm, well since the bores are smaller volume stays similar...
...so modulation isn't affected by any volume change since there isn't really. You should drive my car next we bump into each other.
I run the ALCON 6 piston in a 13" with the 298mm rear disc running a PAGID 4-2 blue pad. This gives me more rear bias than stock, which I like.
But more than anything, the biggest difference over the Brembo 4 piston's I was running before was the increase in pedal feel (using the same pads). I've now switched to a more aggressive front pad so I know that skews the feel. But the ALCON without doubt was more responsive to pedal input, especially when you're trying to be very finite like in light or medium braking. I was unwilling to go back to the Brembo's after driving on the ALCON's.
I've driven on the StopTech's and I find that they are too "grabby". So either everyone's car I drive is running too aggressive a front pad, or the piston sizing is smaller than I like up front and I don't get enough travel to really modulate. Again, this is just MY EXPERIENCE.
What setup do you run front and rear (and pads)? Curious to see your thoughts. But either way, you should drive my car and see if you can tell the difference. I found it to be very noticeable over the Brembo 4's.
I run the ALCON 6 piston in a 13" with the 298mm rear disc running a PAGID 4-2 blue pad. This gives me more rear bias than stock, which I like.
But more than anything, the biggest difference over the Brembo 4 piston's I was running before was the increase in pedal feel (using the same pads). I've now switched to a more aggressive front pad so I know that skews the feel. But the ALCON without doubt was more responsive to pedal input, especially when you're trying to be very finite like in light or medium braking. I was unwilling to go back to the Brembo's after driving on the ALCON's.
I've driven on the StopTech's and I find that they are too "grabby". So either everyone's car I drive is running too aggressive a front pad, or the piston sizing is smaller than I like up front and I don't get enough travel to really modulate. Again, this is just MY EXPERIENCE.
What setup do you run front and rear (and pads)? Curious to see your thoughts. But either way, you should drive my car and see if you can tell the difference. I found it to be very noticeable over the Brembo 4's.
12-07-2004, 09:27 AM
#7
AudiWorld Super User
Join Date: Feb 2001
Posts: 11,579
Likes: 0
Received 0 Likes
on
0 Posts
Hmm, I've had slightly different experiences.
What I was trying to get at in regards to modulation and pedal feel was the fact that a longer pedal stroke (to supply more volume) reduces the driver's ability to modulate the pedal because it takes less force to create more stopping power. It's nice for street driving, but I'd much rather have smaller pistons and a firm pedal.
I'm rollin' on stoptech's four wheel kit with 332's up front. It's going to be a bit of a balancing act because nobody has really tried to race on that setup. Because the rear bias goes up significantly, stoptech uses the larger front caliper. So I'm looking into a couple different solutions to bring back a firmer pedal. The car sucks my eyeballs out as it is (PFC01 front pad/PFC97 on the rear I believe).
I'd be interested in checking out the alcons. I haven't driven any since the set I had on my camaro.
I'm rollin' on stoptech's four wheel kit with 332's up front. It's going to be a bit of a balancing act because nobody has really tried to race on that setup. Because the rear bias goes up significantly, stoptech uses the larger front caliper. So I'm looking into a couple different solutions to bring back a firmer pedal. The car sucks my eyeballs out as it is (PFC01 front pad/PFC97 on the rear I believe).
I'd be interested in checking out the alcons. I haven't driven any since the set I had on my camaro.
Trending Topics
12-07-2004, 09:50 AM
#8
ahh, i see what you're saying, I'm totally the opposite way on track...
...i like having travel as I find it easier to modulate. I don't want instant braking at the slightest hint as I find it too hard to let off just a little bit.
Sounds like just a preference thing. So you're running a standard ST 332 front with their rear kit? That would (in my understanding) have you a lot more rear biased. Or are you running the 4 wheel kit but with a 13" front instead of 14"?
If you want to firm up the pedal, you should swap out your front caliper for the standard 13" front only caliper. That should shorten the pedal travel.
I'd be interested to see what it feels like. I'm betting from how it sounds you like the car to feel, you'll probably find I have more travel than you prefer and vice versa.
You want to see trick, you should check out the 252 vane ALCON discs, lighter and better heat properties. I don't have them on (no 13" yet as far as I know, only 14" and 14.5"), but they are f'in sweet.
<img src="http://pictureposter.audiworld.com/4359/252_vented_disc.jpg">
Ahhhhh, the beauty of aftermarket. Everyone can be happy.
Sounds like just a preference thing. So you're running a standard ST 332 front with their rear kit? That would (in my understanding) have you a lot more rear biased. Or are you running the 4 wheel kit but with a 13" front instead of 14"?
If you want to firm up the pedal, you should swap out your front caliper for the standard 13" front only caliper. That should shorten the pedal travel.
I'd be interested to see what it feels like. I'm betting from how it sounds you like the car to feel, you'll probably find I have more travel than you prefer and vice versa.
You want to see trick, you should check out the 252 vane ALCON discs, lighter and better heat properties. I don't have them on (no 13" yet as far as I know, only 14" and 14.5"), but they are f'in sweet.
<img src="http://pictureposter.audiworld.com/4359/252_vented_disc.jpg">
Ahhhhh, the beauty of aftermarket. Everyone can be happy.
12-07-2004, 10:12 AM
#9
AudiWorld Super User
Join Date: Feb 2001
Posts: 11,579
Likes: 0
Received 0 Likes
on
0 Posts
uhh, check it out...
I have what you could diagnose as a "soft pedal". There is a ton of stopping force, but the pedal pressure needed to create that stopping force is nill (not a good thing). The problem being that the pistons are too large. I have a four wheel kit with the 332 front rotor with the 355 front caliper. The reason being that when you put on the stoptech rear kit, the bias in the rear goes way up. That's why I needed the larger front pistons to equal out the balance.
So while the total package is balanced very nicely, it's not very driver friendly. This is a NEW thing that I'm playing with and stoptech has already expressed a lot of interest in finding a way to make the smaller four wheel kit work in the racing environment. Notice that stoptech doesn't really push their four wheel kit unless you want it for the bling factor. Don Istook is the only guy actively racing an Audi on stoptechs, but he is running the S8 hardware in the rear.
I'd like to get the four wheel kit sorted out and I think it can be as simple as putting a larger master cylinder on the car to replace the factory S4 one. Marc @ AMS is actively looking into that possibility. You might have an insight on that as well.
I don't want to have to run a bias controller and I don't want to have to go to a dedicated pedal box. Although that would be pretty sweet.
That alcon rotor is pretty nice. Definitely some high grade, expensive booty! Looks like you're going to have to find some bigger wheels to fit your new 14" kit under ;P Cause I know you're going to break down and buy it!
So while the total package is balanced very nicely, it's not very driver friendly. This is a NEW thing that I'm playing with and stoptech has already expressed a lot of interest in finding a way to make the smaller four wheel kit work in the racing environment. Notice that stoptech doesn't really push their four wheel kit unless you want it for the bling factor. Don Istook is the only guy actively racing an Audi on stoptechs, but he is running the S8 hardware in the rear.
I'd like to get the four wheel kit sorted out and I think it can be as simple as putting a larger master cylinder on the car to replace the factory S4 one. Marc @ AMS is actively looking into that possibility. You might have an insight on that as well.
I don't want to have to run a bias controller and I don't want to have to go to a dedicated pedal box. Although that would be pretty sweet.
That alcon rotor is pretty nice. Definitely some high grade, expensive booty! Looks like you're going to have to find some bigger wheels to fit your new 14" kit under ;P Cause I know you're going to break down and buy it!
