More pistons != better braking?

[overst33r]

Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

 

[angry hampster]

More even pressure against the rotor could provide more contact area for the pads, meaning more braking force. Theoretically, they can make a difference.

 

[ja1484]

Diminishing returns. More pistons does apply more pressure through a constant surface thereby generating higher amounts of friction. Theoretically, this would decrease speed faster (assuming you didn't lock the tires) and shorten stopping distance.

That said, the difference between 4 and 14 probably translates to inches or less in actual stopping distance differences.

 

[Zenmervolt]

The more even the pressure on the pads, the smaller the risk of the pads chattering and the better control you have over the pads.

Most brakes today are floating caliper, single-piston designs, though a few use floating caliper dual piston designs.

On a floating caliper setup, the piston(s) is (are) on only one side of the caliper and the caliper itself slides slightly side to side on pins. Fixed caliper setups have pistons on both sides of the caliper and the caliper does not slide at all. Fixed caliper setups provide more even brake pad wear than floating calipers and also provide more consistent pressure between the two sides of the caliper because this setup does not rely on the caliper's sliding.

Fixed caliper designs, of course, require at least two pistons; one for each side.

Larger pads provide a greater swept area which means a greater area over which heat is generated. Because the total heat for a given stopping force is always the same, greater swept area means better heat dissipation and less brake fade. Having multiple pistons per side helps apply more consistent pressure over the entire surface of the pad which not only allows the larger pads, but also reduces chatter and flex, both of which generate additional heat as well as reducing overall brake feel.

So, while a one-time emergency stop will not show much difference between a single piston sliding caliper and a 6-piston fixed caliper, the multi-piston fixed-caliper design will be more resistant to fade over several hard stops in quick succession.

ZV

 

[EightySix Four]

Originally posted by: Zenmervolt
The more even the pressure on the pads, the smaller the risk of the pads chattering and the better control you have over the pads.

Most brakes today are floating caliper, single-piston designs, though a few use floating caliper dual piston designs.

On a floating caliper setup, the piston(s) is (are) on only one side of the caliper and the caliper itself slides slightly side to side on pins. Fixed caliper setups have pistons on both sides of the caliper and the caliper does not slide at all. Fixed caliper setups provide more even brake pad wear than floating calipers and also provide more consistent pressure between the two sides of the caliper because this setup does not rely on the caliper's sliding.

Fixed caliper designs, of course, require at least two pistons; one for each side.

Larger pads provide a greater swept area which means a greater area over which heat is generated. Because the total heat for a given stopping force is always the same, greater swept area means better heat dissipation and less brake fade. Having multiple pistons per side helps apply more consistent pressure over the entire surface of the pad which not only allows the larger pads, but also reduces chatter and flex, both of which generate additional heat as well as reducing overall brake feel.

So, while a one-time emergency stop will not show much difference between a single piston sliding caliper and a 6-piston fixed caliper, the multi-piston fixed-caliper design will be more resistant to fade over several hard stops in quick succession.
ZV

Does it not also affect the amount of force that can be applied to the pads at high speeds? It may not have much of an affect at 60 mph, but at 160 mph I believe the brakes with a greater number of pistons would stop better.

 

[ja1484]

Originally posted by: crazySOB297
Does it not also affect the amount of force that can be applied to the pads at high speeds? It may not have much of an affect at 60 mph, but at 160 mph I believe the brakes with a greater number of pistons would stop better.

A good question. I was operating under the OPs "all else being constant" assumption.

The higher the speed you're traveling when you begin braking, the more increased piston numbers would make a difference.

 

[cheesehead]

AFAIK, Brembo makes some 8-piston (4 per side) brakes for use on Ferraris and the like. I've seen similar on motorcycles, as well.

 

[halik]

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

If you have shitty tires, then yes. Generally speaking though, tires aren't the weakest link or what's limiting your brake performance.

More pistons = more force exerted on the pads = more friction force (friction coefficient stays the same-ish) = more stopping force.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

 

[EightySix Four]

Originally posted by: halik

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

If you have shitty tires, then yes. Generally speaking though, tires aren't the weakest link or what's limiting your brake performance.

More pistons = more force exerted on the pads = more friction force (friction coefficient stays the same-ish) = more stopping force.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

Depends on how fast you're going, if you can cause you're brakes to lock up and/or ABS to kick in, you've exceeded the amount of traction your tires have. As I said earlier, the only time this will make a difference is when you're going fast enough to not be able to lock the tires up.

 

[overst33r]

Originally posted by: halik

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

If the civic and ferrari were the same weight and had the same tires, they would stop in the exact same distance, as long as the speed isn't greater than the lock-up limit of the civic. i.e. civic can lock up at 90mph, but can it lock up at 150mph?

The amount of traction available is the same regardless of the brakes.

 

[EightySix Four]

Originally posted by: mariok2006

Originally posted by: halik

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

If the civic and ferrari were the same weight and had the same tires, they would stop in the exact same distance, as long as the speed isn't greater than the lock-up limit of the civic. i.e. civic can lock up at 90mph, but can it lock up at 150mph?

The amount of traction available is the same regardless of the brakes.

That's the whole point, the Ferrari is able to lock them up at speeds because the brakes are far superior.

 

[RichieZ]

4 pot fixed calipers FTW

 

[ItTheCow]

Another benefit:
more pistons => larger caliper => larger thermal mass/dissipation => less brake fade => better overall performance during extreme usage (racing)

 

[mwmorph]

Originally posted by: crazySOB297

Originally posted by: mariok2006

Originally posted by: halik

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

If the civic and ferrari were the same weight and had the same tires, they would stop in the exact same distance, as long as the speed isn't greater than the lock-up limit of the civic. i.e. civic can lock up at 90mph, but can it lock up at 150mph?

The amount of traction available is the same regardless of the brakes.

That's the whole point, the Ferrari is able to lock them up at speeds because the brakes are far superior.

Or because the Civic maxes out at around 112-118mph...

Truth of the matter is, stopping is easy, I remember reading that usually brake are about 4x the hp of the engine of a performance car. Supra TT brakes had the stopping ability of about 1200hp pulling the other way, SC400s, about 900hp, the limiting factor at speeds you will be traveling at will be the tires, unless you have Laguna Seca or the Nurburgring a part of your commute home everyday.

Up until well over triple digit speeds do really most performance cars lose the ability to lock tires on decel.

 

[Apex]

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

There's also the time it takes to reach maximum clamping force. If there's a difference of 1/10th of a second, at 60mph, there's an 8.8 foot difference between the two systems.

 

[StageLeft]

In one time stopping the limiting factor is tire grip. This is why it's funny for people to talk about engine braking and larger rotors/pads because in this context they have no impact whatsoever.

 

[Demon-Xanth]

The larger number of pistons don't help on lap 1, they help make sure there's a lap 10

 

[vshah]

larger pad area = less energy dissipated per area of brake pad = less brake fade?

 

[JulesMaximus]

I have dual 4 piston calipers on my bike. The contact patch of the front wheel is tiny compared to a car and I could easily lock the front wheel under braking if I grab a fistful of brake. That said, the 4 piston calipers provide better brake feel with less pressure than the 2 piston calipers my bike came with.

 

[JulesMaximus]

Originally posted by: mwmorph

Originally posted by: crazySOB297

Originally posted by: mariok2006

Originally posted by: halik

Originally posted by: mariok2006
Keeping everything else constant, having 14 pistons vs 4 pistons would not decrease stopping distance. My reasoning is that the only factor in stopping distance in this example is the amount of grip the tires can exert on the ground. Since that doesn't change, the stopping distance shouldn't either. Right?

Even 2 pistons are enough to overcome the friction provided by most tires, so the only upside of going to more pistons is that it provides more even braking/better feel/etc.

Otherwise ferraris with carbon ceramic brakes and pirelli p0s would stop as good as a honda civic of the same weight and the same p0s.

If the civic and ferrari were the same weight and had the same tires, they would stop in the exact same distance, as long as the speed isn't greater than the lock-up limit of the civic. i.e. civic can lock up at 90mph, but can it lock up at 150mph?

The amount of traction available is the same regardless of the brakes.

That's the whole point, the Ferrari is able to lock them up at speeds because the brakes are far superior.

Or because the Civic maxes out at around 112-118mph...

Truth of the matter is, stopping is easy, I remember reading that usually brake are about 4x the hp of the engine of a performance car. Supra TT brakes had the stopping ability of about 1200hp pulling the other way, SC400s, about 900hp, the limiting factor at speeds you will be traveling at will be the tires, unless you have Laguna Seca or the Nurburgring a part of your commute home everyday.

Up until well over triple digit speeds do really most performance cars lose the ability to lock tires on decel.

A Formula One car can generate about 1g under acceleration but 4g's under braking and cornering.