4-pot brakes stop a car faster?

[MarkCup]

Two modern cars, identical in every way except for the brake setup.

One has 4-pot calipers, bigger discs, larger swept area. The other has a standard single-piston setup.

Which one stops quicker?

 

[holtt]

im gonna go with 4 pot, larger force exerted on the disc from the pad surely...

 

[The Boosh!]

The former, surely?

 

[Midnight]

The former, surely?

Long as the pad compound is similar yes surely the 4 pot.

 

[MarkCup]

I'm not talking about after several laps on a trackday.

One stop, from whatever speed you want. Which hauls up quicker?

 

[MarkCup]

The former, surely?

Long as the pad compound is similar yes surely the 4 pot.

If the standard setup is enough to trigger the ABS, why would 4-pots slow the car faster?

 

[cat171]

Are they the same ?

I hate four pots, they're rubbish unless stamped on, then when I do that I almost go through the windscreen

 

[Midnight]

I was always told if ABS is kicking in too often you're usually doing something wrong??

 

[The Boosh!]

If the standard setup is enough to trigger the ABS, why would 4-pots slow the car faster?

ABS isn't deactivated just because you've got 4 pots though - It's still there.

 

[Midnight]

Are they the same ?

I hate four pots, they're rubbish unless stamped on, then when I do that I almost go through the windscreen

I remember having 8 pots on a previous car and like for like AP's which was only 4/6 was dramatically better.

Saying that on a whole the more surface area with a good compound tends to be better...

 

[Chip-mk1]

There is not one specific answer to this question IMHO, it will depend on the 2 setups, so its going to be a case of the devil is in the detail, but essentially it shouldnt be any different greatly on a first stop, both should be capable of pressing the pad onto the disk nice and hard if you stand on the brakes, so then you are down to the friction co-efficient of the compound as to which works better really.
More leverage from a bigger disk can help, but it can also stop a pad hitting its temperature sweet spot.




The main advantages with 4 pots are not to do with actual outright breaking performance, they are things like not having slides that stick and make the breaking effort unevent and they typically have better heat dissipation properties.

 

[172Ben]

id go with standard single piston

 

[Clart]

Is this a trick question?

 

[Midnight]

id go with standard single piston

Ben, have you seen the calipers on the S2000?

 

[MarkCup]

OK, ignore the feel, ignore how well they last, ignore the detail.

The only difference is in the number of pistons and the swept area.

Both setups have the ability to trigger the ABS at will, and both cars are running the same tyres.

Which stops quicker?

 

[172Ben]

Ben, have you seen the calipers on the S2000?

no mate i havent

 

[Chip-mk1]

OK, ignore the feel, ignore how well they last, ignore the detail.

The only difference is in the number of pistons and the swept area.

Both setups have the ability to trigger the ABS at will, and both cars are running the same tyres.

Which stops quicker?

It depends on the weight of the car, the details of the size of the disks etc, and even the pressure generated in the brake lines and the friction co-efficient of the disks, there isnt one answer that will always be true.

 

[Midnight]

no mate i havent

You're lucky, I believe the DC5 have the brembo calipers. OEM S2K calipers look like they should be on a 1.1 saxo desire.

 

[172Ben]

Yes!! DC5 are 4 pots yeh! LOL, just looked at a picture, they are terrible!

 

[MarkCup]

It depends on the weight of the car, the details of the size of the disks etc, and even the pressure generated in the brake lines and the friction co-efficient of the disks, there isnt one answer that will always be true.

I'll say again...the two cars are identical.

They can both trigger the ABS at will so BOTH setups have enough braking force readily available to overwhelm the grip available from tyres.

Which stops faster?

 

[Ian_s]

The answer you're fishing for is that they're the same given the tyre is the limiting factor. You could argue that the 4 pots will allow you to get closer to the threshold without activating the abs.

 

[Chip-mk1]

I'll say again...the two cars are identical.

They can both trigger the ABS at will so BOTH setups have enough braking force readily available to overwhelm the grip available from tyres.

Which stops faster?

And I will say again, it depends what the cars and brakes are!

If its a 2 tonne car on very small standard disks (like most things in the 80s for example), and you are stopping from a high speed then it will get MASSIVELY outperformed by a bigger 4 pot setup for example.


There is NOT one answer that fits all the possible cars and brakes combinations that your post is saying.

Its like me asking you "which is faster, a ford or a renault" and then refusing to give you details of which ford and which renault I am thinking of.

Your question does not have an answer that will always apply, it might have an answer for the specific car you are thinking about, but without that being part of the question its just a meaningless question!

 

[Chip-mk1]

The answer you're fishing for is that they're the same given the tyre is the limiting factor. You could argue that the 4 pots will allow you to get closer to the threshold without activating the abs.

If you are doing a big speed when you brake there arent many brakes capable of straining the tyres initially.

 

[botfch]

Single piston would stop in a shorter distance due to the way ABS currently works on most cars, stop-start-stop-start to keep you on the verge of skidding.

 

[Chip-mk1]

Single piston would stop in a shorter distance due to the way ABS currently works on most cars, stop-start-stop-start to keep you on the verge of skidding.

It depends on the specifics of the car and the brakes and the road conditions at the time as to whether the ABS is greatly useful or not.

 

[John Gordon]

If you are asking if 4 pot calipers will greatly reduce your stopping distance, the quick and simple answer is no, they will not. They do greatly improve overall braking performance, but they will not drastically reduce your stopping distance. If you don't think your car stops soon enough, buy new tires. The calipers are, in fact, the only part of your car that ever touches the ground. The reasons for this are quite simple and based in physics.


How a Car Stops
According to the Standard Kinetic Friction Equation, it takes more energy to begin an object's motion than it does to sustain it. So how does this apply to stopping a car? Well, the reverse of this law states that a tire in contact with the road will absorb more kinetic energy (e.g. momentum) just before it slides. Assuming the coefficient of friction is the same, (same tire, same road,) a braking system that applies more force to your rotors will bring about this threshold of sliding only milliseconds sooner. This will result in your ABS kicking in sooner to try and maintain this threshold. Now, if the tire contact patch is greater, and the rubber stickier, this point of force at which this threshold occurs changes greatly--making your car stop sooner.


4 Pot Calipers in Relation to ABS
In many instances, (especially in cars equipped with ABS,) 4 pot calipers can only elongate your stopping distance, even when correctly biased and tuned. This is because the ABS system activates sooner. Even the most modern ABS systems overcompensate. Meaning it releases pressure from the brake lines, allowing the wheels to move, and then reapplies said pressure, making them lock up again. The goal of the ABS is not just to keep the tires from sliding, but also to keep them right on the threshold of sliding, where energy absorption (again, momentum) is greatest. Even the most modern ABS systems cannot do this completely just yet. So we are stuck with a "lock, roll, lock, roll" pattern that brings us to a stop as fast as possible.


4-Piston Opposing Calipers

So what can 4-piston opposing calipers do for your ride, besides looking awesome? The number one performance increase occurs not when slamming on the brakes the first time (as previously discussed in the physics lecture) but, the second, third and tenth time. 4 pot calipers will react with much less brake fade than single or dual piston sliding calipers. It's because with larger calipers and rotors, heat dissipation is greater. This can be magnified with the use of sport brake pads and larger rotors of different composites. Having larger calipers with opposing pistons also means that the braking force will be increased with less pedal movement. A car equipped with opposing piston calipers and larger rotors will have a harder-feel brake pedal, and will emit more force on the wheels as a sliding caliper with less pedal movement. So in essence, will your car stop sooner with bigger 4-pot calipers up front? No. Will it stop more consistently after time, with less brake fade and a firmer, short throw brake pedal? If installed right, and tuned correctly, absolutely. And it still looks awesome.

 

[botfch]

It depends on the specifics of the car and the brakes and the road conditions at the time as to whether the ABS is greatly useful or not.

Aye I agree, Just giving him the answer to his specific theoretical question its never going to happen in a real scenario as its impossible to get everything completely the same.

 

[Ian_s]

If you are doing a big speed when you brake there arent many brakes capable of straining the tyres initially.

You could argue that given almost all road cars generate lift you will get to a point where it gets easier to lock up the bigger the speed, but I won't because I suspect the speed required would be many hundreds of miles per hour.

 

[Chip-mk1]

Aye I agree, Just giving him the answer to his specific theoretical question its never going to happen in a real scenario as its impossible to get everything completely the same.

Its possible to get things the same, but what I am saying is that if its a case of:
a light car and the standard brakes are well upto the job = bigger disks and 4 pots will make it worse (and in the wet even more so)
a heavy and the standard brakes are woefully inadequete = bigger disks and 4 pots will make it better

Im not saying the 2 test cars cant be the same, I am saying that it depends what that baseline is as to wether fitting bigger brakes with 4 pots will make it better or worse.


Its like asking the question "will my car corner faster with firmer springs" and not saying what car or springs it is in the first place!

 

[botfch]

Its possible to get things the same, but what I am saying is that if its a case of:
a light car and the standard brakes are well upto the job = bigger disks and 4 pots will make it worse (and in the wet even more so)
a heavy and the standard brakes are woefully inadequete = bigger disks and 4 pots will make it better

Im not saying the 2 test cars cant be the same, I am saying that it depends what that baseline is as to wether fitting bigger brakes with 4 pots will make it better or worse.


Its like asking the question "will my car corner faster with firmer springs" and not saying what car or springs it is in the first place!

Ah I get ya, yeah that makes sense.

Although saying that I do like the feel 4 pots give you over standards especially on a track.

 

[Dave..]

If both setups are capable of locking the wheels at the same given speed, both brake setups will stop the car in the same time and distance. It no longer becomes a braking issue, instead it's about the level of friction between the road and the tyre. No ifs, no buts.

 

[Chip-mk1]

If both setups are capable of locking the wheels at the same given speed, both brake setups will stop the car in the same time and distance. It no longer becomes a braking issue, instead it's about the level of friction between the road and the tyre. No ifs, no buts.

Agreed, although you have slightly overlooked the level of control the driver or the ABS has of keeping the braking at the very limit of the tyres traction ability.



But basically the way this thread will end up no doubt is that Mark Cup will say "on the specific example I am thinking of, for a first time application of the brakes, upgraded brakes that are about longevity on track arent an improvement for that very narrow test"

Which is going to surprise me as much as if he says his fridge is better for putting milk in than his freezer even though the freezer can get colder TBH.

 

[John Gordon]

I think the easiest way to deal with this thread is...

[h=2]4-pot brakes stop a car faster? = NO[/h]

 

[cs_dave]

Agreed, although you have slightly overlooked the level of control the driver or the ABS has of keeping the braking at the very limit of the tyres traction ability.



But basically the way this thread will end up no doubt is that Mark Cup will say "on the specific example I am thinking of, for a first time application of the brakes, upgraded brakes that are about longevity on track arent an improvement for that very narrow test"

Which is going to surprise me as much as if he says his fridge is better for putting milk in than his freezer even though the freezer can get colder TBH.

I think the easiest way to deal with this thread is...

4-pot brakes stop a car faster? = NO

Done end thread!

 

[Dave..]

Agreed, although you have slightly overlooked the level of control the driver or the ABS has of keeping the braking at the very limit of the tyres traction ability.

If we're bringing a driver into this then no one can draw any conclusions. 2 variables ain't science.

 

[Chip-mk1]

If we're bringing a driver into this then no one can draw any conclusions. 2 variables ain't science.

Car without a driver is irrelevant and the same setup isn't optimum for all drivers.
So your target audience is important when specifying a car.

 

[...]

i would say there is next to nothing in it .

the 4 pot vs single pot in this scenario will be negligible .


the factor here moreso is the larger swept area which should have the ability to produce more friction and therefore more stopping power , however i will go with they stop pretty much the same

 

[MarkCup]

If both setups are capable of locking the wheels at the same given speed, both brake setups will stop the car in the same time and distance. It no longer becomes a braking issue, instead it's about the level of friction between the road and the tyre. No ifs, no buts.

I think the easiest way to deal with this thread is...

4-pot brakes stop a car faster? = NO

This is where my thoughts are.

Chip... you've missed the point that if both setups can overwhelm the tyre's available grip at will at any speed, what good does the extra braking force available from a 4-pot setup do?

As for why I asked this question...I believe the answer is both will stop in the same time/distance as the tyres are the limiting factor, not the braking force.

This is a debate I'm having on FSTOC in response to someone saying their Civic with massive brakes would easily outbrake the current ST based upon the number of pistons and swept area.

 

[Chip-mk1]

This is where my thoughts are.

Chip... you've missed the point that if both setups can overwhelm the tyre's available grip at will at any speed, what good does the extra braking force available from a 4-pot setup do?

If you apply the brakes at say 140mph, then on most standard setups, by the time you are down say 60, the brakes are so hot they are no longer working effectively, so by having bigger brakes it means that on the first application of the pedal at big speeds, you will stop faster.

Then obviously if you speed up and want to slow down again before the brakes have cooled, the effect gets even more noticeable.

As for why I asked this question...I believe the answer is both will stop in the same time/distance as the tyres are the limiting factor, not the braking force.

Depends on the vehicle and the conditions, at big speeds if you progressively apply the brakes initially and then load them up most standard cars dont have enough braking force to still overcome the tyres the whole way down.

In the wet though for example, Ive never had a car that needed bigger brakes, but in the dry I have many times.

This is a debate I'm having on FSTOC in response to someone saying their Civic with massive brakes would easily outbrake the current ST based upon the number of pistons and swept area.

Im sure in certain circumstances he is right, although im also sure that on the road, even at legal motorway speeds there will be little or nothing in it.

 

[John Gordon]

Disc size is changed for heat dissipation.

The amount of pots in the piston has nothing to do with heat dissipation.