Why do some cars have bigger brakes?

[wezzel98765]

I was thinking the other day,

Why do some cars with bigger engines, have bigger brakes than the SAME car with a smaller engine

E.g. A Renault Clio 2.0 has much larger brakes than a Renault Clio 1.2

Why is this?

Reason I ask, is, the speed limit is the same for any car, so why would the 2.0 need bigger brakes if both cars are travelling at 30mph for example?

 

[HDi fun]

I was thinking the other day,

Why do some cars with bigger engines, have bigger brakes than the SAME car with a smaller engine

E.g. A Renault Clio 2.0 has much larger brakes than a Renault Clio 1.2

Why is this?

Reason I ask, is, the speed limit is the same for any car, so why would the 2.0 need bigger brakes if both cars are travelling at 30mph for example?

Higher performance variants of the same model are capable of much swifter acceleration. As such the brakes will be required to work harder and more often simply because the car can get to higher speeds between situations wher brakes are required. Milton Keynes and it's incessant roundabouts is a good point to note.

Back to your question a 1.2 Clio set beside a 2.0 one would both stop similarly if that was the first stop of the test. Repeated acceleration and braking tests would see the 2.0 working its brakes much harder. Simply because it builds up speed faster and therefore gets to the point that it needs to be slowed again much sooner.

It is possible to have brakes oversized and rated for the car's weight and performance that they never really perform to their best ability.

Even OEM discs and pads work s little better after a couple fo very gentle stops.

 

[old-git]

Higher performance variants of the same model are capable of much swifter acceleration. As such the brakes will be required to work harder and more often simply because the car can get to higher speeds between situations wher brakes are required. Milton Keynes and it's incessant roundabouts is a good point to note.

Back to your question a 1.2 Clio set beside a 2.0 one would both stop similarly if that was the first stop of the test. Repeated acceleration and braking tests would see the 2.0 working its brakes much harder. Simply because it builds up speed faster and therefore gets to the point that it needs to be slowed again much sooner.

It is possible to have brakes oversized and rated for the car's weight and performance that they never really perform to their best ability.

Even OEM discs and pads work s little better after a couple fo very gentle stops.

I agree, up to a point

Today's modern brakes are so good that the 1.2 Clio brakes will easily deal with the 2.0 in normal day-to-day driving, even if driven 'enthusiastically' but legally. However, if pushed to the limit (or rather, beyond) the bigger the better, as in most walks of life . I assume that the cars are of a similar weight.

The brakes on the 1.2 would not be sufficient if the car spent its life on the track.

I think that there is also a certain amount of the buyer expecting bigger brakes with bigger engines, so the manufacturers supply what the customers want.

 

[HDi fun]

I sort of tried to cover this in paragraph 2 but missed the bloody obvious bit about deterioration of braking performance. Ooops, sorry.

Bigger brakes often give better pedal feedback as well. Provided that the pads are working in their linear range. ie. No use having ceramic pads in a 1.2 Clio fitted with 340mm discs that never get remotely warm.

 

[obi_waynne]

This question is pretty much covered but I have a couple of observations here...

May I add the sidepoint of the 2.0 weighing a lot more than the 1.2. Extra weight requires better anchors. (I know its only a minor point but it does have a bit of an effect on the results.)

Often the 1.2 models are aimed at a low price point so money is saved by using smaller discs and pads etc...

 

[hemingway]

i think the weight difference between the 2.0 and 1.2 is about 100kg so its not much in that department and that will be down to the 2.0 engine i would of thought.

 

[obi_waynne]

Yup Not much real world difference there. In actual fact I just looked up a 1.2 Clio at 1570 kgs and the 2.0 Clio Sport 172 is 1490 thus completely demolishing my angle.

 

[obi_waynne]

Heres another thought though. Are narrow wheels more likely to lock up with bigger discs? (Might be an interesting debate!)

 

[HDi fun]

Narrow wheels can perform better in the wet than excessively wide ones.

 

[obi_waynne]

Well that adds to the confusion! I have heard this though but surely not on bends, isn't it the straight line aquaplaning resitance that is reduced with thinner wheels?

 

[old-git]

I Bigger brakes often give better pedal feedback as well. Provided that the pads are working in their linear range. ie. No use having ceramic pads in a 1.2 Clio fitted with 340mm discs that never get remotely warm.

Good point.

 

[HDi fun]

Well that adds to the confusion! I have heard this though but surely not on bends, isn't it the straight line aquaplaning resitance that is reduced with thinner wheels?

The theory is that the force per unit area exerted upon the tyre tread is greater, simply because the contact patch is smaller.

Obviously this cannot be taken to extreme otherwise we'd all be on bicycle wheels.

But a 1.0 Nova with 245/45 ZR 18s will be likely to skate all over the place in the wet especially.

The other reason is that the contact patch becomes very wide and short which can reduce lateral grip enormously.

 

[old-git]

The theory is that the force per unit area exerted upon the tyre tread is greater, simply because the contact patch is smaller.

Take issue with this point......

As I understand it, the size of the contact patch is more or less independent of the width of the tyre. The weight of the car is distributed over the contact patch so each square mm of tread supports a set amount of the car's weight, irrespective of the tyre's width. All that happens is that the shape of the contact patch changes. On a narrow tyre it is long and narrow and on a wide tyre it is short and wide.

So, wider tyres do NOT increase the area of tyre in contact with the road, this is a common mis-understanding of how tyres work.

 

[HDi fun]

Take issue with this point......

As I understand it, the size of the contact patch is more or less independent of the width of the tyre. The weight of the car is distributed over the contact patch so each square mm of tread supports a set amount of the car's weight, irrespective of the tyre's width. All that happens is that the shape of the contact patch changes. On a narrow tyre it is long and narrow and on a wide tyre it is short and wide.

So, wider tyres do NOT increase the area of tyre in contact with the road, this is a common mis-understanding of how tyres work.

I covered this in my last paragraph - the geometry of the contact patch is crucial as well. And this changes constantly - radial ply tyres allow sidewall flexing. THat's how they offer such advantages of grip (lateral and longitudinal) over crossply designs.

The thing that most disregard (you're not in my 'most' category, incidentally) is how crucial it is to use the correct inflation pressures for the geometry of your wheel rim/tyre/car combination.

 

[old-git]

I covered this in my last paragraph - the geometry of the contact patch is crucial as well. And this changes constantly - radial ply tyres allow sidewall flexing. THat's how they offer such advantages of grip (lateral and longitudinal) over crossply designs.

The thing that most disregard (you're not in my 'most' category, incidentally) is how crucial it is to use the correct inflation pressures for the geometry of your wheel rim/tyre/car combination.

I think that we are on the same wavelength here, just highlighting different aspects of a very complicated, but interesting, subject.

 

[J0K3R]

My head hurts. Imagine a nuclear detonation of information going off inside a Vauxhall Aguila. That's what just happened in my head, but hey, it's all learning =]

 

[HDi fun]

I think that we are on the same wavelength here, just highlighting different aspects of a very complicated, but interesting, subject.

It is a complex topic.

Yet you're average driver gives tyre selection about as much consideration as he/she gives air freshener selection.

 

[obi_waynne]

I've been known to spend 20 minutes choosing between the Pine or Lemon magic trees before.

 

[old-git]

I've been known to spend 20 minutes choosing between the Pine or Lemon magic trees before.

To quote Jack Dee, 'putting a magic tree in your car is telling people that you stink'