Why do more powerful cars need bigger brakes?

[DaveInLA]

I've read several times in magazines that big brakes are necessary to "stop all that power", but that doesn't make sense to me. Not entirely, at least.

I understand that brakes stop a car's momentum, and that's the product of mass x velocity. Therefore, heavier cars should have bigger brakes, not necessarily cars with more powerful engines. After all, won't a 160 hp Camry going at 110 mph need the same braking power as a 330 hp M3 going at the same speed, assuming they are the same weight?

Or is it the assumption that cars with more power are more likely to drive fast on the street and track, where optimal braking performance is necessary? If so, the vast majority of people don't need 14" brakes.

 

[michaelc80]

"Or is it the assumption that cars with more power are more likely to drive fast on the street and track, where optimal braking performance is necessary? "

I would have to say yes to that statement.

 

[k1xv]

Cars with bigger engines can be driven to higher speeds between turns or other "events" that require braking. Therefore, more speed needs to be scrubbed off.

Think of a car driving around a race track road course with multiple corners. The more powerful car will build up more speed on the straightaways, thereby requiring more energy absorbing capacity in the brakes than a second, less powerful car, that cannot build up as much speed on the strightaways.

 

[DaveInLA]

quote:

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Originally posted by k1xv:
Cars with bigger engines can be driven to higher speeds between turns or other "events" that require braking. Therefore, more speed needs to be scrubbed off.

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Yeah, that's what I thought. But the majority of folks in sports cars don't track their cars and don't necessarily take corners much faster than they would if they were driving a Civic. I just think it's overkill.

I have a cool little E30 325is that I drive pretty aggressively on the street, hwy, and occsaionally a curvy mountain road, and the brakes have always been fine for me. I understand this car is a "sport sedan", but when I bought brake pads, I was shocked at how small they were. And this car stops great.

 

[T-Keith]

The more powerful a car is, the faster you get to speed, and the higher speed you can acheive in the same space.

 

[thooks]

"Bigger Brakes" = larger, thicker rotors, larger calipers and larger, thicker pads.

All of that results in better (quicker) stopping power, reduced runout (warpage) and a better, longer-living system all around.

 

[simple_gifts]

quote:

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I understand that brakes stop a car's momentum

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I think this is a kinetic energy (1/2mv^2) issue, not momentum. To stop a car, the kinetic energy must be converted into heat (applying the brakes) Momentum involves a vector value (direction) where kinetic energy is scalar (single #)

 

[DaveInLA]

quote:

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Originally posted by simple_gifts:

quote:

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I understand that brakes stop a car's momentum

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I think this is a kinetic energy (1/2mv^2) issue, not momentum. To stop a car, the kinetic energy must be converted into heat (applying the brakes) Momentum involves a vector value (direction) where kinetic energy is scalar (single #)

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Ah, you might be right... in which case, the speed of the car is exponentially more important than the weight.

 

[mechtech]

Better brakes are rarely a downside.
An enthusiast who gets a more powerful engine will usually want a better suspension and brakes.

 

[eljefino]

I prefer to think that most econoboxes come with undersized brakes, to save a couple bucks during manufacture and get a tiny bit better gas mileage with less weight and rotational inertia. A more-styled "driver's car" has fewer compromises under the fenders.

My intrigue with 195hp has massive rotors compared to my saturn with 100hp even though the car is not twice the weight. I would then look at the saturn and say it's "under-braked".

Incidentally saturn's 124hp motor upgrade has the same lousy brakes, though rear discs were a sometimes-option.

Look at, say, a cavalier with the nice 16 inch alloy wheels, and the super wussy rear drums they stick on these things.

 

[Shannow]

think burnouts.

 

[Patman]

A lot of the move to bigger brakes is about bragging rights these days. With bigger rims that have larger openings, people want to see nice big rotors in there!

But honestly, it's almost overkill sometimes. I know bigger brakes are always better, but you reach a point where your stopping ability can almost hurt you! Let me explain. With my Corvette, I can outbrake 99% of the cars that are on the highway with me on my daily commute. So if I were to slam on my brakes all of a sudden, it's almost guaranteed that the person behind me would not be able to stop in time.

So when you drive a car like this you're always looking in your rear view mirror whenever you make a hard stop.

 

[surfstar]

quote:

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Originally posted by Patman:
With my Corvette, I can outbrake 99% of the cars that are on the highway with me on my daily commute. So if I were to slam on my brakes all of a sudden, it's almost guaranteed that the person behind me would not be able to stop in time.

So when you drive a car like this you're always looking in your rear view mirror whenever you make a hard stop.

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Patman, I think about this all the time in traffic here in CA. In CA if you're rearended, the person who hit you is at fault for following too close.

So all I have to worry about is being able to out-brake the person behind me in a panic stop.

Kinda like when two people are running away from a bear - you don't have to outrun the bear, just the guy next to you.

 

[brianl703]

It's happened a few times that someone has been tailgating me, traffic comes to a sudden stop, then the tailgater is steering for the shoulder to avoid hitting my car.

 

[Matt_S]

Also consider that a lot of the people that are into modifying their car DO race those cars and would have a legitimate need for bigger brakes. I think there's a lot of truth in what Patman says, too, but I also think a lot of people just like having extra stopping power "just in case."

 

[JHZR2]

One of the problems becomes when the average joe gets the cheapest parts and does the minimal service at the lowest bidder, and then there are well designed brake systems on the fancier cars... the fancier cars get rear ended a lot.

Happened to my 83 MB vs. an 88 olds that didnt stop anywhere near in time (though idiot driver error was to some extent a cause), and neither of those are up to todays standards...

Im amazed at how well my saab 9-3 stops... I believe its 108 from 60 or 70-0, one way or another, its REALLY good braking.

JMH

 

[1sttruck]

Good brakes are nice. The '76 RD400 that I had could do 'brakies', standing up on the front wheel. Mt Dodge truck has 14in discs all around, and while it doesn't stop on a dime it stops pretty well, well enough to hear people screeching tires behind me on a regular basis when I need to stop quickly. When I get some silly money or if I end up towing often I'll get an engine brake, which as I recall has something like 250 braking hp :^)