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View Full Version : Is there such a thing as too much brakes?



DarkBuddha
12-27-2004, 08:54 PM
With the obsession over 13" (or bigger) brakes, I have to wonder: is there such a thing as having too much braking power?

Maybe I'm opening a can of worms... I've done a bit of research regarding brake design, even reading some OEM engineering documentation (from when I was trying to figure out the viability of retrofitting ABS), and one of the things I seem to recall is that braking systems can be overbuilt. Essentially, based on the mass of the vehicle and the weight distribution, there is supposedly an ideal amount of braking potential for each corner. Of course, one of the contributing factors is rotor diameter. Going too small causes longer braking distances, but going to big can result in either quick locking or not generating adequate heat. Heat is supposedly necessary for brakes to work correctly, especially effecting the efficiency of the pads. :dunno:

Anyone?

dennis68
12-27-2004, 10:59 PM
Once you have enough to lock all 4 wheels evenly with the tires you intend to drive on AND not fade from overheat then you officially have enough brakes. Until then....go bigger.

DarkBuddha
12-28-2004, 02:39 PM
I suspected tires were the lowest common denominator in this equation. If tires can't hold traction then the brakes are adequate? Seems reasonable enough...

spanky the wondermuffin
12-28-2004, 03:59 PM
my camaro is a little lighter than some at #3000.i run shaved victoracers 265/16 up front.i use temperature indicating paint to read my high temps.i run 12.19 rotors,1.25 up front(curved vane),.810 rear(st.vane).i have brake cooling ducts and hoses.rotor size is based on adequate heat dissapation.if you aren't getting too hot,you don't need a bigger rotor.braking force is controlled by caliper and m/c piston sizes.i think too much rotating weight would be a bigger problem with giant rotors.overall braking feel is most important.you rarely use threshold braking on a race track.more often you use them a bit to settle the car and help it point a bit better.and if you are using your brakes that hard on the street slow down and pay attention.

Salt Racer
12-28-2004, 04:10 PM
What Jon (spanky) said.


...If tires can't hold traction then the brakes are adequate?...

For a daily driver, probably. Whether you'll be able to lock up the wheels or not is primarily a function of available traction, rotor diameter, and caliper clamping force. So you could lock up the wheels with good clamping force, 15" x 0.375" solid rotors, and 0.25"-thick pads even if you have super sticky tires.

BUT, would the system described above hold up to repeated use? Nope. Either rotors/pads would fade due to their insufficient thermal capacity, or fluid would boil (thin pads = less heat insulation) after a couple of hard stops from 60mph.

On the other hand, you can have smaller combo like Jon has on his car. This naturally requires more clamping force (larger caliper piston area, smaller m/c bore, larger pedal ratio, more aggerssive pads, more foot force, etc) to lock up wheels for the same amount of available traction. But overall this is a better system for track use b/c it will be able to withstand repeated hard use.

I don't know the exact reasons why modern race cars use larger diameter/thin rotors, as opposed to small dia/thick rotors. Larger dia. rotors place more mass on larger radius (more inertia) compared to smaller dia./thick rotor of identical thermal capacity. Large dia. also means greater potential for deflection (pad knock back). Large dia. rotors probably decreases air flow for a given wheel diameter as well. So why large rotors?

It gives you better pedal modulation or feel by allowing you to use larger m/c bore (again, for a given combination), so that's probably one reason. Thinner packaging also helps reducing scrub radius - it's challenging to fit monster fixed calipers inside the rims with large positive offset due to spoke/caliper clearance, and thick rotors would move balljoint further away from the rim centerline.

As for the large brake obsession among street car people, it's one of those hot rodder things. "Gotta have bigger [fill in the blank] than the Jones" - I'm a very practical engineer and I never understand the mentality of wanting the widest tires in your town, but I suppose this isn't a bad thing (within reason) when it comes to brakes, since shorter stopping distance generally means better safety. On the other hand, I've heard of more than few people installing aftermarket mega-dollar brakes only to end up with lesser stopping power than OE drums due to improper pad break-in procedure, and they can't figure out what is wrong...

Anyway, yes, there is such thing as too much stopping power. Try a combination of 14" rotors, 1.5" 6-piston calipers, 3/4" M/C on 7:1 raito and hydroboost. Light tapping on the pedal is all it takes to lock up 13" wide slicks. That's neither safe on street nor fast at the track.

DarkBuddha
12-28-2004, 07:23 PM
As for the large brake obsession among street car people, it's one of those hot rodder things. "Gotta have bigger [fill in the blank] than the Jones" - I'm a very practical engineer and I never understand the mentality of wanting the widest tires in your town, but I suppose this isn't a bad thing (within reason) when it comes to brakes, since shorter stopping distance generally means better safety. On the other hand, I've heard of more than few people installing aftermarket mega-dollar brakes only to end up with lesser stopping power than OE drums due to improper pad break-in procedure, and they can't figure out what is wrong...
Pot stirrer! :scared: j/k

Thanks for that obviously informed bit of insight. More please. :icon_razz

Salt Racer
12-29-2004, 07:09 AM
Pot stirrer! :scared:

As a matter of fact I am, and long timers on this board already know that (I've been here since '02).

I just can't see why people would bother buying high performance parts, that they'd never be able to get the most out of, just to out-do neighbors or to satisfy their ego. Let me give you an example - Everyone knows what's going to happen if you put a 280*@.050", 0.750" lift solid roller cam in an otherwise-stock GM Goodwrench 350 (with proper valvetrain clearancing, of course). Would anyone do something like this just to get cool-lumpy idle at the expense of huge loss in torque/hp curve? I doubt most people would. I don't know why so many people can't understand tires, suspension, brakes, etc, are no different than engine. Good combination of parts and subsequent tuning are very important to make a car actually work.

If having a cool-looking car satisfies them more than having a fast car, more power to them. But if building car with cool-but-mismatched parts is what modern hot rodding is all about, I'd rather not to be called a hot rodder. I'd rather own/build well-balanced cars that actually work. I get much more satisfaction from going around road course as fast as I can, than getting a lot of ooh-ahh's at cruise nights and car shows.

nvawgn
12-29-2004, 09:57 AM
i heard the same thing, too much rotating mass is hard on the brakes

Ripper
01-03-2005, 02:14 AM
I'm with Katz on this one.

What many people forgets is a good cooling setup for their brakes. Doesn't matter how big brakes you have if you don't have any cooling (well... you won't notice it on the street, but places where you use the brakes - autox, trackdays etc).

I never had any brake fade on my (330mm discs with C5 calipers and Hawk pads), so I guess they're slightly overkill. When I build my new front end, I'll go with something around 300 mm instead.
Bigger brakes, produces bigger mass that consumes energy to be stopped, accelerated etc. It also gives more unsuspended mass, which give problems with traction and so on...