Do all cars really need bigger brakes?

In reply to Pete. (l33t FS) :

Sounds like Nissan nailed the pad choice.

They were (gack) NAPA Ultra Premium or whatever their top tier ceramics were called.  They didn't work worth a flip when cold and wet, though, which is the only similarity the two cars had 

This was close to twenty years ago, I am sure things have changed since then.

ShawnG said:

If you can lock up the wheels, you have enough brake.

What you want is good modulation and fade resistance. 

I've been on record before that I vehemently disagree with that line of thinking. 

For example on old motorcycles with drum front brakes; lets say 15lbs of lever results in point .5g deceleration and then 20 lbs results in .6G of deceleration............after that you get nothing until at 50lbs of lever pressure which finally results in the tire locking up.

That is not a modulation problem; that's a basic design problem usually a result of undersized brakes.

Standard Datsun 1200s have this issue; at high speeds there is a point where increased pedal pressure offers no more increase in deceleration and eventually an exponentially higher pedal effort results in wheel lock up.

I know the whole if you can lock a wheel thing is widely accepted but it's an oversimplified statement that simply isn't accurate.......I could add examples ad nauseam (and probably have)

In reply to Tom1200 :

It sounds more like a design problem in the brake linkage. If that force isn't transferred to the pads you might get that sort of behavior. There could be a lot or reasons for it. Flex, mechanical limits, leverage changes in motion range. Better designed brakes might help, but larger brakes... maybe just as a byproduct of fixing design issues.

theruleslawyer said:

In reply to Tom1200 :

It sounds more like a design problem in the brake linkage. If that force isn't transferred to the pads you might get that sort of behavior. There could be a lot or reasons for it. Flex, mechanical limits, leverage changes in motion range. Better designed brakes might help, but larger brakes... maybe just as a byproduct of fixing design issues.

I'll stick with the Datsun for the moment

The stock front brakes are 8" rotors with 42mm x 62mm pads. These are fine for a 1600lbs car traveling 60 mph but ratchet that up to 80 mph and the brakes aren't really capable of bringing the tire to the point of lock up. 

So you end up with the aforementioned monster pedal force before they finally lock up; the braking doesn't really increase between 50lbs of pedal pressure and say 150lbs where the tires finally lock.

There are numerous economy cars from the 70s and 80s that suffer the same fate; they were never designed to be making hard stops above 70-75mph. 

So back to more modern cars. My 2011 Outback is boderline. The pedal effort between very hard stop and threshold braking to tripping the ABS is not linear. The brakes are adequate but it really needs more/bigger brakes.  Granted in the 14 years I've owned it a brake upgrade would have been truly used 5-6 times. 99.9% of the people driving them would never notice.

In reply to Tom1200 :

I've had pads where the response was decidedly nonlinear.  More pedal force did not lead to more deceleration once past a certain point.  This is definitely a pad composition issue.  It's like pads that are grabby but with the knee in the curve further out.  New/different pads always cured it.

Last week I had a vehicle with a "spongy pedal/pedal goes to the floor" concern.  The pedal feel was actually rather good, but it took so much force to slow down that you were able to mush things through.  The pads had no initial bite and they never really increased in force from there.

In reply to Pete. (l33t FS) :

So early on with the 1200 we went with Ferodo pads and for the street they were pretty good. The initial bite was good and they got rid of the wooden feel but the overall issue was still there.

I do realize most modern cars will never have this issue but older Japanese cars had very undersized brakes........especially the economy cars.

Tom1200 said:

theruleslawyer said:

In reply to Tom1200 :

It sounds more like a design problem in the brake linkage. If that force isn't transferred to the pads you might get that sort of behavior. There could be a lot or reasons for it. Flex, mechanical limits, leverage changes in motion range. Better designed brakes might help, but larger brakes... maybe just as a byproduct of fixing design issues.

I'll stick with the Datsun for the moment

The stock front brakes are 8" rotors with 42mm x 62mm pads. These are fine for a 1600lbs car traveling 60 mph but ratchet that up to 80 mph and the brakes aren't really capable of bringing the tire to the point of lock up. 

So you end up with the aforementioned monster pedal force before they finally lock up; the braking doesn't really increase between 50lbs of pedal pressure and say 150lbs where the tires finally lock.

There are numerous economy cars from the 70s and 80s that suffer the same fate; they were never designed to be making hard stops above 70-75mph. 

So back to more modern cars. My 2011 Outback is boderline. The pedal effort between very hard stop and threshold braking to tripping the ABS is not linear. The brakes are adequate but it really needs more/bigger brakes.  Granted in the 14 years I've owned it a brake upgrade would have been truly used 5-6 times. 99.9% of the people driving them would never notice.

I think you're missing the point. I'm not saying it doesn't happen. I'm saying its likely to poor design decisions in the brake system not directly related to the brake size. The ability to lock up at any pressure suggests that the SIZE is okay. It just need something else fixed. Lots of cheap slide calipers for example will flex like crazy. A really non linear pedal doesn't sound like a brake sizing issue. I'd bet cars with these really non linear pedals get bad pad taper if used in that region much.

I also strongly disagree with the miata.net chestnut that being able to lock the wheels up means there's enough brake. 

By this logic the ideal brake diameter would just be a few inches and you just need a caliper rigid enough to clamp it hard enough to stop the axle from rotating.

It completely ignores what brakes are actually used for, which is slowing the car WITHOUT locking the wheels. Nobody actually wants the axle to stop turning completely, that's not a real use case. 

This mantra was repeated over and over to me and it held me back for years. The stock 1.8 brakes on a miata are not adequate for a car with 250+ whp. They just aren't. The end. They can't shed enough energy quickly enough. Because that's what brakes do, they turn the kinetic energy of the car into heat energy. If the pad area is too small, there will be too much heat in very very short order and the disc will rapidly expand, the pad will start melting, and the brakes will not be predictable or reliable, and modulation, which is actually super, super important, will go out of the window. Brakes are for shedding energy. Not stopping the axle from turning, that's just a side effect of their function. 

In reply to theruleslawyer :

Both the 1200 caliper and the 280ZX are sliding calipers......trust I understand the whole flexing brake parts (I raced vintage motocross) but in this case it's a brake sizing issue.

dr_strangeland said:

The stock 1.8 brakes on a miata are not adequate for a car with 250+ whp. They just aren't. The end. They can't shed enough energy quickly enough. Because that's what brakes do, they turn the kinetic energy of the car into heat energy.

For street driving the weight of the vehicle (or combined vehicle in the case of towing) is much more important to the brake size than the horsepower.  A car with double the stock horsepower will accelerate twice as fast, but assuming you're driving in a normal way it doesn't really change how often you brake, or how much speed you bleed off when you brake.  Track driving is obviously a totally different case.

There are also other reasons for wanting to upgrade the stock brakes, such as improving modulation and reducing unsprung weight.

codrus (Forum Supporter) said:

There are also other reasons for wanting to upgrade the stock brakes, such as improving modulation and reducing unsprung weight.

 

I think upgraded brakes on the Outback would benefit the modulation; I can't stand brakes that are the least bit non linear.

My brake benchmark is a motorcycle. An Aprilia with Brembos.

All the power you could want, totally linear, not at all grabby.

Agree strongly with the folks who point out that there's so much more to ideal brakes than whether they can lock the tires, or even whether they can do it repeatedly or with low effort.

 Virtually all cars could be improved with better brakes, even if they're pretty good.

In reply to codrus (Forum Supporter) :

if you can lock up the wheels at speed, then you have maximum "stopping power".

if they fade....can't lock up...then you need heat management :

reduce speed

space out runs

pad compound 

ducting

better disc venting

larger disc mass

In reply to wspohn :

corvettes also used the magnesium fans.

good time to note that "ducting" must go all the way to the center of the disc.

I've been looking at 'upgrading' my 94 e36 front brakes because of the v8 swap. Currently I doubt it's making much more HP than stock, but I have a feeling torque is exceeding factory spec, and as I get things more sorted out that number is going to go up. Plan is just the E46 330 front rotors and calipers (still looking more into this) and figure out what will be a good street pad for it, then upgrade the rears to a same / similar pad compound. 

In reply to BimmerMaven :

I invite you to get a Datsun 1200 up to 90mph and then try to stop it rapidly. Yes you can lock up the wheels..............if you use 150lbs of pedal pressure. There are many systems that will do nothing between say 50lbs of pedal pressure and the aforementioned 150lbs of pedal pressure.

I know I am flogging a dead horse here but that statement is so casually used and it's not accurate when it comes to the older cars I race. 

In reply to Tom1200 :

I used to spend all my time on a bike.  The local trails are slow and technical, with some steep sections.  Lots of soft black dirt, leaf coverage, roots, rocks.

One of the favorite things I used to do going downhill was to creep as slow as possible, keeping the back tire hovering off the ground.  I had my cantilevers set up so that the modulation was incredible, the ability to find the braking force vs traction balance, only two fingers needed on the lever.  It was exhilirating.

If you want to lock up the brakes, throw a stick in the wheel.  If you want to be able to maximize how effectively you can use the traction you have, you need good brakes.

Also, floor pivot brakes in a car are superior for ergonomic reasons and you can't change my mind

In reply to Pete. (l33t FS) :

That's exactly what I am talking about.

BimmerMaven said:

In reply to wspohn :

corvettes also used the magnesium fans.

good time to note that "ducting" must go all the way to the center of the disc.

Yes - I have seen some half-assed installations where the ducting ends in the vague region of the disc and does far less than it could or should.

Best arrangements are basically a sheet metal can with a slot cut in the side so that it fits over the rotor and a hose ducting air into the open end of the can.  You have to be careful to make sure that nothing can touch on full suspension bounce or full steering lock.  I will admit to coming up short on that myself during my learning/development curve on one of my race cars, when I failed securely attach the hosing (I was using plastic coated heater dryer hose) away from anything that could conceivably touch it. I ended up looking like my car was trailing a huge eviscerated worm behind the car, as a tire had touched the accordion hose and  and torn it apart.   

I the case where the brakes were being asked to stop a heavier car than they were designed for, is it safe to say that a longer lever (bigger rotor) is a good idea? The Molvo is essentially a 2700 lb Miata and the brakes are not as confidence inspiring as a stock Miata.  Plan is 11 inch rotors a proportioning valve and some testing on a quiet country road.

In reply to NOHOME :

Let us know how it goes.