DerekACS

Does anyone have any test data that indicates whether the Sport front brakes (part of the AMG Sport package on 2014-W212), with their larger drilled rotors, actually decrease stopping distances ?

Are the front callipers the same size on Sport and non-Sport front brakes ?

ss3964spd

My first guess would be no, not likely, because by and large stopping distance ultimately comes down to friction between the tire and the road. Fitting larger, or stickier tires would decrease stopping distance - assuming the brake system has enough power to lock the wheels.

The most likely benefit of the sport brakes is resistance to heat induced brake fade from repeated hard/high(er) speed stops, and perhaps an extra helping of brake feel.

DMan918

ss3964spd is correct. Tires for stopping distance, brakes to reduce fade.

DerekACS

Yes, your first statement makes perfect sense. From my experience of driving various BMWs and MBs, I am very aware that stickier tires (e.g.. summer performance tires vs all seasons) improve braking performance.

And your 2nd comment is pertinent to the drilled rotors supplied with the W212 Sport front brakes. The main purpose of the drilling is to disperse heat faster.

My questions arose after a MB sales representative claimed benefits of Sport brakes ("10-15% shorter stopping distance"). I have yet to read of any study backing up his claims, but I thought I should ask Forum members for their input.

Thank you for your logical comments !!!

KEY08

If shorter stopping distances were easily achievable with big brakes, every manufacturer would have a simple way to make their cars "stop on a dime". As said, It doesn't work that way. Big brakes, drilled rotors, 6 piston calipers, will provide less fade and potentially more reliability and that is it. It takes the right suspension and TIRES to bring the car to a stop in a shorter distance. Race cars run with slicks to create the largest contact patch possible to use all of the brakes they have. Simple physics and your sales person is full of it.

ss3964spd

How can that be?

To be fair, one could make the argument that under certain circumstances the bigger brakes do reduce stopping distance over the smaller brakes.

First off the only difference for the comparison is the brake rotors and calipers. Everything else is the same; suspension, weight, wheels, tires, pad compound, even road surface and temp.

Say the small brakes will haul the car down from 60 in 120 feet in 3 back to back hard stops before they get hot and start to fade. Once they fade stopping distance increases. The big brakes, however, may be good for 1 or 2 more of those same hard stops before they start to fade. Under that scenario the big brakes do reduce stopping distance. Another scenario where bigger brakes have an advantage is at high speeds, like slowing the car down from 120 to 60. The small brakes may over heat and fade very quickly whereas the bigger brakes will hang in there a bit longer. But that's not "stopping distance".

To make the statement that the bigger brakes reduce stopping distance without adding some qualifiers is just incorrect.

Arrie

Are you sure the non-sports smaller brakes are strong enough to lock the front wheels if the car is going 150 mph on dry pavement with good gripping tires?


The AMG model cars can go even faster than that (have seen many times) and these cars are built for the speed on German Autobahn.


At those speeds you need to count for the down force, which I don't know how much it is, but it is present and can significantly add to the force between the tire and the road surface, i.e. the stronger brakes can actually give the benefit of the stronger brakes when the smaller bakes would not be able to come close to locking the wheels, which is the max braking force possible.

KEY08

Yeah, I don't think the discussion was necessarily about stopping a car from 150 to 0 . Wrong forum for that.

pamiboy

And wrong car as well.

cleankutazn

Interesting, you learn something everyday. I always thought bigger brakes meant better stopping distance. So all I have to do to stop better is to get wider tires? How much wider than the stock 265 would make a difference?

KEY08

It's the contact patch and compound. The widest and stickiest tire gets the advantage on dry pavement. On snow, it is the skinny tire that rules the day as it can cut down to the pavement quicker instead of riding on top of it. I would not put wider tires on the front unless you live outside the snow belt.

petee1997

If both cars have the same tires the sport brakes will stop the car faster with less fade. If you compare four pistons to six, again much more braking power at high speed. The combination of stickier tires and a larger six piston cross drilled brake is the best option for braking.

I have owned many Porsches 911's and the S model has the bigger six piston cross drilled brakes. You can feel the difference on the first drive. These cars are always rated in 0 to 60 and 60 to 0. Quality brakes do make a difference.

ss3964spd

You're going to need to explain how this is so, Pete, under what circumstances.

In a typical 60-0, all out emergency stop it all comes down to tire to road friction (assuming the brakes aren't already hot/over heated). If the small brakes have enough power to lock the wheels during the duration of that single stop (before ABS intervenes) then bigger, more powerful brakes are not going to stop the car any shorter - assuming all else is equal; contact patch, rubber compound, road surface and temp, etc-etc.

Start throwing in other scenarios/conditions then yes, bigger brakes can stop the car sorter. But referring to the comment the OP's sales guy made, which is a blanket statement, it isn't factual.

I'm pretty sure drilled rotors are also a trade off because of the slightly decreased friction area of the rotor (decreased by the sum of the area of the drilled holes). Theoretically, a solid disk should perform better at typical commuting speeds whereas a drilled rotor should perform better at much higher speeds.