Braking distance for ONE hard stop...

Shouldn't most modern cars with (good quality) ABS stop in approximately the same distance, provided the tires are the same? Above certain speeds, the heat dissipating qualities of the brake system surely come into play, but from, say, 80-100mph to a complete stop (on a smooth surface), should we not see fairly consistent results?

Seems to me that the ability to modulate on the edge of traction is the most significant factor, which modern ABS is pretty excellent at.

Reason I ask is because I recently drove a rental Altima S with extremely touchy brakes, and whatever tires it was running were enough to haul me down from 80mph MUCH faster than my Miata with high performance summers.

If your not breaking traction abs isn't really doing anything. Also there's a whole lot more to braking than just abs and tires, like the brakes themselves, rotor diameter, pad dimensions, caliper piston sizes ect. Miatas don't have good brakes anyways so it's no doubt a new Altima stops faster

Well, in fact if you are talking about only the modulation at the limit of traction (like in a single panic stop situation), then you are right, rotor size, pads, thermal mass, etc don't make any dang difference at all.

(if you don't believe me, I ask you if the car can lock up the wheels if you brake hard enough. Every car almost ever could do this. If it can't something is not working properly. So stock brakes almost always have enough power to overcome the traction of the tires.)

We have to remember though that with braking comes weight transfer. And with weight transfer comes suspension movement. and with suspension movement comes changes in traction. So absolutely some cars can 'use' the traction of the tire more effectively under braking than others.

Finally, ABS now /= ABS in 1995. I dunno when your miata is from, but modern ABS systems are much more effective than early systems.

chiodos wrote: If your not breaking traction abs isn't really doing anything. Also there's a whole lot more to braking than just abs and tires, like the brakes themselves, rotor diameter, pad dimensions, caliper piston sizes ect. Miatas don't have good brakes anyways so it's no doubt a new Altima stops faster

Brakes/rotors/pads shouldn't make a difference in braking power for the first stop (where heat capacity isn't a problem), assuming that the brakes have enough power to lock up the wheels (in other words, no icy cold race pads or incredibly crappy pads)

ABS optimizes brake usage and brake bias, but there are other factors to consider apart from tire size: Weight is a big one. Aerodynamics will even make a tiny difference (think of it as how much always-on air brake your car is using).

So if you had two random modern ABS cars with the same wheels and tires and the same weight, and they both have brake pads that will bite well when cold and brake systems that won't fade within the first stop, then their first-stop performance should be very similar.

Wouldn't vehicle weight, and weight distribution still play a huge role in stopping distance by affecting how well the tires can grip before slipping (when ABS kicks in)?

I'd also ask if you tested your hypothesis or if you simply went with "butt-dyno" to confirm that the Altima stopped better than the Miata.

I thought my Passat had AMAZING brakes until I autocrossed it and discovered that they really struggled. By comparison my Miata doesn't ever "feel" like it's slowing as aggressively but the numbers tell the tale differently.

All that said, I've driven Miatas that didn't brake well. Maybe yours needs some help.

The answer you're looking for is yes, tires (traction) are the #1 factor in braking distance.

FanBoi.....Yo, I’m upgrading my brakes

Engineer...I’m sorry to hear you’re currently experiencing brake fade

FanBoi.....What are you talking about, that never happens

Engineer...

STM317 wrote: Wouldn't vehicle weight, and weight distribution still play a huge role in stopping distance by affecting how well the tires can grip before slipping (when ABS kicks in)?

Weight distribution does -- the tire grip goes up with the weight on the tire but it's not linear, so a car with a rear weight bias (like a 911) is going to give better max theoretical braking performance.

And yes, early ABS systems are way less effective than modern ones. Electronic brake force distribution (EBD) substantially improves the amount of braking you can do on the rear wheels over the mechanical prop valves on early Miatas.

Also note that alignment will come into effect. A Miata is often set up with a bunch of negative camber to provide cornering grip, but that works against you when braking where you'd ideally want to have 0 camber.

I suspect the biggest butt-dyno factor though, is that Miatas don't have grabby brakes like many cars do these days. Your butt dyno is much more sensitive to the "jerk" than to acceleration, so something that goes to max braking faster is going to feel like it's braking more. ("jerk" being the rate of change of acceleration, or the 3rd derivative of position).

Of course, suspension, alignment, tire type, current level of wear, and pressure as well as the entire brake system all play a role.

Newer cars like the Altima you drove may also be equipped with brake assist, boosting the brake line pressure for you when the system senses a sudden, heavy application of the brake pedal. Pretty common these days.

RX Reven' wrote: FanBoi.....Yo, I’m upgrading my brakes

So /DRIVE just published a 50-0 mph brake test using a late model BMW 328i. Wheels/tires were the same on every run; pads/rotors/calipers were the variables. Their results?

Stock brakes, first run stopping distance - 86' 5"
Hawk pads, first run stopping distance - 75' 3"
AP Racing big brake kit, first run stopping distance - 71' 5"

Maybe Fanboi was on to something?

Single stop distance is all about tire quality and proportioning. Wheelbase and cg height are also factors, but mostly it's about the brakes' ability to use the traction available.

In reply to nderwater:

No, you are right. There is such a thing as functional brake upgrades. My theory is the pad heats up, even though its a single, 60-0 run. The stock pad was already worn, and probably heats up faster and thus loses stopping efficiency. The new pad is able to stay grippier over a longer braking distance because its newer and made of a better compound.

I guarantee this effect and the difference between the two pads would be dramatically exaggerated with a greater speed (say 120-0 mph)

If all the cars were equipped with identical abs and tires, they would all make that one test stop in nearly the same distance. Which, when you look at overall testing, they already kinda do. There generally isn't a huge difference between cars.

Add in tire differences, especially sticky performance tires on one car and low friction eco-weenie tires on another car, and you force the two to have different stopping differences.

Weight bias can also have an effect. As well the pitching of the car. Not huge tremendous differences normally, but an empty pickup truck is trying to stop with its front wheels only (slight exaggeration), while a Miata is actually using all 4 wheels.

The nature of the ABS can also make a difference. They work differently and can produce somewhat different stopping differences as a result. Rate of cycling, sensitivity, etc.

Lastly the braking system itself can significantly affect how quickly the brakes can be applied. GM in general are hard to slam the brakes on in. It's like there's a restrictor that blocks it, forcing a slower gradual pressing of the pedal. So you're a fair ways down the road still waiting for the wheels to brake hard. Unlike say a Nissan, where when you slam the brake pedal the wheels instantly lock.

In summary, if all things were equal, the stopping distances would be identical. All things are not equal, so the stopping distances are not equal.

Keith Tanner wrote: Single stop distance is all about tire quality and proportioning. Wheelbase and cg height are also factors, but mostly it's about the brakes' ability to use the traction available.

This right here. I thought the whole point of ABS was keeping the ability to steer in a panic stop situation, assuming you're not panicking and still able to steer. All things equal, a non-abs car should stop slightly quicker/shorter, than an abs equipped car. Remember, all things equal, most being the tires.

nderwater wrote:

RX Reven' wrote: FanBoi.....Yo, I’m upgrading my brakes

So /DRIVE just published a 50-0 mph brake test using a late model BMW 328i. Wheels/tires were the same on every run; pads/rotors/calipers were the variables. Their results? Stock brakes, first run stopping distance - 86' 5" Hawk pads, first run stopping distance - 75' 3" AP Racing big brake kit, first run stopping distance - 71' 5" Maybe Fanboi was on to something?

Interesting. I wonder if this is from an advantage in initial bite, or from the pad advantage during the steady state stopping, or both?

Or poor testing techniques? I can't watch the video right now, but you could get quite a variation by trying to do this test with only human drivers and cones.

Robbie wrote: (if you don't believe me, I ask you if the car can lock up the wheels if you brake hard enough. Every car almost ever could do this. If it can't something is not working properly. So stock brakes almost always have enough power to overcome the traction of the tires.)

Most cars can do this with cold OEM pads. Lets say you brake from 50-0. At the 30mph point during that stop, you may have put enough heat into the brakes that even if you stood on them they could no longer lock the wheel.

I.E. they may be traction limited for the first 50ft. of an emergency stop, then thermally/compound limited afterward.

on an older car without ABS, the braking distances would be more or less the same, based on the tyre and how much black stuff you wanted to leave behind in a skidmark. Simply because almost all cars have the ability to lock up the tyres with their brakes.

With ABS involved, pads and rotors come into play as now they are forced to actually work, rather than grabbing on and not letting go.

foxtrapper wrote: In summary, if all things were equal, all things would be equal.

I get what you mean though Foxtrapper.

gjz30075 wrote:

Keith Tanner wrote: Single stop distance is all about tire quality and proportioning. Wheelbase and cg height are also factors, but mostly it's about the brakes' ability to use the traction available.

This right here. I thought the whole point of ABS was keeping the ability to steer in a panic stop situation, assuming you're not panicking and still able to steer. All things equal, a non-abs car should stop slightly quicker/shorter, than an abs equipped car. Remember, all things equal, most being the tires.

Where do you get that? ABS equipped cars stop sooner than non-ABS cars. Given that best braking happens at impending lock-up, a car that can put each tire at absolute maximum and regulate the braking force many times a second WILL stop faster than the one with all four wheels skidding or waiting for that incredibly slow organic being to recognize that the car is skidding and tries to modulate his braking force.

nderwater wrote:

RX Reven' wrote: FanBoi.....Yo, I’m upgrading my brakes

So /DRIVE just published a 50-0 mph brake test using a late model BMW 328i. Wheels/tires were the same on every run; pads/rotors/calipers were the variables. Their results? Stock brakes, first run stopping distance - 86' 5" Hawk pads, first run stopping distance - 75' 3" AP Racing big brake kit, first run stopping distance - 71' 5" Maybe Fanboi was on to something?

Hi nderwater,

Admittedly, my post was overly simplistic…I was trying to be funny and direct attention towards the most important factor.

Getting more technical, I would expect that a pad / rotor system that’s operating near its limit would have more variability than one that has significant reserve capacity. This variability needs to be accounted for by operating at a reduced average braking force level so that the peaks in braking force don’t exceed the tires gripping limits resulting in a skid.

So yes, I do believe upgrading the brakes will reduce stopping distance even if the existing brakes are capable of locking the tires. However, assuming we’re talking about an upgrade that includes larger rotors, both rotational mass and un-sprung weight will be increased which is bad M-Kay.

KyAllroad wrote:

gjz30075 wrote:

Keith Tanner wrote: Single stop distance is all about tire quality and proportioning. Wheelbase and cg height are also factors, but mostly it's about the brakes' ability to use the traction available.

This right here. I thought the whole point of ABS was keeping the ability to steer in a panic stop situation, assuming you're not panicking and still able to steer. All things equal, a non-abs car should stop slightly quicker/shorter, than an abs equipped car. Remember, all things equal, most being the tires.

Where do you get that? ABS equipped cars stop sooner than non-ABS cars. Given that best braking happens at impending lock-up, a car that can put each tire at absolute maximum and regulate the braking force many times a second WILL stop faster than the one with all four wheels skidding or waiting for that incredibly slow organic being to recognize that the car is skidding and tries to modulate his braking force.

I think in the earliest iterations of ABS this may have been true to some extent. I remember some kind of test where a pro driver could stop an identical car quicker with non-abs brakes than with abs. I think this was solely a result of the ABS of the era being pretty dumb and not keeping the car as close to max traction as the pro driver could. Even then a normal driver would probably be out-braked by the old ABS. I remember retaining directional control being touted in the media some as well. With today's level of controls shorter braking distance is the biggest benefit, but I wouldn't discount the importance of maintaining directional control. I remember specifically tuning drum brake vehicles to lock the rears first (barely) for that very purpose.

RX Reven' wrote: Admittedly, my post was overly simplistic…I was trying to be funny and direct attention towards the most important factor.

I wasn't trying to be critical, by the way -- in fact, I was just as surprised by their 'real world' test results as anyone. This seems to be yet another instance where YMMV, and where conventional wisdom may not always apply.

Suspension geometry plays a much larger role than is being credited.

An aside, I have NEVER had a car that could lock the brakes on dry pavement at all speeds unless you spiked the brakes instead of applied them

KyAllroad wrote:

gjz30075 wrote:

Keith Tanner wrote: Single stop distance is all about tire quality and proportioning. Wheelbase and cg height are also factors, but mostly it's about the brakes' ability to use the traction available.

This right here. I thought the whole point of ABS was keeping the ability to steer in a panic stop situation, assuming you're not panicking and still able to steer. All things equal, a non-abs car should stop slightly quicker/shorter, than an abs equipped car. Remember, all things equal, most being the tires.

Where do you get that? ABS equipped cars stop sooner than non-ABS cars.

Right here: http://media.daimler.com/dcmedia/0-921-657486-1-803841-1-0-0-0-0-1-11701-614318-0-1-0-0-0-0-0.html

It all has to do with control, not distance, which is the OPs concern.

Given the fact that today's cars have wider, grippier tires than cars in the past, skews results