Why Big Brakes Won't Stop You Faster but Wider Tires Will - Friction and Surface Area Explained

I have made a few 75+ mph to zero stops recently (started highway commute) and full, hard as possible, brake press at 75+ did not lock up the tires and I did not feel or see the dash light up, that ABS triggered. I am wondering if a BBK would shorten the braking distance for me. Also, I am running oversized tires.

 

That seems concerning to me. Are you sure your braking system is working properly?

TBQH, I don’t know if ABS lights up on the dash when braking hard because I’m always looking out the windshield with my teeth clenched in those cases (typically when driving on snow/ice). I can definitely hear the pump operate though.

CAVEAT: I have an off-road thus I have a different ABS pump which I know is louder than the standard pump.

 

OP's taking a lot of heat for posting this video. It's not a bad video, it's just not the full picture of why people move to big brakes. Most people don't judge their brakes based off of the braking distance on the first application. The thing that moves most people to big brakes or performance brakes is brake fade. If you mountain bike, you 100% know the importance of good tires and big rotors for improving braking. Hell, rim brakes can lock up a tire several times. But on any decently long descent they are trash compared to disc brakes.

 

One thing in the video that confuses me is that he's spends a lot of time talking about how disc brakes can be modeled by Coulomb friction and thus a greater surface area does not equate to a greater friction force, but doesn't mention that the torque on the wheel is greater for larger diameter discs. In the end, I don't think it matters as long as the braking system is capable of applying enough force to lock up the wheels.

I think the title of the video is a bit misleading. His larger intention seems to be to describe the differences between Coulomb friction and the friction/adhesion of tires on a road surface.

 

He should have just left brakes out of the conversation altogether.

 

I have activated ABS before (like in the snow and ice) and dash lights do come on as well as I can hear and feel the pump coming on.

Not sure if my brakes are up to snuff. I assumed they're normal, they might not be. I do have warped rotors as the front vibrates when I press the brakes.

I want to replace the front brakes and was thinking of going to a BBK. If a BBK will not decrease my braking distance, I might stick with stock (which is great news).

I do drive pretty spiritly (supercharger, sway bars), as in curvy mountain roads at fast speeds - thinking that is now I warped my rotors.

I did put a BBK on my old 1994 4,200 pound Impala SS and it was an improvement on the road course. It did (mostly) stop fading the brakes which happened with the stock brakes.

 

My only thought is, what nut-job driver is making 8 successive panic stops to need that upgrade? It looks to me like the OEM parts did better for the first 5 stops.

 

I'm just one data point yet I've got a library of old car mags with tests from pretty much every major brake company that also shares the same data points. As well as racing background and even car manufacturers (which I gave an example of). Oh and my one data point also is actual real world testing not just a Youtube video with now actual scientific data to back up the claims (like actual testing).
You're right physics don't lie especially when you actually apply the physics to the real world and put them to the test and not just talk about it but do it and prove or disprove. They also don't lie when you apply all the different equations into the hypothesis and not just pick and choose which ones.

That's what my point was is there are many variables.

No the math is not that simple. Time to brake lock up, and if you have ABS, abs cycle time is also a factor. You get overrun of the brakes before lock up if the braking system is mismatched to the size of the wheel and tire. IF it was only about locking up a tire then newer performance cars wouldn't be coming with the brake packages they are coming with because we could technically lock up a super car tire with Ford pinto brakes. In fact we'd all be using drum brakes still........ Tire adhesion to the road surface is the final point in the equation. Which is why I pointed out how my big ass MT tires suck and you'd get better braking from stock size HT tires.

You're absolutely correct that tires will react different to different surfaces as well as conditions on those surfaces. But when we're talking purely about BBKs and their benefits or lack of then you have to assume and use the same tire same road surface and conditions as the constant. Otherwise you can skew your experiment.

 

Push harder.
https://www.youtube.com/watch?v=EGUZJVY-sHo

 

I've tripped abs at... wanna say like 60ish? Started braking due to slowing traffic at like 75, was full-on panic crushing the peddle at like 60. I'm on 33s with some extra weight, not alot maybe 100-150 pounds.

 

While not an engineer, I worked for StopTech for 15 years. I know a thing or 2 about BBKs

 

Seems like my stopping distance might not be shortened with a BBK. They do look cool and I don’t really want warped rotors again. Not sure what I’m going to do. Replace stock or BBK.

 

Your stopping distance will most certainly be shorter with a BBK, but not because it creates more torque. It's because they make the same torque with a larger rotor, and smaller hydraulic sizes...as well as Stainless Braided lines, and a few other contributing factors that result in a firmer, higher brake pedal. This gives you the ability to modulate the brakes much better, and keep them closer the threshold of lockup with a greater level of control....which is where your "performance" comes from. You'll also typically have greater heat capacity, or not, depending on rotor size and design, and pads.

also, rotors don't warp. (this should end well....lol)

 

Here is a follow-up video in which he addresses the question about larger discs having more torque.

https://www.youtube.com/watch?v=Ql9eYh31kTw

 

When I step on the brakes my tires shimmy and my steering wheel goes back an forth in rhythm with my speed. The vibration starts immediately when I hit the brakes and stops immediately when I let off the brakes. If not un-smooth rotor surfaces, what is it?

 

Rotors dont really warp, its pad material transferring to your rotor.

 

Every time this subject comes up, I truly do want to hear out both sides… I’m not a very stubborn person, but I really cannot deny the night and day difference between the stock setup and the Stoptech bbk kit (front and rear)...

Some people may say it’s the extra pistons, some may say it’s the brake surface, the slots, the rear disc upgrade, the braided lines, the pads, rear brake load bias, and some say it’s all in my head… all I know is the difference is so obvious it feels odd to debate it. I brake harder, faster, and most importantly, with more control. I can modulate the brakes with more precision, and achieve max braking performance with less effort and faster.

The biggest difference is on the highway. I live in South Florida, lots of accidents, lots of traffic, and lots of blind hill cresses to stopped traffic or debris.

The truck doesn’t nose dive as much. Discs are still arrow straight even after a couple highway speed panic stops… for me, it’s made a huge impact and I feel much safer as a result. Not sure if it one particular reason or a combo of a little bit of everything.







…Plus they look cool

 

As I mentioned earlier, when we increase the rotor size with a BBK, we need to REDUCE the piston surface area. The objective is not necessarily to create a higher torque...we can achieve plenty of torque the with the OEM brakes to lock up the wheels. With the smaller pistons (and the SS lines) as well as a well designed stiff caliper, you get a firmer pedal which creates the same torque with the same pedal effort but much less pedal travel and mush. This is where the increased control comes from and the consequent shorter stopping distances.