Braking distance
 

After a close call with a deer jumping over the hood of my camaro, I'm curious what is the largest factor in determining a car's stoping distance. Is it the tires or brakes, assuming all other factors are equal? Also, not in track type situation where the brakes are getting cherry red, but a street type scenario where you make one panic stop and inches really matter.

A chain is only as strong as its weakest link. Put cheap tires on and there’s your limiting factor. Great tires but so-so brakes? Well, brakes are your limiting factor. Then of course there’s road conditions to consider. Dry, wet, warm, cold, surface type.

Definitely tires for a single dry panic stop.

Fuel economy focused all season tires with high treadwear ratings take around 100' to stop from 50mph vs. under 80' for sticky tires with lower treadwear ratings around 200.

https://m.tirerack.com/tires/tests/t...b=ResultCharts

https://m.tirerack.com/tires/tests/t...b=ResultCharts

Remaining tread depth makes a huge difference for wet panic stops:
https://youtube.com/watch?v=zA6MUlVNkLM

Any brake pad designed for a specific car is going to be able to engage ABS on the first panic stop (or lock up the tires if the car doesn't have ABS). Unless there is a condition along the lines of zero brake pad material remaining or low brake fluid or some part of the braking system being broken, then brakes will not be your limiting factor for a single panic stop.

You could even stop an average car with the accelerator stuck at 100% throttle without the brakes failing:

"even with the engine racing at full throttle, Popular Mechanics editors have demonstrated a 2010 Toyota Camry with none of the recent fixes braking uneventfully to a stop from highway speed, so the brakes should easily stop the car."

https://www.nbcnews.com/id/wbna35783011

The ABS system, the brakes, the suspension, the tires... they're all part of a complete design intended to work together. So you mostly only have the opportunity to weaken the complete system by swapping in components that are of lesser capability than what was baked into the original design.

Your point about the tires having the biggest impact makes sense as it's the one thing that the consumer may replace with something that doesn't carry the same abilities as the original ones. And, even if they're replaced with something "better", the rest of the system may not be able to take full advantage (although the ABS may kick in later due to reduce wheel slip, and that could shorten up the stopping distance). Even with a significant upgrade, though, the improvements are only likely to go "so far."

That Camry also only has 170hp/tq

I won't be the one to test it, but do you think a high-power sports/muscle car (Camaro, Mustang, Chally, M4, S/RS5, AMg 'vette, etC) would be able to overpower their brakes?

That would be vastly more interesting than a Camry, though I understand why the Camry was chosen.

I recall an article in either Car and Driver or Road and Track from, I'm guessing mid '80's - early '90's. It was back when "unintended acceleration" was a major topic of debate in automotive circles. Anyway, they compared the stopping distances for a wide variety of vehicles under normal conditions and with the throttles rigged wide open. The stopping distances at w.o.t. weren't appreciably longer for any of the vehicles tested. Granted, no vehicles from that era had anything close to the power of a current gen ZL1, but the results were still surprising. It would be interesting to repeat this testing with modern vehicles.

I didn't realize unintended acceleration went back that far, I recall it being an "issue" circa 2010 for Toyotas.

I'd hope the brakes could overpower, but would be interesting for someone to test with a ZL1, GT500, Hellcat, etc.

Your stereo is only as good as your worst component

Same for computers, and cars.

These cars are also designed that under track/panic braking the car down shifts hard to the lowest possible gear and in doing so you deaccelerate faster as long as your foot is off the gas pedal which is usually the case in such scenarios.

Think of it like an engine brake for a semi-truck.

I did personally have an incident involving a construction truck and a construction barrel.

Tires are the first step to effective braking. I had summer tires 300 TW in the front and 220 in the back. Responsive handling at high speed in my case 60mph avoiding a construction barrel that was hit by a construction truck which threw the barrel the equivalent to 4 highway lanes in front of me. Braking hard and swirving at the same time to avoid the first barrel, and again to avoid the second barrel.

Modern cars in the US all tend to have electronic throttles rather than cable throttles so it is easy for manufacturers to program them to cut the throttle if the car sees full throttle and hard braking at the same time. In 2019, "NHTSA said all automakers have voluntarily installed brake throttle override systems on all new vehicles and the agency does not anticipate any automakers removing the system.". Technically this is not required though because NHTSA dropped the proposed requirement in 2019.

https://www.businessinsider.com/brak...tandard-2012-5

https://www.reuters.com/article/us-a...-idUSKCN1SJ1UL

Side note: on the Camaro SS 1LE I have experimented with using a light brake pedal application for around a second with my left foot while at a steady throttle position in a specific turn on one track to slightly modify the front to rear balance for a bit more front grip and the car did not cut throttle so there may be a delay or minimum amount of braking required before throttle cut kicks in. Similarly, I have seen PDR videos of Camaro drivers who manually blip the throttle to rev match downshifts during hard braking on track and the car allows that too without cutting throttle.

If you are already threshold braking or have engaged ABS, that is the limit of grip that the tires can provide. Downshifting during this time won't make you stop any faster but it will reduce brake pad wear and reduce the amount of heat generated by the brakes.

The concept you guys are describing is correct, but it is only true in a "heavy use" situation such as driving on a road course track or maybe, MAYBE, canyon runs.

The OEM brakes in any car are normally fine to stop the car for a few panic stops in row before the pads get overheated and fade. Like was said by others here, if you can lock up the brakes (ABS), then the brakes are more capable than the tires (thus tires will be the thing to improve stopping distance).

On the track, it can be a different story because the brakes get used far more heavily and frequently than they do on the road or typical enthusiast driving. For a track driven vehicle, once you start upgrading any single part (tires, brakes, engine, suspension improvement, etc) you typically put more demands on the other components, and one of those components then becomes the weakest link in the overall system performance.

Providing additional braking from the engine is not likely to add much, if any, to the overall braking power. In a front-drive vehicle, you're still going to be at the full limit of braking power from the brakes alone before ABS kicks in. In a rear-drive vehicle, you're adding braking strength to the weaker half of the braking system - weight shifts forward to the front wheels and reduces the overall capability of the rear wheels to provide meaningful amounts of braking effort whether by brakes or from the engine. The rear wheels have a big reduction in grip during heavy braking.

It will shorten your stopping distance, due to reverse torque of the gear.

Its not a true engine brake like on a semi, but it will definitely stop you faster than running at the highest possible gear under the same condition.