Braking Distance - Explained

What determines how quickly a car can stop? How do tires and brakes affect braking distance? This video explains an equation that can be used to determine how well a car brakes.

Want to include factors such as rain or ABS no ABS? Here is how to alter the equation. In the original equation, multiply u (frictional coefficient) by acceleration, so the new equation reads:
D=0.5*V^2/(u*a)
Leave a as 1, and change u according to the condition.
With ABS ON: u can be considered 1, since ABS will attempt to maintain peak friction.
With ABS OFF: u will be less than 1, and will equal the frictional coefficient of a tire slipping on pavement.
With RAIN, and ABS ON: u will be less than 1, and will equal the frictional coefficient of a tire on wet pavement.
With RAIN, and ABS OFF: u will be less than 1 (and than with ABS ON), and will be equal to the frictional coefficient of a tire slipping on wet pavement. This is the worst case scenario of the four listed.

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[it]

rewatching this 10years later as a long term subscriber, you have changed up your style since this video, but points remain as clear as always.

[EngineeringExplained]

Frictional coefficients can greatly exceed one when you consider how soft rubber sinks into the pavement, thus creating a barrier that either has to shear off (burnout) or move (acceleration).

[jean-pierreagosto]

just had to say i just started a school for automotive technology, nd one of my first classes is to learn the basic info for all car systems and your videos have giving me an advantage in clas, as i listen to the teacher i remember things from ur videos, just want to say thanks and keep it up

[EngineeringExplained]

This is completely true. Grip goes well beyond what the eye can see. And wider tires will have more contact, allowing more rubber to mesh with the pavement. There is a flip side, however, as with the weight more spread out, the tire won't sink in as much. This is why the grip effects are as not drastic with wider tires rather than softer rubber, nonetheless it is something important to point out, thanks.

[EngineeringExplained]

Yes. Since we have the equation u=fN, f is the frictional coefficient. If it's less than (say .8) then it makes our maximum stopping G's 0.8g's, so it adjusts the stopping distance accordingly.

[EngineeringExplained]

Hey, glad I can help, that's awesome. Good luck to you!

[EngineeringExplained]

Not if your standard brakes can lock up. If your brakes can lock up, there is no greater force you can apply (with purpose). Now tweaking the ABS can yield improvements, if it cycles more times per second, keeping you closer to the edge of the frictional limit of the tires.

[EngineeringExplained]

I may eventually make a few more videos on braking. It's not as simple as dividing the mass with acceleration by the number of brakes, as the front brakes will carry more of the load since weight transfers to the front under braking.

[EngineeringExplained]

Eventually, probably. The first number is the viscosity of the oil when it's cold (when starting the engine). The second number is the viscosity when it's warmed up, the higher the number, the thicker.

[Roi]

I really appreciate you effort and excellent work! Greetings from Portugal.

[oldfashionedwrx]

ABS stops in a shorter time because the coefficient of static friction is much larger than kinetic friction?
is that right?
also thanks for the video, I am watching all your videos, I appreciate the time and effort you put into them, I have learnt a lot and this are inspiring.

[EngineeringExplained]

yes, I'm an ME. Thanks for watching!

[egeagustos]

I am sad because I just found you. You are amazing, as I am an engineer, it has been great to listen you. Greetings from Turkey. Can you give the book name or any article that you take the equations :)

[EngineeringExplained]

Hahah maybe, though my feelings for electrical engineering are similar to yours. Honestly it's quite similar to mechanical when you break it down, but I didn't enjoy studying it at all. Perhaps I can get around to it eventually.

[omerkhan]

you can drive the equation through work energy theorem Fd=1/2mv2. where F=ma. very nice explanation by the way. thanks.

[EngineeringExplained]

Test run, it's probably illegal for them to do it just from a calculation, unless they put an asterisk and say "estimated." It's probably impossible to account for every real world influence on braking distance mathematically, so real world testing is necessary.

[dragospahontu]

This is an easy straight to the point vid. Well done.

[EngineeringExplained]

Better tires! Haha, well I don't know. Carbon ceramics used in greater quantities for sure. It's a great relatively new technology. Also a friend of mine showed me an Audi wagon that used flower shaped disc brakes to shave off some extra weight. Thought that was cool.

[leganjan]

are you a mechanical engineer?

you know a lot of crazy stuf :)

you should definetly be professor. My profesor for Engines was awsome, but you are even better. I would like if you would give more car brand examples when talkin about some car parts.

owerall you are doing awesome work, just don't stop

[oldfashionedwrx]

I see ABS as a performance enhancement for brakes, though many people over look reaction time, as 1 second reaction time could make a huge difference.