4WD/AWD Help You Stop Better (a lesson for Beyonders)

[HiTempguy1]

https://youtu.be/EMnT1gCYjP8

Just in case hearing it from me isn't good enough, here is Wyatt Knox explaining it in nice laymen terms. Considering he helps run the #1 rally school where many drivers getting started learn their skills (Subaru Rally Team USA sends everyone there to start their careers, Bucky Lasek, Dave Mirra, Ken Block, Travis Pastrana all went there).

Is it a high quality, perfectly produced video that'll grab your attention? Nope, its for people to actually learn something.

If you actually want to really learn about it, read up on active differentials in the WRC, they do a lot more than simply lock the center diff under braking. And the reason for that? Because it helps with control and stopping power of the vehicle.

Finally, one thing Wyatt does not cover is that using an engine is superior in terms of braking due to the forces involved with the engine and drivetrain rotating. This rotation helps prevent SOME lockup.

On loose/slick surfaces, PARTIAL LOCKUP IS THE QUICKEST WAY TO SLOW DOWN. There is a difference between friction and mechanical traction (mechanical traction is insanely complicated due to the variables at play). Rotational braking forces are the easiest to modulate in allowing a tire to slip, while continuing to rotate, allowing continued used of both the friction force generated by the tire and the mechanical traction of the tire.

With friction braking, the problem is that once a wheel experiences lockup, you actually have to reduce braking force BELOW the nominal traction point of the tire. If you've taken basic physics, you know a sliding object has less grip than a stationary/rotating object. The same goes for the brake pads, to get them to allow the wheel to start moving again, you need less brake pressure then what you would use at the threshold of lockup.

So in short, 4wd/awd does help you stop better. There is no debate on this. On pure, clean, nice warm asphalt, the effects are largely mitigated, but on anything deviating from perfect, awd/4wd does help.

[Darell_n]

Thanks! Now i can drive 20 over the limit with my pickup truck on icy roads instead of just 10 over like usual.

[firebane]

Demonstration: https://www.youtube.com/watch?v=y-gEXP6hECA

[BerserkerCatSplat]

Interesting video, I can definitely understand how a locked center diff can essentially alter your brake proportioning - I've experienced that many times, and it can indeed be quite beneficial in low-traction situations where you don't get any weight transfer.

That said, their previous video on the subject claimed that 4WD stops quicker than 2WD with all 4 tires locked under panic braking in both tests, which is utter bollocks and just means their test sucks.

[killramos]

I’m pretty sure this is the Marth of physics.

[zhao]

This video is a bit outdated as most people do not drive a vehicle this applies to. It's also very narrowly focused a unique combination of things/situations. It's like me saying the best way to take corner 4 at castrol is to enter with your right wheel left of the centerline of the track and get on the power hard way before the apex. 100% correct for that corner, but if you applied that to other corners or other race tracks, 100% wrong.

Less mass helps you stop better, usually (there are one off situations, digging down in loose surfaces come to mind). awd/4wd adds weight. Its why a freight train with 60 cars loaded with iron can't outstop a train with 60 cars that are empty. Its why a loaded oil tanker takes 600000 miles to stop, and one weighing nothing instantly stops. Not having awd/4x4 saves hundreds of pounds, and also improves fuel economy.

ABS in modern cars solve the 2 wheel lock situation.

No one is driving on pavement with their diff locks on either.

awd is often a 1 tire fire in many modern "awd" vehicles. Take a look at the honda CRV........ I think my FD rx7 is closer to an awd vehicle than that thing.


Otherwise, good video. Not joking either, that guy should get more views.

[HiTempguy1]

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awd is often a 1 tire fire in many modern "awd" vehicles.

Which is fine. I'm talking about vehicles with either locked center diffs/transfer cases (4wd) or continuously engaged center differentials. Clearly, the video utilized the Cherokee with a transfer case to explicitly highlight what is taking place.

Awd/4wd adds a negligible amount of weight. It is not what is helping you stop better, especially since you have to counteract that weight. Please show me an example of any vehicle stopping before and after a couple hundred pounds is added. It won't stop quicker. Good try though.

ABS does not solve this issue in poor conditions.

A center diff does not need to be locked to have this affect. Again, nice try, but completely incorrect.

I don't know either wtf you are going on about of unique situations and corners. As mentioned, you could be bothered to read about how center differentials are used at the highest levels of motorsports to help aid in braking, or you could keep spewing garbage, possibly sticking to Miatas and RX7's :p The situation is not unique, it is extremely common, like I dunno, the hundreds of thousands of drivers in Alberta today barely able to make it down the road.

Anyways, and on it goes. Leave it to Beyond to argue this

[Tik-Tok]

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That said, their previous video on the subject claimed that 4WD still stops quicker with all 4 tires locked under panic braking, which is utter bollocks and just means their test sucks.

But it does? ABS is meant to keep your vehicle maneuverable during panic braking, not to stop you quicker.

[zhao]

^ locking does not stop you faster, usually. Lots of reasons why.

[BerserkerCatSplat]

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But it does? ABS is meant to keep your vehicle maneuverable during panic braking, not to stop you quicker.

Nothing to do with ABS, sorry for not being clear. The video claims that with ABS disabled, and all 4 tires locked, 4WD stops quicker than 2WD. You can tell in the video that the guy slows down just before the braking zone when he's in 4WD and it screws the test up.

[Tik-Tok]

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Nothing to do with ABS, sorry for not being clear. The video claims that with ABS disabled, and all 4 tires locked, 4WD stops quicker than 2WD. You can tell in the video that the guy slows down just before the braking zone when he's in 4WD and it screws the test up.

Ahh, yeah, that I can agree with.

[zhao]

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Awd/4wd adds a negligible amount of weight. It is not what is helping you stop better, especially since you have to counteract that weight. Please show me an example of any vehicle stopping before and after a couple hundred pounds is added. It won't stop quicker. Good try though.

This coming from a racing driver, uhg lol. The stig did a braking test with a fiat panda with just him in it, and again with 4 people in it. It blew past his old brake marker by some crazy distance. Awd = heavier = shittier for braking all other things equal.

Mass is one of the key factors in decelerating a car. If drivetrain is not negligible in a few situations, then mass is not negligible as it is a factor in all instances of deceleration.

200-400lbs more for awd is significant.


And as you probably know, another key factor in braking is friction. How do you increase friction? Weight. But if mass hinders deceleration, and weight helps it, how do you increase weight without mass? Downforce. But are there cases where adding mass could help instead of hindering your braking? ...with friction being a key factor in decelerating. Yes. Lots of variables with braking on random surfaces/bumps/suspensions/etc.


This topic is not binary. It has a lot of variables which make different things superior in certain situations.

[C4S]

Interesting ... I have changed from AWD to RWD on exact vehicle .. of course AWD version from full stop and go/uphill is better on snow is better, but I don't notice any braking advantage ... but I have noticed much more fun ....

[The_Rural_Juror]

Popping your transmission into reverse stops your car faster than all of the above. It's quantum super biological burger intelligence proven.

[ExtraSlow]

Techniques applicable to rally cars being driven by trained rally drivers are not appropriate to be teaching to average drivers in average cars. I know this doesn't apply to the OP, but truth is, he's not average.

When people can figure out what lane they want to turn from and turn into, then I'll worry about teaching them advance techniques. Until then, yeah jam on the ABS, use traction control when accelerating, simplify what you are trying to accomplish and pay attention to what's happening outside your car and you'll do fine out there in the real world.

[zhao]

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Techniques applicable to rally cars being driven by trained rally drivers are not appropriate to be teaching to average drivers in average cars. I know this doesn't apply to the OP, but truth is, he's not average.

When people can figure out what lane they want to turn from and turn into, then I'll worry about teaching them advance techniques. Until then, yeah jam on the ABS, use traction control when accelerating, simplify what you are trying to accomplish and pay attention to what's happening outside your car and you'll do fine out there in the real world.

I dont really like that mentality.

I'm a licensed FIA driving instructor and teach road racing, and in a weekend I can greatly improve a driver's skill level; i'm not just talking about lap times and going fast, but understanding how a car works and handles, understanding racing theory, understanding cause and effect of inputs, and then putting it all together and developing car control. If it is their first time its night and day. How that translates to the real world is all kinds of accident avoidance. Its actually kinda sad but I believe there are less than 100 of us in all of western Canada, for what, 10+ million people?

I feel we spend what, 30 minimum a day in a car x 365 days a year x 50-60 years. That's over 10000 hours a life time of just driving, which is statistically one of the most dangerous activities and likely causes of death they'll do... and people think being a total noob at driving their entire life is adequate? i think that's pathetic. A defensive driving course is what, 30 hours of your life maximum, and an advanced driving course like our road race school is 16 hours.

If we had to handle guns for that amount of time daily for survival, do you think it would be acceptable for after 30 years to still not know how to hit the broad side of a barn, or to have piss poor gun safety? I'll never figure out why its acceptable to not know how to transfer weight balance in a car or stop a spin or how to recover.

[J-hop]

I agree with you zhao. I used to have to do regular driver training for work and they would always ask “who thinks they are a good driver?”. Often everyone but me would put their hand up. They’d always ask me why I didn’t. I’d respond with I don’t drive for a living, I don’t go to a track and practice technique regularly I don’t know good vehicle control as I don’t practice it on city streets. I simply don’t have the seat time and pratice to claim I’m a good driver, anyone in a similar situation of just commuting on week days and a drive or two on the weekend is delusional to think they are a great driver.

Take football for example, nfl players are great, uni/college level players are good. The guy that works out and plays some touch football on the weekend with his buddies isn’t good... maybe above the layman average, but truly good? Nope. Same applies to driving.

All about perspective (dunning-Kruger)

Building someone’s vehicle control can only do good things IMO when it comes to city streets. Most people (including most on here) don’t know proper vehicle control (complacency/overconfidence doesn’t count), meaning they split more energy/attention into vehicle control than they should

[Tik-Tok]

And yet cab drivers are terrible.

[J-hop]

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And yet cab drivers are terrible.

Yea seat time isn’t a gauruntee.

Like the football example There are tons of football players aspiring to play at the nfl or even uni level that put in the time and will never make it.

But no football player and no professional driver ever made it without huge field/seat time

[Buster]

Apparently good driving skills don't make a person a good scientist. Let's set aside my personal thoughts on the matter for a moment, but their experiment here is poorly designed, as it does not eliminate variables. Science is about isolating variables. They should disconnect the rear drive shaft. Then run a few hundred tests comparing 2wd/4wd/disconnected rear drive, and then get back to me.

This would also conveniently eliminate the "argument from authority": that these guys know better because Travis Pastrana went there or some such. If you want to prove a point, it's always best to simply avoid these types of arguments.

This smells like the ABS thread all over again.