Thoughts on 4WD vehicles and winter weather...

[steeltoe]

16v>32v

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24v>16v>32v

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[fiveohhhstang]

48v< *

 

[steeltoe]

48v< *

I see what you did there. lolololol.

 

[Planter]

driven everything from fwd, to rwd, to 4wd, and never had any more or less problems in one or the other.

if you apply common sense, take your time, and you know and understand the limits and capabilities of your vehicle in the conditions you are driving in, then you can get around in just about anything with any vehicle, regardless if it's front, rear, or four wheel drive.

 

[2001Bullitt]

correct, you did, but for the wrong reasons.



There is no less weight transfer on ice than there is on dry road. If you are decelerating from 50 mph to 25 mph at the rate of 5 mph per second, there will the exact same amount of weight transfer on ice/snow as there will be on asphalt because the rate of deceleration is the same. Weight transfer is only affected when traction is affected.



First off, not all 4wd systems split the acceleration forces 50/50. Nissan skylines, r33 and r34 (if i'm not mistaken) are primarily rwd until the center diff decides the rear tires are spinning too much and the front tires need to step in.

Audi's quattro system is constantly scanning the wheel speeds and deciding what amount of power can go to what axle, but will never send more than 30% of the power to the front tires. This means they will never experience a 50/50 torque split.

However, in both of these examples, braking force stays at a constant (besides computer intervention in high performance driving situations). If a skyline driver is accelerating and the center diff decides on a 40/60 torque split, and the driver decides to use all the braking power possible, the brakes will still be doing their normal 70/30 or 65/35 or whatever their braking force is set to. The front tires will not be doing 40% of the braking simply because the center diff wanted them to do 40% of the braking.

The reason for this, and the answer to your question in bold is because they are completely separate systems.

The situation is the same in older trucks with open diffs and solid locked transfer cases. If someone is travelling along in a 1975 3/4 ton chevrolet and needs to brake, all four tires may be forced to do the same speed, but it is still the front brakes are still doing 80% of the braking.

In an earlier post, you state this:



This is 100% correct, but the rear wheels are not locking up because of even braking power. They are locking up because of mechanical drag/lockup. If the rear brakes are completely disabled and 4wd is locked in, the front/rear braking bias is 100%/0%. You are implying that because the drive system is forcing the rear tires to stay at the same speed as the front tires, the brakes are sharing the work. In your scenario, how can the rear brakes be doing the same amount of work as the front brakes if they are not even operational?

If the normal amount of pressure for the front brakes is 600 lbs per square inch, and the normal pressure for the rear brakes is 400 lbs per square inch, then the total pressure is 1000 lbs per square inch. When the brakes are applied at full power, in 2wd or 4wd, the front brakes are still pushing at 600 lbs, and the rear brakes are still pushing at 400 lbs.

If you cut off all fluid going to the rear brakes and try it again, the front brakes are still pushing at 600 lbs, where as the rear brakes are now pushing at 0 lbs. However, it's not braking force that's keeping the rear tire speed in check with the front tire speed, it's the gears inside the transfer case, transmission, and differential doing the work.


Everyone here gets what you are getting at, but you are simply thinking of it all wrong. Brake bias is just that, the bias by which the brakes are working. Brake bias is decided by a proportioning valve, brake fluid, and your foot, not the power of the engine or where the center diff/transfer case sends that power. Total stopping power will be affected by all of this, but total stopping power is not brake bias.

+1

 

[drex]

PIIHB> 4wheel drive

 

[HYBRED]

You can test this concept by putting your vehicle in 4wd, finding a loose surface and locking up the e-brake...I believe you'll find that all 4 tires lock up if the rears lock up(not all e-brakes work that well...)

In most vehicles (at least the ones I'm familiar with), the e-brake is completely separate from the brake fluid system; it's cable driven, and isn't even connected to the front wheels.

Im pretty sure that braking force does not transfer through the driveline from the front wheels to the rear. I dont have the physics to back up my position but im pretty confident in it

You don't need physics to back it up, they're completely different systems. Saying the 4WD system affects the brake system is like saying your nerves can transfer the flow of blood if an artery gets backed up - it just doesn't work that way. They work together, sure, but they don't control each other.

In 2wd, the brake bias is mainly affecting the front wheels, which means the rear axle isn't providing a lot of braking force.

This is true regardless of how and how many of the wheels are driven.

In slick conditions, braking bias should be closer to 50/50, as there will be less weight transfer.

Kyle covered this pretty well. When talking acceleration in a dynamic system such as a vehicle, weight will transfer regardless of the surface friction.

When its locked into 4wd, front braking power is getting shared by both front and rear axles. So YES, the front pads are providing the stopping force, but it is being spread to both axles as the transfer case is locked in. If acceleration is split 50/50, why wouldn't braking power?

You're on the right track, but you're confusing stopping force and braking force. The brakes are not the sole provider of stopping force in the instance you are arguing. Stopping force is provided by the brakes as well as the mechanical force of the 4WD system and the engine. The question at the end of your post, which you obviously intended to be rhetorical, only points out your confusion.

So, getting to my main point that braking bias should be closer to 50/50 under slick conditions, having it in 4wd equilizes the braking to 50/50. Which means better stopping.

Key word here is SHOULD. You are confusing what makes sense to you, with what actually exists. Your entire argument is based on your false assumption that, because power is split via the drivetrain, so must the hydraulic pressure in the braking system. This is simply not the case. Should it be? Possibly. But is it? No. Now, this is not to discount the possibility that some manufacturers may be developing or already using "smart" brake systems that will adjust the braking beyond that of a simple ABS system, but I have yet to hear of one that does.

 

[stangin99]

As was said, AWD/FWD/RWD are all equally dangerous in snow, in the WRONG hands. There is a reason why so many trucks/SUV's get stuck: stupid drivers think AWD is a smart system that can correct itself somehow.

However with that said, AWD is much better with regards to starting off(obvious). In regards to regaining control, AWD is king. AWD wins this everytime, but if you know how to drive in snow, FWD/RWD is "ok" with some good snow tires.

AWD you can pull yourself out of a slide/spin by using the go pedal and aiming where you want to go. It takes a little practice but is pretty neat once you get the hang of it. It is what makes drifting a ton of fun in AWD.

FWD you can do this to an extent, but not completely. The front wheels will try to pull the car, but if the back is sliding it's hard to get it out.

RWD you can have lots of fun but you lose a lot of control. You can try to push the car in the snow, but if the front is sliding you have even less control of where it's going.

 

[SonicDTR]

In most vehicles (at least the ones I'm familiar with), the e-brake is completely separate from the brake fluid system; it's cable driven, and isn't even connected to the front wheels.

True. I was simply trying to get across that in low-traction situations instead of the front tires locking up, it would transfer it to the rears and either none would lock up or they would all lock up(assuming no center diff). Even if the majority of the braking force is up front.

 

[Never_Enough]

4wd helps, but as others have said, once it's gone, hang the hell on.
Rwd you can usually wrangle it back in.

This.

Spent the last 3 winters w/AWD (FWD & RWD in the years before w/no problems) & it was much better, but I do recall one time I lost traction (Unplowed AC Expressway in a big storm) & there was no stopping the spin out. Luckily, I didn't hit anything.

Back to RWD this winter.

 

[vettez062002]

my winter beaters have been.
1993 3000GT VR4 TT... IT WAS AWSOME!!!!
2005 Legacy GT lmited 2.5 turbo 5MT... AWSOME with bliazzacks!!!
beater civics... not bad if you dont care if the car gets wrecked
04 chevy diesel lifted with mudders.. it sucks!!
07 wrangler... worthless. it sucked
06 montero full size limited... was a freaking tank
3 evos.. blizzacks are a must!!
05 wrx.. good with the right tires.
05 grand cherokee limited 4wd V8.. ripped through the snow
07 Tacoma... awsome! was a million times better then the diesel and would plow through anything

currently I picked up a 00 Legacy gt limited auto awd. so far so good.

 

[fiveohhhstang]

Your mudders comment makes me lol.

I love when people think their big wide tires are going to help them get through the snow (not implying you said this). It makes me LOL.

Skinny > wide on ice and snow.

-f_r

 

[vettez062002]

Your mudders comment makes me lol.

I love when people think their big wide tires are going to help them get through the snow (not implying you said this). It makes me LOL.

Skinny > wide on ice and snow.

-f_r

I know it would of sucked. it actually does very good when its fresh snow and no one has driven through it. the damn tires are so wide it pulls all over the place. I was never expecting it to do good in the snow. its not why I bought the truck. its a tow rig. it sits in the garage along with everything else now while its winter.

 

[SonicDTR]

Your mudders comment makes me lol.

I love when people think their big wide tires are going to help them get through the snow (not implying you said this). It makes me LOL.

Skinny > wide on ice and snow.

-f_r

Not entirely true. If they are the proper tread type then wider=better.

Mud tires really dont have that much gripping surface on something smooth like packed snow or ice. Its all about biting edges, and those big flat lugs only have 1 biting edge, but a bunch of smaller blocks on an A/T tire is probably going to provide alot better traction in snow/ice.

 

[fiveohhhstang]

Yeah, like I said, I wasn't implying that you were one of the people I was talking about. People around here with lifted trucks swear they will be able to get wherever they want because of their big tires, but as soon as the roads get snowy and iced over, they are sliding into shit and ruining their vehicles.

If you try to explain to them that it's pressure that helps you get around, not surface area, they just don't understand.

-f_r

Not entirely true. If they are the proper tread type then wider=better.

Mud tires really dont have that much gripping surface on something smooth like packed snow or ice. Its all about biting edges, and those big flat lugs only have 1 biting edge, but a bunch of smaller blocks on an A/T tire is probably going to provide alot better traction in snow/ice.

With similar tread designs, thinner will always be better. Less width equals more pressure per square inch. More pressure means it will be harder to lose traction and easier to get around, while giving the edges you talk about more chance to cut, on ice and packed snow.

Tread design is important for clearing loose snow, but not as important on ice and packed snow.

Myth number 4 on this site - Tire Myths...and Reality - Car Care - Motor Trend

Myth: Wide tires provide better traction under all weather conditions. In fact, putting oversize snow tires on a car delivers better snow traction.
Fact: The opposite is actually true. Wide tires tend to "float" on deep snow, and the tread lugs never have a chance to "dig" through to the road surface to gain traction. Narrow tires are a better option in deep snow. The tire acts similarly to a knife cutting through butter; the blade works best when using the narrow edge to push through the butter rather than the wide flat side of the blade.

 

[SonicDTR]

With similar tread designs, thinner will always be better. Less width equals more pressure per square inch. More pressure means it will be harder to lose traction and easier to get around, while giving the edges you talk about more chance to cut, on ice and packed snow.

Tread design is important for clearing loose snow, but not as important on ice and packed snow.

I hadnt really thought of the higher pressure per square inch of it, that does make sense...but I never thought about floating on top as a bad thing?

Seems to work for these contraptions, and yes, I know its not a fair comparison.

[youtube_browser]mkleAMR3IyI[/youtube_browser]

 

[fiveohhhstang]

FWIW, here's a vid that proves the fronts don't always lock up when the rears do:

[youtube_browser]hlf0w3sRMsI[/youtube_browser]

 

[SonicDTR]

That car must have a center diff.

 

[king nothing]

I love when people think their big wide tires are going to help them get through the snow (not implying you said this). It makes me LOL.



-f_r

Big wide tires DO help get through the snow..... deep snow. now on ice, they suck.....

 

[fiveohhhstang]

That car must have a center diff.

Indeed. But Tractorman never specified what kind of four wheel vehicle, so I posted one that's badass and full of awesome. I'm not saying I disagree with his statement, or anyone else's,about locking up one set of tires and the other follows on vehicles with more primitive 4WD setups.

Big wide tires DO help get through the snow..... deep snow. now on ice, they suck.....

Deep snow isn't really relevant to the conversation, but yes, in really deep snow, they do, simply because you can drive over the snow and not through it.