Common 4X4 myths

[derf]

Even I had it partially wrong. You are right. It is not using manifold vacuum. sometimes I type without fully thinking.

I'd make fun of you but I've been known to type without thinking too...

 

[JR74CJ5]

Interesting thread...

Nothing to see here... just learning new stuff...

~ JR

 

[BusaDave9]

I've got another one. This one is not only for 4x4's. It applies to any car on the highway.

Myth #3: A lot of people say that having a head on collision at 60 mph is like hitting a brick wall at 120 mph. Actually it's like hitting a brick wall at 60 mph. Sure the two cars have a combined velocity of 120 mph but if the two cars weigh approximately the same, and hit each other directly, then each car will have to absorb it's own energy. If you imagine such a head on collision niether car will be able to continue forward. They would both immediately stop their forward motion. There might as well be a brick wall between them.

This myth is so common I even read news papers quote police officers saying the 60 mph head on collision was like hitting a brick wall at 120.

The only way a 60 mph head on collision would be like hitting a brick wall at 120 would be if one vehicle had such momentum that it would continue at 60 mph. If a car could have a head on collision with a freight train the initial impact for the car would be like hitting a brick wall at 120 mph. I say "initial impact" because the car would suddenly find itself going 60 mph backwards and no longer have wheels that roll. There would be secondary impacts as the car continues to roll and crash.

 

[CJ]

Physics 101. You are correct.

Mythbusters did an episode on this and even they predicted the outcome wrong.

 

[derf]

Yeah, the combined speed may be 120 MPH but you have two cars absorbing the impact, not one.

 

[BajaEdition]

can I refer back to myth #2
I think before you should argue that a long way you should look at the different platforms common in wheeling
A tj and builds of buggies and stuff go for max articulation, but it has been argued that max articulation does not mean max traction.and I have seen a lot of arguments that make you agree, such as getting a tire under a undercut, and also the spring pressure arguement stated here. I have heard others.
If you look at the H1 you see an amazing machine with Limited articulation, it is a fact it depends on lockers and a flat wheeling style where a stiff platform continues on stable and often 1 or 2 wheels can be off the ground, wheel with a group of these things over rough terrain and you are amazed at the terrain they can get across, I have been up rock trails I thought they never could take in my friends H1, the H2 is a pig, too heavy for it's own chassis, but the H3 with the V8 also is a nice wheeler, sans rocks, but in hills and such it rules.
The Jk re wrote the TJ rules, with the 4 door development went away from max articulation, back to controlled articulation and big tires.

so, I see that buggies and stuff may be cool, but overall it seems that a controlled amount of articulation seems to work just as well on a platform designed for that.

I think this debate will be around for a while, I had a TJ that was so flippy I replaced the rear suspension with some thing a bit more stable and loved the way it wheeled. It may be personal choice and personal pucker factor.

 

[BusaDave9]

Well Baja, I don't know if I can really disagree with much of that. If you drive over a big rock and the antisway bars pull one tire off the ground, that may not be too bad, especially if you have lockers.
My point in bringing up myth #2 is that people (and advertisers) often say that antisway bars will help keep all the tires firmly on the ground but that's opposite from the truth.

Now if your jeep is rolling over a big rock would you ever really want an anti-sway bar pulling the other tire off the ground? I don't think that would ever be an advantage. Your example of a tire getting caught under an undercut was an interesting but very rare exception.

If your jeep is going over some very rough terrain I think it is best to keep the weight evenly distributed over all the wheels. If your front right tire is going over a big rock you would want as much weight as possible on the left front tire. That would add stability. The tire on the rock may slip off or the whole rock may roll. If the front left tire still has plenty of weight on it there shouldn't be much chance of it moving.

My whole discussion has been based on the assumption that we have full lockers in the diffs. Most off-roaders don't have lockers in the front. Many don't even have them in the rear. If you have open differentials you are going to have much more problems on rough terrain.You don't even have to pull a tire off the ground to spin a tire on rough terrain. With open differentials it's much more important to keep the weight as even as possible over all 4 tires.

BTW, it's good to have you back, Baja

 

[BajaEdition]

thanks Busa, it is good to be back
Yea, I guess it is a locker thing, until about 15 years ago, lockers were a luxury and we used Limited slip in the rear and if you had it in the front also you were rich. And we wheeled different. But somewhere in the TJ years we all jumped on the locker thing. I now run detriots front and rear. I NEVER fully understood the max articulation thing and see a lot of buggies with anti rock in the rear now. I think they are trying to stabilize a bit also. Saw some amazing wheeling being done at Hump and Bump a few weeks back and will tell you there were some amazing rigs, but in the end it is all driver. Too many experienced guys in mildly built rigs making guys with all the bells and whistles look bad.
I see your point about the Myth 2 now, the anti rock is not designed to give max articulation but instead to give balanced articulation and that means limiting the twist of the suspension. no it wil not hold both tires on the ground equally, it will keep the vehicle from getting to squirrelly.

 

[johnbilt]

It seems that the critical element in a crash is the deceleration. What is the change in velocity vs the change in time. This would determine the amount of g force imposed on my tender little body. Unless I'm impaled or crushed by some other item in the melee. Then it's a moot point. If the scenario of the crash would cause you to decelerate even faster than hitting a stationary wall, then it would be worse. Like hitting a heavy tank coming the other way. The crunch factor of your vehicle would essentially stretch out the time to decelerate to zero velocity. Just in time to be crushed by the tank...

 

[IOPort51]

excellent post gentlemen!! I most ponder a few of these things and reconsider the mass X velosity and the coefficient of friction concepts that have run around in my head for years. I do think I will take a guard rail over a head on and I am of the opinion that the anti sway adds a lot to on road performance.
I should like to ask a question about another "myth" I was told many years ago concerning transfer cases. It was considered a foolish thing to enguage 4 low with the hubs open because the amount of torque applied to the rear drive would result in a broken TC rear output. Am I the only one who heard this?? I know that twin sticks are quite common and some even use front wheel drive as an option, the weaker of the two axles, generally.

 

[johnbilt]

I think I remember a warning label on my 56 M38A1 about the "danger" of using the low range in 2 wheel drive. Or did someone warn me ?... I'm not sure anymore. I personally have never broken a Transfer Case by doing this. I'm certain I could break something if I abused my jeep by applying too much throttle in the right situation. I would guess that by being easy on the power and using a good helping of common sense, you would never have a problem with that. I'm always hoping that the u-joint continues to be the weak point in the drivetrain. It's the easiest to fix.

 

[BusaDave9]

It seems that the critical element in a crash is the deceleration. What is the change in velocity vs the change in time. This would determine the amount of g force imposed on my tender little body. Unless I'm impaled or crushed by some other item in the melee. Then it's a moot point. If the scenario of the crash would cause you to decelerate even faster than hitting a stationary wall, then it would be worse. Like hitting a heavy tank coming the other way. The crunch factor of your vehicle would essentially stretch out the time to decelerate to zero velocity. Just in time to be crushed by the tank...

Exactly. Deceleration and G force would determine the force on your body.
IF both vehicles weigh the same the deceleration would be the same as if you hit a brick wall. The front bumper would stop immediately. The deceleration (and G Force) would depend on the crumple zone of your car.
If the other vehicle is much bigger than yours then you would experience much higher G force because you vehicle would suddenly be propelled backwards.

 

[CJ007]

X2 Great post and topics, keeps getting more interesting.

Dave, someone posted this on my local clubs site TrailDamage.com and I thought you might want to know about if you didn't already. Lots of Colorado trials. ok, back on topic.

you should look at the different platforms common in wheeling

A tj and builds of buggies and stuff go for max articulation, but it has been argued that max articulation does not mean max tractionThe Jk re wrote the TJ rules, with the 4 door development went away from max articulation, back to controlled articulation and big tires.

so, I see that buggies and stuff may be cool, but overall it seems that a controlled amount of articulation seems to work just as well on a platform designed for that.

I think this debate will be around for a while, I had a TJ that was so flippy I replaced the rear suspension with some thing a bit more stable and loved the way it wheeled. It may be personal choice and personal pucker factor.

Very good and interesting points. I had not really thought that through before and it really should be considered in the type of build.

I am of the opinion that the anti sway adds a lot to on road performance.

Me too, I learned this first hand. I left my disconnects off after a trail and planned to connect at the end of the dirt road before the pavement....make that gravel covered dirt road. I came over a hill a little too fast and lost control. I proceeded to do a few of those crazy over adjusting moves before sliding off the road sideways and into a dirt bank.

The cj have thinner, flexy leafs in the front, YJ's might be ok, but you won't catch me disconnected on any road.

 

[BusaDave9]

I should like to ask a question about another "myth" I was told many years ago concerning transfer cases. It was considered a foolish thing to engage 4 low with the hubs open because the amount of torque applied to the rear drive would result in a broken TC rear output. Am I the only one who heard this?? I know that twin sticks are quite common and some even use front wheel drive as an option, the weaker of the two axles, generally.

there shouldn't be a problem with 4WD low with your front hubs unlocked. Just like you pointed out IO, it would be the same as a twin stick putting the TCase in 2WD low. The rear output won't break.
If you are in true 4WD low then the front is helping pull the jeep. I guess you could reason that since the front is helping out the rear isn't experiencing as much torque. That may be true but the rear sure better be strong enough to pull the jeep on it's own.

 

[Old Dog]

IO, I run in rear wheel low on the trails most of the time. (twin sticked 300)
Haven't broken it this way yet. I do engage the front for the harder stuff though.

 

[BusaDave9]

I am of the opinion that the anti sway adds a lot to on road performance.

I agree 100%. That's were anti-sway bars add a lot. The advantage of an anti-sway bar is when the momentum of the vehicle tries to sway and tilt the vehicle to the outside of the curve. That really applies to street use but also when you are at speed off-road.
When you are going around a curve, the axle without anti-sway bars is the one that will loose traction.

I am of the opinion that the antisway bar has no advantage when you are at slow speeds on rough terrain. I know there are others that disagree with that but it's my opinion.

 

[BajaEdition]

Busa, that is why I included the H1 discussions, they wheel real good flat, I like more articulation though.
I know a lot of guys with the antirock, and a bunch who have taken them off. it is a matter of personal style and wheeling style.

 

[Purple77CJ7]

What is the next myth? Patiently waiting. Good stuff Dave!

 

[BusaDave9]

I can't think of any more myths right now.

As for the H1 I know there are some 4x4s that can perform well DESPITE having poor articulation. But I don't think a 4x4 would perform well BECAUSE of poor articulation.
Anti-Sway bars decrease articulation and that is really the point of myth #2.

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Look at this picture. I get good articulation. You don't want to roll over a rock and have a front tire get pulled up off the ground then as you descend, that tire will drop back to the ground suddenly increasing the angle of your jeep. The momentum may cause you to roll.

It is my opinion that having a supple suspension that always tries to keep all four tires on the ground is the best situation for low speed off-roading. If you don't have lockers front and rear then I think it is much more important to have good articulation.
Once your vehicle is going fast enough that the momentum going around curves come into play then anti-sway bars help stability and control.

 

[CJim7]

It is my opinion that having a supple suspension that always tries to keep all four tires on the ground is the best situation for low speed off-roading. If you don't have lockers front and rear then I think it is much more important to have good articulation.
Once your vehicle is going fast enough that the momentum going around curves come into play then anti-sway bars help stability and control.

Quoted for truth