When you are running in 4x4 what % of the power goes to the rear wheels and what % goes to the front? Is every machine different? Is there a difference between the awd wheelers and the 4x4 wheelers since the 4x4 generally only power 3 tires. I have never seen a topic and I am curious.

Ryan

 

On an Polaris AWD it's 100% to the front and rear.

 

Maybe I worded it wrong. You can't 100% to the front and rear, you don't have 400%. My question is, is it 25% to each tire or are the rear tires getting more power than the front tires on certain machines?

 

[img]i/expressions/face-icon-small-smile.gif[/img] 100% of the engine power is running to all four tires ... not 25% per tire ... 100% of the engine power is at each tire.

In Polaris's AWD all the wheels are locked together, as such they get 100% of the engine power.

IMO, you are thinking for 3 wheel drive (Limited slip) where as one tire will get more power than the other.

 

Im not aware of any quad having a center differential, its direct gearing, so the front differential will get the same amount of torque as the back differential. From there, the rear tires get equal amounts, because there is no differential back there, they are solidly locked together, (except for some quads, like a bayou300 and the polaris atp, which do have a differential back there).
Front ends are where there is alot of difference. On the polaris, there is zero going to the front tires, until the back tires loose traction, so polaris is basicly 2wd, until traction is lost.
Most, so called 3wds, are actually 4wd, as long as the traction on the two front tires are equal.
Then there is the locking type of front differentials, ( grizzlys, kodiaks, prairies, and so on) they get full power, to all 4 tires, when locked.
Actually, 100 % is available at each tire. Whether or not 100% is used , is another story. For instance, if you were on ice, with 3 tires, and the 4th tire was on dry pavement, and you had a locking diff front end, that one tire with traction would get , up to 100% of the power. In reality, there are friction and ineffiences, and drag, which keeps the tire from getting 100%, but its close enough for argument. Another way to look at it, is all 4 tires can have equal power, and that amount can be asumed to be the full power available, so....they all get 100%. But dont add them up, it doesnt work that way. (400%)

 

Hello MNWolverine01. On most every 4x4, most of the tractive effort is supplied by the rear wheels. This comes about because when you accelerate, the weight transfers towards the rear. The amount of tractive effort that can be supplied by a tire is determined by the weight on the tire and the coefficient of friction between the tire and the ground. Since most of the weight is transfered to the rear, the front tires become unweighted and can easily slip in the dirt. The question becomes much more complicated when the quad goes around a corner. In this instance both front tires slip on a locked 4x4 system. The Polaris 4wd is the only system that does not slip the front tires on a corner. The exact % torque split is dependent on how hard you accelerate. On high acceleration, probably 90% of the tractive effort is supplied through the rear tires. On very low acceleration, 50% goes to the front and 50% goes to the rear. On low traction surfaces, it depends on which wheels slip. The ideal 4wd system can supply 100% torque to any given wheel in low traction surfaces. This includes any 4wd system with a front locker and the Polaris system.
I hope this clears things up for you
BryceGTX

 

FYI, Hondas are geared slightly taller in the rear than the front (so the steering will be lighter), but except for that slight difference the front and back each get 50% of the power. In the rear, if you have a solid axle each tire is going to get 25% of the total power. Different front differentials have different amounts of "bias", so the power distribution differs with different designs so they can split up that other 50% different ways.

This brings up the issue of "lockers" on the front diff. When locked you only get half of the 50% to each tire, so that's 25% to each. With a diff with a good bias, you can get something like 70% to the wheel that has traction. Seems like that is better than just 25% to me! So I just stay away from lockers.

Can't comment on what the diffs on the rear of an IRS will do. Nor do I know anything about machines like some Polaris where the front doesn't kick in until the back slips.

 

I think the question should be worded as such: When four wheel drive is engaged, how much power (with 2 wheel dive being 100%) is required to turn the fronts? The answer would be the 100% minus the torque/power required to turn the front drive system. Only a dyno could give you the correct answer for each particular machine.

 

Sorry 4xZuk. A dyno doesn't help you here. If all four tires have the same amount of traction, then the torque is equally split between all 4 wheels. Unfortunately, in the real world, each tire has different amount of traction, therefore the torque is split differently. Particularly in high acceleration. The weight transfers to the rear, the front end comes up due to the rear torque trying to lift the front, the front becomes light and virtually no torque goes to the front axle. This clearly is not a 50% torque split. If what you guys suggest is true, then 4x4s would always out accelerate 2x4s. But that is not the case. The reason is that virtually all the torque goes through the rear tires. In low traction situations is where the 4x4 will have a more equal torque split. However, even here, since the rear tires are wider, they will probably provide more torque. I think you guys are confusing the ability to provide torque with the torque that really is at the wheels. In order to see the real torque at the wheels, you need to instument the quad with in-line torque transducers. Then you will see real world torque. Also as you have pointed out, there are cars with AWD that are capable of changing torque bias between the wheels; front to back and side to side.
BryceGTX

 

Bryce-Wouldn't it be accurate to say if you pulled the dyno in 2wd, got the number, then pulled in 4wd, and recorded that number, the drop would give you the % ?