Four-wheel drive; Not all tires turning
- Thread starter Jimbabwe
- Start date
If the R4s fill with dirt they are like having slicks on. Try airing down and attempt the hill in a higher gear, say 2nd or 3rd instead of 1st, too much power to the wheels will cause them to break loose.
Thanks, y'all. I'm not towing anything. Dirt is dry and does not fill lugs of tires.
It's just physics. I'll stay away from hills that are too steep.
It's just physics. I'll stay away from hills that are too steep.
nbryan
Well-known member
Equipment
B2650 BH77 LA534 54" ssqa Forks B2782B BB1560 Woods M5-4 MaxxHaul 50039
Hi Jim,
I agree with you that it is just too steep to climb. Can you post photos to show us what you are dealing with? Your Rhino and many other off road vehicles will out climb a tractor, horses for courses.
When I am filling gabbions to retain my sandy hill I can get all 4 wheels spinning and that is as high as the tractor will climb.
I agree with you that it is just too steep to climb. Can you post photos to show us what you are dealing with? Your Rhino and many other off road vehicles will out climb a tractor, horses for courses.
When I am filling gabbions to retain my sandy hill I can get all 4 wheels spinning and that is as high as the tractor will climb.I never understood this. If the wheel with less traction is the one that gets power, it's a bit useless if you're mired down in the muck. I've had the same problem in my 4x4 truck. Just seems like the wheel with the most traction should be the one to get power -- you know, so it can actually pull!
Anyone out there know why this "is the way it is?"
Thanks!
Yeah...it’s because of the differential. When you make a turn, none of your 4 wheels follow the same path as the others. You can clearly see this in fresh snow. The sharper the turn, the more pronounced this difference becomes. Basically the outer wheel travels further than the inner wheel; furthermore the rear wheels and front wheels also cover different distances in a turn.
So because each wheel is naturally turning at a different speed in a turn you need the differential to compensate while still supplying power from the engine. If all you had was a ring and pinion gear in the diff, you’d feel binding and chirp your tires with every corner you take. And wear your tires out quickly or break something. The tug you feel in sharp turns with your 4x4 pickup (in 4x4) is actually the difference in speed between the front and rear axles. Both you axles have a differential but there isn’t one BETWEEN the axles. Some vehicles do have a center differential as well; others offer a clutch based 4x4 which can slip in corners to smooth out the tug. Anyway, a differential has side gears which allow the wheels on an axle to travel at different speeds without binding. These gears also mean that torque from the engine does not have to be spread equally to both wheels. When not forced, power naturally follows the path of least resistance. Unfortunately that would be the wheel in the snow, mud, etc.
Our tractors have a rear locking differential which when activated locks both sides of the diff together and forces power out equally to each rear wheel. Many pickups have some type of rear locker or limited slip to accomplish this same task.
See, this is why I ask you guys these kinds of questions. Ya'll know stuff.
Thanks for the excellent explanation!
Thanks for the excellent explanation!
This is not actually an accurate description of how an open differential works. The sentence “These gears also mean that torque from the engine does not have to be spread equally to both wheels.”. Is not correct, In fact it’s the opposite. The way an open (normal, not diff locked, or limited slip) differential works is that the torque on the 2 axels driving the wheels is always exactly equal, 100% of the time. The differential allows the 2 wheels to turn at different speeds at the same torque level. The piñon gears (between the side gears) attached to the outer carriage, which is driven by the driveshaft, applies exactly the same amount of torque to each side gear attached to the 2 axles.
So what happens when one wheel gets in low traction and the other is not is the low traction drops the amount of torque on that can be applied to that wheel, it just spins, this drops the torque on the high traction wheel to exactly the same amount. If that amount of torque in not enough to make you move your stuck. But both wheels are pulling with the exact same amount of torque.
If this is the rears, and you have split brakes, you apply braking to the spinning wheel, to bring up the torque requires to turn it, and the torque will go up on the other wheel, and will pull you out if it has enough traction. Experienced operators do this all the time instead of diff lock, it’s much faster and easier to do.
A locked differential, is simple, the opposite happens, both wheels turn at same speed, the torque on the wheels can be greatly different depending on what’s under the tires.
A limited slip differential has a slipping clutch between the two drive axels, which means when one wheel spins faster than the other, it applies more torque to the slower moving wheel through the slipping clutch. So it is something in between an open differential and a locked differential. The slipping clutch can be implemented different ways. On cheap differentials it’s little friction plates with tension on them and they wear out. This is now the old posi rear ends worked on crappy old American cars. Or it could be a oil based viscous coupler similar to a torque converter that never wears out. Which is how modern cars work.
So in general it is misleading to day, in 4 wheel drive, with open differentials you get 2 wheel drive, one front, one back. You do get 4 wheel drive, the fronts get equal torque limited to the torque requires to spin the lowest traction tire, and same goes for the rears. Add rear diff lock, you get equal speed on both rears, equal torque on the fronts.
All wheel drive cars add a third differential between the front and rear axel so the car can turn on dry pavement with no problem. If all differentials are completely open, then you get equal torque on all 4. But modern cars have computer controlled clutches on all 3 differentials so it can move torque to the tires with traction. A Subaru is very good at this, it can climb a steep hill with any 3 tires on rollers, and the forth on solid ground. Not many cars can do this because the limited slip function is not as good.
That’s my long differential story, not really busy right now.
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On this sight you can watch a video that shows you visually how an open differential works, its very good.
You’ll have to use your imagination for the diff lock and limited slip part.
https://www.geek.com/geek-cetera/a-brilliant-explanation-of-how-a-cars-differential-works-1450429/
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You’ll have to use your imagination for the diff lock and limited slip part.
https://www.geek.com/geek-cetera/a-brilliant-explanation-of-how-a-cars-differential-works-1450429/
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A long long time ago when I used to wheel my old Toyota pickup I always carried a couple pairs of vise grips. My old truck only have open diffs so when 1 or 2 tires would come off the ground you were left there spinning your wheels. All you had to do was get a friend to hold the brakes on while I pinched the flex hose on the wheel that was off the ground therefore putting the power to the wheel that had traction. Saved my butt more than once.
Subaru AWD systems vary greatly by model and they really are no better than many other AWD systems. Subaru design mimics Audi Quattro or even Land / Range Rover systems. Even the Haldex system used on some transverse engine vehicles is extremely effective. Subaru just has good marketing.
Subaru systems use to vary by model, they don’t now, same system on all models. The audi quad, and others are mimicking them, Subaru was the first to have the type of system they have now. All Wheel Drive (AWD) is actually Subaru branded term. But in the general public use it’s become the generic term for a four wheel drive system that can be used all the time. Other manufacturers didn’t call it AWD, they say Full Time Four wheel dive, 4-motion, quattro, AllTrac .... until more recently, where AWD has become a generic term like Kleenex. Yes there are some system that are about as good at 2-3 times the price. In spite of that, there are lots of uphill snow races with completely stock cars where Subaru beats everything.
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Subaru introduced their AWD in 1972. The 1970 Range Rover had permanent four wheel drive including a lockable center differential plus low range. So AWD is not something Subaru invented. There is no two wheel drive mode in the Range Rover.
Subaru’s AWD is effective. Too bad the rest of the car is a thinly built, underpowered tin can. They do go well in snow, but it’s not like there is some situation where the Subaru is going to make it through a snow covered road and some other good AWD car or SUV is not.
Subaru’s AWD is effective. Too bad the rest of the car is a thinly built, underpowered tin can. They do go well in snow, but it’s not like there is some situation where the Subaru is going to make it through a snow covered road and some other good AWD car or SUV is not.
didn’t say they invented it, I said AWD was a subaru branded term that became a generic term because of Subaru’s success with it.
Where going to have to disagree on quality on cars, Consumer report rates Subaru as the best overall car company today based on reliability and quality and crash safety, an accolade the Land Rover never has and never will get, in fact quite the opposite. Under powered? Really, I’ll put my money on a stock STI over any stock Land Rover ever made on any on road or off road rally conditions you can pick.
Anyway way off topic here. My main point was to explain how differentials work.
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Yeah we are way off topic. As an aside, the 2019 WRX STI clocked a 4.5 second best time from 0-60mph; the 2019 Range Rover Sport SVR clocked a best time of 4.3 seconds. Granted, it costs $115k. But impressive for a 5500lb SUV. I used to be a huge Land Rover fan all the way to the mid 2000's when their focus used to be on off-road and luxury. Now their focus is luxury and on-road performance, and their styling has taken a turn for the worse. I don't care about them at all anymore.
As for Subaru, we have a 2014 Outback we bought new as one of our company cars. It now has about 100k miles on it and will likely be traded soon. I've had this on many runs to the airport or local customers. The positives have been the low purchase price, good fuel economy, roomy interior, and good AWD system. It has been reliable with only a few issues not unexpected for a car of this age / miles. The negatives include a noisy interior at highway speed, the weak 170HP engine, a very cheap interior, and the car is burning oil now for the last 15k miles or so. The rate is about a quart every 2500-3000 miles. Not horrible, but this rate will increase as the car gains more miles. Our other company car is a 2016 Ford Fusion AWD. It has similar miles on the 2.0L turbo engine. The Fusion isn't nearly as roomy and gets worse fuel economy, but is much quicker, has a nicer interior, goes just as well in snowy conditions (nobody is driving either car up ski slopes), and burns zero oil between changes. WRX / BRZ aside, a Subaru is an extremely boring car. Practical sure, but so is a Honda which generally offers a slightly more exciting driving experience.
Anyway, at least we agree on tractors!
Yes, agree on tractors, especially the 4060 you’re getting.
Cars are supposed to be boring, like a toaster ovens, anything else is a waste of money. But for some strange reason, the average car purchase is an irrational emotional decision. S&P500 is a better use of money.
One more thing about differentials, you have to be careful with the diff lock. People sometimes break them. Use them in low traction situations only, don’t turn, don’t engage with one tire spinning fast, but you most of the time need one tire to turn faster than the other to get the pins to line up and engage.
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Cars are supposed to be boring, like a toaster ovens, anything else is a waste of money. But for some strange reason, the average car purchase is an irrational emotional decision. S&P500 is a better use of money.
One more thing about differentials, you have to be careful with the diff lock. People sometimes break them. Use them in low traction situations only, don’t turn, don’t engage with one tire spinning fast, but you most of the time need one tire to turn faster than the other to get the pins to line up and engage.
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I've heard the diff locks in the BX are perhaps a little easier to break than the others? From my own experience if I lose traction, whether turning or not, I just press the pedal down and after a revolution or two it engages and I go. Once I am moving I release it again. I think that in the typical situation a diff lock is needed, there is enough slippage available to prevent any damage to the diff even while turning. I've never broken a diff lock. However, the one on my B2920 became very reluctant to engage after that machine accumulated hours and years. I engaged it fairly often, and after a while you had to repeatedly stomp down on the lever and press extra hard to make it work. It's like it went out of adjustment somehow, like you needed to press the foot lever further down than it had travel for. But the dealer said there was no adjustment available.
I am excited about the 4060.
I am a car guy, and definitely someone that would spend irrationally. I have significant towing requirements, and the last most irrational purchase was a Ford Raptor pickup with the twin turbo engine. Somehow convinced myself it could tow more than it was rated for. Didn't work out and owned the truck only for a few months. Currently driving a RAM dually. Not exciting, but capable.