My wife has an all wheel drive car while I have a truck with 4-wheel drive. I live in snow country, and during the winter months I sometimes put my truck in 4-wheel drive on slushy roads or in parking lots.
When I switch from 2-wheel drive to 4-wheel drive it becomes much harder to steer, which makes sense since the wheels used for steering are now being used for power too, but why don’t I have this steering issue with my wife’s all wheel drive car? What’s different about the steering in an AWD compared to 4WD? Could they make my 4WD truck steer like my wife’s AWD car?
Hmm. My Dodge 1500 does not have different steering feel in 4 vs 2wd, unless you get some binding when the traction is good. My wife’s CRV is AWD, which means FWD unless slipping is detected, I believe, so the steering wheels are always getting power. What kind of truck? How’s your temperature forecast up there? Thursday here is forecast high of -7, low -28!
Ask yourself if front wheel drive cars are difficult to steer because the front wheels are used for both power and turning.
Without knowing what truck you drive, I’d guess that you have a locking front differential. I’d also caution that if you’re feeling that much of a difference, the surface may not be slippery enough to justify engaging the locking diffs. Locking the diffs with too much traction is hard on the drivetrain.
Yeah–my truck has limited slip diffs, but not locking. You definitely get some axle bind at high steering angles. But steering feel is not greatly affected.
It’s a 2019 Tacoma. My 2010 Tundra did the same thing, so I assumed all 4WD vehicles did it. It’s 12 degrees F today and will be dropping down to -8 by mid week. Binding is a good description of what I am feeling, and it doesn’t seem to matter what the temperature is or how much ice or snow is on the road. I have to fight it to turn, such as into a parking space, when it is in 4WD high or low. If I put it back in 2WD the steering is normal again. No locking hubs. I have snow tires on it. I suppose I could ask Toyota.
This amazing (and often shared) video that explains how differentials work might help explain what’s happening when you lock a differential, thus allowing it not to work.
Most AWD cars either have open differentials or limited slip differentials that allow some wheel slip before engaging, so they’re not as clunky.
All Wheel Drive is kind of a misnomer, All of the wheels are not powered and driving all at the same time. A 4 wheel drive uses a transfer case to power all the wheels all of the time. The trannsfer case acts like a locking differential. AWD sends power to each axle depending upon the need. Your AWD is not powering all of the wheels all the time. You may be driving down the road in your AWD and only two wheels are powered, like a normal 2 wheel drive car. When slip is detected the other wheels will get power. 4 wheel drive is powering all the wheels as long as 4 wheel drive is activated.
This depends entirely on the characteristics of the center differential. An open differential like the original Audi Quattro system distributes torque equally to all wheels. What you are describing is a “smart” differential. It can be mechanical like a Torsen differential or electronically controlled like the sophisticated systems on car like the Nisan GTR or Subaru WRX.
The difference is not in the steering, but the presence of a center differential in an AWD drive car. This allows all axles to turn at whatever rpm they need, so no binding.
4WD has a fixed center differential, a transfer case. Thus the front and rear driveshafts have to turn at the same speed. When turning, the front axle wants to spin at a different rpm then the rear and the front wheels bind. Worst case the front wheels hop up and down to relive the binding and damage can occur.
There is no simple rule for the mechanics of AWD versus 4WD. There are extremes, so you won’t find AWD vehicles with a manual mechanical engagement of drive. But you can easily get highly capable off road 4WD vehicles with fully automatic torque vectoring and permanent 4 wheel drive, needing little more than a flick of a switch to go from highway to rock hopping.
AWD versus 4WD is more market segment than hard and fast designation of the mechanical design. People have tried to retrofit a taxonomy onto the terms, but it is a moving target.
Every manufacturer designs their AWD differently, but the basics is that they’re FWD 98% of the time (not sure if there’s one that’s opposite) and the computer supplies power to the rear to correct as needed. Counterintuitively, on some cars you might want to turn of transaction control in snowy or sandy conditions as the computer gets “confused” and can cut control to wheels.
They can still have a centre differential. But using viscous coupling or automatic locking and the like. No manual control needed. A centre diff is not the province of either 4WD or AWD specifically.
Viscous coupling could be argued as a better fit to what the market calls AWD, as it is slow to act and doesn’t provide the needed instant torque needed for something like driving in sand. Automatic locking diffs provide instant torque as needed, but are a bit more agricultural in action. One can see bad matches in many manufactures, where the choice of technology is more driven by what is available to them from their suppliers than what is the best fit.
One can look at the various drive trains used over the by JLR in Range Rovers. The first ever Range Rover was permanent 4WD with a centre diff that was manually locked with a switch on the dashboard. They then used viscous coupling centre diffs for ages. Modern Range Rovers and indeed other member of the Land Rover family use a range of technologies. JLR try to position cars in different markets, something like the Velar is termed an AWD, but can be specced with a locking rear diff for some offroad work. Not that you would really buy the car for that purpose.
Look at a Subaru WRX and there is a whole raft of technology thrown at the centre diff. That car is never going off road. But my parents did many thousands of off road miles in their Range Rovers without anything worse than a flat tire.
Toyota OTOH remain with very basic and agricultural technologies in their Land Cruisers. But it doesn’t break, which is a huge win.
One thing that does divide the technology available is whether the car is based on a FWD or RWD engine layout. Options are more limited if retrofitting rear drive onto an existing FWD.
AWD versus 4WD is really mostly marketing. The exact underpinning design can vary considerably.
Depends on what you mean by off road. As manufactured the WRX is not a high clearance vehicle. But it and the Mitsubishi Evo ruled high performance rallies which are on bad roads and good.
My favorite look at the two was on Top Gear. Jeremy tried going around a circular skid pad with the electronics switched off. He got to 30 mph or so and could no longer keep the car on the track. He switched on the diff and holy cow! He sailed right by 30mph, 35, 40 and finally had to pull over and vomit. He could not tolerate the Gs, but the car could have kept on going faster.
