Shop Talk: What’s the difference between 4WD and AWD?

I’ve got an all-wheel drive. Is that as good as a 4-wheel drive?  

Joe: It depends on what you’re doing. 2WD, AWD, 4WD, first question we ask is what do you want your vehicle to do?

Rodney: Here’s the difference. 4-wheel drive, like a pick-up truck or a full-size SUV, most of them are electronic now. You’ve got a dial on the dash, you flip the switch, you go from two-wheel drive to splitting torque to the front and rear wheels 50/50.

Joe: An all-wheel drive is automatic. You don’t have to turn a knob, you don’t have to shift anything. You have 80% of your power going to the rear, 20% to the front at all times. When the sensor tells your car your wheels are slipping, it’s going to apply torque to the other wheels to get your traction.

Rodney: 4-wheel drives, they also usually have a low range. It’s all about torque and keeping the speed down. You don’t go too fast, but it multiplies the torque of the engine, so it’ll pull itself through two-foot snow drifts, crawl over rocks and obstacles, get out of mud, that kind of stuff. If you’re really into off-roading, you need a 4WD.

Joe: It’s not just the power. People forget it’s also the clearance. An AWD can’t do a lot of things a 4WD can, just because there’s less room for things to pass under the car.

Rodney: There are a few AWD vehicles you can lock into four-wheel drive, so it’s not constantly changing the torque from the front to the rear wheels. Some of the Subarus, for instance, they call it X-Mode. But there are a lot of people, probably most people in my opinion, who never actually use it.

Are two-wheel drives always a bad idea if you’re in a place where it snows?

Joe: Not at all. Again, it depends on how you drive. How much driving do you really do in the wintertime? Do you have a long commute or do you have to travel a lot for work? Are all the roads you travel the ones the snow plows hit early and often, or are you on a side street that sometimes takes days to get clear?  If you’re putting 5000 miles a year on your vehicle, you can probably stay with a front wheel drive vehicle, and invest in a good set of true snow tires – like Bridgestone Blizzaks – at least for the front of your vehicle in the wintertime.

Rodney: People don’t know how much difference a good tire can make. You can have an AWD, 4WD with bad tires and you’re going to be all over the road, whereas you can have a 2WD with great snow tires on the front and you’ll be driving right by them.

Joe: Here’s a story. My nephew had a Jeep Grand Cherokee. He father calls me up and says, “Joe, I don’t know what it is, but he’s out there and he’s all over the place skidding.” Well, I knew exactly what it was. The kid had the tire tread down to 2 or 3/32nds of an inch – just barely passing inspection. We put good tires on it, and I haven’t heard a thing since. Moral to this story: even if you’ve got a Jeep, one of the best 4x4s in the world, if you’ve got a street radial tire that’s down to 3/32nds, don’t expect to be living the Jeep commercial.

OK. One more question. 2WD, AWD, 4WD, isn’t there a difference in terms of gas mileage?  

Rodney: You probably give up a little gas mileage with an AWD versus a 2WD version of the same vehicle.

Joe:  But it’s a lot less than a 4WD vs. a 2WD truck. I’ll bet all the money in Rodney’s wallet right now, the difference between a front-wheel drive and an all-wheel drive medium crossover, like a Honda CRV, the percentage is going to be a lot less than a 4WD full size truck and a 2WD truck.

Rodney: In the truck, you add a lot more components and a lot more weight. You’re putting a big front wheel drive axle in the truck, you’ve got a big transfer case, you’ve got a front drive shaft that’s really big, whereas in the AWD units, they’re already front wheel drive, you’ve got a small little transfer case on the transmission, some kind of smaller rear drive shaft and they put differentials in the back, rear axles that are minimal additional weight.

Joe: It’s going to be less of a decrease in gas mileage in all AWD midsize vehicles vs. a full-size truck or SUV.

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