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2wd vs 4wd

Four wheel drive (4WD) is the most common concept in increasing traction. In a 4wd system both the front and rear axle receive power. It is common for base-model 4WD vehicles to have “open diffs” (see below). While it has definite benefits, 4WD generally costs more to purchase, insure, maintain, and lowers MPG.

In trucks and cargo vans a two wheel drive (2WD) vehicle only receives power at one axle, usually the rear axle.1).

All Wheel Drive (AWD) is a usually a full-time system found in cars and light SUVs.


The usual type of stock differential is an open differential, a simple arrangement that is inexpensive and works well on surfaces with sufficient traction. The problem is that when traction is not always sufficient; in those situations one tire spins, one tire is stationary, and the vehicle is stuck.

One way to meet this challenge is to use a locking differential (LD). A locker can be changed, electronically or by air pressure, between two states:

  • an open diff configuration for normal use; and
  • a locked diff for use in low traction scenarios. When locked both driving wheels rotate at the same speed, ensuring the tire with the best traction is getting enough force to make use of that traction.

Another way to meet the challenge is to use a limited slip differential (LSD), whether physical or virtual. A physical or traditional LSD uses clutch packs or worm gears to limit the difference between wheel speeds. A certain amount of spinning of one wheel relative to the other results in a clamping effect which can either lock them together or limit the difference, as in a torsen type LSD. Some GM vehicles came stock with a clutch type G80 limited slip; a VIN decoder or vehicle info tag will reveal this information.

The sensors and controls associated with ABS brakes allow for virtual forms of limited slip. A subset of Electronic Traction Control (ETC), Brake-lock differential (BLD) can control wheelspin with an otherwise-open diff by selectively braking the wheel that is spinning. In addition to stability controls that will not be addressed here, many ETC systems can be configured on the fly:

  • traction control completely disabled
  • brake-lock differential (BLD) only, no throttle management. This may be best when forward momentum is critical or traction at both tires is bad, as when stuck in mud or snow. Note that differential braking with higher wheel speeds can increase heat and wear on brake components.
  • full traction control - Engine throttle management + BLD. This may be best when accelerating when tires are on surfaces with different traction: one tire is on gravel or ice, etc. This mode will wear brake components less than BLD only. It is common for a dash light to come on when traction control is active.


Tires on the drive axles can make a major difference on a vehicle's ability to reach secluded camping spots. All terrain tires favored on CRVL are:

  • Goodyear Wrangler2),3), particularly with kevlar sidewalls
  • Michelin LTS M/S 24),5),6)
  • Bridgestone Duraviss R5007)
  • Firestone Destination AT8)
  • Bridgestone Desert Duelers9)
lifestyle/traction.txt · Last modified: 2016/12/24 15:43 by frater_secessus