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lifestyle:traction

Words of Wisdom: “In the end, an ounce of prevention is worth a pound of cure. If you are in any way unsure of the way ahead, stop the car and walk the route to determine grade, clearances, and firmness.” – USExplorer1)

“By far the best bang for your buck is a 12 volt air compressor and air down your tires. Just airing down your tires to 10 pounds will get you unstuck an amazing amount of times. It should be number one on your list for taking your van in rough country.” – akrvbob2)

Traction

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.3).

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

differentials

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

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 Wrangler4),5), particularly with kevlar sidewalls
  • Michelin LTS M/S 26),7),8)
  • Bridgestone Duraviss R5009)
  • Firestone Destination AT10)
  • Bridgestone Desert Duelers11)

tire pressure

Having a lower tire pressure is like wearing a snowshow. – BleepinJeep12)

Airing down tires in soft terrain can help increase traction.13),14) You may want to procure an air compressor before you need it so you can air your tires back up afterwards.

Airing down works because:

  1. it increases the amount of tread in physical contact with the ground
  2. an underpressure tread can conform more easily to uneven surfaces.

In sand, airing down to pressure of 12-15psi is common, with some going down to 8psi (with bead locks). This video shows the difference between full pressure and 15psi in wet sand. This video shows the difference between 22psi and 10psi in dry sand

In loose rock, air down somewhat less so the sidewalls are less likely to be damaged by sharp rocks. This video shows the difference between 30psi and 5psi.

recovery devices

snatch strap

A snatch strap is a nylon strap that has some stretch in it. Not only does this greatly reduce the violence of pulling someone out, but it also allows the rescue vehicle to get keep forward momentum when the strap pulls tight. It is a rubber band or bungie cord effect, only much stronger.

Before you get stuck:

  • choose straps that have loops on the end, not hooks
  • buy clevises that fit your recovery points and the strap loop. Test fitment ahead of time.

When you are stuck:

  • attach to tow/recovery points on the vehicles when possible, not on trailer hitch balls

This Australian video shows excellent safety procedures.

  • the stuck vehicle should “help” by giving their vehicle some gas as the strap starts to pull tight. Sometimes it takes very little pull to get out a stuck vehicle that is “trying”.
  • the towing vehicle should get some momentum going, but it does not require wide open throttle or other violent approaches.

come-along

winch

traction aids

mats

grabbers

lifestyle/traction.txt · Last modified: 2018/05/09 17:42 by frater_secessus