Is a rear locker any good in sand for towing?

Reader question:

“Hi Robert,

I hope you don’t mind me asking a direct one on one question.

I have a 2016 200 and tow on sand quite a bit. ABH, that kind of thing.

I have generally been very happy with the traction control but feel the one situation where it lets me down is towing up dunes. I have been considering a rear diff lock which TBH I find hard to justify apart from this situation.

I was reading your Prado review https://practicalmotoring.com.au/4×4/toyota-prado-offroad-systems-work/ and saw your comment that the rear diff lock probably wouldn’t help much in sand.

I am not concerned about the cost, I just wouldn’t want to do something and add an after market accessory unless it added value.

I am interested why you think a rear diff lock won’t help much, especially towing ( Tvan)

Also your new videos are fantastic. Keep it up.

Maybe you could compare the merits of different after diff lock types. I see there is some criticism on the Harrop ones which unlock when changing direction of travel. Thanks. I’ll try not to make a habit of asking these questions. 

Regards,

[ note – if you find my work useful, please support me on Patreon, particularly if you want questions answered! ]

Cross-axle lockers prevent wheelspin, and are most useful when one wheel on an axle has significantly less traction than the other. This is most apparent when the weight on a wheel changes, as the more weight on a wheel, the greater the traction. This video explains the concept with use of the Traction Circle:

In sand, the weight is most fairly well equally distributed over both wheels on an axle, and speeds are relatively high compared to rock. So, you tend to get few situations where one wheel is spinning in the air like you do in rock or ruts. That reduces the value of a locker.

And lockers come with a disadvantage; they increase the turn radius as the vehicle’s inside and outside wheels cannot spin at different speeds around a corner. This increases drag, and in effect rolling resistance…so increases the chance of bogging when sand driving and requires additional power.

That’s why I don’t suggest lockers are important for sand driving. They aren’t really needed, and can work against you.

Now as always there are exceptions, and one is a straight ascent up a rutted dune, like you find in the desert. Here there is no turning problem, and there is a wheel-in-air potential. So there lockers may make a difference, but even so I wouldn’t rush to fit them as a little change of line, momentum, and air pressure reduction usually does the trick, and worst case just fill in the ruts and/or use traction ramps. But a rear locker is always a handy aid to have, can help ease out of bogged sand situations for example.

More on how diffs work here: