Differential in tyre diameters cause problem?

Thanks for the info. I didn't think it would be too much of a problem, particularly on the loose stuff. Have already calculated speedo error for both. Don't particularly want to purchase an extra "fatty" and mount it underneath. More likely to need the extra 'skinny' for Anne Beadell etc. than on the beach.

Thanks Robin.
Good advice re the pressure reduction. One of those common sense solutions that often escapes us city slickers!!

Not wanting to hijack the thread, but would that work on a vehicle such as mine, an 80 series Toyota with constant 4WD?
Jack

I probably have read this the wrong way ?? Robin, you say that you drop tyre pressure so that you have same height off ground, ok I get that BUT when on the sand/beach we drop our tyre pressure to get increase our rolling diameter ?? so by you dropping your pressure aren't you increasing the rolling diameter not decreasing ?? Just that mine is full time 4wd as you know and have been interested in these type of scenarios Regards Steve

Steve, you don't let your tyre pressure down to increase the rolling diameter, you do it to increase the amount of tread in contact with the road. When you let the pressure down the tyre footprint lengthens.

The term “Constant 4WD” does not mean that 4WD is working all the time so the reference to tyre size is the same as any type of car. During normal use with the center diff lock OFF you are only driving one or at best two wheels at a time. As a diff only drives the axel with the least resistance, the center diff only sends drive to the front or rear diff at one time, the diff in the front or rear then sends power to one wheel at a time. The use of LSD or center diff locks or locking front or rear diffs (not to be confused with center diff locks) can alter the way the power is used by the diff but if a car of any type was “full time 4WD” as the makers would have us believe they would not last more than a short trip on a hard surface as this would be the same as driving a part time 4WD in 4H or 4L. This is only the basic info on the subject and it is far to detailed to try and describe here. John C

I don't understand What John C is trying to get across. There are several styles of constant 4WD. You have the simple type pioneered by Land Rover with 3 diffs, on in each axle and one at the transfer case. There are in addition several types with viscous couplings that replace the centre diff.

When you are running on a hard surface with a 3 diff system the power is delivered to all wheels equally. If not then you would be going nowhere.

When you encounter a soft patch, one of the wheels may loose grip and start to spin. When this happens there will not be much power applied through the wheels and as this happens the motor will rev its head off, a bit like it will when you slip the clutch. When this happens, you lock the centre diff and hopefully one axle will drive you out of trouble.

I think it is the last piece that John is trying to explain.

Yeah ok I'm a dope...stop picking on me!!

thatll make it pull to one side.
Dont even bother-2mm will make NO difference whatsoever.