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It's certainly true thatyou should always buy tyres in sets of four for a 4 x 4. In the olden days, when there were really only Land Rovers, they had no centre differential, and it was easy to break a half shaft - or worse.  Of course, that was only if you used four wheel drive on the road. (Sometimes you had no option if you needed low range).

What happens is that all the wheels have to turn at the same speed and you get transmission wind up. Either a wheel has to slip, or something has to break. If you correctly use the four wheel drive on loose surfaces, it won't hurt anything.  Also, these days, many 4 x 4s have the centre differential, which allows a bit of leeway. Still better to give that an easy life if you can.

As long as the existing tyres still have deep tread, it will be ok. Never mix sizes on a 4 x 4 though. All four tyres must be the same size.  Same make if you can, but that's good practice for any car anyway.

Jim

Hi

I remember reading an article in one of the magazines in my dentists waiting room about the 4WD Volvo XC70.

The magazine "help me complain" section were challenging a dealer on behalf of the customer to get back £3000 worth of diff repairs after they had only changed 2 tyres on his car, despite the manual advising having all 4 changed.

I was surprised that the tolerance should be so small on a ruggedised vehicle.

What does it say in your Toyota handbook?

HTH

Paul

If you only use the four wheel drive off road, or in snow - that is when the tyres can slip on the ground, you won't have problems.

On newer vehicles with a centre differential, the problem is not so severe, but you still don't want one side of the diff going faster than the other all the time.

The major damage I've seen has always been with the older Land Rover type, with no centre diff.  Sometimes with a maximum weight trailer, you would need low range for hills, even on the road, and that's when the gearbox can be destroyed.  Seen quite a few, but not recently.

Even the same nominal size of tyre, from a different manufacturer, can have a substantially different rolling radius.  If in doubt, take a piece of string, and measure right round the circumference of the tyre. Then do the rest.  That can be a bit fiddly, so you can just make a chalk mark on the tyre right at the bottom.  Make a mark on the floor next to it, then move the vehicle forward until the mark on the tyre gets to the bottom again.  Make another mark on the floor, and measure back to the first one. That is how far your tyre will travel for each revolution.  You may be surprised how different they are, and that's why we don't want to make the situation worse.

Jim

I have a Discovery.Its permanent four wheel drive.I only ever replace a tyre when it needs it and never four at a time.I have had no problems and its just clocked up 121k.The handbook simply states  a tyre must be replaced when its indicator band becomes visable or when its tread depth reaches the minimum permissable depth that legislation allows.

I should check your handbook but to me it sounds like they were trying it on.