[30ONA]

I have 4 new tyres all the same size but a little larger than my spare.

I've been told if I put two different diameter tyres on the back of my car in an emergency it will bind the diff, BANG. so if I get a flat on the back put a good front one in its place and put the spare on the front. Because if I do it on the front it's ok because open diff. But if I do it on the front it's it ok in 2wd but not ok in 4wd? Or is it not ok at all? This is on a manual GV.

[bumstein]

I’d be using the mismatched spare only to get you to where you can have the busted tyre fixed or replaced. If that happens to be a long way then yep you could def use the front to help along the way

[Gwagensteve]

Someone is being a touch dramatic. It won't cause the death of a busload of nuns or your diff to go bang, but in an ideal world, if possible, you'd put it on the front.

You'd only ever be using 4WD on low traction surfaces so the small difference won't kill you if it's in 4WD.

If you're doing lots of highway km's with the "odd" spare on definitely ensure it's on the front.

Consider in a regular GV 1/2 the front diff is spinning in 2WD anyway, it's only that the left and right sides aren't locked together (only one axle "breaks" when you're in 2WD, not both like an older Vitara/sierra with free wheeling hubs.

[30ONA]

Consider in a regular GV 1/2 the front diff is spinning in 2WD anyway, it's only that the left and right sides aren't locked together (only one axle "breaks" when you're in 2WD, not both like an older Vitara/sierra with free wheeling hubs.

Are you saying it will break an axle?

[Gwagensteve]

No. Your car “breaks” one axle when you put it in 2wd.

[fordem]

Gwagensteve wrote:

Consider in a regular GV 1/2 the front diff is spinning in 2WD anyway, it's only that the left and right sides aren't locked together (only one axle "breaks" when you're in 2WD, not both like an older Vitara/sierra with free wheeling hubs.

Gwagensteve wrote:

No. Your car “breaks” one axle when you put it in 2wd.

This is not my understanding of how the GV front freewheel mechanism works - mind you - I haven't gotten around to pulling one apart yet, but from the service manual, it appears that both axles are connected to the side gears at all times - it would appear that the entire differential assembly disconnects from the ring gear.

30ONA wrote:

I have 4 new tyres all the same size but a little larger than my spare.

I've been told if I put two different diameter tyres on the back of my car in an emergency it will bind the diff, BANG. so if I get a flat on the back put a good front one in its place and put the spare on the front. Because if I do it on the front it's ok because open diff. But if I do it on the front it's it ok in 2wd but not ok in 4wd? Or is it not ok at all? This is on a manual GV.

- first question - why should it make a difference front or rear - they are both open diffs.
- second question - have you ever seen the difference in tire diameter when a manufacturer supplies a "space saver spare"? They don't tell you in the manual not to use the spare on the front or rear of the car - and remember they are warranting the vehicle that way.

Your tire diameters are always slightly different, different levels of wear, different pressures - running with large differences wears the differential gears faster, and should be avoided - it really is that simple...

[30ONA]

Thanks all.