different wheel size on same axle

[grind hog]

i have 33" tyres on all 4 wheels, but have noticed that the spare is a standard size, if i have a puncture, and use this wheel, will it work as a get me home, same as a space saver wheel in a modern car, or will it potentially screw something up in my diff, or as its not ever in 4 wheel drive on the road will it be fine if fitted as a temporary spare on either front or back

Thanks

Grind Hog.

[Gamedawn]

This topic has come up a few times now and the general consensus seems to be that, while it is not ideal, having a spare of the wrong size will not cause damage as long as you treat it as a space saver i.e. stay slow and careful. Also it should be fitted to the front as it will then have no effect on the diff / drive train.

[silvtr1000]

I remember this coming up too. I looked at loads of stuff on the web about diffs, this included...

http://auto.howstuffworks.com/differential3.htm

One of the main functions of a diff is to allow two wheels on the same axle to rotate at different speeds, so from that point of view, I can't see mixed sizes being a problem, but I could easily be wrong - I'm no engineer. But note that I recently raised my Surf's rear axle and when I rotated one wheel, the opposte wheel turned in the opposite direction.

My opinion is that with different sized tyres on the same axle, the vehicle will list and probably handle like sh1te, and suffer abnormal tyre wear. Over longer periods, bearings, seals etc may wear excessively because of the uneven weight distribution.

Most importantly, of course, 33" tyres look way cooler than standard size, so my motivation to get the spare off would probably be aesthetic...

[Morr]

Its true that a diff is designed to allow two wheels rotate at different speeds, however if the diff is constantly doing so it will accelerate wear on the internal components as they are have to work harder than when in a normal equal rotating condition. That said, how significant the extra wear caused by the use of different diameter wheels is debatable.

Short answer as stated above - Use the odd sized wheel for temporary use, treat as you would one of those ridiculous money-saver spares (I refuse to acknowledge them as space saver when so often they are supplied in a full size wheel well just to save the cost of an alloy rim), ie reduced speed & distance, replace original as soon as possible and do not engage 4wd

[NiftyNev]

If the spare is around the 29' then this is a big difference.I would also think a bit dangerous.

Neville

[da SLUG man]

space saver wheels have the same diameter as the regular wheels, they're just narrower so take up less space in the boot... cheapskete way for them not to give 5 alloys if you ask me!

[Grimreeper]

Diffs

I recently raised my Surf's rear axle and when I rotated one wheel, the opposte wheel turned in the opposite direction.
:

What you describe, where 1 wheel truns in the opposite direction, is a standard diff....some have LSD (limited slip diffs) they will both turn the same way.
If you have a LSD with different sized tyres it will wreck the diff internally.

The only safe way is to get a spare of the same diameter, but if you are really stuck only use the odd size on the front and in 2wd at low speed.

[scottidog]

wheel

You may find that if you take the spare off and compare there wont actually be much difference between the overall size of the 2. The wheels and tyres will be different sizes but the overall circomfrence will be very similar

scottidog

[exmee46]

Agree with all comments - nothing basically wrong but it will tend to cause the diff to wear if kept on for long periods.
Maybe you could keep the spare nice and hard and let down the pressure in the other remaining wheel on the axle to reduce the rolling radius to something nearer the spare.

Cheers

Kev