different sized spare

[turbo6i]

Hi
just a silly question

I have BFG muddys size 265/75/r16 on the disco s1 update
and a spare of 275/70/r16
it is slightly smaller

can i use it for a spare for short periods?
with centre diff turned off

or is this a no no?

thanks

[Blknight.aus]

you can use that as a temporary spare, just make sure the CDL is disengaged and any other lockers are also disengaged.

keep the speed down and you shouldnt have any problems other than its technically illegal to fit different size/treaded tyres across an axle.

[Quiggers]

check the outside diameter, you wont upset your diffs if the outside diameter is the same on all tyres...

be accurate.

i've mentioned before about the failure of a Volvo XC90 due to this issue:

new tyres on the front, well worn tyres on the rear, took only a week for the 'wind up' to wreck the centre diff/box etc on that machine...a very expensive fix...

the owner of that XC was warned by Volvo, and even showed where it's noted in the owners manual...

GQ

[Lotz-A-Landies]

Hi
just a silly question

I have BFG muddys size 265/75/r16 on the disco s1 update
and a spare of 275/70/r16
it is slightly smaller

can i use it for a spare for short periods?
with centre diff turned off

or is this a no no?

thanks
Turbo

There is actually a relatively simple fix and actually a good idea to do especially on long trips with a load.

Instead of checking tyre pressures, check rolling radii, which is actually more important than equalising pressure. What you do: with the tyres hot (20-50 Km highway driving should be sufficient) and on a level surface, is get a tape measure, and measure from the road in the middle of the tyre foot-print to the centre of the wheel. You then equalise the radius of each wheel by adjusting the pressure in each tyre. (You should not under-inflate a tyre, but usually increase the pressure in the tyres carrying the load.) This means that in a straight line the drive-train is doing the same revolutions irrespective of the load carried by the individual wheel. There is usually only a difference between front to rear!

You can do the same with your different sized tyre, but as you suggest only for a short time.

Hope this helps.

Diana

[CraigE]

check the outside diameter, you wont upset your diffs if the outside diameter is the same on all tyres...

be accurate.

i've mentioned before about the failure of a Volvo XC90 due to this issue:

new tyres on the front, well worn tyres on the rear, took only a week for the 'wind up' to wreck the centre diff/box etc on that machine...a very expensive fix...

the owner of that XC was warned by Volvo, and even showed where it's noted in the owners manual...

GQ
I do have to say that if new front vs old back tyres caused this type of failure there is something terriblly wrong. We are talking mm's difference if they are the same size tyre. I hope you mean new different sized tyres??

[Dougal]

check the outside diameter, you wont upset your diffs if the outside diameter is the same on all tyres...

be accurate.

i've mentioned before about the failure of a Volvo XC90 due to this issue:

new tyres on the front, well worn tyres on the rear, took only a week for the 'wind up' to wreck the centre diff/box etc on that machine...a very expensive fix...

the owner of that XC was warned by Volvo, and even showed where it's noted in the owners manual...

GQ

With a true open diff (like an unlocked LT230) it's not a problem.
The centre diff wouldn't know any difference to continually driving in circles.

[loanrangie]

I do have to say that if new front vs old back tyres caused this type of failure there is something terriblly wrong. We are talking mm's difference if they are the same size tyre. I hope you mean new different sized tyres??

Exactly, otherwise most on this forum would have destroyed the tc by now although with an unlocked cdl the centre diff differentiate power f to r so this would be very rare on a landy - even different diff ratios at each end if the diff is small will be ok.

[turbo6i]

cool

thansk for the info

its only a little off.
and im not going to buy a fifth wheel
i'll equalise them if needed


regards

[PhilipA]

According to the BFG site there is a 1% difference between the two tyres
MT 265.75=405 Revs per Km, 275.70 TA=417 Revs per Km.
This is nothing.
AFAIR the manual says 10% is acceptable for emergengy use.
Regards Philip A

[PhilipA]

That should be 3%.
And it is still negligible, not as much as worn vs unworn.
Regards Philip A

[Ralph]

I had occassion to fit a 31" spare on the rear when all others were 33" (just how things happen some times....)

I have ABS!

On a long sweeping curve that I wanted to slow down on, the brakes felt rock solid but the ABS was working overtime and the car was only being stopped at a minimal rate - The ABS thought I was on ice or something and wouldn't allow the brakes to work too hard. Needless to say when I did manage to stop (about 300m) I pulled the ABS fuse out. I managed to get home without further drama (or damage to gearbox, Transfer Case or diffs).
I'm just grateful that I didn't find this out while trying to pull up at a set of traffic lights or something.