Thread: spare tyres - actual times you needed a second spare

"Similar circumference" usually means within ±5% or so in OEM circles. On the vehicles I am involved in engineering it is well above that before we get out the worry-beads. Tread depth variation will be much, much less than that even looking at a new mudder vs a fully-worn highway tyre. On a typical ~Ø30" D3/4 tyre the difference would be well under 3% (ie. brand new to fully-worn) and you'd likely see that with differences in tyre pressures and loading differences front to back anyway. I wouldn't condone nor ever run heavily worn tyres anyway. Nor would I condone running a significantly dissimilar-sized spare for any distance or time or speed. I don't run my tyres down below about half tread depth as a personal choice.

Up until recently my off-road vehicle hasn't had clutch packs anywhere outside of the auto so a moot point for me. The LT230 doesn't care at all, nor does my Detroit locker, nor my Trutrac. And for my newer vehicle that has clutches, I have zero concerns over small variations causing slight relative differential speeds. The effect of one tyre on one corner is halved at the transfer case anyway. Plus there are benefits to having the clutches slightly rotating (not whizzing around, but very slight relative movement) as this gently wipes the friction surfaces and can sometimes have a beneficial effect renewing the 'cushion' interface and pulling fresh oil in where it would otherwise get squeezed out over time. The amount of wear that a wet clutch sees under light load, low-speed motion is somewhere below negligible as it's mostly viscous drag rather than surface-to-surface friction. You'd do more damage turning into your driveway... I've dealt with wet clutches that have developed serious issues because of a lack of relative rotation and relatively high loading. It's almost akin to galling, to visualise the concept.

I have absolutely nothing against five, or six tyre rotations at all. I don't think it's a bad idea actually as it stops the spares from ageing and means you refresh the whole set at the appropriate time. But I don't believe that it shouldn't be justified with a fear of damaging the drivetrain in any way. These things just aren't that fragile or sensitive to these minor effects.

FWIW I have five identical wheels and tyres on the new L320 and I'll likely rotate the lot as the spare will need to be deflated and squashed up in there. This will give them all a turn. it's only fair really

Five tyre rotation is a good idea.
Some tyre companies offer 4 for 3 tyre deals, so people just get 4 and keep the best of the others as the spare.

I have scottish blood in me and the number of people i see that have a brand new spare that never gets used, what a waste. Then you sell the car or buy another different set of tyres which might also be a different size, and then you have issues.

Maybe some people dont quite twig that if you get 60,000km out of four tyres, you will get 75,000km out of five.

A friend had a very high performance car that has a different tyre on each wheel. The rear rims are wider than the fronts and the tyres are LH & RH, and drive and steer. No spare wheel supplied. Just one of those cans of gunk and a connection hose. The tyres are very expensive and very soft sticky compound. They don't last very long.

Originally Posted by Bigbjorn

A friend had a very high performance car that has a different tyre on each wheel. The rear rims are wider than the fronts and the tyres are LH & RH, and drive and steer. No spare wheel supplied. Just one of those cans of gunk and a connection hose. The tyres are very expensive and very soft sticky compound. They don't last very long.

Four spares when he takes it offroad then, or at least two, but not sure if he will have anywhere to put them.

Originally Posted by rammypluge

Four spares when he takes it offroad then, or at least two, but not sure if he will have anywhere to put them.

It is a Corvette with a lot of the high performance options including the wheels & tyres. There is definitely not enough space to carry a spare. The only off road it does is up & down his driveway. A great future buy for someone. He is same age as me, 77, and it is a genuine "driven only on Sundays on bitumen roads by a little old man." Might do 2000 k's a year in a busy year.

Oh dear, I think I’ll have to give this year’s trip a miss. Not only have I not rotated my tyres, I’ve now been told by a Toyota driver that the Defender will break down in the Simpson. Sounds like I am in great peril.

YouTube

Seriously though, while I think 5 or preferably 6 tyre rotation (I like having two spares, but not necessarily on the vehicle) isn’t a bad idea, I’ve found if the tyres are not being used exclusively on-road then any benefit from extended life is often negated by damage such as chipping making me want to change some tyres earlier anyway. I have approx 65k on the original Contis now and they are probably good for another 10k plus. However with a Simpson trip coming up in a couple of months I’ll replace them as a matter of course and would do so even if they had another 20k in them. So again any extra life by adding the spare in would have been negated.

Cheers,
Jon

Coincidently today i decided my 70 series LC was squealing a little too easily on the bends, so gave them all a breath of air, the spare was especially flat, so much for company servicing every 5,000 km

About 50 years ago on the Lae Wau rd in PNG, lets say 150 km. 2 flats going, 3 flats back, a 190 merc only has 2 spares :-/