Is a same size but different offset spare tyre OK?

Advice on the right rolling stock for your 4WD
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Joined: March 14th, 2016, 6:46 pm

Is a same size but different offset spare tyre OK?

Unread post by Luvvt » March 14th, 2016, 6:54 pm

Hi all,

I have 4x maverick fuels with a 25p offset. Factory reccomendation 30p
My question is for my spare am i safe to have an 18 with that same tyre choice but different off set. Im thinking a factory 18inch

Peter Aawen
Posts: 20781
Joined: June 17th, 2005, 8:01 pm

Re: Is a same size but different offset spare tyre OK?

Unread post by Peter Aawen » March 14th, 2016, 8:46 pm

If you are only gonna use it as a spare, and you are aware that it could make a fairly significant impact on the handling & stability of your vehicle on the road, then yeah, when the rolling dia of the tyre is basically the same even if the offset of the rim isn't then it still should be OK!!

The rolling dia of the spare tyre is fairly critical for a 4WD, especially if you need to use the spare off road & in difficult conditions - any major (ie more'n about 20 mm) variation in rolling dia could contribute to trans case or cross axle diff lock 'wind-up' in the drive-line and break things in the worst possible place for you to suddenly find you have a vehicle that ain't goin anywhere under it's own motive power!! Snapping an axle trying to get up the last & on the steepest hill before you get black on the black top can be a pain & is bad enough, especially if you are on your own & hafta walk out for help. A different offset might mean you hafta be careful with your wheel placement & it can introduce unexpected handling or steering responses, but if you are off road & 4Wheeling that shouldn't be such an issue, you are meant to be travelling slower than you would on the Hwy & there are gonna be fewer people around for you to run into & hurt!! So the offset's not such a biggie, but blowing your transcase terminally (ie, broken casing & gears & shafts dropping onto the dirt!) when you are deep into 4Wheeling country &/or remote is potentially much worse, but oh so easy if you have just fitted a tyre that has a significantly different rolling dia than all the rest - even if it's just 24mm or so diffference!! :eek:

That's why you really should carry & use a spare that is identical to the tyres on the road AND you should include it in your 10,000km tyre rotation so that even as your road tyres wear the tread down over km travelled, the spare isn't going to be too far off the same rolling dia/state of wear as all the rest!! This is important enough for Part-Time 4WD's for the above reasons when they are off road & in 4WD, and doubly important for Full-Time 4WD's for the same reasons off road in 4H &/or 4Lo-Locked Centre Diff, only it can also be a traction & handling issue even if it's not quite such a potential breakage factor when its in 4Auto &/or on the road due to that centre diff doing it's thing & making your 'Four Wheel Drive' effectively just a ONE wheel drive at any given instant!! :p :sillywink:

So as mentioned above, when you are aware of the potential for handling & steering issues due to the different offset, it's not such a biggie - but it will also make it harder for you to include the Spare in your rotation so it wears at the same rate or nearly so as the rest & that can be a fairly significant issue off road in the long term too; so it's definitely not really ideal!! ;)
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