Spare Tire Size??
- Thread starter Josh41
- Start date
rayra
Expedition Leader
If you have to use the different size spare, you put it on the undriven axle, rotating a larger good tire to the drive axle if you have to. That will save your axle gearing.
But get a matching size spare if you can. A used tire would be fine if it's a question of money, preferable to a shorter tire anyway.
But get a matching size spare if you can. A used tire would be fine if it's a question of money, preferable to a shorter tire anyway.
Stroverlander
Adventurer
Really depends on the vehicle and drivetrain...
4x4junkie
Explorer
The clutches in a limited slip differential could be damaged by prolonged driving with different size tires (requiring you switch the tires around as rayra mentions to avoid this). If your axle has an open diff (or unlocked selectable locker), then I see no issue, barring the speed sensor thing tarditi mentioned.
red EOD veteran
Adventurer
Even with an open diff it will cause damage over time if driven like that on pavement. Rotate the oddball size tire to the unpowered axle
quickfarms
Adventurer
The pinion, the ring gear carrier and axles ride on tapered roller bearings.
The spider gears simply ride on a metal shaft and prolonged spinning could cause damage.
Why risk it, unless a full size spare will not fit.
4x4junkie
Explorer
I'm just not seeing how the slow RPM could damage it... It's a 21 RPM difference between the two tires the OP mentioned @ 60 MPH, that's less than the speed of an old 33-1/3 RPM record. Every axle I've seen also had spiral grooves of some sort cut into the cross shaft to pump gear oil in between the gear and the shaft while the gear spins too.
Maybe it just depends on the vehicle like was said above. I did it once on one of my Fords (8.8" axle)... one tire was a 33 and the other a 235/75R15 (a much larger difference than the OP's case), though it was only for about 15 miles. Still, there was nothing unusual I saw inside the diff when I had it apart some years later for an axle seal replacement. The spare I currently carry is 33¼" while my main tires are 34½" (which I'm contemplating swapping back to true 35" tires soon). I'm not too worried about it with my ARB.
Maybe it just depends on the vehicle like was said above. I did it once on one of my Fords (8.8" axle)... one tire was a 33 and the other a 235/75R15 (a much larger difference than the OP's case), though it was only for about 15 miles. Still, there was nothing unusual I saw inside the diff when I had it apart some years later for an axle seal replacement. The spare I currently carry is 33¼" while my main tires are 34½" (which I'm contemplating swapping back to true 35" tires soon). I'm not too worried about it with my ARB.
red EOD veteran
Adventurer
Did you take a dial indicator and measure the difference it each gear and bearing when you tore into the diff? You will find excessive wear from the difference and it adds up pretty quick. Much more damaging with a spool, locker, or limited slip (snapped axle shafts/burnt up clutches) but even an open diff will experience problems from prolonged use. Why accelerate the wear so the diff has to be rebuilt sooner, when you can either run the proper sized tire or rotate it to a non powered axle?
4x4junkie
Explorer
Because sometimes you're with others in a group (and/or it's getting late), and rotating it to the non-powered axle would consume more of everyone's time.
And a spool is completely immune to any effects of this, there are no moving parts to wear inside of a spool (of course your handling & tire wear will be completely out the window though, your car will try to drive in a circle lol, so that alone is reason enough to switch the tire around).
To each his own. No I didn't mic the parts, but I also didn't see any sign of discoloration, sloppiness, scoring, worn grooves, etc. Spider gears are not exactly precision-made parts (not like R&P gears are), so even if things were to wear enough to where you could measure without seeing some small difference vs a new set of parts, it's unlikely it would make much, if any difference (have you ever seen the amount of slop a limited slip diff develops as the clutches wear?).
Remember, we are talking about doing this for a few dozen to maybe some hundreds of miles tops, not for the lifetime of a set of tires.
And a spool is completely immune to any effects of this, there are no moving parts to wear inside of a spool (of course your handling & tire wear will be completely out the window though, your car will try to drive in a circle lol, so that alone is reason enough to switch the tire around).
To each his own. No I didn't mic the parts, but I also didn't see any sign of discoloration, sloppiness, scoring, worn grooves, etc. Spider gears are not exactly precision-made parts (not like R&P gears are), so even if things were to wear enough to where you could measure without seeing some small difference vs a new set of parts, it's unlikely it would make much, if any difference (have you ever seen the amount of slop a limited slip diff develops as the clutches wear?).
Remember, we are talking about doing this for a few dozen to maybe some hundreds of miles tops, not for the lifetime of a set of tires.
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rayra
Expedition Leader
lol for a TIRE CHANGE? Ludicrous. Precious snowflakes. Just have the impatient proceed ahead at a slowed pace and have the tail end charlie wait on the guy to change an extra tire. It's not even 10mins. Tell them to stroll around, look at the scenery, hunt a Pokemon.
Or can nobody move until you do / say?
/really puzzled by your seemingly constrictive and imposed criteria. I mean if you are conducting things like a tour group operator you probably ought to be teaching them how to change a damned tire anyway, as well as performing a practice recovery / extraction. Instead of treating them like veal / divas.
4x4junkie
Explorer
********
No, I have a little bit of consideration for others, especially knowing that running a 1-2" smaller tire on my open diff for a short period of time isn't going to damage a thing.
As I said, to each his own. If you want to send your group all ahead without you (many of whom will probably insist everyone sticks together instead) because you are scared your axle will drop dead, then you are certainly free to do so.
No, I have a little bit of consideration for others, especially knowing that running a 1-2" smaller tire on my open diff for a short period of time isn't going to damage a thing.
As I said, to each his own. If you want to send your group all ahead without you (many of whom will probably insist everyone sticks together instead) because you are scared your axle will drop dead, then you are certainly free to do so.
Stumpalump
Expedition Leader
A plug kit, compressor, ratchet strap and flammable aresol fix most flats. Buy those first and learn to use them. It won't hurt a thing to run the wrong tire size for a few hundred miles.
red EOD veteran
Adventurer
If stopping to change the tire slows down others enough to where they are complaining, and not helping out, they need to leave or learn some manners and patience.
A spool itself will likely suffer no problems but the axle shaft that is attached to the smaller tire will not last. The tire will skip on the dirt to compensate for a little bit but each time that happens it's twisting/untwisting that axle shaft like a spring and it will break within a few miles. On pavement even faster.
To each his/her own is fine, but your advice of just install the smaller tire on a powered axle is misguided. Rather accelerate wear or damage your axle than spend a few extra minutes to fix it right (with the local equipment), that's your choice on your rig.