Spare Tire Size

[TJMexico]

This is specifically regarding my new XJ acquisition, but I think that the question is universally applicable to most any 4x4.

The XJ has a stock spare in the cargo hold, but it is running 31x10.5/15s. I plan to replace that small spare with something compatible, likely a A 245/75R16 in a highway configuration as the diameter is almost exactly that of the one's I'm running and it would be a narrower and much lighter tire, taking up less space and weight (not to mention cheaper to purchase).

I'm curious as to just how bad it is to run a smaller tire like the current spare with the big ones that are mounted. I feel certain that it would play hell on the differentials (not to mention poor handling and stress on the suspension), but curious as to what general wisdom here says. Would you drive home on a spare like this? Might seem like a doofus question and I know that I would not go out into the wilds with it, but just curious if most everyone else concurs...

 

[JKP]

You wouldn't want to run it on a LS diff for a long period.

If that XJ has the vacuum disconnect on the front axle like a YJ, the front diff wouldn't care at all.

 

[rouxbicon]

You wouldn't want to run it on a LS diff for a long period.

If that XJ has the vacuum disconnect on the front axle like a YJ, the front diff wouldn't care at all.

Running even significantly different tire sizes won’t bother an open diff in the least. An open diff can spin each side at different speeds indefinitely. An ls diff would experience accelerated clutch wear, but I’m guessing that would not be a great big deal assuming the spare was only run to get home or to a tire shop

 

[TheBoogieman]

Option #2 for a matching spare and saving cargo space.

I miss the extra cargo space on my XJ.

 

[TJMexico]

Option #2 for a matching spare and saving cargo space.


View attachment 692968

I was looking at those (the receiver-hitch-mounted swing-down carrier). It would be an practical and economical solution, but I have doubts as to whether it would be tough enough to withstand the weight of a full-sized tire over rough roads.

Now, as I said, I do plan to get a narrower, lighter highway tire of the same diameter as my spare, something like a 245/75R16, which has almost identical diameter. But still, the bouncing that I experience on the roads I run make me question if that joint where it drops down would be able to handle the abuse. It'd suck to be bouncing along a mountain trail and have the tire drop off.

ETA: Another thought is how it might affect my angle of departure. Some of the gullies and arroyos that I pass through are pretty steep. I run a cargo basket on the receiver hitch of my TJ and it's pretty beat up from dragging in those spots. Granted, this is a lot shorter, but still ...

Really, the bumper mounted swing out solution would be best, but it's costly and I don't know if I'll be able to swing (pun not intended) it for now.

 

[TJMexico]

Running even significantly different tire sizes won’t bother an open diff in the least. An open diff can spin each side at different speeds indefinitely. An ls diff would experience accelerated clutch wear, but I’m guessing that would not be a great big deal assuming the spare was only run to get home or to a tire shop

So, that's my question. Not sure if the Cherokee is running open differentials or not. (Excuse the ignorance, that's why I am here.)

At any rate, I still would rather have a full sized spare for the sake of handling and such, even if the tread and width are different.

 

[JKP]

If stock, the front is definitely an open diff. I'm not sure if the XJs had the vacuum disconnect on the axle, but pretty sure the did.

The rear could be either, LS usually has a metal tag attached to the diff cover stating to add LS additive. If you jack up the rear and turn one tire by hand, and the other tire turns the same direction, it has a LS, if it turns the opposite direction, it's open.

And even if you have a LS, by this point the clutches may be worn and it may not have very much holding capability.

 

[ColoJeep]

This is specifically regarding my new XJ acquisition, but I think that the question is universally applicable to most any 4x4.

The XJ has a stock spare in the cargo hold, but it is running 31x10.5/15s. I plan to replace that small spare with something compatible, likely a A 245/75R16 in a highway configuration as the diameter is almost exactly that of the one's I'm running and it would be a narrower and much lighter tire, taking up less space and weight (not to mention cheaper to purchase).

I'm curious as to just how bad it is to run a smaller tire like the current spare with the big ones that are mounted. I feel certain that it would play hell on the differentials (not to mention poor handling and stress on the suspension), but curious as to what general wisdom here says. Would you drive home on a spare like this? Might seem like a doofus question and I know that I would not go out into the wilds with it, but just curious if most everyone else concurs...

View attachment 692881

It's not a big deal for driving home on , my concern would be with a limited slip diff . You could drive a long ways on a mismatched tire to get it home.
Do you worry about how many left turns vs. right turns you will make with 4 equal sized tires ? Your plan is sound in my opinion.

 

[TJMexico]

It's not a big deal for driving home on , my concern would be with a limited slip diff . You could drive a long ways on a mismatched tire to get it home.
Do you worry about how many left turns vs. right turns you will make with 4 equal sized tires ? Your plan is sound in my opinion.

That kind of sums it up.

The TJ and the XJ will very seldom see pavement, save a very rare emergency run into town if my pickup is down. (I literally live where the pavement ends, and everywhere I go is off-road. It gets hairy during the rainy season!)

The more I think about it, the more I think that setting up with a 245/75R16 highway tire and figuring out how to squeeze into the original stock spare location is my best option. I plan to get a large cargo basket, so the tire taking up cargo space won't be a big drawback.

 

[Dan The Video Man]

I wouldn't think it't a huge deal, especially considering all the vehicles that come from the factory with a smaller sized donut spare. In the end, it's a temporary use to get you to where you need to be to get the downed tire fixed.

 

[TJMexico]

I wouldn't think it't a huge deal, especially considering all the vehicles that come from the factory with a smaller sized donut spare. In the end, it's a temporary use to get you to where you need to be to get the downed tire fixed.

Agreed. My concern, however, is that I am often several hours from home or a tire repair place. Carrying plugs and a compsessor, minor punctures can be fixed without even removing the tire, but the spare is for something extreme like a damaged sidewall or a blowout. I have had sidewall damage on the road and had to change the tire. (But I was hotdogging so that sidewall cut was entirely my fault.)

 

[TheBoogieman]

If stock, the front is definitely an open diff. I'm not sure if the XJs had the vacuum disconnect on the axle, but pretty sure the did.

None since 1992 and front axle only.

 

[TheBoogieman]

The more I think about it, the more I think that setting up with a 245/75R16 highway tire and figuring out how to squeeze into the original stock spare location

I had a 31" spare in my 99' XJ before going to 33s. Very minor mods are needed to fit a 31 in the stock location.


View: https://youtu.be/_BLkN78l_4M?t=257

 

[Ashim]

Likewise, I was able to fit a 31" matching spare in the stock location of a Cherokee. A little massaging of the floor with a hammer and modifying the attachment hardware worked fine. I have had 4 Cherokees over the years and believe it'll be a great choice for your use.

 

[KennethS]

If you jack up the rear and turn one tire by hand, and the other tire turns the same direction, it has a LS, if it turns the opposite direction, it's open.

Minor point - the transmission has to be in neutral for this test.