Using a spare tire that's one size up or down from the other three in an emergency

[kcjaz]

I'm installing my Dissent rear bumper and will move my spare to the swing out. I'm considering carrying a second spare in the stock spare tire storage location. Ultimately, I would buy an additional 17" wheel and matching tire but I have my OEM wheels/stock size tires just sitting in my garage. I could just mount one of them as an emergency spare. It would kinda be like a "donut spare". I'm running 285/70/R17 now. I think this would work to get me off a trail. I probably would have to have the CDL off running with one different size tire. Would this work?

Edit: Some good conversation in this thread but if you just want the answer go to posts #16 and #43.

 

[40Man]

I'm installing my Dissent rear bumper and will move my spare to the swing out. I'm considering carrying a second spare in the stock spare tire storage location. Ultimately, I would buy an additional 17" wheel and matching tire but I have my OEM wheels/stock size tires just sitting in my garage. I could just mount one of them as an emergency spare. It would kinda be like a "donut spare". I'm running 285/70/R17 now. I think this would work to get me off a trail. I probably would have to have the CDL off running with one different size tire. Would this work?

As I recall the tolerance for the torsen diff is 2-3%.

 

[tbisaacs]

I'm installing my Dissent rear bumper and will move my spare to the swing out. I'm considering carrying a second spare in the stock spare tire storage location. Ultimately, I would buy an additional 17" wheel and matching tire but I have my OEM wheels/stock size tires just sitting in my garage. I could just mount one of them as an emergency spare. It would kinda be like a "donut spare". I'm running 285/70/R17 now. I think this would work to get me off a trail. I probably would have to have the CDL off running with one different size tire. Would this work?

Why two spares? Honest question.

 

[TXLX100]

In an Emergency with wrong size tire, what other choice do you have?

Used 285/17 tires are a dime a dozen.

 

[Madtiger]

I think donuts in other cars always have same diameter as the regular tires. Only difference is that they are skinny.

It is just not CDL that you have to worry about. Traction control across same axle may freak out. VSC may not like it. Both of these systems sense speed differences among the tires.

Using mismatch size tires on the trail is easy. The problem is when you get on highway at higher speeds…where the smaller tires will spin much faster than the others which may trip the traction control and VSC computer.

 

[kcjaz]

Why two spares? Honest question.

The two spares thing is mostly cause I can and it woudn’t cost anything if I just use my old stock wheel/tire. Also my Duratrac sidewalls are getting chewed up and it’s just a matter of time before I cut a sidewall and need my spare. I’ve bees in trails where others have destroyed a tire and need their spare. Then they continue without a spare and depending on what u r doing, that could end your day.

 

[kcjaz]

I think donuts in other cars always have same diameter as the regular tires. Only difference is that they are skinny.

It is just not CDL that you have to worry about. Traction control across same axle may freak out. VSC may not like it. Both of these systems sense speed differences among the tires.

Using mismatch size tires on the trail is easy. The problem is when you get on highway at higher speeds…where the smaller tires will spin much faster than the others which may trip the traction control and VSC computer.

Good points, I was wondering about all the traction control and if it might get all pisses off or confused. Probably best to just find a 18” tire that’s the same diameter as my other tires and just use my OEM wheel.

 

[Fisher23]

I have been on a few trails where I had double bow outs. Both tires hit the same sharp outcrop on the sidewall.

In dirt with open differentials (not locked) if they are slightly different sizes it's not going to mater much in an emergency situation. The one tire will slide.

 

[grinchy]

I’ve had good luck finding used tires in odd sizes on eBay. If you’re just looking for an same diameter sixth , maybe try there. Just back calculate the 18” equivalent for your new size.

 

[yonah]

Why two spares? Honest question.

Not sure of the OP’s requirement, but dual spares seem to be more common on touring/overland vehicles in SA and Australia. Although, from what I’ve seen on those rigs, the dual spare tires are both the same size, and appear identical.

The idea behind dual spares is redundancy. It gives the vehicle another spare tire to fall back on in the event that the main spare is installed and the original tire is damaged beyond what can be repaired in the field. I could see this being an advantage in a remote area where tire damage is a real threat and tire shops are few and far between - or a dual tire failure event, as mentioned by @Fisher23

 

[lx200inAR]

I could be wrong, but as I understand it. The LC has open diffs in front and rear, so as far as on the axle, a different size won’t matter at all. If the mis-sized tire caused the Torsen to engage a bit, that may happen, but I don’t think that would be too big a deal. If you lock (seems like you installed lockers recently) the axle the smaller tire is on you will get some wheel hop, but at low speed in low traction, not a big deal.

So while not ideal, I don’t think it would be a big deal.

 

[Madtiger]

I could be wrong, but as I understand it. The LC has open diffs in front and rear, so as far as on the axle, a different size won’t matter at all. If the mis-sized tire caused the Torsen to engage a bit, that may happen, but I don’t think that would be too big a deal. If you lock (seems like you installed lockers recently) the axle the smaller tire is on you will get some wheel hop, but at low speed in low traction, not a big deal.

So while not ideal, I don’t think it would be a big deal.

Traction control and VSC (and ABS for that matter) monitor wheel speed at each tire. A faster spinning tire may cause the computer to think that that tire is slipping……thus, will erroneously engage the brake on that tire……which may cause instability on the highway and/or fry your brake and/or de-throttle you (because again, computer is thinking that one tire is losing traction).

 

[Madtiger]

Good points, I was wondering about all the traction control and if it might get all pisses off or confused. Probably best to just find a 18” tire that’s the same diameter as my other tires and just use my OEM wheel.

Carrying an extra spare will just add more weight to your already heavy vehicle.

Maybe just get BFG KO2 or something like that that has 3-ply sidewall.

(I have had one tire failure on the trail…..no damn fun to change tire on the trail! That is why i place a higher emphasis on sidewall strength than most people. Once you experience tail failure, it changes your outlook!)

 

[lx200inAR]

I certainly don’t want to be arguing doing something not ideal. There’s no doubt a matching tire would be best, But the difference between a stock tire and a 285/70R17 isn’t much. I assume the OP understands the weight trade offs and feels it’s worth it, so I’m not going to question that
In an emergency, I’d certainly run it over trying to get AAA to meet me on the side of a trail.

 

[1world1love]

Why two spares? Honest question.

Ask @indycole

 

[bloc]

I'm not sure of the exact size difference, but once upon a time discount tire sold me a full set of 285/65R18 KO2s the day that I left on a colorado trip. Thing is, they installed 3 of those, and 1 275/70R18 KO2 on the front right. I didn't notice until I had driven 900 miles to Silverton and went to air down.

The VSC/TC couldn't have cared less.

The discount tire in durango was awesome.. they looked up the ticket, got the correct tire on really quick, and wrote it up for their insurance in case I had problems with the transfer case in the future.

 

[1world1love]

Yeah, I think in a situation where you needed to drive 60 miles at relatively low speeds, there would be minimal risk.

Disengage anything you can and take it easy but these systems aren’t that fragile.

 

[LC Mike]

I'm not sure of the exact size difference, but once upon a time discount tire sold me a full set of 285/65R18 KO2s the day that I left on a colorado trip. Thing is, they installed 3 of those, and 1 275/70R18 KO2 on the front right. I didn't notice until I had driven 900 miles to Silverton and went to air down.

The VSC/TC couldn't have cared less.

The discount tire in durango was awesome.. they looked up the ticket, got the correct tire on really quick, and wrote it up for their insurance in case I had problems with the transfer case in the future.

Good data point; I have been hoping someone could report that condition. That difference 275/70R18 and 285/65R18 is about 2% in diameter. I was looking at Nitto Ridge Grapplers 285/65R18 (32.6 inch diameter) with a spare 265/70R18 (32.9 inch dia) to get another 0.6 inch of ground clearance under the spare (going from 11.3 to 10.7 inches in section width); that diameter difference is only 1%, so thinking it shouldn't be an issue for temporary use spare. Now leaning toward 275/70R18 (33.2 inch dia) with a 265/70R18 spare, but only gains me half that (0.3 inches) and may not be worth it; the difference is still only 1% in diameter (the other way). The spare underneath is the lowest point for me, so I am looking for what ever helps.

 

[kcjaz]

Good data point; I have been hoping someone could report that condition. That difference 275/70R18 and 285/65R18 is about 2% in diameter. I was looking at Nitto Ridge Grapplers 285/65R18 (32.6 inch diameter) with a spare 265/70R18 (32.9 inch dia) to get another 0.6 inch of ground clearance under the spare (going from 11.3 to 10.7 inches in section width); that diameter difference is only 1%, so thinking it shouldn't be an issue for temporary use spare. Now leaning toward 275/70R18 (33.2 inch dia) with a 265/70R18 spare, but only gains me half that (0.3 inches) and may not be worth it; the difference is still only 1% in diameter (the other way). The spare underneath is the lowest point for me, so I am looking for what ever helps.

Good thought about using a less wide tire. I catch and drag my OEM bumper all the time (hence the Dissent mod) but don't really seem to hit my spare much.

WRT adding weight, I understand it’s weight. Like everything else, it comes down to use case and preferences. I was initially planning to add a 24 gal aux tank in that space which would weigh a lot more than a spare tire. But for me, the times I would need 48 total gallons is really never. I'm starting to think about a 12 gal tank (which I would use) plus the second spare. After seeing someone waste a brand new tire on a trail in the morning of the first day of an extended weekend trip and then be worried about doing it again the rest of the weekend, it just made me think about a second spare as a piece of mind thing. Though rare, I know of at least one fellow mudder who has a good story about being in the boonies and needing a second spare and now sports two spares mounted on swingouts.

 

[bloc]

A long time ago I did some reading on tire sidewall repair procedures.. and regular punctures are already quite easy to deal with. Seems like as rarely as you'd need two flats on the same trip, simply having the tools and training to deal with one of the two in the field would save a lot of weight and space 100% of the time.

Plus, don't the 12-gal aux tanks still move the spare tire down noticeably?