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

[Fisher23]

I did see some Auzies on youtube roll when backing up when they had dual spares. So that would be the one thing to be very carful about.
I think I posted that video on here a while back, as it really didn't look like it should have rolled.

My one swing out switches out so I have dual spares. On long trips with my offroad camper I'll bring the double spares. My camper runs the same size wheels n tires.
It's rare, usually I carry just one.

If the 2nd spare was slightly smaller I wouldn't worry about it. You would need to be on you 2nd blowout to even use it.

 

[bloc]

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

Is that per tire out of 4, or difference front to rear axles? (what the actual center diff would see)

 

[LC Mike]

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?

I initially thought that sidewall repair was impossible, then you got me looking. I came across this for sidewall repair and it's going to become part of my tire repair kit.

BEST SXS Tire Repair Kit (Includes Sidewall Repair)

And yes, the 12-gal aux tank did lower the spare some - about an inch. Struggled with the decision to do this, but the extra fuel capacity is a game changer for me and I really did not want to lose the spare storage underneath. I did take out that tire stop bracket (held on by 2 bolts) just behind the rear diff and it gave me back an inch of clearance (although the departure angle clearance did not change).

 

[kcjaz]

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?

not sure on how much lower if at all the spare gets with the 12 gal tank. Something to figure out though before proceeding. I agree this is a rare event and that ultimately, I may add something that is more important. Its just at this time I can do it, and I'm a little worried about my Goodyear Duratracs. I'll pick a better tire the next time around but until then I may just carry a spare spare.

On the one side wall flat I've seen on a trail, it was a slice a little more that an 1" long. Not sure how field repairable that really is but agree its worth have a repair kit and knowledge to use it. I do carry a repair kit and know how to fix a typical tread puncture.

Anyway, we can debate whether its really necessary to carry a spare spare or not for ever like anything else we might carry or do to our rigs. Good discussion and the other considerations are worthy to note. Your story about your 900 mile trip with one wrong sized tire is the answer to my question, simply that it can be done.

 

[AnyMal]

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.

And they resent you for watching them perform every step. Is it the same guys that wire wheeled the hubs for you?

 

[Sandroad]

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.

Just a point of reference, the donut spare tires on vehicles with them are usually significantly smaller diameter than the road tires. That’s one reason the owners manual calls for low speeds and short distance usage only.

 

[Omega3651]

I don't get it.

Why not just get all your tires the same size?
If you want to carry 5 spares it doesn't matter-get all the same size and be done with it.

 

[eatSleepWoof]

I don't get it.

Why not just get all your tires the same size?

Not always possible/cost effective.

I bought 5x 33" Falkens, intending to run them year round, and did that last winter. It quickly became obvious that on the street, I needed proper winter tires, not "good enough" ATs. So this year I bought a set of 20" Tundra wheels and installed a set of Blizzacks that I had in OEM size. There is 3" difference in diameter between my currently installed winter set and my spare (a 33" Falken). It's not ideal, but I think it'll be fine for a slow trip to a tire shop, should the need arise.

Buying another wheel + tire to have a matching set will run me an easy $600 CAD, and at this point I don't think that's a necessary expense.

 

[grinchy]

Can always dump a lot of pressure from that 33” to reduce diameter and go at 40kph to the tire shop or trail exit.

 

[bloc]

not sure on how much lower if at all the spare gets with the 12 gal tank. Something to figure out though before proceeding. I agree this is a rare event and that ultimately, I may add something that is more important. Its just at this time I can do it, and I'm a little worried about my Goodyear Duratracs. I'll pick a better tire the next time around but until then I may just carry a spare spare.

On the one side wall flat I've seen on a trail, it was a slice a little more that an 1" long. Not sure how field repairable that really is but agree its worth have a repair kit and knowledge to use it. I do carry a repair kit and know how to fix a typical tread puncture.

Anyway, we can debate whether its really necessary to carry a spare spare or not for ever like anything else we might carry or do to our rigs. Good discussion and the other considerations are worthy to note. Your story about your 900 mile trip with one wrong sized tire is the answer to my question, simply that it can be done.

To do it right you'd need to break the bead, but it can be done without just to get off the trail. You'd need heavy nylon string and some specialty curved needles, which will hold structurally. Then one of the sidewall repair patches to put over that and help hold air.

But yeah, valid point about running a tire known for poor sidewalls changing the math here a bit.

And they resent you for watching them perform every step. Is it the same guys that wire wheeled the hubs for you?

They did also damage my OE wheels enough to give me a $500 credit. It's the location at burnet and braker, which was the only one with the tires in stock. But no I don't think they polished the hubs, as I was already telling tire shops not to do that. And I was watching. Just didn't catch the one different size.

 

[Str8Laced]

I was just thinking about this last week, had a screw in a tire and wouldn't hold air for more than 15 min. I put on the spare which is a 275/55/20 31.9" diameter and my others are 285/65/18 32.6" which is only 2.1% difference. I was debating on getting a 285/55/20 diameter spare to get it as close as possible to the 18" but after reading this I think the 2% difference should be fine. Side note, the 275/55/20 looks so small even though it's only .7" difference

 

[Madtiger]

So, regarding spare and how small you can go….here is the 2021 Honda Ridgeline. It uses a donut spare. The spare apparently is load rated to handle towing…BUT Honda advises to stay below 50 mph and to replace it ASAP. Also, recommended PSI for spare is 60 PSI!!

Now, I am using Ridgeline because it has modern VSC and traction control…AND its rear axle has VTM-4 which is a quasi—LSD/locker type diff. So, a lot of electronics and calculations going on.

Apparently 3% difference in diameter is OK with the electronics??? But remember Honda’s warning about speed limit with the smaller spare and the inflation PSI.

 

[AnyMal]

What bout magic flex seal?

 

[TheIcemanCometh]

While infrequent a good friend was out in the desert of Utah with two spares. They used both and got a third flat. They would drive 10-15 minutes and air up the tire, drive 10-15 minutes and air up the tire, drive 10-15 minutes and air up the tire. They did that for a couple of hours.

On a different vehicle, we had the sidewall taken out. In that case we got two replacement tires so keep the all wheel diff happy.

 

[Madtiger]

While infrequent a good friend was out in the desert of Utah with two spares. They used both and got a third flat. They would drive 10-15 minutes and air up the tire, drive 10-15 minutes and air up the tire, drive 10-15 minutes and air up the tire. They did that for a couple of hours.

On a different vehicle, we had the sidewall taken out. In that case we got two replacement tires so keep the all wheel diff happy.

Dear goodness, where was your friend at? What tires did he have? Water balloons?!

 

[silver tuna]

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.

I don’t think traction control would say anything, it doesn’t care about the differential in wheel speed while making a turn. Can also disable it anyways.

im also going to end up running my oem spare as I only found 4 Rock warriors.

 

[ScotyDosentKnow]

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.

Oddly enough the full size spare on my 2017 VW Alltrack is smaller than the factory wheels/tires. I am aware of this because I have had 2 blow outs in the last year lol Each time had to drive around 100 miles on it, once on front and once on rear. No issues *knock on wood* Obviously the AWD setup on it is different than the 200 so who knows.

 

[Markuson]

Why two spares? Honest question.

One legit motive—If on a long boonies trip (tough-Trail-only camping)…or Alaska, baja, desert, etc…and you get an early failure…its a bummer to have to choose to drive out—for lack of a spare, or drive deeper at risk of being stranded with another failure.

Thats one nice thing about being in a group… You can often tgrow someone else’s spare on if two or more fail…

 

[Tex68w]

Screw the second spare, put a LRA Aux tank in there.

In all seriousness though, the need for a second spare arises more often than you think. My buddy has a RAM 3500 with a flatbed and a FWC on 37's and they experienced a slashed sidewall in Big Bend Ranch State Park a few weeks back. They were deep into the park and had to swap out the tire but were forced to return through very same area where the tire damage occurred on the way out and he was very nervous about not having a second spare for his rig.

 

[AnyMal]

Screw the second spare, put a LRA Aux tank in there.

In all seriousness though, the need for a second spare arises more often than you think. My buddy has a RAM 3500 with a flatbed and a FWC on 37's and they experienced a slashed sidewall in Big Bend Ranch State Park a few weeks back. They were deep into the park and had to swap out the tire but were forced to return through very same area where the tire damage occurred on the way out and he was very nervous about not having a second spare for his rig.

My eventual plan is, subtank skinny steel spare size matched underneath, and full size 5th rear carry. I also carry plugs and slime.