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

[linuxgod]

If you can fit a correct diameter spare I'd check craigslist for something used. Or even discount tire. It's probably worth the $50-100 to not worry much about it. Keep in mind that a new tire with tread vs a bald one will be different circumferences even in the same size (which is yet another good reason to always do 5 tire rotations).

That said I would absolutely run the wrong size tire to get off a trail. I would try to avoid engaging any lockers unless absolutely necessary in that case, and I'd keep the speeds low. You'll be generating additional heat in the center diff regardless of whether you're locked or not as the diff has to continuously slip.

@Madtiger, when it comes to donuts, it depends on the vehicle, but many RWD-only or FWD-only vehicles have spares which are both smaller in width as well as diameter.

 

[1world1love]

According to AAA a flat tire is overwhelmingly the most common reason for calling roadside assistance. While there is no data that I know of, I would suspect that the most likely failure experienced on the trail is also tire related.

Like everything else, there is a risk equation and that may differ for everyone. If you mainly wheel in sandy terrain or on maintained roads, the thought of carrying a second spare seems crazy. But experiencing a tire failure 20 miles from nowhere over rough terrain can make you think differently.

Also, having a tire failure doesn't magically decrease the chance of having a tire failure.

 

[gaijin]

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 wrote a couple of years ago:

• Mar 9, 2018
• #7

Well ... I'm probably going to surprise some folks with my comments here - hell, I even surprise myself at times - but I have evidence that Toyota supports using the stock P285/60R18 wheel/tire combo as the spare when mounting the LT285/70R17 tires with TRD RW wheels on the Land Cruiser.

Look at page 8 of this pdf about mounting the LT285/70R17 tires on the RW wheels and pay attention to the Tire Pressure Sticker (Part number 00602-60110) that is supposed to be put over the stock tire pressure sticker:

https://www.toyotapartsdeal.com/installation/40362D86F9D917D98825767800785BB2_Tundra_Sequoia_Land Cruiser TRD Alloy Wheel PTR45-34070-34120 IssF.pdf

This sticker is VERY hard to find, but I found one - here's a pic of the tire pressure sticker as I received it attached to the Toyota invoice:

You will find in the pdf that Toyota only talks about mounting 4 wheels/tires with the LT285/70R17 tires, and the new tire pressure sticker clearly shows the spare as the original P285/60 18 tire.

Usually, with any AWD vehicle, it is important to assure that all 4 tires are within a % or 2 in circumference in order to avoid any drivetrain damage. However, it appears Toyota is OK with the difference in circumference in this case.

Obviously, if one were to use the odd-size spare, it should be for emergencies only, for short distances only, and should be replaced with a correctly sized tire as soon as possible.

So ... @LBridges , if you are planning on mounting the recommended LT285/70R17 tires on your RW wheels, I'd say you are safe to continue to use your stock spare until you can source a 5th RW wheel. Any other (larger) tire size, you're on your own.

HTH

Edit to Add: If you do mount the LT285/70R17 tires, ignore the 46psi recommendation and use 40psi - it's a long story

*************************************************************
I know the link in that old post is broken, but I can't find a new one But if you search the web for "PTR45-34120 & PTR45-34070" you will find a link to open the.pdf in question.

HTH

 

[kcjaz]

As I wrote a couple of years ago:

• Mar 9, 2018
• #7

Well ... I'm probably going to surprise some folks with my comments here - hell, I even surprise myself at times - but I have evidence that Toyota supports using the stock P285/60R18 wheel/tire combo as the spare when mounting the LT285/70R17 tires with TRD RW wheels on the Land Cruiser.

Look at page 8 of this pdf about mounting the LT285/70R17 tires on the RW wheels and pay attention to the Tire Pressure Sticker (Part number 00602-60110) that is supposed to be put over the stock tire pressure sticker:

https://www.toyotapartsdeal.com/installation/40362D86F9D917D98825767800785BB2_Tundra_Sequoia_Land Cruiser TRD Alloy Wheel PTR45-34070-34120 IssF.pdf

This sticker is VERY hard to find, but I found one - here's a pic of the tire pressure sticker as I received it attached to the Toyota invoice:

You will find in the pdf that Toyota only talks about mounting 4 wheels/tires with the LT285/70R17 tires, and the new tire pressure sticker clearly shows the spare as the original P285/60 18 tire.

Usually, with any AWD vehicle, it is important to assure that all 4 tires are within a % or 2 in circumference in order to avoid any drivetrain damage. However, it appears Toyota is OK with the difference in circumference in this case.

Obviously, if one were to use the odd-size spare, it should be for emergencies only, for short distances only, and should be replaced with a correctly sized tire as soon as possible.

So ... @LBridges , if you are planning on mounting the recommended LT285/70R17 tires on your RW wheels, I'd say you are safe to continue to use your stock spare until you can source a 5th RW wheel. Any other (larger) tire size, you're on your own.

HTH

Edit to Add: If you do mount the LT285/70R17 tires, ignore the 46psi recommendation and use 40psi - it's a long story

*************************************************************
I know the link in that old post is broken, but I can't find a new one But if you search the web for "PTR45-34120 & PTR45-34070" you will find a link to open the.pdf in question.

HTH

Thanks. That is the straight answer to the original question! @bloc 's post #16 is real world confirmation that nothing bad will happen if you run one tire one size smaller.

 

[TLC2013]

@kcjaz to get super close to that Lt285/70r17 size you could run a Lt285/65r18 on the factory wheel, They are Essentially the same size.

 

[AnyMal]

Also, having a tire failure doesn't magically decrease the chance of having a tire failure.

On the road, i would take those odds. On the trail, statistical anomalies.

If i only had a skinny btw, i would probably rotate it to the rear instead of asking it to steer for me.

 

[MikeVpdx503]

@bloc 's post #16 is real world confirmation that nothing bad will happen if you run one tire one size smaller.

Just to clarify, @bloc ’s example above seems to be that of running one tire that is 1.8% larger (not smaller) for 900 miles. Not sure if you care about the difference or not…but that is how I read it. I have ran 1 tire smaller, my usual are LT285-70/17 KO2s and I used the OEM spare, 285-60/18, to drive a few miles to get one tire fixed. I’m pretty sure I could have made it to Discount Tire on the one with the screw it in, but I thought it would be fun to use the spare for once.

 

[kcjaz]

Just to clarify, @bloc ’s example above seems to be that of running one tire that is 1.8% larger (not smaller) for 900 miles. Not sure if you care about the difference or not…but that is how I read it. I have ran 1 tire smaller, my usual are LT285-70/17 KO2s and I used the OEM spare, 285-60/18, to drive a few miles to get one tire fixed. I’m pretty sure I could have made it to Discount Tire on the one with the screw it in, but I thought it would be fun to use the spare for once.

Yes. I should’ve said one tire size up or down to be clearer.

 

[1world1love]

I wonder what the narrowest 5x150 wheel you can find is? I would be tempted to throw a narrow 2nd spare up in my empty spare space. I plan on adding an LRA but it may be a while and carrying a "donut" as a last resort type option sounds like not a bad idea.

 

[grinchy]

I wonder what the narrowest 5x150 wheel you can find is? I would be tempted to throw a narrow 2nd spare up in my empty spare space. I plan on adding an LRA but it may be a while and carrying a "donut" as a last resort type option sounds like not a bad idea.

Steelies come in 17x7.