I still have all five OEM tires (same size) but was thinking about the spare when the time comes for new tires. Decision is with replacing just four or including the spare too if increasing the tire size. Will probably consider 275 or 285/70 17s when I am ready. With the cost and labor of tires, I think this is a relevant topic.

I assume there can be negatives of having to use a smaller spare if the need arises, just not sure of how big of a deal it can be. Distance traveled would certainly be a factor - maybe the only one?

Thinking about different scenarios:
Having to use the (smaller) spare while 10-20 miles off road and needing to get back to town.
OR
Having to use the (smaller) spare while 10-20 miles off road and having to drive back to paved roads and then driving another 10/20/30 miles to wherever the next stop needs to be.

If the drivetrain, or something else, can be put at significant risk of damage by driving over 50 miles or so on a smaller spare, then the obvious choice would be to have a matching size spare. I just want to be able to justify the added expense of buying/mounting a full size spare.

Also, does the location of where you are using the spare matter? If I had to use a smaller spare for 50+ miles, would I want it NOT to be in a certain location (front vs back on a 4WD), requiring me to change two tires?

what have your differentials done to deserve such hate

To point out some numbers, going from a 265/70/17 to a 285/70/17 is a 3.5% difference in tire circumference & rotation in your differential.

If you were to drive your vehicle in a circle so that the outside tires followed a diameter of 350ft and your inside tires were on a 338ft diameter (assuming 6' tire center to center) you would achieve the same 3.5% rotation difference in the differential. That's basically turning around the length of a football field.

Your vehicle can handle turning at this rate. It is not designed to handle a turn like this at high speed for 50 miles straight. I think you already know that its a bad idea, will create heat, unnecessary wear, and possibly damage. Now if you limp at 40 mph like the cars on doughnuts are supposed to do you will probably make it back to town fine.

You 100% should not be offroad without a full size spare. If I didn't have a full size I would shy away from every challenging trail & obstacle. No fun. You are playing with too much uncertainty and will limit what you feel comfortable doing offroad. You shouldn't even consider it, especially when a 285/70/17 fits perfectly in the factory spare location.

Yes, it is common to see a vehicle with a different sized spare than the running tires, but these are typically front wheel drive cars with an open differential.

If you have a flat on the rear of a straight axle vehicle and your spare is a different size you would want to put your spare on the same side front wheel, and then put your front wheel on the back. Yes this is double the changing but this is the most correct way to keep things going. If you must have a different size spare from your running gear
1) keep plugs and an air pump
2) make sure the air pump leads are long enough to reach from your battery or 12v plug to each of the 4 tires (so many now-a-days wont reach)
3) hope you get a flat on a front wheel
4) if you get a flat on a rear wheel, be prepared to change the front and rear wheel out because you will want to put the spare on the front, and then put the full size tire from the front onto the back.

When i have the money, and i am changing tires, i purchase all 5 so i can swap out all of them and the spare to have the same size.
There have been times when i didnt have the money to get all 5 at once so i bought the 4 and saved up a few more weeks and bought the 5th matching size for the spare when my money wasnt funny.
If you are changing tire size to something considerably different from stock i would strongly suggest buying a matching 5th. Matter of fact, my wife swaps vehicles pretty quickly usually she was going thru a new one about once a year, and rather than buy 5 expensive tires to put on her new toy i bought the 4 i needed and bought the exact same tire USED on Ebay for like 1/5th the price and put the used tire on as the spare. Sure it was 50% worn but who cares it saved me well over $250

#differentiallove

just buy a used cheapo spare on Craigslist in the correct size.

This is not an intelligent place to save money. If you can afford upsizing tires, you can afford upsizing the fifth tire. If you can only afford 4.0 tires and labor and not 5.0, then what you can afford is remaining on your current 5 OEM tires.

I get it, prices suck, we all complain about them, but it is what it is. I spent $1,400 on 5 AT3W Wildpeaks shortly after buying my 2023, been there. The guys ruining their rigs with 35-37" LTs are paying a LOT more for tires than these 32" stock or near-stock sizes.

With your new tires, are you going to go offroad, or be a pavement princess? If I was offroading and had a flat, I'd hate to have to rely on an all-season tire (...and in the wrong diameter) to get me back to civilization. Five years ago on a very rural trip, we had a flat in the third hour. No tire shops were open for two days. Happily, we used our matching spare tire for the remaining 600 miles of the trip, rather than ruining the trip by cheaping out on a knowingly incorrect spare tire.

If I had to limp somewhere on 1 smaller tire with anything other than a full-time 4WD Limited, I'd put it on the front axle, and keep the truck in 2WD.

Agree with the others that if you don't lock your differentials, you should be fine.

One thing they don't mention is the traction control system and stability control system can get confused when it senses different rotational speeds, making it think you have some slippage when you don't. Thus drive carefully, slowly, and don't make hard turns.

But will a 285 fit in the space provided for the spare?

Will bigger spare tire fit?

Does 285/70/17 spare tire fit under 4runner?

285/70/17s do fit in spare spot (PICs)