Exact match for spare tire diameter?

This might be an overthinking-type question but worth asking I guess.

I got a set of 4x 35x12.5r17 Mickey Thompson Baja Boss AT* back in October and love them. I'd like to get a matching sized tire on the OEM steel spare wheel, but its been hard to find 35x12.5r18 in the same tire... plus they are rather expensive for something I hope to never use.

I don't have a 5th matching wheel to do 5 tire rotations so my question is how close can a spare tire be to be considered the "same" size? At some point with treadwear, and not doing 5 tire rotations, the mismatch between the two could be 0.25" at worse—even with a stock setup I'd think?

The tire I'd like to get is the Yoko Geolander AT but it's slightly smaller diameter than the MT's. See below:

• Mickey Thompson 35" dia. = 34.8" *
• Yokohama Geolander AT 35" dia. = 34.6"

How close of a match should a spare be you think?

 

I have toyo at3s but picked up a used at2 same size as my spare.
https://www.utires.com/

 

Word. I guess my question is less around the specifics and slight difference in diameter even though the tires are "sized the same"

 

I’m not sure how big of difference a quarter inch would make. It not much at at all. Wear on your others would match that eventually.
As long as it’s not in the rear it won’t matter. You can run smaller in the fronts. I bought the same size spare because I didn’t want to change 2 tires if I had a flat on the rear.

 

I bit the bullet on a matching spare wheel/tire. Gives me peace of mind but my tires are getting road thrashed now and I will replacing current set soon; definitely not looking forward to the expense. If you destroy one of your tires I am assuming you will replace with same at some point- maybe get a "gently" used tire for a spare in current size and get a matching 5th when you can. How are you liking the Baja Boss? I am up in the air now with Baja Boss or BFG KO2(295.70/17) and/or Toyo ATIII or Nitto RG (305/70/17). Like to hear your thoughts.

 

.25” is not really going to cause an issue. If it makes you feel better make sure to put it on the front and run 2wd if you have to use the spare.

I have 275/60/20 tires with a 275/70/18 spare.

So a .20 difference and I am not worried.
Also to save money no need for the tire to be so wide. Buy a narrower tire only the diameter makes a difference.

I always buy closeouts from Tire Rack or Discount Tire for my spare.
I got a 275/70/18 Goodyear Wrangler with Kevlar from DT for $149 since it was the only one they had in stock

If I were you I would find the cheapest (but decent quality) 285/75/18

35s are just silly money these days and 33s will handle anything I am going to throw at it in my off-road ventures so I have no need to spend that money.

 

I hear you, tires are so expensive right now! I really like the Baja Boss so far. I've only been mild off road a handful of times but they were fantastic. It's been rainy here as well and on the wet roads I felt good about them. 4WP did a great job balancing them so definitely try to get to a good shop if you can.

Thanks guys. Was hoping for some peace of mind just like this! and @Black thats a good point about the width. It might be easier to find the 285/75/18 anyway

 

i've always been told that so long as you aren't using 4x4 and the time on the spare is measured in days not weeks you should be fine.

 

Do it once right the first time and you won't have to regret anything else down the road. All bases are covered knowing you have the right diameters on your wheels and tires should you need it out in the middle nowhere.

I would rather bit the bullet once and cry once rather than having to forcefully, use a spare regular tire because of my decision from the beginning should I ever need to use it.

Rather this will also save me money and my differential will thank me.

 

Get the Yoko tire and drive around until your Mickeys are worn down to match diameter, problem solved. Once you're there don't drive anymore or else the Mickeys will be smaller than the Yoko and you'll be frustrated.



You should be fine. Even with 4x4 if you put the Yoko on the front end I don't think you'll cause any harm. I think the mismatched tire size only hurts mechanical lsd, your front diff doesn't have lsd (I assume) and if you aren't in 4wd it should just roll along. For short term driving you should be fine.

 

I'd say you're fine. 0.2" ~= 7/32. Your tires have a whopping 21/32 of tread depth. How far do you plan to wear them down? All the way to 4/32? So that's 17/32 of wear down but on both sides of the tire. So at 4/32 of tread depth your daily tires will be over an inch smaller. At which point your spare is bigger. No worries.

 

Hahaha thanks everyone. Spending too much time worrying on the internet!

 

Buy 5 wheels and tires the same and just do a 5 tire rotation..should get 20% more tire life.

 

If you're looking for a matching spare wheel, I have an extra BR Rapid that I'm looking to sell.

 

Bare minimum I'd get a 17" steel spare and a matching tire. Rotate the spare occasionally.

 

Well, I ended up taking @Black's advice and went with a 285/75r18 sized Yoko on the steel wheel. The internet tells me it has a 34.7" dia vs the 34.8" dia of the Mickey's. It hurt how much it cost these days, but its nice to have the piece of mind that it'll work if needed. It's also nice to not need to carry a wheel spacer to fit a 12.5" wide tire.

It's a good looking tire, also 3 peak mountain snowflake, severe weather rated

 

I have a question, Are you guys that are using the OEM steelie spare with aftermarket alloys keeping 5 OEM lug nuts on board? Or does the aftermarket alloys your using have the same tapered L Nut seat?

 

I do keep 5 extra OEM lug nuts in the truck for that exact reason. My Black Rhino wheels use extended thread Gorilla lug nuts which I don't think would work well... although I've never tried.