Brand new spare tire vs 4 others with 20k miles - is this an issue?

[Lavender Jones]

Looking to get a full size spare tire put in at next rotation. The other 4 tires will be at about 20k miles, is it too late to add the spare to the rotation and do a 5 tire rotation going forward? Thinking it would be OK, read a few threads and some say difference is immaterial using brand new spare while other tires are used.... would like to get some use out of the spare if going to pay ~ $300 for it. Would greatly appreciate anyones feedback!

 

[Super77]

It’s not about mileage per se. Try to avoid tires of different circumference because the drivetrain likes them to spin them at the same rate. If your spare measures the same as the others, it will be fine.

In reality, your wheels rarely all spin at exactly the same rate when you consider turns and slippage, but it’s a good practice to follow.

 

[Lavender Jones]

It’s not about mileage per se. Try to avoid tires of different circumference because the drivetrain likes them to spin them at the same rate. If your spare measures the same as the others, it will be fine.

In reality, your wheels rarely all spin at exactly the same rate when you consider turns and slippage, but it’s a good practice to follow.

Ok great, thank you for the response!

 

[toyuda]

Tire Rack used to offer a service where they would grind material off one of their new tires for a fee. Not sure how you would spec the amount or if they still offer it, but I believe it was for circumstances like yours.

 

[whitec13]

I’ve seen many people run their spare as a main wheel and revolve all 5 as the spare to remedy this. Doing the swap during rotation intervals. Keeps all of tread within relative ranges of each other.

 

[Trunk Monkey]

That's normal 5 tires rotation. Advantage is you go longer between buying tires, disadvantage is you have to buy 5 tires.

Personally, I would wait until you're buying new tires and then start the rotation of your new spare, 20k is maybe halfway worn, depending on the tire and your driving.

 

[VR6GURU]

OK I have to chime in here because I have a related dilemma.

I must say. We drive what are basically indestructible tanks engineered to withstand time and abuse. We are talking about a difference in diameter that is measured in 32nds of an inch. Are our rigs really that sensitive to what seems like a negligible difference? Are diffs not built to withstand certain variances? I totally understand the point of not running mismatched tires and the damage they can cause, but when the difference is that small? By this logic we would have to check our tire pressures daily to ensure matching diameters of our tires.

I have been doing some searching on these forums ands the general concensus is the same. My dilemma is that I bought 17" wheels and went with a 285/70/17. Our spare underneath is a 18" wheel and unfortunately 17" steelies are non existent. I was just going to mount a 285/65/18 on the spare and call it a day. But all the threads I have read seem to advocate on running a matching set and do a 5 tire rotation. Except for 1 where a guy says that Toyota is OK with running a different size spare in reference to the folks that opted out for the 17" Rock Warrior wheels It calls out the 4 17" wheels and 1 18" wheel.

 

[Lavender Jones]

OK I have to chime in here because I have a related dilemma.

I must say. We drive what are basically indestructible tanks engineered to withstand time and abuse. We are talking about a difference in diameter that is measured in 32nds of an inch. Are our rigs really that sensitive to what seems like a negligible difference? Are diffs not built to withstand certain variances? I totally understand the point of not running mismatched tires and the damage they can cause, but when the difference is that small? By this logic we would have to check out tire pressures daily to ensure matching diameters of our tires.

I have been doing some searching on these forums ands the general concensus is the same. My dilemma is that I bought 17" wheels and went with a 285/70/17. Our spare underneath is a 18" wheel and unfortunately 17" steelies are non existent. I was just going to mount a 285/65/18 on the spare and call it a day. But all the threads I have read seem to warn of running a matching set and do a 5 tire rotation. Except for 1 where a guy says that Toyota is OK with running a different size spare in reference to the folks that opted out for the 17" Rock Warrior wheels It calls out the 4 17" wheels and 1 18" wheel.

I do feel like the actual chance of any damage is very low like you said, at least in my case where i want to run same size tire / wheel just with different tread depth.... but even if just a slight chance i will probably err on the side of caution and wait until i get a new set to start doing 5 tire rotation with the spare

 

[Super77]

Using AI to reason over the broad scenario of a new tire vs identical one with 20k miles, plus some assumptions like no slippage, proper alignment, etc:

The worn tire will turn 5-6x more revolutions per mile.

But that’s imagining the vehicle rolling on a giant treadmill. In the real world, the difference could be twice that or zero depending on number of turns and road conditions.

I think our vehicles are pretty resilient.

 

[NearJetties]

It’s much more of an issue with a vehicle that has clutch based AWD or LSD in terms of driveline wear and damage.

I don’t think it’s too late to start the 5 tire rotation but now is the cutoff imho. It can impact ABS too. Unlikely but piece of mind.

 

[VR6GURU]

Using AI to reason over the broad scenario of a new tire vs identical one with 20k miles, plus some assumptions like no slippage, proper alignment, etc:

The worn tire will turn 5-6x more revolutions per mile.

But that’s imagining the vehicle rolling on a giant treadmill. In the real world, the difference could be twice that or zero depending on number of turns and road conditions.

I think our vehicles are pretty resilient.

Out of curiosity do you happen to have the figure on how many revolutions it will take to drive that mile? I’d like to see the percentage of difference.

These things happen in the real world all the time. All the non enthusiasts that bought these trucks I guarantee drove with a tire or two over/under inflated, something was misaligned and caused uneven wear on the tires. All things that would cause the scenario the OP is talking about. These trucks never became known for having a weak driveline / differentials which would have happen if you factor out the car nerds like ourselves. The Toyota engineers have to design these things with variances and tolerances built into them for the very reason i listed above. Let’s be honest with ourselves here. Our trucks aren’t fine precision instruments that are that sensitive to a change so minimal. It’s not like they’re F1 cars.

 

[Super77]

AI generated answer, so take it with a shaker of salt.

Personally I think 0.5% is a little obsessive, but to each their own.

 

[VR6GURU]

AI generated answer, so take it with a shaker of salt.

View attachment 3968893

Personally I think 0.5% is a little obsessive, but to each their own.

The bot is just responding based on the prompts we give it. It’s based on information from this form which is all anecdotal. As you said i take it with a grain of salt.

We are talking about a spare here which is a temporary solution. When prompted this way this is what the bot says.

chatgpt with a different prompt:
is it ok to use a 285/65R18 as a spare on an lexus LX470 with 285s/70R17 tires in an emergency?

Short answer — yes, in an emergency, but there are important caveats.

⸻

1. Size Difference

Your original tire: 285/70R17


• Sidewall height = 285 × 0.70 = 199.5 mm


• Wheel diameter = 17” = 431.8 mm


• Overall diameter ≈ 431.8 + (2 × 199.5) = 830.8 mm (≈ 32.7”)


Your spare: 285/65R18


• Sidewall height = 285 × 0.65 = 185.25 mm


• Wheel diameter = 18” = 457.2 mm


• Overall diameter ≈ 457.2 + (2 × 185.25) = 827.7 mm (≈ 32.6”)


Difference = ~3.1 mm (0.1”), which is well under 1% — so rolling diameter is nearly identical.


⸻


2. Fitment Concerns


• Bolt pattern: Must match your LX470’s hubs (same as Toyota Land Cruiser 100 series).


• Brake clearance: 18” wheel will have more brake clearance than 17”, so no issue there.


• Offset/backspacing: If the spare’s wheel offset is significantly different, it could rub suspension or fenders — especially on the front.


⸻

3. AWD/4WD Caution


Your LX470 has full-time 4WD.


• For long-term driving, all four tires must be closely matched in diameter to prevent drivetrain stress.


• In an emergency, you can run a single slightly different tire to get to a repair shop, but avoid high speeds, long distances, or engaging the center diff lock on dry pavement.


⸻


Verdict:


• Safe for short-term emergency use — the size difference is negligible.


• Drive moderately, avoid aggressive cornering or high speeds, and replace/repair the damaged tire as soon as possible.

 

[whitec13]

Here, use this and check the data it spits out. Of course it doesn’t factor in used vs new. You can make measurements of your tread depth and go from there though with an overall circumference measurement.

Tire Size Calculator - Compare Tire Sizes | Tacoma World

Tire size calculator compares diameter, width, circumference and speedometer differences for any two tire sizes. Supports tire sizes in metric and inches.

www.tacomaworld.com