That makes little sense

ueww40 · May 19, 2026

Confusion at its best. I call up tire places to shop for tires for my 2004 Tahoe. They all say that the tires for my Tahoe need to be 265/70R16. I look what's on the car now and they are 265/70R17. I look at the label on the driver side door and it gets even weirder. It says that the correct tire is 265/70R17 and the spare is a 265/70R16. Now why would that be. The spare (I assume SPA means spare) is a different diameter than the rest of the tires? Never heard of that. I know that the 17" size tires that are on there now is probably what the car came with from the factory, because my speedo is correct and I am pretty sure that the rims are original. Why do the computers of all the (so called) tire experts insist that I need 16" tires. Can anybody shed any light on that?

Blackcar · May 19, 2026

I would go by manufactures label on door for correct tires for your vehicle just my view.

ueww40 · May 19, 2026

Blackcar said:
I would go by manufactures label on door for correct tires for your vehicle just my view.

Yes, of course. But why is my spare different in size than the rest of the tires. That could burn up a differential in no time on a long trip. And I looked it up on the service parts identification label, the spare is a 16" and the other 4 are 17". Makes no sense

homesick · May 19, 2026

ueww40 said:
Yes, of course. But why is my spare different in size than the rest of the tires. That could burn up a differential in no time on a long trip. And I looked it up on the service parts identification label, the spare is a 16" and the other 4 are 17". Makes no sense

Maybe it's a confined space issue.

joe

SilverSport · May 20, 2026

I’ll bet it was to cover ALL the optional tire and wheel packages offered with one spare tire size…here is my sticker from my 2005 Yukon Denali...

ReaperHWK · May 20, 2026

Probably several different wheel/tire combos offered on your truck when new. Def go by the sticker and what’s on your truck now, get the 17’s and call it a day.

As far as the spare that’s strange to me but if you get a flat Just make sure you get the spare on the front axle vice the rear to mitigate any diff issues and you’d be OK.

mikez71 · May 20, 2026

Because GM is a cheap@ss and trying to use up their inventory of 16" wheels...?

swathdiver · May 20, 2026

GM knew what they were doing. This is from the owner's manual:

pronstar · May 20, 2026

The outside diameter of the tire matters, wheel size not so much.

TJ Baker · May 20, 2026

SilverSport said:
I’ll bet it was to cover ALL the optional tire and wheel packages offered with one spare tire size…here is my sticker from my 2005 Yukon Denali...

View attachment 485770

My 2005 Yukon matches your tire sticker. The OP has a different profile spec'd for the spare, 70 vs 75. That makes a difference.

The OPs specs...

Our specs...

mikez71 · May 20, 2026

None of those explanations give a reason WHY GM went with a 16" wheel, only that it's do-able..
Same reason the spare is usually a cheaper steel rim.. because it's cheap..
They had a bunch of leftover 16" wheels is the only explanation that makes sense?

mikez71 · May 20, 2026

To clarify, I find it perfectly acceptable to be cheap on the spare tire..
So long as you're not forced to swap a rear tire to the front, to clear brakes that the spare won't fit over..

Blackcar · May 20, 2026

There is a difference in tire pressure between spare and vehicle tires but usually spare is just used to get to shop for repair of tire that was on vehicle pressures will change diameter when installed on vehicle so ...

265/70 R17 vs 245/75 R16 Tire Size Comparison Table with Graphic Visualization

The difference in sizes and parameters between the 265/70 R17 tire and 245/75 R16 tire. Detailed calculations and graphics.

tire-calc.com

ueww40 · May 20, 2026

Great explanations from all of you, but ever since Carl Benz and Gottlieb Daimler separated the horses from the carriage it is common engineering knowledge not to have wheels of different sizes on your car. Before I knew any of this I blew out a rear tire and had to travel 260 miles on my spare to get home, because it was at night. Not too good for my differential. But I guess I was lucky, so far no funny noises from the rear end.

ueww40 · May 20, 2026

I just looked at the VIN ID label on the driver door of my 2010 Silverado and all the tires are the same P245/70R17. Nothing weird here.

Marky Dissod · May 20, 2026

ueww40 said:
I call up tire places to shop for tires for my 2004 Tahoe. They all say that the tires for my Tahoe need to be 265/70R16.
I look what's on the car now and they are 265/70R17.

Your sticker wins. If they disagree, go somewhere else. Don't argue with the illiterate,
or they will drag you down to their level and beat you with experience.

ueww40 said:
I look at the label on the driver side door and it gets even weirder. I says that the correct tire is 265/70R17, and the spare is a 265/70R16.
Now why would that be? The spare (I assume SPA means spare) is a different diameter than the rest of the tires? Never heard of that.
I know that the 17" size tires that are on there now is probably what the car came with from the factory,
because my speedo is correct and I am pretty sure that the rims are original. Why do the computers of all the (so called) tire experts insist that I need 16" tires?
Can anybody shed any light on that?

No it does NOT.
265/75R16 - 31.64"
265/70R17 - 31.60"
265/65R18 - 31.56"
ECM cannot tell the difference.
Wheel diameter is irrelevant - TIRE radius / diameter / circumference is the only thing that matters.

ueww40 said:
it is common engineering knowledge not to have wheels of different sizes on your car.
Before I knew any of this I blew out a rear tire and had to travel 260 miles on my spare to get home, because it was at night.
Not too good for my differential. But I guess I was lucky, so far no funny noises from the rear end.

YOU ARE CONFUSING WHEEL VS TIRE.
Luck is an important residue of design.
Doubt it? Try 2 different OEM tire sizes with the same wheels, say, 265/70R17, & 265/60R17 - the latter is GM OE for Tahoe PPVs.
Same size wheels, different rolling diameters.
Bet your Gov-Lock understands what we're saying here.
Think carefully about why you disagree with your Gov-Lock, after 260 miles of "everything's fine"?

Actually, please do NOT try using tires with different circumferernces. SERIOUSLY.

Oh, and GM used 16" wheels as spares because line must go up every quarter.

ueww40 · May 20, 2026

No Marky, I am not confusing wheels and tires. The tires are the same, except the spare is 1" smaller in diameter. The wheel of course is therefor a 16" wheel but it is also 1" narrower. Sane people make all 5 wheels and tires the same (except compact skinny spares of course). You are right, the only thing that matters is the outside diameter where the rubber meets the road. Who ever came up with that idea at GM deserves to get fired yesterday. Tomorrow I am going to measure the exact diameter of the spare and see if it varies in size. I am curious now. It ain't no big deal, I have seen dumber stuff. Don't get me started on swapping out a radio.

pronstar · May 20, 2026

ueww40 said:
Great explanations from all of you, but ever since Carl Benz and Gottlieb Daimler separated the horses from the carriage it is common engineering knowledge not to have wheels of different sizes on your car.

Not too uncommon for high performance cars to have different wheels sizes front and rear…some C8 Vettes have 19” or 20” in front / 20” or 21” rear as one example.

What was extremely uncommon was when GM put wider front tires on some FWD V8 models in the mid-2000’s

LsHart · May 20, 2026

It's always been common practice for the dealer to put a smaller tire and or rim. Compact but full size. It's only mint to get u to a tire shop. He'll, the new camaros don't even come with a spare. It's a obsolete option.

Blackcar · May 21, 2026

ueww40 said:
No Marky, I am not confusing wheels and tires. The tires are the same, except the spare is 1" smaller in diameter. The wheel of course is therefor a 16" wheel but it is also 1" narrower. Sane people make all 5 wheels and tires the same (except compact skinny spares of course). You are right, the only thing that matters is the outside diameter where the rubber meets the road. Who ever came up with that idea at GM deserves to get fired yesterday. Tomorrow I am going to measure the exact diameter of the spare and see if it varies in size. I am curious now. It ain't no big deal, I have seen dumber stuff. Don't get me started on swapping out a radio.

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