Spare Tire Size?

Jimmy-Mack · November 11, 2020

Just ordered 2021 GMC SLT 6.6 Gas last week with 20" wheels. The order form only lists 17" or 18" spare tire options. This is not good for a 4WD and a limited slip rear when the spare is needed, no matter how far the drive is. The salesman just shrugged his shoulders when I asked.

Anyone have a truck that came with factory 20" wheels and got a 20" spare instead of a 17" or 18"?

walshie · November 11, 2020

Its same overall diameter

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CamGTP · November 12, 2020

Exactly. It doesn't matter if the rim is a 17in or 18in. The tire diameter is going to be the same size as the 20in rim with tire.

They have been doing this for like 15+ years or more on trucks. The spare tire is always smaller in rim diameter on vehicles equipped with large 18's, 20's or 22's.

Jimmy-Mack · November 13, 2020

Thanks for the responses. I guess an old dog learned something today. My 04 GMC 2500HD had 5 - 16" wheels.

Another JR · November 14, 2020

I'm about to order a 2021 3500HD SLT CC LB SRW, so I've been using the GMC build and price page quite a bit and looking at options. Regardless of the wheels you order, the provided spare is 275/70-18, same as the standard wheel. According to on line tire size calculators the diameter of a 275/70-18 is about 33.2 inches, and the diameter of the optional 275/65-20 is about 34.1 inches, for about a 2.8% difference.