Spare Tire Size?

[Jimmy-Mack]

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]

Its same overall diameter

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[CamGTP]

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]

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

 

[Another JR]

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.