If I'm wanting to switch from the factory 20x9's to something smaller like an 18" what size tire do I need?

[ADClope]

Long story short, I'm a little confused on tire sizes. 

 

I've got a 2016 Sierra 1500 Denali with 20x9's. They have 275/55/R20's right now. 

 

If I went with an 18" wheel, what size tire would give me the same overall diameter? I'm asking because as I understand it (and maybe I'm completely wrong), you cannot increase overall diameter without causing issues with speedometer, trans shift timing, etc.. 

 

So with an 18, what size tire could I put on it to get back to the same overall diameter? 

 

Thanks

[CamGTP]

You'd just need to go with the stock 18's tire size which is a 265/65/18.

 

The 275/55/20 is a 31.9in tall tire and the 265/65/18 is a 31.6in tall tire, it's a 0.9% difference.

 

 

[pokismoki]

yup, the z71 package takeoffs is what you want, low milage for $550 -600 a set

 

i have gun metal versions from a Tahoe 4x4 z71, they look slick as owl shiot