20’s and 18’s

hotfish23 · September 9, 2019

I have a 2019 RST Z71 with the 18” wheels. Today I was looking at a buddies truck that has the 20’s and realized that something looked very different and it wasn’t just the rim size. I then noticed the actual tire sizes are very different. In the past chevys with the 18’s had 265/65r18 tires and still do, while the 20’s got 275/55r20 tires. This was a difference of a 31.5” tire vs a 31.9” tire. So a very negligible difference. In the 2019’s the 20’s come with a 275/60r20. This is a 32.99” tire. A 1.5” difference from the 18’s. This is enough to cause about a 4mph difference on the Speedo and a difference in the odometer too. (Before anyone says it, I also measured the tires as well, since we all know manufacturers aren’t always the most honest). I find all of this interesting because it would mean that Chevrolet programs the comps based on your tire/rim package. This baffles me as it seems as though that keeping a very close tire size across the board would result in less work on their end. Does anyone have any light to shed on this?

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Mikebtte · September 9, 2019

In order to look like they are setting new standards with the EPA they have to run a smaller tire and gear ratio. The truck used to meet the EPA looks hideous and in order to sell more trucks they put on a bigger tire with trim levels that look more appealing to the people. The whole assembly process is set to run ahead of time, it does not affect them to run different tires on trucks. You could have a work truck being built behind a Denali.