20 to 18 equivalent

[Bink]

I’m struggling with the search on here...I type something in I’m looking for and rarely does it pop up without spending just as much time scrolling through the posts. So real quick...

I have a Laramie with sport package and 20” wheels. I’d like an all-terrain tire and new wheels and was thinking of possibly going the 18” route. Here is my question...If I don’t want speedo to be off, how big of tire would I need to put on the 18” wheel to get the equivalent of my current 20” setup? Thanks for help.

 

[PorBoy]

Hello, when I went from my 18” to my 20” wheels I just went oem tire sized. Went to the dealership afterwards to get recalibrated and since it was stock size all was good. Again this is just my personal experience and NOT a guarantee. My oem size was 275/65/18 and the new size was 275/55/20 A/T..

 

[silver billet]

Going from 20 to 18 changes the inner rim size. The outer diameter tire doesn't need to change, so when you do it that way you just get more sidewall between inner rim and outer tire. So you would need to use the same size tire that is on factory 18 inch rims (maybe use the rebel tires?), and then no speedo change is required.

 

[spaightlabs]

Discount Tire's comparison calculator:

https://www.discounttire.com/learn/tire-size-calculator?&ef_id=eaiaiqobchmi1o-3plap6qivo__jbx0cyw5neaayasaaegiatfd_bwe:g:s&gclid=EAIaIQobChMI1O-3pLap6QIVO__jBx0cyw5nEAAYASAAEgIAtfD_BwE&ef_id=XrgEowAABEohliMC:20200510084314:s

 

[Bink]

Thank you, all very helpful! Looks like 275/65 18 will keep me right on with speedo

 

[Scram1500]

I went from 20" to 18" oem size and speedo is right on. Even if you did change size, rumor has it these trucks will self calibrate