What offset do I need.

[allgonoshow2]

I am considering 285-65-18 tires and wheels for my 2024 RST.

 

What offset do i need to have the tires flush with the wheel arches.

I have Air Designs wheel arch molding installed with add about 3/4 inch to the width of the fenders.

[AlanK]

This is not an easy question.  I have done sizings for jeeps, corvettes and silverados.  You need to measure the geometry of your wheel setup and then use a tool like below to compare the existing wheel/tire setup with the new tire size to get the wheel offset.  

 

https://www.wheel-size.com/calc/?wheel1=255-75-17X6.5ET45&wheel2=285-70-17X8.5ET42&wheel3=285-70-17X7.5ET40&wheel4=305-60-18X9.5ET43&wheel5=275-65-18X8.5ET45&wheel6=305-60-17X9.5ET48&wheel7=295-70-17X9ET40&wheel8=285-65-17X8.5ET47&fcl=1.96875in&wcl=1.1875in&scl=1.96875in&sr=0in

[allgonoshow2]

Hi   Thanks for the info, I had found that very helpful website.

I decided to keep my stock  20x9.5 inch factory wheels and try 305-55-20, which is very close to the 275-60-20 stock tires height but about 1.2 inches wider.

My truck has the Max trailer package and is also lowered 2 inches.

The tire shop is willing to install the front tires and let me test drive for rubbing and if they rub too much, they will take them off.

Going to the tire shop Friday.

[Mack10290]

They're probably gonna rub. My truck was a dealer custom with a 3" lift and it came with 305-55-R20 BFGs mounted on custom rims with +12 offset and the custom shop made modifications to the wheel wells to avoid rubbing. Then I bought new rims that were -18 offset and the same size tires and it rubbed pretty bad so I took it to a body shop and they made more wheel well modifications. I think the Chevys have a little more wheel well room than the GMCs but you're likely gonna have some rubbing. 

[allgonoshow2]

I installed the tires. 305-55-20 and they fit without rubbing.

They are VERY close to the upper ball joint but not touching and lots of room in the fender well.

They sit flush with the wheel arch moldings and look great.

Bridgestone Dueler A/T Ascend, 10 ply.

I'll post a pic when it stops raining.

 

I will recheck in a week or so for any rub marks, if there is any I could probably add a thin wheel spacer.

 

Happy camper..

 

 

Mack10290.... I assume your issues are offset related.

Edited November 28, 2025 by allgonoshow2