17" Factory Back spacing??

Hello everyone,

I have an 04 Denali with the 17" wheels. Without me having to go take a wheel off I was wondering if anyone would happen to know the factory back spacing?

I am looking to go with a 20" wheel and kind of wondered what's the proper back spacing to go with.

If anyone has lowered a Denali and knows any tire or back spacing tips that would be great as well. I am going with a 2-3 drop tomorrow and ordering wheels next week so any help would be great.

Thanks for your time