Changing rim size?

mikea57 · September 6, 2013

My baby needs new shoes. It's an '07 GMC Sierra SLT Crew Cab with the Vortec Max engine in it. I'm running 285/60R20 Cooper Discoverer S/T's on it with a Rough Country 3 1/2" lift. Due to some rubbing problems I'm considering changing the rims out from stock to something with an offset and maybe widening the stance of the truck. I do have rubbing on the right fender well when I turn hard right too so that is a factor as well.

I'm thinking that I might go down in size from 20" to 18" but I'm wondering if there are any benefits in changing to smaller rims? 20" tires are bit more pricey than the smaller sizes so that would be one benefit, (but I don't think I'd save enough to cover the cover the cost of new rims!). Except for a modest savings on the tires then, and getting an offset to widen the stance and reduce rubbing, is there any reason for me to change or not to change rim size? How much offset or backpacing would work on my truck. I've read some of the articles I've found on the subject but I'm still not 100% clear on the concept.

Thanks,

Mike

MikeNH · September 6, 2013

I can't help with offset but a smaller wheel will usually have more tire choices and less costly choices to boot. More tire sidewall will soften the ride a bit as would the reduction of unsprung weight by going to a smaller wheel. Maybe a fractional savings on gas. But that's a big maybe.

blackout07 · September 6, 2013

Less offset = more rubbing and a decrease in wheel diameter will do nothing to help and only hurt the looks IMO. There's a reason people can get away with running larger tires on factory wheels and that's the ultra conservative offset and width. You need smaller tires.

mikea57 · September 7, 2013

Well, I was thinking in the other direction with the offset Blackout. I don't know though about hurting the looks. The wheels just look so BIG on that truck. I kind of thought that a shade smaller might look better. Most of those trucks are running 17s & 18s. Heck, even my spare is a 17 so something must have gotten upgraded at some point...

blackout07 · September 8, 2013

Your factory wheels have a + offset of 31. If you want them to stick out more you're going to need less offset. 0 and down into the negative range is where you'll need to go and that will not help your situation. And just FYI all spares come in 17.

mikea57 · September 10, 2013

Thanks for replying Blackout. I'm sorry but I don't quite understand. If I am rubbing against the wheel well now with stock rims, why would going to a lesser offset not prevent this? The tire is sticking out farther from the wheel well so why would this not prevent the rubbing? From what I understand, a negative offset will push the mounting surface towards the rear of the tire, right? That is going to make the tire stick farther outside of the wheel well like you said. Wouldn't that put the back side of the tire further away from the wheel well? What part am I missing?

blackout07 · September 10, 2013

You are correct. However the offset is not your problem. Your tires are too big. Guys can get away running larger tires on factory wheels than they can on aftermarket. This is due to width in some cases but typically backspacing. As you push your wheels outward it will cause the tires to rub primarily on the rear outside bottom edge of your fender. This is very common and a lot of guys cut the metal out of the fender behind the fender liner as a result. Unless you just want new wheels, it's not worth the cost. I would trim.

zach1990 · September 10, 2013

You are correct. However the offset is not your problem. Your tires are too big. Guys can get away running larger tires on factory wheels than they can on aftermarket. This is due to width in some cases but typically backspacing. As you push your wheels outward it will cause the tires to rub primarily on the rear outside bottom edge of your fender. This is very common and a lot of guys cut the metal out of the fender behind the fender liner as a result. Unless you just want new wheels, it's not worth the cost. I would trim.

Good example for you. I ran 305 70r16 maxxis mudders on my stock rims with no rubbing. Had just a 2.5" leveling kit then. I now have 4" of lift and 18x9 -12 offset wheels with much smaller 285 60r18 nittos and had to hammer my inner fenders back and still rub in reverse.

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