03 2500 hd Ideal wheel offset

[Ryan03]

I have an 03 2500HD reg cab long bed 4x4 with a Dmax allison combo. My stock alumimnum wheels are looking pretty bad, and I am looking to upgrade to some new chrome steel wheels and larger tires. I currently am running 265/75r16s on stock wheels with no lift and tbars turned up 1 1/2 turns. I would like to run some 305/70r16s or 285/75r16s. I am looking at some chrome 8 spoke wagon wheels made by US wheel on summits site, they are 16x8, with a 5 in backspacing, I realy would like to put some chrome pro comp crushers on it, but they only have 4.25 bs in an 8 inch width, which does not sound like enough to me, as I want to maintain as much of the tucked inb look as I can. Would 5 in backspacing on a 8 in wheel interfere with the suspension or frame with a 305 or 285 tire ? How bad would the 4.25 BS fit. Any thoughts, sugestions or opinion on fitment are welcome. Thanks Ryan.
.

[GMC D-Max]

The 305's are going to be a bit wide, and you'll have rubbing problems no matter what backspace you go with. The 285's should be just fine (might have a tiny bit of rub, but only at full steering lock, and only on the back and inside part of the wheel-well liner).

On my previous truck ('02 Sierra, same configuration as yours) I had 285/70-17's on 8" wide rims with 5" backspacing. Worked out perfectly!

[DmaxMaverick]

The ideal backspace for a 16x8 is 4-5/8". 5" is too deep (larger number is narrower wheel center stagger, and too narrow causes suspension component interference). 5" will work with a 17" wheel. A 5" backspace will require a 1/4" to 3/8" spacer. 305's will rub with anything less than a 2" lift (NO cams/keys, they won't work). 285's will work well with the correct backspace, but require some minor adjustment to prevent rubbing under all conditions.

[Ryan03]

Thank you for the replies. The water just got a little bit muddier for me lol. Sounds like the 5 in backspace 16 inch wheels are a no go. There dont seem to be many 4 5/8 options on Summits site. There are lots of 4 1/2 bs. options though, which is pretty close. What are your thoughts on the 4 1/4 bs. wheels in a 16. I would prefer to run a 305 if possible, Dmaxmaveric, did you mean that 305's will work with torsion bar keys? I am prepared to shim out the bumper, do some very mild trimming and swap keys if needed. The main thing I am trying to avoid is ending up with that look where the tires stick way out from the body, I would like to keep them tucked in as much as possible.

[DmaxMaverick]

Thank you for the replies. The water just got a little bit muddier for me lol. Sounds like the 5 in backspace 16 inch wheels are a no go. There dont seem to be many 4 5/8 options on Summits site. There are lots of 4 1/2 bs. options though, which is pretty close. What are your thoughts on the 4 1/4 bs. wheels in a 16. I would prefer to run a 305 if possible, Dmaxmaveric, did you mean that 305's will work with torsion bar keys? I am prepared to shim out the bumper, do some very mild trimming and swap keys if needed. The main thing I am trying to avoid is ending up with that look where the tires stick way out from the body, I would like to keep them tucked in as much as possible.

The torsion bar "keys" are essentially useless. If you can't get the height you need with the OEM keys, cranking the OEM bars further becomes counterproductive. You can get more "lift" with the keys, but it comes at the expense of the suspension geometry. If you need more lift, get a lift. The keys are snake oil, and will cost you CV joints, bushings, diff bearings/seals, bump-steer, repeated alignments, loss of control, and ride.

The 305's won't work without a REAL lift. You could get away with it, if you never get off road or turn sharp at any speed. Fine for those trucks that don't get dirty. The wheel well is only so large. The problem isn't the tire height, but the width becomes a problem at turning extremes. I have some pics of my 2001 with 285 mudders on 16x8 Centerlines in the "truck stuff pics" in my sig. An extra 3/4" width (over the 285) isn't worth the hassle. The tires are more expensive, don't wear as long, and hurt mileage even more.

[Ryan03]

The torsion bar "keys" are essentially useless. If you can't get the height you need with the OEM keys, cranking the OEM bars further becomes counterproductive. You can get more "lift" with the keys, but it comes at the expense of the suspension geometry. If you need more lift, get a lift. The keys are snake oil, and will cost you CV joints, bushings, diff bearings/seals, bump-steer, repeated alignments, loss of control, and ride.

The 305's won't work without a REAL lift. You could get away with it, if you never get off road or turn sharp at any speed. Fine for those trucks that don't get dirty. The wheel well is only so large. The problem isn't the tire height, but the width becomes a problem at turning extremes. I have some pics of my 2001 with 285 mudders on 16x8 Centerlines in the "truck stuff pics" in my sig. An extra 3/4" width (over the 285) isn't worth the hassle. The tires are more expensive, don't wear as long, and hurt mileage even more.

Thanks for the info on the keys. I will definately follow your advice. I checked out the pics of your truck. That is pretty much the stance I am looking for.

[More Power]

From what specs I’ve read, it appears GM used the same wheel offset for all 1988 and newer full-size 1500-2500-3500 Single Rear Wheel (SRW) series pickup trucks and Sport Utility Vehicles, which is a positive offset of 30/31mm for all of their factory wheels. This means that the machined hub surface of the wheel that mounts against the rotor is 30/31mm closer to the outside of the wheel by 30/31mm, as measured from the centerline of the total wheel rim width.

Factory GM wheel offset and backspacing:
16 x 6.5” wheel = +30mm positive offset, 5” backspacing
17 x 7.5” wheel = +31mm positive offset, 5.5" backspacing
18 x 8” wheel = +31mm positive offset, 5.7" backspacing
20 x 8.5” wheel = +31mm positive offset, 5.9" backspacing

Backspacing is the distance from the hub mounting surface to the inside wheel lip (back side of the wheel) and is usually measured in inches. Obviously, narrower rims have less backspacing and wider rims have more, even though the offset ratio remains the same between rims of different widths.

If the offset remains the same, backspacing will increase when using a wider wheel. It’s important to pay attention to the backspacing and tire size because of the potential for rubbing. I doubt anyone would have a problem when using any GM factory wheel with the factory recommended tire size for that wheel, though some here in The Diesel Page forums have reported rubbing with 305 tires on factory wheels. I installed a set of 20” factory wheels equipped with the factory 275/55R20 tires sourced from a 2003 Chevy SS K1500 on my 1989 Chevy K1500 (90's body style). No rubbing.

For anyone else contemplating aftermarket wheels, I recommend using the GM wheel offset of 30/31mm for any wheel they might be considering. Moving the hub in or out, in relation to rim width, could cause too much backspacing and excessive tire rubbing while turning short. In addition, a different offset could affect how well the truck tracks on well-worn highways, and less offset could produce what is termed “bump steer”. Changing the offset can also reduce the life of ball-joints and steering components.

Jim

[leolkfrm]

strip the enamel off the stock wheels...sand them with wet sandpaper...then rebuff....they will look 90% better!