Offset / Backspacing chart

Tire sizing and wheel offset.

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Offset / Backspacing chart

Postby socal1200r » Fri Sep 25, 2015 5:38 am

Thought this would be a handy reference for this forum. It's a simple chart that shows wheel width down the left column, backspacing along the top row, then offsets filling in the matrix. Ties everything together. I used this chart when I got my new wheels. Went with 17x8 fronts with zero offset, which kept the backspacing at 4.5". Went with 17x9 rears with 8mm offset, which got me a backspacing of a little more than 5.25". 245/45s up front, and 285/40s on the rear, gave me the stance I was looking for. Also, I think the truck is lowered 2", but this wheel/tire combo fills the wheel wells nicely, and still leaves room for the suspension to work without hitting the fender lips. The fronts rub at full lock, but I'm okay with that, since I rarely turn full lock anyway. Wheels are US Mags Bandits, $165 ea for the fronts, $172 ea for the rears, from JEGS.

http://www.wheelspecialists.com/wheel-specs

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Robert Brooks
Newport News, VA
2000 GMC Sonoma: mid-90's fuel-injected LT1/T56 trans, Cobalt SS seats, 17x8 / 17x9 wheels with 245/45s and 295/45s, steel cowl hood, flush bed cover, coil overs, traction links, aluminum driveshaft, headers with true dual exhaust, conversion done right (wiring harness, computer, etc., so factory gauges work like they should).
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Re: Offset / Backspacing chart

Postby Keys85 » Fri Aug 26, 2016 2:53 am

Nice. What is that bed cover you got there!?
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Re: Offset / Backspacing chart

Postby SleeperSS » Fri Aug 26, 2016 3:23 pm

I like the wheels. Just as a comparison, I'm running 245-47-17 up front on 17X8 with4.5" b/s...the rears are 285-40-17 on 17X9.5 with 5.5 b/s. I'm dropped 4/5 with shaved bump stops/brackets. There is plenty of clearance in the rear, and the rub at full lock has gone away completely with the LS brake conversion.
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Re: Offset / Backspacing chart

Postby socal1200r » Mon Aug 29, 2016 6:38 pm

I'm thinking of replacing these US Mag wheels with a set of Corvette sawblades, same 17" diameter, but I think the sawblades are 8.5" front and 9.5" rear. I'm not worried about the extra half an inch in width, but what does cause me concern is the huge 56mm offset of the Corvette wheels. Based on this chart, and some other research I've done, it appears that in order to run the sawblades, I'll have to use at least 2" spacers on the front AND back, in order to get these 56mm offset sawblades to work (two inch spacers will get this 56mm offset almost down to zero). I can get a set of four 2" spacers off Amazon for about $120, and a local set of sawblades for $300. Then I'd have to pay to get the tires swapped over to the sawblades, which will run about $100 for all four, so it's a little pricey just to run sawblades. But at least it could be an option, and with the Corvette flags on the center caps, it'll tie in nicely with the flags on the fenders, and the Corvette engine covers.
Robert Brooks
Newport News, VA
2000 GMC Sonoma: mid-90's fuel-injected LT1/T56 trans, Cobalt SS seats, 17x8 / 17x9 wheels with 245/45s and 295/45s, steel cowl hood, flush bed cover, coil overs, traction links, aluminum driveshaft, headers with true dual exhaust, conversion done right (wiring harness, computer, etc., so factory gauges work like they should).
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Re: Offset / Backspacing chart

Postby Rickracer » Tue Aug 30, 2016 9:11 am

No offense, but NO WAY IN HELL would I run any combo of wheels and tires that required spacers like that...... :? :? :?
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Re: Offset / Backspacing chart

Postby socal1200r » Wed Aug 31, 2016 5:01 am

Rickracer wrote:No offense, but NO WAY IN HELL would I run any combo of wheels and tires that required spacers like that...... :? :? :?


I hear ya, but if I want those Corvette wheels to work on my current setup, that's about the only option I have. It's in the "what if" stage right now, and the more I look at the truck with my current US Mag wheels, the more I like it, so there's a good possibility this Corvette wheel thing won't happen. I don't race the truck, so putting the sawblades on would definitely be more for looks than anything else. Like the old saying goes, "if it ain't broke, don't fix it"!
Robert Brooks
Newport News, VA
2000 GMC Sonoma: mid-90's fuel-injected LT1/T56 trans, Cobalt SS seats, 17x8 / 17x9 wheels with 245/45s and 295/45s, steel cowl hood, flush bed cover, coil overs, traction links, aluminum driveshaft, headers with true dual exhaust, conversion done right (wiring harness, computer, etc., so factory gauges work like they should).
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