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Old 05-20-2010, 07:29 AM   #1
DonandJudy_12
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Oversize tires for GM dually

The new GM duallies have 17" rims and tires- My 05 has LT215/85R16E tires as OE- I would like to upgrade to LT235/85R16E for a better ride and increased mileage- I realize spacers are necessary between the duals to compensate for the increased tire width- There is adequate clearance in the wheel well- My question is- have others done this upgrade? Are you satisfied with the outcome? Did you change the speedo gear? I did this upgrade on my old 95 F350 dually with positive results and would like to repeat that outcome- I await the comments of my fellow Mocers- Don
 
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Old 05-20-2010, 08:51 AM   #2
SlickWillie
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I went to a little bigger tire on the 04 Duramax 2500HD. The LT245/75R16 tires just looked small to me. Moved up to the LT265/75R16 and the speedo was not off enough to worry about. You don't have a gear on the speedo to change out. You just need to get GM to adjust for tire size in the truck's computer. Or, you can buy one of the tuners that will let you do it yourself. I had a Diablo Predator for the 04 Durmax, and it had that feature. You just select your tire size, and bingo, it corrects the speedo.

I thought about one other thing after Skypilot posted. The LLY Duramax engines (04 & 05) were prone to overheat issues when towing heavy. I did notice a lot more fan activity on my 04 after going up in tire size. I never had the overheating issue, but our rig isn't that heavy, and I've never been out of TX or LA.
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Old 05-20-2010, 12:18 PM   #3
skypilot
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Don: I don't know that you'd have any problem -- I've recently seen both Dodge and GMC Sierra duallies with 19.5 tires on them and they had no problems. These were conversion kits to give them the right lug patterns but no changes to the trucks themselves other than the computers for the tires. Both owners claimed that ride was better; stopping was better; acceleration was a bit slower but not that it impacted on anything. Both of these were 'students' in the university's Rodeo Club and they used their trucks to haul their stock trailers with living quarters and animals to and from various Collegiate rodeo events.

That said, if the trucks can handle the 19.5 tire weights, etc., then I don't see where going up a few sizes in 16 inch would create any problems. LonnieB may have some better insight though.
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Old 05-20-2010, 03:11 PM   #4
LonnieB
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If the distance between your rear duals is great enough with the stock tires, you may not even need spacers. The 235/85R16 is about 1.3 inches taller than the 215/85R16 and .79 inches wider. As long as you can keep an inch between the duals at the bottom where the bulge is, you should have no problem. As far as the speedo goes, SlickWillie hit the nail on the head.
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