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Old 05-31-2011, 08:37 AM
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Matching Gears for bigger tires?

Hey all, just getting ready to pull the trigger on a 2011 6.7L SD CC. Just putting together some plans on what I am going to do to it in the near future. I am looking at putting 35" tires on it and was looking at the available gear ratios. From what I have found the general consensus is that the 3.31 gears give the best fuel economy but not the best towing. Though I only plan on having about 3000lbs in the bed and 6000lbs out the back, I think the truck has more than enough power to handle the lower gear ratio. But in order to maintain the lower factory ratio overall with 35" tires, if I understand the calculations, I will need to move up to the 3.55 gear ratio. This will give me a ratio of about 3.35 at the rear. Am I looking at this correctly?
Also I would assume that I can get the dealer to make an adjustment to the computer for the 35" tires which will then reflect the 3.35 final ratio when it comes to the speedo readout etc...? Thanks.
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Old 05-31-2011, 09:33 AM
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Originally Posted by Slider78 View Post
Hey all, just getting ready to pull the trigger on a 2011 6.7L SD CC. Just putting together some plans on what I am going to do to it in the near future. I am looking at putting 35" tires on it and was looking at the available gear ratios. From what I have found the general consensus is that the 3.31 gears give the best fuel economy but not the best towing. Though I only plan on having about 3000lbs in the bed and 6000lbs out the back, I think the truck has more than enough power to handle the lower gear ratio. But in order to maintain the lower factory ratio overall with 35" tires, if I understand the calculations, I will need to move up to the 3.55 gear ratio. This will give me a ratio of about 3.35 at the rear. Am I looking at this correctly?
Also I would assume that I can get the dealer to make an adjustment to the computer for the 35" tires which will then reflect the 3.35 final ratio when it comes to the speedo readout etc...? Thanks.
Your math seems accurate, the trucks with 355 and 20 inch wheels which are 34 inches tall are not seeing as good of mileage as the 331 empty don't know about pulling
if you are going to have 3k in the bed alot you will want to put airbags on the rear. Either gear should do fine
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Old 06-03-2011, 08:26 PM
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So does the dealer have the ability to adjust the computer in the truck to accommodate the new tire size?
Technically speaking if a person were running 3.55 gears with 35" tires the overall axle gear ratio would be back down to 3.35 which though not exactly 3.31 is pretty close and should show mileage close to that of a truck equipped with 3.31 gears and 33" tires. Should it not?
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Old 06-04-2011, 04:50 AM
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Originally Posted by Slider78 View Post
So does the dealer have the ability to adjust the computer in the truck to accommodate the new tire size?
Technically speaking if a person were running 3.55 gears with 35" tires the overall axle gear ratio would be back down to 3.35 which though not exactly 3.31 is pretty close and should show mileage close to that of a truck equipped with 3.31 gears and 33" tires. Should it not?
The dealer can only callibrate so much on tire size not sure how much, having the bigger taller tires does lower the gear ratio but you have to account for heavier wheel and taller truck which will affect mileage.
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