3.31 rear end and 20 inch tires 4.2 liter
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04-04-2017, 01:42 PM
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3.31 rear end and 20 inch tires 4.2 liter
Good Day and thanks for all the great information.
My son came by last week with a 2003 F150 XL 4x2 4.2 lt he had just picked up. The 1st thing I noticed was it had huge chrome rims and P275/55/20 rubber on it. Being old school I mentioned that this set up was too much for his engine and differential.. Of course he disagreed..
Now a week later and he needs a new pinion gear and bearing kit..
Am I right by suggesting a return to 16 inch wheels and maybe something like 245/75/16 ??
I tried researching this question prior to posting and found many conflicting opinions..
Thanks in advance..
My son came by last week with a 2003 F150 XL 4x2 4.2 lt he had just picked up. The 1st thing I noticed was it had huge chrome rims and P275/55/20 rubber on it. Being old school I mentioned that this set up was too much for his engine and differential.. Of course he disagreed..
Now a week later and he needs a new pinion gear and bearing kit..
Am I right by suggesting a return to 16 inch wheels and maybe something like 245/75/16 ??
I tried researching this question prior to posting and found many conflicting opinions..
Thanks in advance..
#2
04-04-2017, 02:58 PM
#3
04-04-2017, 02:58 PM
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Location: Madisonville, KY
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FXSHD,
That truck would have normally came with 235/70R16 or 255/70R16, which have diameters of roughly 29" or 30" respectively. The 245/70R16 you suggested is a 29.5" diameter tire, so it's definitely in the ballpark. The 275/55R20 has a diameter of 31.9" (basically 32"), so it's definitely tall for his truck, coupled with that somewhat high 3.31 gearing. Assuming his truck came with the 29" tires (worst case), those tall wheels/tires yielded an actual ratio of 3.00:1. That's a lot of torque to give up, and a lot of added stress on the drivetrain, which I guess you already know. Besides the torque being given up, you also have to consider that 20" wheels and tires weigh a lot more than 16" ones, so it takes more grunt just to get them rolling. So overall, as you've already suggested, yes, it should have something put back on in the same diameter ballpark. I had a '98 F150 SC Lariat once upon a time, which had the 255/70R16's stock. I wanted a wider wheel/tire, so I went with the 17" wheels with 275/60R17. Height/diameter changed almost nothing at all, but I had a much wider footprint. Even a 20" wheel a 275/45R20 (which I think was the stock size on the first Harley F150's) would work. Don't know what you're wanting to spend or how far you want to go with it, but I might actually consider going with 3.55 gears. I know they used to strongly advise against doing much of any towing with the trucks with 3.08 gears, and the same might be true with the 3.31's. It's a good highway gear if fuel mileage is a factor. Hope any of this has helped.
That truck would have normally came with 235/70R16 or 255/70R16, which have diameters of roughly 29" or 30" respectively. The 245/70R16 you suggested is a 29.5" diameter tire, so it's definitely in the ballpark. The 275/55R20 has a diameter of 31.9" (basically 32"), so it's definitely tall for his truck, coupled with that somewhat high 3.31 gearing. Assuming his truck came with the 29" tires (worst case), those tall wheels/tires yielded an actual ratio of 3.00:1. That's a lot of torque to give up, and a lot of added stress on the drivetrain, which I guess you already know. Besides the torque being given up, you also have to consider that 20" wheels and tires weigh a lot more than 16" ones, so it takes more grunt just to get them rolling. So overall, as you've already suggested, yes, it should have something put back on in the same diameter ballpark. I had a '98 F150 SC Lariat once upon a time, which had the 255/70R16's stock. I wanted a wider wheel/tire, so I went with the 17" wheels with 275/60R17. Height/diameter changed almost nothing at all, but I had a much wider footprint. Even a 20" wheel a 275/45R20 (which I think was the stock size on the first Harley F150's) would work. Don't know what you're wanting to spend or how far you want to go with it, but I might actually consider going with 3.55 gears. I know they used to strongly advise against doing much of any towing with the trucks with 3.08 gears, and the same might be true with the 3.31's. It's a good highway gear if fuel mileage is a factor. Hope any of this has helped.