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Discussion Starter #1
First if this belong in a different category apologies up front..

Have a 4x4 that sits on 215/85/16. Fronts are in need of replacing. I have new set of 245/75/16 that according to the interweb are only a .3 percent difference in diameter. The 4x4 is rarely used and if it is it's at slow speeds. I know that it's been discussed with axle ratios here but the grey matter doesn't retain like it used to. I'm sure it'll be fine but chime away..
 

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Be careful of advertised tire dimensions, safer to check a live tire. Tire company dimensions are like salesman's words. Dry pavement with a load is the hardest on drivetrain, so if it is wet and slippery, that is a safer situation. Best to get same size tires, though.

Ed
 

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I just ran it through grim jeeper and at 20 MPH in 1st gear with a ZF you are looking at a 12 RPM difference with the front turning less, I'd think you are OK...........$.02
 

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Discussion Starter #4
I did some more interweb lookin..if you fall into the 1-2 percent its acceptable. Mine would be less than 1 percent at .3
Add to the equation that 4x4 would be used in dirt or snow I'm going forward. No need to spend 400 n tires when we've got em..I did find previous thread here too sorry..but what's a forum without old farts re hashing things?!!
 

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Are you sure the axle ratios are matched from the factory? ie. Old Ford's had 3.70 & 3.73 between the 9" & Dana.

The error compounds if you don't have matching ratios.

Ancillary, getting the transfer case out of 4wd with a mismatch is going to be difficult regardless of what surface you are on.
 

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Are you sure the axle ratios are matched from the factory? ie. Old Ford's had 3.70 & 3.73 between the 9" & Dana.

The error compounds if you don't have matching ratios.

Ancillary, getting the transfer case out of 4wd with a mismatch is going to be difficult regardless of what surface you are on.
if you`re going forward when you want out of 4X4, stop and start pulling on the transfer case shift lever then start backing up. the transfer case will easily shift out of 4X4 when the gears are no longer in a bind. this method has served me well for the last 67 years. if you were backing up before you wanted out of 4X4 pull on the shift lever and start moving forward and it will shift out of 4X4 no matter what surface you happen to be on.
 

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I just ran the numbers. Your old tire side would had a diameter of 30.4" and the new ones would be 30.5". Not sure that .1" would have much affect, assuming the tire manufacture's specs are accurate.
 

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Discussion Starter #8
Factory 4:10 front/ rear. Really wanting to re gear to 3:55 but I only drive it less than 5000 miles per year. Looking at 255/85/16 tires. Ought to gain some mileage compared to the 215/85/16??
Used rp sets are a couple hundred bucks tires are 1500..rp more work, tires easy. Might sell it...bingbingbing..
 
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