I know this is an old thread but I have much the same issue so I'm opening it back up.
I have 7.50 x 16 tires on split rims that need to be replaced on a 1971 F 250 Camper Special whose main purpose is life is trips to "Home Depot" and the wood recylers or the dump. It doesn't get a lot of miles per year.

By my calculations the rotations for a 7.50 x16 tire would be as follows
Total Tire height = 2 x Side Wall Height + Rim Size = 2 * 7.5 + 16 = 31"

Tire Circumference = PI * Diameter; = 3.1416 * 31 = 97.389 inches
Convert circumference to feet = 97.389 / 12 = 8.116 feet

Rotations per mile = Feet_In_a_Mile / Tire_Circumference =
5,280 Feet_per_mile / 8.116 foot_circumference = 650.58 rotations

So assuming my calculations are correct I found a nice tire size conversion calculator at
Car / SUV / Van / Light Truck Tire Calculations which shows the width, speed and rotation difference for an alternate tire compared to the original size but it only has metric sizes

To create a reference tire, by trial and error I found that the specifying a tire size as 305 x 75 x13 yields a tire that has 650.337 revolutions per mile. The reference tire is just for comparison.

OEM Size____Tire Width__Rotations Per Mile___Speed Reading
7.50 x 16____7.5"_______650.58____________65 MPH
305x75x13___n/a________650.337___________64.975 MPH (plenty close for a ref.)

So the 305x75x13 will now be the "65 MPH" tire for comparison to altrenate sizes using the calculator

Size_________Width___Rotations per Mile____When Spedo Reads 65, actual speed is
305x75x13___*7.5"____650.4_________________65.0 MPH
235x85x16____9.3"____635.6_________________66.6 MPH
245x80x16____9.6"____641.6_________________65.9 MPH

just playing around to get closer to the original width
215x90x16____8.5"____645.6__________________65.47 MPH

(*width of the 7.50 x 16)

If the extra 1.4" width isn't a problem the 245's seem like a good bet. I can keep my foot off the gas for a .9 mph difference.

Thanks for any opinions,

Gene

 

Looks like you figured it just right. A mile or two an hour probably makes absolutely no difference whatsoever, especially when its just around to the Home Depot, etc. Looks like whatever you have availble for rims would be your only other consideration and that would be for the width of the new wheels meeting the requirement for the recommended width for the new tires. Enjoy!

 

Thanks MotorDog, I've yet to find a definitive answer on how wide a tire the F series will take without creating any problems.

 

Actually, considering all the varibles such as wheel offset, size, width, etc. and etc., suspension heighth, and on and on, I believe it will be always different from truck to truck seeing as how it's highly unlikely any two trucks will be exactly the same in all respects. Even spring strength and bow will be different. Clearance problems eventually will be apparent after larger sizes are attempted or used. Tie Rods, fender wells, almost anything can become a clearance problem with a larger tire. It will have to be determined on a case by case basis, in my opinion.

Isn't it fun to have so many potential problems to choose from? Hahahahaha!

 

I found a fellow who has four LT 235 x 85's on rims . Tomorrow he'll be checking to if they're 8 lugs on 6.5" or 170mm. He didn't know there are two styles, of course neither did I until I read a bunch of forum posts. So yes the potential problems are great fun but at least there are helpful places like this to mitigate some of them. If they are 6.5", even though they'll be 1.8" wider, at the asking price I'll take the chance.

Check for grins I checked Les Schwab, for only $785 I can get some 7.50 x 16's or go bargain basement with 215 x 85's for $630, just tires - no rims. The used market is looking real good.