Re: [ihc] RPM, Gearing formula needed

[bearbvd@xxxxxxxxxxxxxx (Greg Hermann)]

At 7:06 PM 9/8/03, ROCKY LEAR wrote:
>I am trying to figure out my gearing questions. Maybe someone here can
>help. I know that there used to be a formula for calculating oversized
>tires that used to be in some of the 4x4 mags but darn if I can find it
>now. I want a truck that will run 80 mph without too much winding. Here is
>what I have:
>
>Two gearing options I have are 4:88 and 6:17
>
>44" tall tires, actual measurement may be closer to 45"
>
>An OD out of a 71 t-all...what is that model number any way? T34?
>
>Is there any way to determine what my RPM will be at 80 mph in OD?
>
>I am simply guessing from past experience that the tires alone will put
>the 4.88's in the equivalent of a 3.50-3.70 range.
>
>Is ther any way to figure out this?
>
>A free 6 pack of your choice to anyone who can give me definite answers!
>
>Rocky

The engine will rev about 2960--2980 rpm at 80 mph with 44"--44.5"  tires
and 4.875 gears--in a DIRECT fourth gear. multipling this 2960--2980 by the
overdrive ratio (.84, IIRC, for a T-34)  gives 2485 --2500 rpm at 80 mph in
your OD gear.

Most tire mfrs. will give you a 'tire rpm per mile' figure in their spec sheets.

Greg