Need help with my math....

[wes-in-nc]

...well kinda.:rolleyes: Most of you saw in my other post about me looking into buying a CUCV truck, I'm trying to go through some formulas to find out what tire size/rpm I will have on the truck. I'm not that good at math and my "Hooked on Phonics" tapes are not here yet, so my question is am I calculating this correctly. The truck has 4.56 gears and I'm trying to find out what RPM it will turn at 60 mph with different tire sizes. I can only assume it has 33" tires on it now because that's what my current K2500 came with.

60mph x 4.56g's x 336 = 2785RPMs :eek:
33"tire
60mph x 4.56g's x 336 = 2626RPMs
35" tire
60mph x 4.56g's x 336 = 2484RPMs
37"tire
Does this look correct? Thanks, Wes.

[Robyn]

Need to know what tranny is in it so we can calculate the output RPM of the tranny and of course input into the rear axle.
??????????

If you have a std auto tranny without overdrive like a 400 or any box with 1:1 out the shaft your numbers are close.
Multiply the tire diameter by Pii (3.1416) this gives the rolling distance or circumference.

At 60 mph you are moving 5280 ft in one minute

You can take the tires circum. and devide the number by 12 to give you a number in feet.

5280 divided by the tire circum will equal the axle speed in rpm
Multiply this number by 4.56 to get the drive shaft RPM and then if you have a direct drive gear box this will equal the engine speed.
Even with an auto box the slip is minimal at road speed
By my calcs your numbers are very close.

Carry on and good luck

Robyn

[NH2112]

Both the SRW K30 M1008 (what Wes has) and K5 M1009 have TH400 trannies. Some M1008s have NP205s (A1 ambulance and shelter carrier models, for example), but otherwise I think they all have NP208s.

[wes-in-nc]

Thanks For the info!!

[Robyn]

Any time ;0)