I have a 1994 e350 with a 7.3 diesel, e40d trans, and a 4.10 dana rear end,
this van does not have a tach
might someone have info on what engine rpm I would turn at various speeds? 50-60-70 mph or any speeds really
thanks for any info possible

 

Hi, I've got a 2000 E350, V10, and 4.10 gearing. At 65 mph, it's turning 2170 rpm - obtained from a Blue Driver scan tool.

 

thanks Pinzer

 

245/75-16's?

 

Figure out the tire diameter, multiply times Pi (3.1416) then divide that into 63360 (inches per mile), then multiply that times the gear ratio to get rpms at 60 mph. This figure is roughly rpms in 3rd gear, to get them in OD, then multiply times .70 ( I think this is the OD ratio, but not sure) Tire diameter is width (in millimeters) times aspect ratio which is the sidewall height, multiply this x 2 then divide by 25.4 to get inches and add that to the rim diameter. Ain't Algebra neat ! And you thought you'd never use it in real life !

 

225/75-16's

 

thanks baddad
I'll get my sister to cypher that fer me
she's the edumacated one in the family

 

that's too much work, there is a simpler formula.
RPM = MPH x transmission gear ratio x axle gear ratio x 336 divided by tire diameter in inches.
or use this Gear Ratio Calculator

 

No more complicated than what you've posted here. Once you've done it a few times it's really simple. Tire section width multiplied by aspect ratio in millimeters: 225 x.75 = 168.75 x 2 (doubled for top and bottom sidewall) =450/ 25.4 (millimeters per inch) =17.71 + 16 (rim diameter)= 33.71. (tire diameter) 33.71 X 3.1416 (Pi)= 105.9. (Circumference in inches) 63360/105.9 = 598.3 X gear ratio = mph @ 60 (in direct, not OD) to get rpm in OD, then multiply that times the OD ratio. Three equations, same as yours

 

Same result but less efficient.

 

What's less efficient ? It takes three equations either way, once you know the tire diameter

 

Do I really need to explain?
It's this
VS this
Both will get you the same answer but the second one is way quicker and easier since its only one equation.

 

It's not one equation but three, same as mine. Apparently you didn't look at what I posted. tire diameter x Pi divided into 63360 x gear ratio gets you rpms @60. That simple enough for you ? If you want rpms at other speeds, then use 60 mph as a constant. I.E. 75/60 = 1.25 they're both algebra.

 

This is one equation, not three.

 

I can see math isn't your strong suit.