i was just wondering about how fast the truck would run in high gear with a direct drive transmission running around 3,000 rpms.

 

10.00-20 tires with a 6.50 ring and pinion

 

Depends on the O.D. of your tires - assuming a 6" sidewall that would be about 32" tall. Works out to around 45 mph.

It is fairly easy to calculate:

3000 rpm(direct drive)/6.50(Rear Gear ratio) = 462 RPM for your rear tires
Rear Tire Circumference(outside) * 462 rpm = Speed in inches/minute
Divide by 63360 to convert inches to miles.
Multiply by 60 to convert minutes to hours.

gives you miles per hour.

Mike

 

Here is a link to an online calculator. Just enter the data in the cells, click calculate, and scroll down to see the chart.

http://www.wallaceracing.com/gear-speed.php


Larry

 

I did that same calculation (using higher math!!.....actually junior high-school math!) My 9.00-20 tires measure out to about 40"(3.33') diameter.

I calculated that I would need to have a rear-wheel rpm of 504 rpm to get 60 mph. (with a 0.7 OD)

Simply calculate the rolling circumference[C=Pi x Dia] of the tires.

C = 3.14 x 3.33'........10.47 ft.......1 mile is 5280 ft.....60 mph is 5280 ft/min.......

Then divide the rear tire circumference into 5280! 5280/10.47 = 504 (rpm)

504 is rear wheel rpm needed to go 60!

Now multiply 504 times the rear axle ratio to get drive shaft RPM to go 60.

504 x 5.83 = 2938 rpm and using the 0.7 OD....2056rpm!

All you need to know to make this work is the rolling diameter of the (rear) tires, Which you can measure and the rear axle ratio (and OD ratio if installed)




Cheers,


Rick

 

My 1948 F7 will do about 60-65-ish. My spedometer isn't very reliable so it is just a guess. Once I get past 50-ish, the front end starts to shake and thump and I get the *******. It has the 337 flathead in it. It has a singe speed rear and 20" tires.

John
NNY