How do you build a fast truck?

Now just keep in mind with all these gearing calculations that they would only indicate top speed in a vacuum. Rolling resistance plays a large part in achievable velocity, and aerodynamic drag increases exponentially above a certain speed as well. Your truck that's geared for 120 might not even be able to hit 105 by the time you factor in rolling resistance, terrain, and drag. The cure, of course, is horsepower, but its got to be enough horsepower at an appropriate rpm.

 

I've always laughed at some of these guys who don't grasp this when there bragging on how fast their truck is. Double the speed, quadruple the drag. This CAT brochure has a good chart that shows the effects of speed. Even 80 mph takes roughly double the power that 60 mph requires. http://pdf.cat.com/cda/files/2222280/7/LEGT6380.pdf

 

And the higher the percentage of overdrive the more horsepower as well, couple that with said drag really makes you wonder.

 

I've always said I wish I had a truck so fast it could blow the windshield back in my lap.

 

That would be rollin, I have looked through the bottom of my windshield and seen the back of the hood pulling up tight on the rubber straps. Always made me wonder what if? Guess it didn't bother me too bad I have done since

 

WOW I was just being a smart #####, I didn't mean to start a physics debate, I just called foul because my truck has a 10 over/3.55's on LP24.5's and I need a serious tailwind to hit 90.

 

Engine=3406E W/ Cranked up ECM
Trans= RTLO-20918B Final Drive 0.78:1
Rears-3.55:1
Tires= Michelin XDN2 275/80R22.5 = 40.6" Diameter.

(2300/0.73/3.55)*(40.6*3.1415926535897932384626433832795)/(5280*12)*60=107.19mph

Spedo cut off at 80, I was guessing on the speed, I figured about 114mph, turns out by the numbers it was 107.

I was 24 and being stupid, it was fun though.

 

Eaton 18B has a final drive of .73 not .78 but assuming I am mistaken about that that would make it 2300=99.5. also the correct equation is RPMx60 divided by axle ratio x revolutions per mile x trans final drive = MPH. I'm sure Eaton uses an average revs per mile, so it probably not exact. The correct formula and Eaton trans chart can be found here... http://big-rig-road-speed-calculator.blogspot.com/2011/03/semi-truck-road-speed-calculator.html
If you put your #'s you will see that the only Eaton trans with a .78 is medium duty 6 spd. I'm not trying to argue I'm just sayin...

 

It is a typo, if you look at the math you will see I used .73 not .78

 

I plugged it into Eatons Calc and got again a different number so I am not sure. Eaton says 103.2

I think there may be a difference in how they are calculating the tire size.