Different ratios difference at 78 miles per hour MPG

At that speed I don't worry about it. You already have a adequate ratio to get near 80 with that 13 speed.

In my experience 13's were not particularly fast however if you can get up and shamble down the interstate at that speed with one it's plenty good.

 

Why 78mph? You’ll have other bigger problems driving at that speed.

 

• Tickets/violations/CSA points
• Higher chance of an accident (frequent lane changes, less following distance, less distance/time to stop, etc.) Higher insurance costs.
• Higher fuel expense. Fuel is usually the highest expense in a trucking business.
• More wear and tear on entire equipment: engine life, tires, leaf springs, air bags, shocks, torque rods, more frequent alignment, increased hose/wire chafing, and so on.
• Many semi tires have a max speed rating of 75 or 72.

 

Are the 10 and 13 od trans or is one a direct drive?

 

And most steer tires are only rated for about 70mph....so there's that as well.

Look around when you are driving. Most independents and O/O's are driving for fuel mileage, not speed. More money going out the exhaust pipe means less money in your pocket.

 

All depends on final ratio of transmission.

Research the different transmissions.

Why 78 mph? Faster you go, the bigger the mess.