I was wondering what's the best cruising speed for my truck for decent gas mileage and to not put too much strain on the engine at highway speeds. I try to keep it under 70. Truck is an 89 pickup 4x4, 22re 5 speed with 4.10s and 28 inch tires. I have no tach so I assume it's buzzing around 3000 at 65 by how it sounds. Thanks

 

Good guess with the RPM. 70 MPH is just a hair over 3,000 RPM, so 65 is just a hair under. I have gone on many road trips cruising at 70 to 75 MPH. The only thing that will suffer is your MPG. The engine and drivetrain is fully happy cruising at that speed. I've also driven long trips on 55 MPH roads and gotten much better gas mileage. Usually at 70 MPH I'll get 17 or 18 MPG. At 55 MPH I can get around 20 to 21 MPG. Keep in mind these numbers rely greatly on driving style and the state of tune of your truck, but relatively speaking that's the difference speed makes.

 

Older rigs and car tend to get better mileage at 55mph. That was the national average on freeways in the 80's so that what a lot of automakers used for there goal of best mileage.

 

Yep. The early to mid '80s Toyota Trucks even had 55 highlighted on the speedometer.

 

Mines been pretty happy around 60 (speedo, not actual) with 33s. Low RPMs, not a lot of throttle input.

 

Slow as you can stand it in 5th gear without lugging.

As speed doubles, profile drag (wind resistance) basically quadruples. I think most engines get the best power per gallon at the torque peak but at that rpm with our not exactly aerodynamic pickups you're just pushing a lot more wind.

I have a friend who was dirt broke driving a 92 2wd from Maine to FL. He wanted to get the best economy possible and I forget the numbers but he did say the best mileage was driving under 50. Doubt he made many friends on the highway.

 

My dad was into hypermiling in a Geo Metro a while back. Could get over 70 MPG. It's just a TBI gasoline engine designed in the '80's. Anyway, generally if you're cruising the best MPG is the lowest speed possible in top gear, or the speed you're going when you shift into top gear. You can also raise up the tire pressure, coast with the engine off on down hill sections, install a throttle stop to prevent inadvertent large throttle input, change transmission/final drive ratios to lower engine RPM at a given speed, and for those cars you could get different cams to actually lower engine power and get even higher mileage.

 

Lol, sounds like Maine drivers on the roads of Massachusetts. Ironically, they have posted 75 mph speed limits. We don't!

 

I remember a buddy had a 77 Monte Carlo with an optional vacuum gauge for fuel economy. The idea was to optimize the vac reading as you drive.
My wife’s 2014 CRV has the same thing in digital form. You can rig one in your truck.

 

Thanks everyone for your responses! I generally stick with the truckers in the slow lane going 60-65 mph (some drafting but not tailgating). I want to take it easy on my rig, she's 30 years old, but only has 114k on the clock!

 

Like many say, 70-75 is good for long distances. I did up to 80 when I did Route 66 in 2016. However, I'm more comfortable with how truck feels and sounds below 70 MPH. Also yes on 55. If I remember correctly 55 was decided upon based on efficiency, not safety, stats.