Will driving at 70 mph instead of 55 decrease my gas mileage?

Question

Or will it stay the same? My truck runs 2,000 rpms at 70 mph if that means anything.

Answer 1

You may not like the answer. But it is No. The simple reason is wind resistance.

There are more complicated changes going on in this speed range. In fact, going from 55 to 70mph is a dramatic change depending on the air package or aerodynamics of the vehicle.

I don't know the actual aerodynamics of your vehicle but the average increase in wind resistance can be anywhere from 33% to 55%. More horsepower and therefore more gas is required to push that air aside.

Usually for the standard type of vehicle the sweet spot is actually about 45mph to 50 mph and if the vehicle is driven in a gas reduction mode. Again there is a dramatic reduction in air resistance between 45 and 55. Many people do not have the patience or the planning for long distance travel at moderate speeds.

For pickups the problems are compounded because the undercarriage is meant to carry weight not to provide fuel effiency. If you have an automatic transmission the gas mileage is a killer because not only is their a horsepower bleed to power the automatic transmission the operator looses a change to change gears at a low rpm.

Worse is the difference in handling on the rubber onto the pavement. Your braking distance increases disproportionally per mile per hour.

To save gas on long distances. I usually looked for the back roads in rural areas or rural secondary highways with less traffic where there were long distances between stops and one can drive slower and the max speed is about 80 mph.

The scary way to improve mileage at high speeds and to counteract the wind resistance is to draft a lead vehicle. The lead vehicle in any string is doing more work. With ten yards or ten meters you do get a mileage benefit.

However the closer you get to a lead vehicle the more perilous the accident situation. It is not a safe practice. To make this work you must know the road intimately. You must have blindingly fast reflexes since the the stopping distance of the trailing vehicle is greater than the lead vehicle due to the drop in air resistance and the loss of traction at the high speed and the buffeting in the draft.

And you must be a very highly skilled driver, with a lot of miles of experience. Drafting another vehicle inside the safety range is not a good idea and very dangerous. But it would mitigate the gas mileage problem at high speeds.

Other things to reduce mileage is making sure you have good tires. Your vehicle must be tuned. Engine tuning is not the same problem as it used to be but lubrications must be regular and constantly monitored. The aim is to reduce friction and horsepower use per unit of speed.

Any exterior appendages or flaws like antennas or dents or bar lights roof racks all contribute to an increase in friction. Open windows increase gas consumption but air conditioning increases it just as much.

Also on a pickup the best thing is to remove the tail gate or put a flat cap on the box. The tailgate up on an open box will sap about a full 8% more gas. It is why you will see many people have nets for tail gates. It is a gas saving measure.

To save gas you also have to drive like an old person. Slow smooth takeoffs. For manual trannies gear change in the low range unless you have a diesel.

I hope this helps answer your question. The short answer is no.

Answer 2

Fraid so. There is a point of diminishing returns based in no small part upon several factors inclufing the transmission, the density of air, frictional loss to the axles, etc.

But all this means is that to get that next 15 mph it is taking maybe 110% the amount of gas it would seem it should. Not an astronomical change - but one that adds up slowly over time.

Answer 3

The efficiency of a gasoline internal combustion engine is typically greatest at between three quarters and full load (throttle opening) and at around the same speed as the maximum torque. So accelerating as slowly as is common in the US does not save significant fuel, but running the engine above its torque peak does rapidly increase fuel consumption. It is generally most efficient to run the engine at about the lowest speed at which it can supply the desired power. so there for the answer is NO.

Answer 4

Listen to your trans, when you are in top gear, 4 or 5 or 6, then that is the speed to go for best MPG. As you increase speed your RPM will increase also thus reducing your MPG.

Answer 5

i guess so.. when i was reading my manual 4 my truck it says " driving at 80 Km/h instead of 105 will save up to 15% gas mileage

Answer 6

if your doing 2000 at 70 your probably ok but the slower you go the more gas you usually save. what kind of tranny is it. thats sounds like an overdrive to me

Answer 7

70 will DEFINITELY reduce gas mileage. That's proven FACT, not opinion.

Answer 8

Yes.

Answer 9

not if going down a mountain