When it comes to saving money on gas, one of the most common questions drivers have is “What speed should I drive to get the best gas mileage?” The answer is not as straightforward as simply driving slower or faster. There are several factors that impact a vehicle’s fuel efficiency, including speed, acceleration, wind resistance, terrain, cargo weight and more. Finding the optimal balance between these elements can help maximize your miles per gallon.
In this article, we will examine how speed affects gas mileage, look at the sweet spot for highway driving based on expert recommendations, discuss other elements that impact efficiency, and provide tips for improving your vehicle’s fuel economy. With gas prices fluctuating, knowing how to optimize MPG can lead to significant savings over time.
How Speed Impacts Gas Mileage
Speed has a major influence on gas mileage due to its effects on wind resistance and engine efficiency. Here’s an overview of how your rate of acceleration impacts MPG:
– Slow Speeds – Driving at slower speeds around town (below 45 mph) provides great fuel efficiency. The engine can run efficiently without needing to work hard against wind resistance. However, driving too slowly can also reduce efficiency in some cases.
– Moderate Speeds – As you increase speed on the highway to around 50-60 mph, gas mileage improves as the engine finds an optimal balance. This allows it to work efficiently without generating excess friction and heat loss at low rpms.
– Fast Speeds – Above 60 mph, wind resistance starts to have a major effect, placing more load on the engine and reducing efficiency. MPG will decline more rapidly as speed increases. Gas mileage at 75 mph can be up to 15% lower than at 60 mph.
– Maximum Speeds – Driving at maximum highway speeds of 70-80 mph causes a huge reduction in MPG due to exponential rise in wind resistance. The engine has to work much harder, using more fuel to overcome air drag.
As a general rule of thumb, gas mileage starts to drop off significantly when driving over 60 mph. However, finding the “sweet spot” depends on the vehicle. The optimal balance of engine efficiency versus wind resistance can vary depending on factors like powertrain design, aerodynamics and gearing ratios.
The Sweet Spot for Highway Driving
While driving slower in town saves gas, what’s the best speed for highway MPG? According to fuel economy experts, the “sweet spot” is typically between 40-60 mph for most passenger vehicles. However, the exact optimal speed depends on the model. Here are some expert recommendations:
U.S. Department of Energy (DOE)
The DOE says the most efficient speed for normal passenger vehicles is 35-60 mph based on testing across a range of speeds. At speeds above 60 mph, gas mileage falls off due to increased wind resistance. For every 5 mph driven over 60 mph, fuel economy is reduced by about 7%.
Fueleconomy.gov
This EPA site which provides MPG data states most vehicles get optimum fuel efficiency around 50-60 mph. Their testing showed an average fuel economy reduction of 15-20% when increasing highway speeds from 55 to 75 mph.
Consumer Reports
Testing by Consumer Reports found the peak MPG for most models is between 35-50 mph. Their analysis showed fuel economy dropping 6-17% for every 10 mph driven above 50 mph depending on the vehicle. The average sweet spot was 45 mph.
Edmunds.com
Analysis by the car shopping site Edmunds found the best gas mileage is achieved between 45-55 mph for most passenger cars and 40-50 mph for trucks/SUVs which are less aerodynamic. MPG declined about 10% above these speeds.
Summary
The consensus among auto experts is that average fuel efficiency peaks around 45-60 mph for modern sedans and SUVs under normal conditions. Still, finding your vehicle’s optimal “sweet spot” requires some experimentation since design factors cause variance. Speeds above 60 mph will rapidly reduce MPG.
Other Factors Impacting Gas Mileage
While speed plays a major role, there are several other important elements that affect your vehicle’s gas mileage including:
Acceleration
Sudden acceleration and braking waste fuel. Smooth gradual acceleration and coasting improves MPG. Aggressive driving like “jackrabbit starts” can reduce MPG 20-40%.
Wind Resistance
Aerodynamic drag becomes exponential at higher speeds, impacting MPG. Luggage racks or carriers without fairings increase drag. Keeping windows closed improves efficiency.
Tire Pressure
Under-inflated tires increase rolling resistance, reducing MPG by 0.2% for every 1 psi drop in pressure. Check inflation monthly to maximize efficiency.
Weight
Added cargo weight strains the engine, especially in trucks. Removing extra weight when not needed improves economy. Reducing average load by 100 lbs can increase MPG 1-2%.
Maintenance
Issues like misfiring spark plugs, clogged filters or low transmission fluid can reduce MPG. Follow the maintenance schedule to keep components running efficiently.
Driving Terrain
Hilly roads and rugged terrain put added load on the drivetrain, decreasing MPG compared to flat highways. Enable overdrive gearing when possible to optimize efficiency.
Cold Weather
Colder ambient temperatures increase rolling resistance and viscosity of engine fluids, reducing MPG by up to 10% in winter. Warming up the vehicle gently helps improve economy.
A/C Usage
Using air conditioning can reduce MPG by up to 25% in hot weather due to the added engine load. Try to avoid excessive use of A/C to maximize efficiency.
Tips for Improving Your Vehicle’s Gas Mileage
Here are some key recommendations from experts for optimizing your gas mileage through proper driving and maintenance habits:
– Observe speed limits and drive at moderate speeds between 45-60 mph for best highway MPG
– Avoid aggressive driving behaviors like speeding and rapid acceleration/braking
– Reduce extra cargo weight and remove attached racks/carriers when not in use
– Make sure tires are properly inflated each month to reduce rolling resistance
– Follow the maintenance schedule in your owner’s manual to keep components in tune
– Limit excess idling and warm up the engine gradually in colder weather
– Use A/C sparingly and rely on venting/windows to minimize compressor load
– Enable overdrive gearing for highway cruising to lower engine rpms
– Plan acceleration carefully when entering highways to avoid wasting fuel
– Avoid constant speed variations and use cruise control to maintain steady speeds
Using MPG Data to Find Your Vehicle’s Sweet Spot
The best way to optimize gas mileage is to learn your specific vehicle’s optimal speeds and driving habits. Here are some tips for pinpointing your real-world fuel economy “sweet spot”:
– Track your fill ups and mileage with an MPG tracking app or fuel log to monitor performance
– Take periodic test drives at different steady speeds and note the MPG after refueling
– Accelerate gently when transitioning between speed ranges to accurately assess efficiency
– Compute your highway and city MPG averages to identify efficiency trends
– Evaluate performance with and without A/C, extra cargo or accessories to determine impacts
– Compare your current MPG to the EPA rating to see if you’re achieving expected economy
– Adjust your driving until you find the sweet spot for acceleration, cruising speed and terrain
With diligent tracking, you can dial in the perfect speed and habits to get every last mile out of each gallon based on your actual vehicle. This allows you to maximize gas savings over the long run.
Gas Mileage Tables By Speed
To illustrate the impact of speed on gas mileage, here are some example tables showing how MPG declines above optimal efficiency speeds for different vehicle classes:
Midsize Sedans
| Speed (mph) | Estimated MPG |
|---|---|
| 35 | 28 |
| 45 | 33 |
| 55 | 30 |
| 65 | 26 |
| 75 | 22 |
Full-size Trucks
| Speed (mph) | Estimated MPG |
|---|---|
| 35 | 22 |
| 45 | 25 |
| 55 | 21 |
| 65 | 17 |
| 75 | 14 |
Compact SUVs
| Speed (mph) | Estimated MPG |
|---|---|
| 35 | 26 |
| 45 | 31 |
| 55 | 28 |
| 65 | 24 |
| 75 | 20 |
The tables demonstrate how driving above 55 mph can rapidly reduce MPG from peak efficiency by 15% or more depending on vehicle type. Finding and sticking to your model’s optimal speed range is key for maximizing fuel economy.
The Effect of Speed Limits on Gas Consumption
Speed limits also have an influence on overall gas consumption across groups of vehicles. Here is some data on how maximum speed laws affect total fuel usage:
U.S. Energy Savings from 1974 55 mph National Speed Limit
| Year | Estimated Gasoline Savings |
|---|---|
| 1974 | 2% |
| 1975 | 4% |
| 1976 | 3% |
Change in Fuel Use After 1995 Speed Limit Increase
| Years | Increase in Total Gasoline Consumption |
|---|---|
| 1995-1999 | 6% |
| 2000-2007 | 4% |
The data shows how lower speed limits translate to less fuel usage nationwide. Individual driving habits also influence results. But laws enforcing maximum speeds intrinsically lead to gasoline savings across the full vehicle fleet.
The Trade-Off Between Speed and Gas Mileage
While slower speeds provide maximum fuel efficiency, there are trade-offs in terms of trip duration that each driver must consider:
The Fuel Economy Difference
Driving 65 mph rather than 55 mph could reduce MPG by 15% or more depending on vehicle. This means 15% more gas consumed for the same mileage driven.
The Time Difference
Going 65 mph instead of 55 mph over a 50 mile trip only saves about 6 minutes of drive time. On a 5 hour 500 mile journey, it saves under 1 hour.
The Cost Difference
Given 15% lower MPG, gas costs would rise by about 15% for an equivalent distance driven at higher speeds above a vehicle’s optimal efficiency range.
Finding the Balance
It requires weighing the fuel efficiency gain vs. time savings for each trip. Slower highway speeds make sense for long trips where gas savings outweighs extra time. But going slower is not always practical on short journeys where speed has minimal MPG impact.
Conclusion
When it comes to maximizing gas mileage, the optimal highway speed for most vehicles is between 45-60 mph. This balances engine efficiency and wind resistance for peak MPG. Driving above 60 mph rapidly decreases fuel economy due to rising aerodynamic drag. Finding your vehicle’s unique “sweet spot” for speed, acceleration and terrain takes testing and diligent mileage tracking. But the gas savings over time is well worth the effort. Slowing down a little on the highway can unlock huge fuel savings without sacrificing too much time for longer trips and commutes.
