What is the best mph for best mpg?
neoiey
There isn't, and no way to calculate it with all of the different variables when driving.
Just drive your vehicle. Don't be heavy on the pedal.
"0" is a really good answer.
Just drive your vehicle. Don't be heavy on the pedal.
"0" is a really good answer.
there are universal principles and obvious ones but you have to remember there's so many variables. Road, weather, traffic, tires, engine, transmission and how they are programmed etc.
On a 2012 Toyota Prius (not a plug-in) driving 45 mph, you will get about 71 mpg.
Pulsing (moderately accelerating) to 45 mph, then gliding (extending your coast with a sliver of electric battery power) to 37 mph, will get you about 79 mpg.
![Image]()
Pulsing (moderately accelerating) to 45 mph, then gliding (extending your coast with a sliver of electric battery power) to 37 mph, will get you about 79 mpg.
Yeah, but it's pretty standard forum etiquette to acknowledge answers to questions that you personally posted.
Not a biggee, just an observation.
Not a biggee, just an observation.
As a former professional trucker, I can confirm there is an optimal MPH for fuel efficiency, which varies by vehicle and conditions. Contrary to the common 4-6 MPG estimate, full-length semis can achieve 7-9 MPG with proper driving—driving slightly below speed limits, typically 63-68 mph in 70 mph zones and 58-63 mph in 60-65 mph zones. This reduces braking and unnecessary acceleration, which wastes energy. Less acceleration means less braking, saving fuel and brake wear, and keeping brakes cooler for better stopping power when they're really needed.
Side note here, heavy trucks like that need 900 feet to stop at highway speed. That gap left ahead isn’t meant for cutting in. You can stop faster than trucks can slow down—safety and courtesy demand respecting that space. Just a friendly reminder for your safety.
So what does that first paragraph have to do with your fuel economy? Simple – these principles from trucking directly apply to most any vehicle. For example, my ‘16 Camry SE averages 38-42 mpg, reaching up to 48-51 mpg highway. And no, it's not a hybrid.
So, you're wondering, "How?" There’s a bit to unpack here, so bear with me.
Hybrids are more efficient mainly because they idle less, but once you factor in a non-hybrid's fuel use at idle, they're not that far apart. And the numbers will prove similar for the MPGe rating for EVs. For example, assuming 75k mileage at purchase, a hypothetical comparison over an additional 70,000 miles between my '16 Camry SE and a '17 Model 3 puts the Camry $29,000 cheaper after charging and battery replacement costs — including property taxes, insurance, etc.
EV proponents tout a 400,000 mile Model 3 used as a taxi, claiming no significant battery degradation. But research shows that Tesla had a $30k service / repair history. EVs mean reduced maintenance, so logic dictates $20k of that was a replacement battery. There's also a 1.24M mile Model S. With 14 motor replacements. And 6 battery replacements. Don't take this to mean I'm crapping on EVs—they work for some—but for most, they don’t make financial sense, and aren't nearly as good for the environment as they're made out to be.
But I'm wandering here — back to the lecture at hand.
Several factors affect fuel economy — driving style, fuel quality, wheel / tire size, tire air pressure, overall vehicle condition, terrain, oil viscosity, even weather. Most vehicles achieve peak efficiency between 45-55 mph; every mph above that saves only seconds per mile, but reduces MPG by about 2%.
Let’s start with driving style / habits. Too fast for conditions encompasses much more than weather and road conditions. Most won’t like this, but bottom line, if you’re on and off the brakes, you’re driving too fast for conditions, which wastes fuel and energy by increased braking and acceleration. Why accelerate in the first place if you’re just going to have to brake? Other thoughts here -- lower cruising speeds mean lower RPM, which means fewer revolutions per mile also. Over time, combined with proper maintenance, this increases the engine's service life.
Fuel quality is a critical factor often overlooked. Using cheap 87 octane fuel with 10-15% ethanol (E10/E15) shortchanges your vehicle and wallet. The 2.5L 2AR-FE and 3.5L 2GR-FE have high compression ratios (10.4:1 and 10.8:1, respectively). Using cheap fuel with these engines isn't the best idea; they simply won’t run their best or achieve peak efficiency on low-octane fuel.
Here's why. For engines below 9.5:1 compression, 87 octane is fine. Higher compression engines are most efficient on 89+ octane, especially ethanol-free. 87 burns faster, causing preignition and timing changes that reduce power and efficiency. Ethanol burns hotter, requiring a richer mixture to prevent thermal damage. After a steady diet of E10 87, my Camry’s mileage rose 3-4 MPG using E0 89–91 octane. A shudder in the steering wheel at idle is gone, and cold starts are easier, even in single-digit temps.
Wheel/tire size — Oversize tires can boost MPG, but avoid rubbing issues by accounting for suspension and steering travel. My Camry’s 225/60R17s are 5% larger than stock, causing a slight 3-5 mph speedo error that I correct with an OBD2 adapter and InfoCar app for more precise virtual speed readings and fuel data.
For those who doubt my claims, and those curious about InfoCar, here are two spreadsheets extrapolated using InfoCar data.
First is VA-IL round trip, 1882 miles. I saw 50.8 average coming back before I hit the mountains.
![Image]()
This one is from more typical use.
![Image]()
Moving on...
Tire pressure — Most say 32-35 psi, but this varies by vehicle and tire model; my tires’ max is 44 psi, ideal at 38-40 psi when cold. Lower pressure improves ride but reduces fuel economy.
Vehicle condition — Standard but vital. Proper maintenance of brakes, steering, suspension, and engine directly impacts MPG.
Terrain — Hilly and curvy routes increase braking and acceleration. Coasting downhill or accelerating downhill rather than uphill saves fuel, so you can sometimes leverage terrain for efficiency. When I can do this, I’ve seen as much as 0.1 mpg increase for every other dip in the road, sometimes every dip in the road, just by reducing throttle for small rises, only accelerating on declines. You’d be surprised how that can add up.
One other thing about terrain. Modern cruise control causes downshifts, both on inclines for acceleration, and declines for engine braking, increasing RPM and fuel consumption compared to coasting. Therefore, I would avoid using cruise control except on the interstate. And even on the interstate, canceling cruise for manual throttle control until the next level stretch can work in your favor as well. It's all about steady, consistent throttle position, engine load and RPM.
Oil viscosity — Crucial. Using 5W-30 instead of 0W-20 increased my oil pump load, creating drag and dropping MPG 33%. Follow manufacturer specs, though, if your engine calls for 5W-20 or 5W-30, don't switch to 0W-20 just for fuel economy, you could be damaging the engine.
Weather — Cold, dense air boosts power, improving MPG. This is why intercoolers increase turbo performance. Moisture from rain can act as water injection, potentially enhancing fuel economy when used properly.
All these things combined have my Camry beating its EPA ratings by 30-35% or more. Hopefully all this helps those here with getting optimal fuel economy. Yes, I might be that guy some of you are having a meltdown over because I won’t go 2 mph faster. But the truth is, I’ll be right behind you at the next traffic light or stop sign three miles after you blow my doors off at over 20 over the limit. How do I know this? Because I see it every day, and I laugh at everyone who does it. Because on average, they're burning $9.00 more in fuel per hour in fuel than they would otherwise.
Side note here, heavy trucks like that need 900 feet to stop at highway speed. That gap left ahead isn’t meant for cutting in. You can stop faster than trucks can slow down—safety and courtesy demand respecting that space. Just a friendly reminder for your safety.
So what does that first paragraph have to do with your fuel economy? Simple – these principles from trucking directly apply to most any vehicle. For example, my ‘16 Camry SE averages 38-42 mpg, reaching up to 48-51 mpg highway. And no, it's not a hybrid.
So, you're wondering, "How?" There’s a bit to unpack here, so bear with me.
Hybrids are more efficient mainly because they idle less, but once you factor in a non-hybrid's fuel use at idle, they're not that far apart. And the numbers will prove similar for the MPGe rating for EVs. For example, assuming 75k mileage at purchase, a hypothetical comparison over an additional 70,000 miles between my '16 Camry SE and a '17 Model 3 puts the Camry $29,000 cheaper after charging and battery replacement costs — including property taxes, insurance, etc.
EV proponents tout a 400,000 mile Model 3 used as a taxi, claiming no significant battery degradation. But research shows that Tesla had a $30k service / repair history. EVs mean reduced maintenance, so logic dictates $20k of that was a replacement battery. There's also a 1.24M mile Model S. With 14 motor replacements. And 6 battery replacements. Don't take this to mean I'm crapping on EVs—they work for some—but for most, they don’t make financial sense, and aren't nearly as good for the environment as they're made out to be.
But I'm wandering here — back to the lecture at hand.
Several factors affect fuel economy — driving style, fuel quality, wheel / tire size, tire air pressure, overall vehicle condition, terrain, oil viscosity, even weather. Most vehicles achieve peak efficiency between 45-55 mph; every mph above that saves only seconds per mile, but reduces MPG by about 2%.
Let’s start with driving style / habits. Too fast for conditions encompasses much more than weather and road conditions. Most won’t like this, but bottom line, if you’re on and off the brakes, you’re driving too fast for conditions, which wastes fuel and energy by increased braking and acceleration. Why accelerate in the first place if you’re just going to have to brake? Other thoughts here -- lower cruising speeds mean lower RPM, which means fewer revolutions per mile also. Over time, combined with proper maintenance, this increases the engine's service life.
Fuel quality is a critical factor often overlooked. Using cheap 87 octane fuel with 10-15% ethanol (E10/E15) shortchanges your vehicle and wallet. The 2.5L 2AR-FE and 3.5L 2GR-FE have high compression ratios (10.4:1 and 10.8:1, respectively). Using cheap fuel with these engines isn't the best idea; they simply won’t run their best or achieve peak efficiency on low-octane fuel.
Here's why. For engines below 9.5:1 compression, 87 octane is fine. Higher compression engines are most efficient on 89+ octane, especially ethanol-free. 87 burns faster, causing preignition and timing changes that reduce power and efficiency. Ethanol burns hotter, requiring a richer mixture to prevent thermal damage. After a steady diet of E10 87, my Camry’s mileage rose 3-4 MPG using E0 89–91 octane. A shudder in the steering wheel at idle is gone, and cold starts are easier, even in single-digit temps.
Wheel/tire size — Oversize tires can boost MPG, but avoid rubbing issues by accounting for suspension and steering travel. My Camry’s 225/60R17s are 5% larger than stock, causing a slight 3-5 mph speedo error that I correct with an OBD2 adapter and InfoCar app for more precise virtual speed readings and fuel data.
For those who doubt my claims, and those curious about InfoCar, here are two spreadsheets extrapolated using InfoCar data.
First is VA-IL round trip, 1882 miles. I saw 50.8 average coming back before I hit the mountains.
This one is from more typical use.
Moving on...
Tire pressure — Most say 32-35 psi, but this varies by vehicle and tire model; my tires’ max is 44 psi, ideal at 38-40 psi when cold. Lower pressure improves ride but reduces fuel economy.
Vehicle condition — Standard but vital. Proper maintenance of brakes, steering, suspension, and engine directly impacts MPG.
Terrain — Hilly and curvy routes increase braking and acceleration. Coasting downhill or accelerating downhill rather than uphill saves fuel, so you can sometimes leverage terrain for efficiency. When I can do this, I’ve seen as much as 0.1 mpg increase for every other dip in the road, sometimes every dip in the road, just by reducing throttle for small rises, only accelerating on declines. You’d be surprised how that can add up.
One other thing about terrain. Modern cruise control causes downshifts, both on inclines for acceleration, and declines for engine braking, increasing RPM and fuel consumption compared to coasting. Therefore, I would avoid using cruise control except on the interstate. And even on the interstate, canceling cruise for manual throttle control until the next level stretch can work in your favor as well. It's all about steady, consistent throttle position, engine load and RPM.
Oil viscosity — Crucial. Using 5W-30 instead of 0W-20 increased my oil pump load, creating drag and dropping MPG 33%. Follow manufacturer specs, though, if your engine calls for 5W-20 or 5W-30, don't switch to 0W-20 just for fuel economy, you could be damaging the engine.
Weather — Cold, dense air boosts power, improving MPG. This is why intercoolers increase turbo performance. Moisture from rain can act as water injection, potentially enhancing fuel economy when used properly.
All these things combined have my Camry beating its EPA ratings by 30-35% or more. Hopefully all this helps those here with getting optimal fuel economy. Yes, I might be that guy some of you are having a meltdown over because I won’t go 2 mph faster. But the truth is, I’ll be right behind you at the next traffic light or stop sign three miles after you blow my doors off at over 20 over the limit. How do I know this? Because I see it every day, and I laugh at everyone who does it. Because on average, they're burning $9.00 more in fuel per hour in fuel than they would otherwise.
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