Anyway me and my cousin were arguing once about gas mileage. I was going kinda slow on the freeway (steady 65, actually, and in the slow lane) and he told me to speed up a little so we would get home faster. I told him it would waste more gas to do so, because I would have to constantly decelerate and accelerate depending on the traffic. He then rebutted that it would use the same amount if I went at a steady 75-80, it would use the same amount of gas, but in less time, and that I could just change lanes do avoid slowing down and speeding up.

I'm 90% sure that I'm right but I can't come up with a logical explanation for it. My guess is that since the RPMs are higher at higher speeds, then it would mean that the engine has to use more fuel because it's working harder. But then it would be using that much fuel for a shorter amount of time, which kind of negates that assumption.

Would going at a steady 65 use the same amount as steadily going 80 when travelling the same distance? What about, say, while going steadily at 100?

I know the Veyron burns up all of its gas in 12 minutes at top speed, but how far would it have gone already at 252 MPH? Theoretically it would have gone only ~50 miles, but would it go the same distance at a steady 65? I know for sure that having 4 turbos and 16 cylinders is not eco-friendly, but theres no way it would only go for 50 miles before a fillup is needed.

 

u need to also factor in drag coefficient, tranny gearing and engine efficiency into the formula... depending on how the car is designed to operate and at also each engine's efficiency will vary between manufacturers... i have a friend with a 750i that gets better gas mileage at 90 mph than at 65mpg...

also your comment about decelerating from a higher speed and accelerating back up to the higher speed will kill more gas... but if u can keep a constant 80mph it is good...

 

Generally, going faster burns more gas. Accelerating burns more gas. There are a few exceptions however.
Motorweek did a test on this with 2 same 300C's. One driver was aggressive, the other granny drove, & the granny car got better milage.

 

Generally cars will get better gas mileage at a lower speed (i.e. 55-65 mph)...

I used to drive 80mph and now do 65mph w/ cruise control on... mucho bueno gas mileage now...

 

the ideal gas saver is 55 mph, I believe.

 

tell your cousin to stick his head out the sunroof when you go steady at 55, and at 75.

he'll understand the difference for sure.

 

It depends on a lot of things as mentioned above. You can even throw in incline/decline. Are you constantly cruising, or sometimes coasting. Lots of factors come in. But 10mph shouldnt make a big difference in mpg. Now i know that my trans am grabbed an average of 28mpg doing 80 on a trip back down from upstate ny. Whereas the same trip doing 60 gave me about 24 mpg. These are estimates and averages though. Lots of factors could have changed either or.

 

gas prices are going way down.. enjoy your car

 

Would any of you guys care to comment on running the AC on high vs low

and

AC vs fan only?

 

Anyone remember the thread where we were discussing how to get the best gas milage and someone mentioned going WOT up to 2800-3000 rpms would be best? Something about pressure and the efficiency of combustion?

 

The slowest speed at which you can drive in top gear is the most efficient.

When driving at a constant speed the power delivered to the wheels is used to overcome two sources of friction: rolling resistance at the point where the tires contact the road (friction) and aerodynamic resistance encountered by pushing the vehicle through the air.

Rolling resistance is directly proportional to the speed of the car.
Aerodynamic resistance is proportional to the square of the speed of the car.

The sum of these two sources of friction is equal to the amount of power delivered to the wheels.

Because aerodynamic resistance increases with the square of the vehicle speed, whereas distance traveled only increases linearly with speed, a car must expend much more fuel to drive at a higher speed in any given gear. That is why slowing down saves fuel.

 

Air conditioning puts extra load on the engine ( by running a condenser ). If you can cruise w/ windows down under 40mph then I would say you are saving gas mileage. If you drive faster than 40mph( I'd suggest running nothing at all if possible) then switch over to a/c because at a high speed, open windows or sun roofs make your engine have to work much harder anyways.

-Make sure your tire pressure is correct.
-Clean and replace air filters
-MAINTAIN PROPER WHEEL ALIGNMENT!!!
-Check and replace sparkplugs
-Smooth airflow is key - roll up windows and sunroof.
-Drive with cruise control when you can it will save you gas mileage.
-Don't be afraid to use heaters or defrosters because they divert the waste heat. This does not hurt your gas mileage.
-Buy gasoline at the coolest time of the day