Speed vs. Fuel Efficiency
04-01-2008, 04:39 AM
#1
Instructor
Thread Starter
Speed vs. Fuel Efficiency
Hi all,
Just in case another 55 MPH federal speed limit is in our future, is there any merit to the argument that modern autos are more fuel efficient at higher speeds than those calculated in the 70s? There appears to be a lot of data floating around out there to suggest that 45-55 MPH are still the optimum speeds. Cripes. Why does my '99 Cab feel like its happiest at 80+?
Dave
Just in case another 55 MPH federal speed limit is in our future, is there any merit to the argument that modern autos are more fuel efficient at higher speeds than those calculated in the 70s? There appears to be a lot of data floating around out there to suggest that 45-55 MPH are still the optimum speeds. Cripes. Why does my '99 Cab feel like its happiest at 80+?
Dave
04-01-2008, 11:24 PM
#2
Rennlist Member
Happy and fuel mileage are inversely correlated.
I haven't seen fuel mileage tests published lately, but I know that my cars got better mileage at 50 than at 60 in the '70s; and better mileage at 60 than at 70. I got to test on the interstate at 50 mph because we lived in Maryland, which had a 50 mph limit during the "crunch" (imagine that speed for hours on a nearly empty interstate). The 60 and 70 mph tests were done before the speed limit was lowered.
But that was then, so your question is a good one. Cars had much less power then, but only 4 foward speeds and no OD. Cars have more power now, but are more fuel efficient. Most also have an OD for the highest gear (I think). Maybe it's time to test again, but I suspect that my car won't get much better mileage at 55 than at 65. I'm pretty sure it's sucking more fuel at 75 than at 65 though.
I haven't seen fuel mileage tests published lately, but I know that my cars got better mileage at 50 than at 60 in the '70s; and better mileage at 60 than at 70. I got to test on the interstate at 50 mph because we lived in Maryland, which had a 50 mph limit during the "crunch" (imagine that speed for hours on a nearly empty interstate). The 60 and 70 mph tests were done before the speed limit was lowered.
But that was then, so your question is a good one. Cars had much less power then, but only 4 foward speeds and no OD. Cars have more power now, but are more fuel efficient. Most also have an OD for the highest gear (I think). Maybe it's time to test again, but I suspect that my car won't get much better mileage at 55 than at 65. I'm pretty sure it's sucking more fuel at 75 than at 65 though.