I tested my car as a hypermiler over thousands of miles on dead flat roads empty of other vehicles, my daily commute was 78miles. The most economical speed was 30mph in 5th gear with cruise control on. For most people that’s not a practical speed for any kind of long journey,but I was getting over 100miles per uk gallon in the summer (hot weather helps with fuel economy, as does not having headlights or ac on). I got through so many audiobooks driving so slowly!
Hot weather does not help with fuel economy precisely because you have to turn on AC (or arrive at your destination a sweaty mess, everyone will LOVE that smell).
Mild weather helps a lot with fuel economy though, engine still warms up faster compared to the winter and you don’t need AC.
The most economical speed was 30mph in 5th gear with cruise control on
That can’t be too good for your engine’s health unless you have a fairly short 5th gear (e.g if you have 6 or more gears anyway or just a short final drive). Most of my manuals have been 5 speed manuals and they aren’t too happy in 5th at 50 km/h.
Since you mentioned below that it’s a diesel, that will cause real issues over a few hundred thousand. I had to clean turbo vanes on a 415k km 1.9 tdi, all gunked up from eco-driving. Vanes don’t get exercised and they don’t get any proper heat either. You’d ideally want to be cruising around 2000 rpm and you should be using most of your rev range, not just the bottom end.
Seriously, that’s why I always just accepted the approximation of 45mph …. The lowest speed you can smoothly drive in the top gear.
But you can hear when the engine is going too slow, when you’re potentially causing more harm than good. Anyone using a standard transmission knows where their shift points are and intentionally going significantly below that is counterproductive
ooooh … you know what, maybe i’ll avoid highways and stick to roads with 30 mph speed limits, too, actually. i drive a hybrid so it might be pretty chill and cost next to nothing.
Economy isn’t just about fuel economy.
Less unsprung weight and highly inflated tyres reduce fuel consumption, but low profile tyres result in damaged wheel rims and lack of adhesion results in lack of control.
Alloy wheels with low profile tyres are lighter, but are also more prone to irreparable damage.
If you have the smallest steel rims that fit over your brakes (and the highest profile tyres to match manufacturer recommendations), you are less likely to have a puncture or damaged wheel, especially in potholed regions. (I live in Victoria, Australia).
If you have the correct tyres inflated to the correct pressures, they will last longer and provide the most optimal grip.
That is not universally accurate. Even at the time, there were vehicles that were more efficient at higher speeds than 55mph. But those weren’t American designs, of course so they were of course ignored in favor of the general majority. And those vehicles that were more efficient at higher speeds, got screwed for simplicity.
Drag is not linear, it is proportional to the velocity squared.
However that is only one of the big factors. Vehicle shape and aerodynamics have a large effect on drag. This is one of the reasons for the flush door handles on some vehicles, lowered drag means increased efficiency. Then you also have the efficiency of the engine and power train at various speeds and power output.
During the Arab Oil Embargo they lowered speed limits on highways to 50 mph, which is the most economical speed to drive.
Windows up is more efficient also, as is fully inflated tires.
I tested my car as a hypermiler over thousands of miles on dead flat roads empty of other vehicles, my daily commute was 78miles. The most economical speed was 30mph in 5th gear with cruise control on. For most people that’s not a practical speed for any kind of long journey,but I was getting over 100miles per uk gallon in the summer (hot weather helps with fuel economy, as does not having headlights or ac on). I got through so many audiobooks driving so slowly!
Hot weather does not help with fuel economy precisely because you have to turn on AC (or arrive at your destination a sweaty mess, everyone will LOVE that smell).
Mild weather helps a lot with fuel economy though, engine still warms up faster compared to the winter and you don’t need AC.
That can’t be too good for your engine’s health unless you have a fairly short 5th gear (e.g if you have 6 or more gears anyway or just a short final drive). Most of my manuals have been 5 speed manuals and they aren’t too happy in 5th at 50 km/h.
Since you mentioned below that it’s a diesel, that will cause real issues over a few hundred thousand. I had to clean turbo vanes on a 415k km 1.9 tdi, all gunked up from eco-driving. Vanes don’t get exercised and they don’t get any proper heat either. You’d ideally want to be cruising around 2000 rpm and you should be using most of your rev range, not just the bottom end.
Seriously, that’s why I always just accepted the approximation of 45mph …. The lowest speed you can smoothly drive in the top gear.
But you can hear when the engine is going too slow, when you’re potentially causing more harm than good. Anyone using a standard transmission knows where their shift points are and intentionally going significantly below that is counterproductive
ooooh … you know what, maybe i’ll avoid highways and stick to roads with 30 mph speed limits, too, actually. i drive a hybrid so it might be pretty chill and cost next to nothing.
If you don’t mind sharing, what car is that, and what year of manufacture?
A Skoda Fabia Estate Greenline Diesel 1.2 litre engine, made in 2011. I took it past 180,000 miles until a deer jumped out and put and end to things.
Economy isn’t just about fuel economy. Less unsprung weight and highly inflated tyres reduce fuel consumption, but low profile tyres result in damaged wheel rims and lack of adhesion results in lack of control.
Alloy wheels with low profile tyres are lighter, but are also more prone to irreparable damage.
If you have the smallest steel rims that fit over your brakes (and the highest profile tyres to match manufacturer recommendations), you are less likely to have a puncture or damaged wheel, especially in potholed regions. (I live in Victoria, Australia).
If you have the correct tyres inflated to the correct pressures, they will last longer and provide the most optimal grip.
That is not universally accurate. Even at the time, there were vehicles that were more efficient at higher speeds than 55mph. But those weren’t American designs, of course so they were of course ignored in favor of the general majority. And those vehicles that were more efficient at higher speeds, got screwed for simplicity.
I did wonder about that actually, questioned it.
It seems odd wind resistance would be higher at higher speeds and not linear to me as well. Idk why but it’s counterintuitive to me.
Drag is not linear, it is proportional to the velocity squared.
However that is only one of the big factors. Vehicle shape and aerodynamics have a large effect on drag. This is one of the reasons for the flush door handles on some vehicles, lowered drag means increased efficiency. Then you also have the efficiency of the engine and power train at various speeds and power output.