Driving 10km slower for gas mileage

My wife and I take care of the high speeds on I90 by staying off of I90. We travel on state and US roads most of the time. I would rather take US 14 across MI & SD than act as a speed bump on the interstate. We are retired so an extra day of driving is not a big deal to us. We have met the greatest people on the 2 lanes. I will not pull at 80 mph. All that being said, don't drive up my butt if I am doing the speed limit on the 2 lanes, I will slow down for you to make it easier for you to pass us.

Recently did a run from Kelowna to Rock Creek, so moderate hills. Kept it mostly to 80 in a 90 zone, pulled over when I could if folks were behind me, and averaged 20 l/100km, so in my mind ~14mpg, or ~12mpg US. Was pretty happy with that.

Heading to Banff shortly and will keep it to 80 or 90 kmh. But will be a hillier drive so I figure 25 l/100km. As a rough guess, 10km/h cost about 1 mpg. For a planned trip of about 1000KM towing, the extra gas is about $25.

For us the sweet spot is somewhere between 60 and 65 mph. We realize that this puts us outside the legal limit of 55 mph in some states and too slow in others that can do 75. However with car traffic and some truck traffic often moving in the 80mph range, the lane turbulence is scary even at 65. We were nearly wrecked in January when some yahoo moving at an estimated 90 mph tried to avoid slowing down for traffic in the opposite lane by squeezing between us and the vehicle to our left. Locked up all the brakes and had a serious white-knuckle event. ugh.
Bill

1320Fastback wrote:
It takes 4X the horsepower to double your speed, mostly all is due to wind resistance.

Drive as fast as you can afford

Personally because it's California law and I live here I tend to drive 55-62mph everywhere I go.

actually it takes 8x the horsepower to double your speed. however when considering the power to travel a given distance you need to consider time. So.... it takes 8x the horespower to double the speed, but for power required for a given distance it is 4x since doubling the speed results in 1/2 the time to cover a given distance.

SoundGuy wrote:
Pipe dream. :W Here in the GTA regular is running $1.30 to $1.38 per litre (has nothing to do with a litter ;) ) depending on the time of day, any reduction Ford invents will quickly be corrected by fuel suppliers taking an even bigger chunk and in the longer term the price at the pump will still be uncomfortably high. :(

That's why I moved out of the GTA. Much like Vancouver prices, Toronto GTA prices are a complete rip off.

Fuel mileage drops considerably with speed when towing. Don't worry about those that want to speed, you will never find a speed that will suit those that always want to go like crazy.

Don't do 80 in a 100 zone unless conditions really call for it (ie: don't run off a curve because you tried to take it at unsafe speeds). If you can safely do the speed limit, stay fairly close to it. At 80, you are a danger on the road worse than someone doing 130. It's particularly bad on 2lane/2way roads where drivers get frustrated stuck behind a slow poke and take risks to get by you.

Generally, you aren't going to see much difference between 90 and 100 but it depends on the drivetrain. Especially with older trucks with fewer gears somewhere around 80-90 you will find a bad spot where the transmission gearing is either too high or too low (It will vary based on engine, transmission and loading), so the engine races under light load or it lugs under heavy load. In that case, it may be more efficient to pick up the pace by 5-10, so the drivetrain is in a more efficient gearing.

It takes 4X the horsepower to double your speed, mostly all is due to wind resistance.

Drive as fast as you can afford

Personally because it's California law and I live here I tend to drive 55-62mph everywhere I go.

it may depend on your truck gearing. On my 2015.5 duramax, towing at 55 I will be in 5th gear for sure in tow/haul mode and likely even if not. At 60mph I'm in 6th when out of tow haul, 62 goes to 6th in tow haul. that extra gear pretty much evens out fuel mileage. Since wind resistance, engine rpm, and tire rotational losses are all square law function vs speed, they will eventually dominate over linear losses, rolling resistance etc. But my experience is that those "square law" losses are balanced by the linear losses up to the 50ish mph range. by the mid to upper 60's they really dominate. But in the 50-low 60 mph range not as dramatic effect on mileage.

you can try but may find the difference in mileage not noticeable enough to be worth the effort.

I haven't had my TT long enough to get numbers, but here are the numbers I had with the Class C that I owned for 10 years.

60 mph - 9 mpg (97 kph - 4 kpl)
70 mph - 6 mpg (113 kph - 3 kpl)

That is a 17% speed increase and a 33% fuel efficiency decrease. (Metric figures rounded off.)

Speed matters.