For a 300 mile trip
- driving at 60mph = 5 hrs
- driving at 70mph = 4:17
43 mins faster; as long as the extra stop was not too far out of your way it would still be quicker doing 70 & stopping than making it all the way there at 60 & not stopping
Yes, and the OP specified Nashville to Knoxville (~180 miles). More than that, the recommendation was from 70 to 65.
Not 300 miles 10 miles an hour slower, but 180 miles at 5 miles an hour slower. A bit different, there.
At 65, that 180 miles is 2.76 hours. At 70, it’s 2.57 hours. Or a difference of about 12 minutes, one way. I guess 12 minutes might seem an eternity to some people, but that’s a subjective call.
Aerodynamic drag goes as the square of the speed. A car’s energy use is essentially bound by the rolling resistance and aerodynamic drag. At highway speeds the aerodynamic force dominates. Over any given highway journey the energy used to overcome aerodynamic drag might thus be 86% at 65 versus 70. Rolling resistance is probably about one third of the energy used, so overall use going 65 is probably closer to 90% energy versus 70.
So it isn’t inconsequential. Nor it is huge.
Over 70 and you will see the impact quickly. Go 80 and energy used to overcome drag goes up 30%.
The thing I find really eye opening is how much energy is used changing altitude. I live a few hundred meters higher than the city centre. I can drive to work and use essentially zero charge. The battery charge goes up for the first part of the journey. The energy used driving home is really significant.
And of course, @Francis_Vaughan’s unspoken amendment, which applies to both EV and ICE vehicles - check your tire pressure prior to any road trip. Properly inflated tires will save you fuel/energy in pretty much all circumstances.
From what I’ve read, aerodynamic drag is closer to 50-60% of the car’s effort at 60-70mph, with rolling resistance being around 40%.
It varies dramatically with the drag coefficient of the vehicle as well. There’s a reason you can get nearly 30mpg in a corvette but only 18 in a suburban.
Indeed. I was spit balling - so one third versus 40% is close enough for folk music.
The overarching problem is that rolling resistance is constant, aerodynamic drag is square of velocity.
At low speeds rolling resistance dominates. At suburban speeds it really matters. Which is one of the reason you see a lot of care taken with rolling resistance on EV tyres. At highway speeds aerodynamic drag dominates, and because it is velocity squared it swings into dominance quickly and becomes brutally bad fast.
Drag coefficient is a somewhat misused figure, especially when it comes to cars. It needs to be multiplied by the frontal area of the vehicle. So even if a Suburban had a fabulously slippery shape, it would still lose out to a small car. All that air needs to be pushed out the way no matter what.
There is a lot of nuance in getting a low Cd. It took quite a while for car manufacturers to get it right. One of the worst parts of the small trucks so beloved of a certain section of the populace is an open tray top behind the cab. Induced drag as air swirls over the cab and hits the open tray is a disaster. (Why the Tesla Cybertruck places a solid cover of it.) Blunt rear end designs are not good either. The best rear end design is a boat tail. Sadly they are not exactly functional. McLaren will sell you one in exchange for your immortal soul plus first-born child.
Something as simple as a wing mirror can have a real effect of drag. And some of the various slots and vents one sees on some modern cars are not for cooling, but for control of flows that reduce the effective frontal area. It is a matter of a percent here, a percent there. Cooling is a real problem as air ingested into cooling systems results in pure drag that can’t be otherwise managed. Which is why EV variants with a solid front grill win over their ICE counterparts with their open radiator grille - even if the car is otherwise identical.
I got back yesterday. My first EV road trip was an unqualified success…
Except for the fact I was rear-ended 20 miles from my house. My car had 1051 miles on it, and some little shit didn’t understand that just because the light is green, you still don’t go until the people in front of you start moving. I’m glad I had installed the dash cam.
I am beyond livid.
Well that really sucks. Sorry for you, hope it’s quickly resolved.
Arrrruuuggghhh! You with the dash cam, they with cell phone. A most uneven match.
The kicker is that he told the cop that I had just stopped in the middle of the road. I showed her the dash cam video. She came back a few minutes later with her report number said, “Make sure your insurance company sees that. You can go. I need to have a talk with him.”
Pro-tip: Don’t lie to the police.
Livid is way further that Knoxville, I hope you had enough charge to get there.
Seriously, it sucks to be rear-ended, but did it occur on the way out or on the way back?
Barely ten miles from home. Other than that, the roadtrip qas an unqualified success.