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I haven't logged my numbers, but I did notice I can go about 75-80 and as long as I regen on hills and such my average usage per mile is fairly low. It's actually about the same as if I try to baby it on the highway.
Mythbusters determined a 11% increase in fuel economy by following a big rig at 100ft. That's not that close and should get you to your target. It goes up fairly linearly too with 20% at 50 ft and 27% at 20 ft and 39% at 10 ft.
If you avoid regen on hills you'll get even better numbers. regen is NOT efficient, it's just more efficient than friction braking. But if you'll find the "glide"point where gravity is taking you down hill at higher speeds and then use that gained momentum on the next flat or uphill you'll net better energy use.
I should clarify, not full regen, but say I'm doing 70 before going downhill -- if I regen enough to keep my speed going then I keep up my speed AND regen. Pretty much free miles!
It's even better not to regen, but to keep the "needle" at full neutral, gaining speed. Bleed the speed off after you've stopped going downhill. Only apply regen if you would otherwise end up going too fast. (What "too fast" means is left as an exercise for the reader.)
What was it at 5 feet?
Seriously, this is why I think that autodriving cars that are in constant real time with the cars in front and behind them is such a great idea. If the front vehicle started braking, the ones behind would immediately (< 10 msec) know about it and start braking in synchrony. A 40% fuel savings would be pretty significant.
dflye
S Sig Perf 414, VIN 814
The car in the front wouldn't see that
Hopefully the vehicles would rotate through positions similar to a bicycle peleton or V-shaped flock of geese, such that all gain an overall benefit. Just happens to suck being the one pulling the train when it is your turn up front!
smorgasbord
Active Member
With what kind of car were they following the big rig? With Model S's low Cd, the increase should be less than a 1980's flat front car, for instance.
Only if it's a short hill so you don't gain more than a few mph. If you gain more speed, you quickly approach a point where increased air resistance gives you more loss than the regen would. For example, consider a long hill where you regen down at 60mhp. If you let the car roll free, you might get to 75mph before increased air resistance cancels out further speed increase. So at the bottom you either have 15mph extra speed or you have regened a few kWs for a few minutes. The 15mph extra soon disappeares if you continue to roll freely.
The impact of drafting was less at <5 ft. The guess was that it's such a challenge to hold that distance that there was more adjustment of the throttle required than with other distances. Realistically, I think, there would be about the same amount of throttle control required at any distance but the margin of error is much greater when you're farther back so you could be a little sloppier with distance.
Maybe not, as the electric motor is more efficient as the ICE one the wind might take a lager percentage of the energy you use then the ICE. So even if the car itself does have less wind 'drag' it might end up with the same or higher percentage of fuel effiency... but well that's hard to tell...
sublimaze1
8Dec2012 / Leeroy Jenkins
+1 and +2 .... I can't wrap my head around how many people want to draft a semi (articulated). DavidM only tips the iceberg - at 100 feet, you will NOT be able to stop not to mention checking if you can see both of his mirrors. Oh well, do what you wish.
Actually even better, the cars behind could start braking before or at the same time as the car in front because the car in front could share data and decisions before they are acted on.
80mph is 117 feet per second, even 10 msec is too long if you want to follow 5 feet apart.
For real world data, see my trip report from today. (Unofficial Road Trip Thread)
I saw an 11% gain from following very safely behind an RV for 50 miles.
I got my first temperature limited power restriction with the model S the other day. I had been driving agressively for about 30 miles with hard accelerations, cornering, passing etc. It was 55 degrees outside and got to a straight stretch and took her to 110 mph and held it there for about 5 minutes. I got the dashed yellow line just under 320kw. I backed off the speed and the indication went away almost immediately. A minor limitation which would have not affected the way I was driving in the slightest. It will be intersting to see how efficient the motor cooling is at higher ambient temperatures.
I think I get that limit when I get a little over 110 and it doesn't need to be for a steady 5 minutes, just pushing it hard still at 110 mph. The car feels really good at that speed
