Some follow up thoughts:
Basic hi-efficiency driving techniques still apply to my argument here; e.g., don’t accelerate more than you need to, use the brakes as sparingly as possible, etc. I am certainly not advocating (nor should anyone else!) that you should intentionally accelerate more than you need to just to take advantage of the regen braking. Entropy’s no friend here! In an ideal world, you would simply accelerate only to the point that would allow you to coast to a natural stop at your destination. Of course, this never happens- we have traffic, hills, (minimum) speed limits, road conditions, limited patience of the drivers behind us, etc.
I still think “coasting” is not the best word for what happens when you take your foot off the gas in D mode. While it brings back wonderful memories of flying down a hill on my bike without a helmet as a kid in the 70s, what’s happening in our EVs isn’t quite so simple. Again, there is no mechanical disconnect from the wheels. Think back to early Electricity and Magnetism sections of Physics- an electric motor is also a generator. Put current into it, and it’ll spin like a motor (i.e. pushing on the gas pedal). Or, spin it yourself, and you’ll get current out (i.e. regen). The “0” on your dash power meter ideally represents the magic point of equilibrium, where the motor is not consuming any current, nor generating any; and the car experiences whatever deceleration is created by the other mechanical frictional losses (tires, bearings, aero drag, etc.). When you take your foot off the gas in D, you’re telling the car’s software to try to hold the throttle at that equilibrium point (aka “0”). The software to do this is fairly tricky stuff, coordinating everything between the motor/generator, the charge controller, and the throttle position (at the least…). Fortunately, it’s all behind the scenes, and we just see the needle pegged to 0. If we can agree that “coasting” = “driving at 0”, then yes! We should all coast as much as possible for the best efficiency. You just don’t have to be in D mode to accomplish that
The important thing here is that it is all software. VW could have decided to set “coast” in D mode to whatever they wanted- using the scale of the dash power meter, they could have set it to 0.5, or -0.5 (or anything else for that matter). They chose something that “feels” right to most people who are used to ICE cars- and then they called that “0” for the purposes of the dash display. A different software setting applies for each of the driving modes. Some EVs set that point to greater than 0 at low speeds, to provide the “creep” function (the slight pull forward) that drivers of ICEs with automatic transmissions are accustomed to.
So, if you’re still with me, driving in B mode with the gauge at 0 is exactly the same thing as driving in D mode with the gauge at 0. Same deceleration effect. The only difference is where your foot is holding the pedal.
Consider a regen situation: you’re driving 60mph on a flat road and you take your foot off the gas. (side note- when can we stop calling it the “gas” pedal?
) If you are in D mode, you would see the power gauge go to 0. If in B mode, you’d see the gauge go to something like -4 (I know- the regen side of the gauge is not numbered, so this is a representation, but you get the idea). If you’re in any of the other regen modes, you’d see the needle go to somewhere between 0 and -4. For argument’s sake, let’s say the “regen 1” setting = -1 on the gauge, 2 = -2, and 3= -3.
The same logic from above applies. Driving in B mode with the gauge at “-2” is the same thing as driving in Regen2 mode with the gauge at -2. Again, the only difference is throttle position.
Inverting the use case a little bit, imagine you are already decelerating, the gauge is currently at -2, and the road conditions dictate that you need to decelerate harder, and should really be at -3:
1. If you’re currently in Regen2, you could “downshift” into Regen 3.
2. If you’re currently in D, then you’re already on the brakes, and you’d have to brake harder. Some of this braking force (maybe all of it? I remain skeptical…) will be recuperated as regen.
3. If you’re super smart and good looking and the envy of all your friends, then you’d already be in B mode, and you would simply ease up on the gas a bit more.
The net energy effect of all of these options is the same (granting, for a moment, that manual braking is 100% regen- which seems doubtful to me). Which choice is easier? Option #3, go w B mode!
I think we can all agree- the best path towards highly efficient driving is to minimize acceleration and maximize the regenerative effects of any necessary deceleration. I (and others) have found this to be easiest to achieve in B mode, and the numbers seem to back it up. Anecdotally, I also found this to be true of my Chevy Volt; I got the best range by using the highest regen setting available.
Lastly, have a theory that supports or refutes? Think up a good test, and test it! Then share your results here
Some specific responses:
@NeilBlanchard
Coasting is much easier in D, and therefore it is better.
Arguable. If it is easier, it’s because it feels more natural to people used to an ICE platform. From the efficiency perspective, it’s no better than driving in B with the power needle at 0.
I use the friction brakes very little - I shift down to D1, D2, and D3, or I go straight to B when I need to slow down.
Totally agree- use the friction brakes as little as possible! But doesn’t this run counter to your previous “easier is better” argument? Why not just use B mode, and regulate the amount of braking force you need with the position of the gas pedal? No need to mess around with shifting!
The main point is, if you have to use B a lot - then you have accelerated way too much. And you have already wasted the energy.
Totally agree- but only if we’re talking about a Stop sign-to-Stop sign example on a flat road with no traffic. If you’re going downhill, if traffic suddenly slows, etc., then this is not the case. And, even in the Stop sign to Stop sign example, most drivers accelerate more than we really need to, just to avoid pissing off the guy behind us! I’d still argue that in this case it’s best to use B mode to slow the car as much as possible before engaging the brakes to come to a complete stop.
Accelerate less, then coast, then use some regen. This will always be more efficient.
Absolutely! I would just tweak the statement by saying: coast (hold the needle at 0) in B mode, so that you can make the most of the regen when you eventually need to slow down.
VW knows what they are doing
I hope you’re right
The e-Golf is pretty buggy, so let’s hope they figure it all out soon…
@cove3
I maintain you don't use friction brakes at all when you brake and therefore there's no need to shift down to D2 or B because you're getting exactly the same regen result by braking. Since this is key to the debate, we should get confirmation from an e-golf mechanic or VW. Is normal braking ALL regen or part regen part friction?
Yes, it would be great to understand this better. Can you think of a way to test your theory? Magic marker on the brake rotor? I dunno… But, until this is known to be a fact, the safest route (from an efficiency perspective) is to use B mode, as we know that it maximizes the regen potential.
When you brake in any normal way, the slowing down of the car is much less than the slow down while in B. You can see this on the energy display. The needle goes much deeper into the red when letting up while in B than it does while braking in D. Therefore, why would friction brakes come into play in anything other than an emergency braking situation?
Not sure I agree with your conclusion. The needle is a measure of regen, not deceleration. I do think there is some tricky stuff happening behind the scenes with how the regen force is mixed with the mechanical braking force. Consider the case of braking in D with a fully charged battery: there’s no regen happening (no place for it to go!), it’s all friction. Sure, this is an edge case which doesn’t help the larger efficiency argument; but it does suggest that the VW is fully capable of blending the regen and braking forces without us really knowing it’s happening.
Anyway, like I said before, test it yourself! Find a there-and-back route (to negate elevation changes), with real-world road and traffic conditions, which you can repeat with reasonably consistent avg MPH and climate settings. I think you’ll find results similar to mine- B is best
-JM
