Volkswagen ID.3 - long-term review

Oil your bike chain and pump up the tyres. Yeah, I know you think you did it only a couple of weeks back, but it was probably way longer. Do it. Now set off down the road. Suddenly pedalling is wonderfully easy, like you're borne along on the wings of the very angels. That's rolling resitance reduced. But then you get to about 15mph, there's little more gained. At faster speeds, what matters is aero drag. Hence Lycra. (Which I don't wear because I'm old and fleshy and value my dignity over my time.)

Same applies to cars. At low steady speeds, rolling resistance absorbs most of your energy (whether battery or fuel for that matter). Aero drag takes over at high speeds.

And when you're accelerating, weight matters most of all. In a combustion car all the energy used in accelerating goes to waste when you slow down, because you're using the brakes, which just turns the kinetic energy in the car into heat in the brakes, which then heats the surrounding air. Which is why fuel consumption goes bad in town and on twisty roads. But in an electric car, you can, if you brake gently, regenerate most of that kinetic energy back into the battery. You're using the drive motor as a generator.

Anyway, I've noticed that the ID.3 seems to be more efficient at motorway speeds than many electric crossovers. Is that because it's not too draggy? It has a smallish frontal area and a decent 0.26Cd. So I did some Top Gear empirical science. An ID.Buzz has the same battery, the same electronics, and the same motor as the ID.3. But it's heavier by 500kg, and its body is nearly 20cm wider and 40cm higher, with a 0.285 Cd. Total drag is proportional to Cd multiplied by area.

So we drove the ID.3 and Buzz in perfect convoy, far enough apart that the rear one wasn't slipstreaming the front. We charged both to 60 per cent at the start, then did a three-hour mile run of inner London, suburbs and some country lanes – speeding up and slowing down but no sustained speed above 50mph. Then we charged again to 60 per cent, noting energy input.

Next, we did a long section with the cruise control set to an indicated 58mph (56 true), again maintaining a big distance in front. It annoyed the truckers who took five miles to overtake us at 56.1mph, but this was science, so sorry. Then another recharge to 60 per cent to measure input for that section.

Finally, the same motorway section at what you might call overtaking speed – 78 on the speedo, a true 74, before another recharge to 60 per cent.

For each of the three sections we recorded three things – the indicated battery percentage depletion in each car, the indicated m/kWh in each car, and the recorded energy input for each. The three measures pretty much give the same results, although statisticians will note slight rounding errors in trip computer readouts which are to only two significant figures. The charge input figures, from the Ionity invoices, are to five sig figs so more robust.

And the results are in. In town, the ID.3 was 34 per cent more economical – that is it went more than a third further on each kWh – than the Buzz. So even in an EV, the weight, which itself causes more rolling resistance, does matter. At a steady 56, the ID.3's advantage was 36 per cent. And at 74mph it was 42 per cent.

In town and at 56, both cars hit or beat their WLTP range, by the way. High speed knocked 90 miles off the ID.3's range.

To be honest, I'd expected the ID.3 to open up even more of an efficiency gap over the Buzz at high speeds, and maybe at French motorway speed it would.

We certainly proved the advantage of electric regeneration in the first test. In town and on country lanes, would your petrol car get the same economy as when teetering along in the inside lane of a motorway? Absolutely not.

Now compare each car against itself. The ID.3 did 4.7m/kWh in the inside lane, and 3.3 going faster. The Buzz did 3.5 and 2.3. In other words, we saw a 42 per cent improvement in economy for slowing down in the ID.3 and 52 per cent for the Buzz. Try it in your petrol car and you'll find something similar. If you have the patience.