Mercedes GLC 400 EV Went 392 Miles in Edmunds' Test Against an EPA 331, but the Efficiency Figure Does Not Add Up

The number in dispute is 28.4. Electrek reported on October 20 that Edmunds drove a 2027 Mercedes-Benz GLC 400 4Matic EV 392 miles in its range test, 18% past the EPA's 331, and attached an efficiency of 28.4 kWh per 100 miles to the run. The car carries a 94 kWh usable pack. Divide 94 by 392 and the answer is 24.0 kWh per 100 miles. Divide 94 by 331 and the answer is 28.4.

That does not make the 392 wrong. It makes one of the two figures in the Electrek write-up a different measurement from the one it is labelled as, and a reader comparing EVs by efficiency is the person who gets misled.

What Edmunds measured: 392 miles at a 40 mph average

Electrek's account, written by Peter Johnson, says the test route is 60% city and 40% highway driving, with the car held within 5 mph of each posted limit and the climate control set to auto at 72 degrees. The average speed is 40 mph. Electrek does not give the outside temperature or name the route. We could not fetch Edmunds' own page, which returned HTTP 403, so every figure from the test below is Electrek's relay of it.

The same write-up lists three rivals from the same programme: the Volvo EX60 P10 AWD at 352 miles, the 2025 Cadillac Optiq at 339 and the 2027 Audi Q6 E-Tron Prestige at 337. The GLC leads that list by 40 miles.

1. GLC 400, Edmunds test392 miles
2. Volvo EX60 P10 AWD, Edmunds test352 miles
3. GLC 400, EPA, low-resistance tires350 miles
4. Cadillac Optiq, Edmunds test339 miles
5. Audi Q6 E-Tron Prestige, Edmunds test337 miles
6. GLC 400, EPA, all-season tires331 miles

Source: Electrek (Edmunds results) and SlashGear (EPA ratings), accessed 2026-10-21

Which EPA number is the baseline: 331 or 350

The 18% depends on the denominator. SlashGear's review reports two EPA ratings for the car: 350 miles on the standard low-rolling-resistance tires and 331 miles on all-season tires, which the reviewer expects most buyers to choose. Kelley Blue Book's September 9 pricing story, by Robert Duffer, gives only the headline "up to 350 miles" and a starting price of $64,950 including the $1,450 destination fee.

Electrek used 331, so the car in the test presumably wore the all-season tires. Against 350 the margin shrinks to 12% (42 miles). Both are real gaps; they are not the same claim.

Baseline	EPA miles	Edmunds 392 is	Tires
Headline rating	350	12% above	Low rolling resistance
Electrek's baseline	331	18% above	All-season

This is also not a one-off for Edmunds' method. The Drive reported in December 2025, in a piece by Joel Feder, that a 2026 Mercedes-Benz CLA EV rated 374 miles by the EPA went 434 miles in the same test, 16% over. A slow, half-city route with the car near the speed limit favours any efficient EV against the EPA's blended cycle.

The efficiency arithmetic: 24.0 versus 28.4 kWh per 100 miles

The number that matters here is not the mileage but the energy per mile, because that is what carries over to a buyer's own commute. Electrek says the GLC used 28.4 kWh per 100 miles, about 14% less than the 33 kWh per 100 miles it attributes to the EPA.

The EPA's 33 is a wall-to-wheels figure, which includes charging losses. A pack-only figure for the same rating is 94 divided by 331, or 28.4. That is the number Electrek printed for the test. A pack-only figure for the test itself is 94 divided by 392, or 24.0, which is 4.17 miles per kWh.

Figure	Source of the miles	kWh per 100 miles
EPA, wall-to-wheels	EPA 331	33 (Electrek)
Pack only, EPA mileage	EPA 331	28.4 (our division; matches Electrek's printed figure)
Pack only, Edmunds mileage	Test 392	24.0 (our division)

These are our divisions of the reported usable capacity, not Edmunds' published numbers, and they assume the test drained the pack from full to empty. If Edmunds measured 28.4 at the wall, the pack would have to hold about 111 kWh to deliver 392 miles, which does not fit a 94 kWh usable battery. So either the printed efficiency is the EPA-derived number, or the capacity and mileage are not the ones reported. Edmunds' page would settle it.

Why the test and the week of driving disagree: 4.17 against 3.3 miles per kWh

SlashGear's reviewer averaged 3.3 miles per kWh over a week with the same car. At that rate 94 kWh yields about 310 miles, which is our arithmetic, not the review's. The Edmunds test at 4.17 miles per kWh is 26% more efficient than that week.

Both can be true. A 40 mph average is slow enough that aerodynamic drag, the dominant load above 50 mph, matters less. A week of ordinary use includes faster stretches, cold starts and cabin conditioning that a controlled route avoids. The Edmunds figure answers "how far can this go under gentle conditions"; the 3.3 answers "what did one reviewer's week cost".

What the charging numbers add: 330 kW and 22 minutes

Range only decides purchases alongside charging speed, and Edmunds' test did not measure it. Mercedes claims up to 330 kW DC charging and 10% to 80% in about 22 minutes on the 800-volt car, according to SlashGear and Kelley Blue Book; Level 2 takes about 10 hours at up to 11.5 kW. Those are vendor figures. Kelley Blue Book also lists the BMW iX3 at $62,850 with up to 434 miles of rated range, which puts the GLC's 331 to 350 miles well below its closest priced rival on paper.

For how buyers weigh numbers like these, see our look at BMW's survey on how much range drivers want, and for a similar pack-arithmetic check on a long-distance claim, the BMW i3 1,213 km test.

What would change this read

Edmunds' own page is the variable. If it shows 28.4 kWh per 100 miles measured at the charger over a different mileage, or a usable capacity above 94 kWh, the arithmetic here is wrong and Electrek's figures stand. If it shows a pack-only figure near 24, the 28.4 is an error in the write-up and the test is cleaner than it looks. Until then, 392 miles is a result at a 40 mph average on tires Electrek did not name, and 331 and 350 are both honest baselines.