Your mileage may vary is a phrase that’s been around since the 1970s, but somehow is most poignant in electric vehicles where efficiency is of arguably higher concern. Remember that, in terms of gross energy on board, the average 300 mile range EV holds the equivalent of 2-3 gallons of gasoline, so even slight variations in efficiency can create wild variances in actual applied range. Thus the Road Trip Range Test (RTRT) was born.
What this test is and isn’t
This is not an attempt to match the window sticker’s range number. The “Monroney label” has a range figure calculated based off consuming 55% of the battery in “city driving” and 45% in “highway driving.” This figure might be useful for some, but when most EV shoppers talk about range, they really mean range under common road trip conditions. Can I make it to grandma’s house? Can I get to Disneyland and back?
One of the fortunate things about being in northern California is our stable weather. Although clearly the drive route we use will be hotter in the summer and cooler in the winter, for most of the year you can find at least one day of the week where most of the route will be in 65-75 degree weather. This helps even out climactic swings, but to be even clearer, all our range tests will now list the average temperature and weather conditions during the run.
Full battery, plugged in overnight
To ensure the battery is completely full we leave the EV overnight at our office in north San Jose plugged into a L2 EVSE. Charging is always complete before 7PM the day prior to testing.
After the car has been left overnight at my office to charge, I use the app or remote to “remote start” the EV for 10 minutes and allow the cabin to warm up (and battery to warm up in vehicles with this feature.) Vehicles that do not have a battery heater but need to heat the battery may have a disadvantage in this area, but not all EVs allow us to see if any energy was used in battery conditioning.
Simulated road trip.
The premise of this rage test is to simulate a weekend road trip that an EV owner might want to enjoy. The total travel time ranges from four hours and 20 minutes to four hours and 30 minutes depending on traffic. In an attempt to make things as repeatable as possible, we set the cruise control to 62 MPH in 55 MPH zones, 72 MPH in 65 MPH zones and 75 MPH in 70 MPH zones. This puts us likely in the 60-70th percentile of speeds on these roadways. Cruise control is used as much as possible and lane choices are made based on the need to keep a constant speed.
The drive route consists of 4 main stages.
Stage 1 – Interstate – 40 miles (Elevation change +300ft/-200ft)
Starting out in north San Jose for 3/10ths of a mile on city streets with stop lights, the route really begins on Interstate 280 for six miles. This interstate is an eight lane divided freeway with a speed limit of 65 MPH and fairly level topography. From I-680 I take US-101 south towards Los Angeles for 34 miles.
Stage 2 – Country Highway – 100 miles (-1,701ft/-1,551ft)
This stage takes us from south Gilroy down Bitterwater Valley via California State Route 25. This drive is “pure California”, going from a suburb of San Jose through some of the most productive farmland in the country. CA-25 runs right through Hollister (yes, that Hollister), where there are a few stop lights and some mild city traffic. Then it’s on to Bitterwater Valley, nestled between the gently rolling foothills of the Gabilan mountain range on the west and the Diablo range on the east. On occasion (as with the BMW i4 testing) our drive route has to be paused as ranchers drive cattle along the highway. This portion ends as we head west on California State Route 198 which crosses the Gabilan range with a maximum elevation of around 1,800 feet from the valley to the peak and around 1,550 feet of elevation loss after the peak.
Stage 3 – High speed highway – 13 miles (gradual elevation loss)
From CA-198 our journey heads north on US-101 through the southern end of the Salinas valley. This portion of 101 has the highest speed limit in the state of 70 MPH, so as any good Californian would do we set our cruise control to 75 so we’re not the slowest car on the highway.
Stage 4 – Miles and miles of freeway – 93 miles (mainly flat)
Heading north after King City US-101’s speed limit drops to 65 MPH. Where it remains for the rest of the journey on the highway. US-101 winds through the Salinas valley, California’s premier lettuce growing region, back up through Gilroy and San Jose’s suburbs before we head east on I-680 back to our start point.
Want to follow along?
Want to replicate the drive route on your own? Check out this Google Maps link.
About that altitude
Curious about the altitude changes I ran through briefly? You can reference the chart above which is an altitude graph derived from the Google Maps route It shows a peak altitude of just over 1,800 feet and the return to home base. I know not everyone that owns an EV will be in a state with an 1,800 foot peak, but this kind of altitude change is common on the west coast and of course our friends in Denver. Flat land will always yield greater range, but this is after-all a “real-world” attempt at discussing range.
Calculating the number
Assuming the car completes the 246 mile journey, we calculate final range based on the vehicles consumption over the 246 miles as shown by the car’s computer. This is currently the most accurate way to measure consumption. Why not use a charging station’s totals when re-charging the EV? A few reasons: we cannot be sure of the onboard charger’s efficiency numbers, how much the vehicle’s battery cooling system is consuming, and we don’t know the exact charge cycle efficiency of the battery pack in each EV. We verify the consumption calculations by using the average consumption figure and the percentage battery consumed as displayed by the car. So if the car says 10% battery remaining and the car has a 100kWh usable pack, we verify that the 2.56 mi/kWh figure on the car’s computer matches the portion of the battery we used, then we calculate the remaining range of 25.6. miles based on that last 10 kWh left, this would give such an EV a rating of 271.6 miles and round up to 272 for an even number.
Reserve not included
Some EVs have a small “reserve” capacity, where they may still travel at some speeds after indicating zero. This test does not take that into account because I see little practical value in it. The rational behind this test is not to see what the maximum miles you can eek out of a pack is, but rather a fair representation of real world use and comparison. Very few EV owners will ever take their battery to indicated zero or beyond, and in a road-trip type situation that’s just begging for trouble.
When you see range test results here or on our YouTube videos, the number will not always match the range on the Monroney label because our tests include higher average speeds, altitude changes, and they are based on constant travel rather than stop and go city driving.