A few years ago, I reported on my experience installing the Tesla roof rack on my Model 3 (apparently the bolts are a bit longer now and easier to install), and shortly afterwards I tested the impact on consumption/efficiency (i.e. how much did the Wh/km change?)
A few months after that last post/video, in the spring of 2019, I received and installed a Stealth Hitch on my Model 3 (post coming “soon”). I decided to re-run the consumption test, but this time including a bike rack, a Northshore rack that I’ve been using for several years on a few different cars. Read on to find the values I use when planning out my longer road trips – because the car cannot recalibrate it’s range estimate enough to compensate for the added consumption (it tries, but it is always wrong), it is important to have these values. You can adapt these values for use with the Model Y as well – see the bottom for more.
What follows are my results – if you prefer to see it in video form, check out my YouTube channel.
The table below is a bit data-dense – have a look, then continue on to my key points below:
- The basics: a Wh = “watt-hour”, a unit of energy. So, Wh/km is how much energy it takes to drive 1 km, analogous to L/100km. The higher the number, the more energy you are using to move your vehicle. Your electricity bill comes in kWh, or 1000W/h increments.
- With the bare roof rack and bike rack mounted as my baseline, I compared the consumption of the different configurations; I then scaled the baseline by 5% to compare it to a naked car (based on my testing from a few months prior), and scaled the remainder of the values
- The absolute consumption of my Model 3 is listed at 160 Wh/km at 110 km/h in ABetterRoutePlanner (ABRP); this row is the value I would use in ABRP when planning road trips etc
- Comparing Test 4 with 3, you can see that the bikes have a much bigger impact on energy consumption than the big ski box; the bikes collective frontal area is smaller, but their coefficient of drag is probably terrible
- Looking at Test 6 with Test 3, you can see that having only 1 bike on the rack is pretty similar to the roof box by itself; I used to have a tray rack on my Leaf (see image in gallery below), which holds the bike sideways to the car, and sometimes alternated with my NorthShore rack; I noticed a large difference between the two when I was carrying only 1 bike; the tray rack essentially had similar consumption whether it was 1 or 4 bikes on it
- Looking at Test 4 to 1, you see that adding the roof box doesn’t add much of an additional penalty above having the 4 bikes, so if you are going on a trip and a bit tight for space, just throw the roof box on – it’ll only add an additional 7.5 kWh of energy consumed over 500km… which basically means about 5 minutes extra at my average Supercharging speed (a few $ only)
- No surprise here – comparing Test 1 and 2, which is the same vehicle configuration, energy consumption increased by 20% when increasing speed from 100 to 120 km/h (force of drag increases in proportion to the square of the velocity; i.e. double the speed = four times the aerodynamic drag, everything else being equal)
- We drove across the United States in spring 2019 on I90 and back on I80 with the same configuration in #1 & 2, and in many places we were doing up to 85 mph (135 km/h) – consumption was an eye watering 230 – 280 Wh/km (400 Wh/mile!) most days (incidentally the car handles awesome at that speed)
- Adding the roof box is what made the Model 3 feasible for our family; as you can see, even with this non-optimal aerodynamic situation, the Model 3 + roof box, which yields the same cargo room as an Audi E-tron, is STILL significantly more efficient! (~195 Wh/km for the Model 3 + box vs E-tron ~260 Wh/km)
- My usable range (e.g. 10% – 85% SOC) is about 220 – 275 km when in full road trip mode on my 500 km Long Range Model 3 on an average highway in BC; I could (and have) stretched it farther than that by going a bit slower or charging higher, but there are enough DCFC + Superchargers that it isn’t worth it (see the map in the gallery below) – I just drive with the flow of traffic. Charging speeds are high enough that it is always faster to do this overall (unless you can skip a charging spot entirely by driving a bit slower, that usually is helpful).
I’ve now used this set-up for 18 months after I did that test over tens of thousands of kilometres and have compared my results against estimates generated in ABRP utilizing the above values – generally I have found it to be very close, within a few %.
How would these results adapt for the Model Y? Because the Model Y has almost exactly the same shape on the roofline, you should be able to use the absolute value increase (i.e. add the value from the bottom row of the table to the ABRP value for your variant).
For example, if you have the Long Range AWD Model Y, ABRP rates consumption at 110 km/h as 190 Wh/km. So, for the configuration where you have a similar bike rack loaded up, along with a larger roof box, start by adding the value from the bottom row for that test configuration, in this case 75 Wh/km; in this case yielding 265 Wh/km.
Note that your decrease in efficiency should be less as a % as compared to my Model 3, since the 3 is more efficient to start with. This is also why when you add a roof box to your gas car (like my old Subaru Forester), the consumption increase was there if you paid close attention, but it wasn’t as large of a % difference… because the car was so horribly inefficient! (~ 1000 – 1100 Wh/km!!!)
Adding a roof box for additional cargo space to get the car to work for you on road trips does impact your range, but I don’t think it is a deal-breaker. For some objects you simply need this space (e.g. skis), and in other cases, it is just much nicer to not have some stuff in the car (e.g. sweaty bike gear!) The impact on cost is relatively minimal; not enough to worry about in my opinion. You do have to pay attention to the fact that your range will be reduced, but with increasing density of chargers and/or using ABRP, this issue is greatly reduced.
If you’ve made it this far, enjoy some photos, cheers 🙂