Range Efficiency Under Various Conditions & Cargo

This is a great idea! I plan to do a similar test, but with 3 different sets of wheels+tires.

I think it's possible that a significantly different idle time (like 35 minutes) could have an impact.

 

"Idle" doesn't mean much with an electric motor, since it's not drawing power if the car is stationary. And all of the interior accessories (radio, displays, air conditioner, etc.) are powered by the 12 V battery like an ICE car, so I'm skeptical that "idle time" would have an impact even if the A/C was going.

The air temperature doesn't seem high enough to cause battery thermal issues. Were the wind conditions similar? I'd also suggest dew point is a more useful measurement than relative humidity (my local news weather have all abandoned relative humidity in favor of dew point). Your relative humidity seems to equate to a dew point of about 69 ºF, which is very high.

 

Oh I see I misinterpreted "idle time" thinking you meant the car was in drive-ready state but not moving. It seems you really meant the car was parked while you were away from it? I still don't think it would have made a difference, my real-world experience indicates batteries perform rather uniformly at least between 0 ºF and 100 ºF. Kind of mysterious why there's such a difference. All I can think to do is get more samples and see if the performance curve smooths out.

 

Will do! (I just need to find the right confluence of personal energy, available time, and consistent weather.)

 

Our Clarity's HVAC is powered by the high-voltage battery. An ICE car's A/C is usually powered by the engine, not the 12V battery. I don't know if the MINI Cooper SE powers its A/C with the 12V battery or the high-voltage battery, but I suspect it is the high-voltage battery. Based on the way Green and Green Plus modes work to stretch the SE's high-voltage battery's charge, I assumed the HVAC system must be powered by the high-voltage battery. I'd agree the HVAC's interior fan is probably powered by the 12V battery, but not the heating/cooling devices (including the heat-pump).

It says a lot about this excellent forum that when you go searching for information to back up a claim you're making about the SE, this forum usually shows up at the top of the search. However, I couldn't find any hard-core data to back up my assumptions about the power source for the HVAC system.

 

Fair point. I was thinking of the fan. Where's the Chilton's manual that we need?

Referencing the fuse chart, it looks like the A/C is controlled by four fuses in the SE: 40 A (#34) and 5 A (#53, #62, #123). Curious since the A/C in the non-electric version only has two fuses, #34 and #62.

 

This weekend, I performed a range test to compare the stock 17"x7" Roulette Spoke wheels with 205/45R17 Hankook Ventus S1 evo 3 tires and aftermarket 17"x7.5" NM Engineering RSe05 wheels with 225/45R17 Michelin Pilot Sport All Season 4 tires. Pictures and discussion on the RSe05 wheels can be found in my Aftermarket Wheels thread.



Method
I have established my own range testing route, which is 62 miles long per Google Maps and verified by a GPS app. Of those 62 miles:

• 6.4 miles are on city streets and on/off ramps.
• 3 miles are at 65mph.
• 52.6 miles are at 70mph. (The speed limit is actually 75mph for 32 miles, but I maintained 70mph as that's the speed limit on any road trip route I'm likely to take.)

For all highway driving, I used the cruise control set to the speed limit according to GPS speed, rather than the car's speedometer. Likewise, average speed was per GPS. This eliminates speedometer error (due to manufacturer offset and/or different overall tire diameter).

Battery State of Charge was sniffed off the OBDII port via bluetooth adapter and mobile app.

The wheel weights shown in the chart are per documentation on the internet. Wheel + tire weight was measured with my own digital scale.

Both sets of tires were set to factory-recommended pressures: 38psi front, 35psi rear.

Commentary
First, I was surprised that these two sets of wheels & tires had the same net weight. I do expect the smaller-size summer tire to weigh less, but nearly 7lbs less! I cannot find any documented weight for that size of Hankook Ventus S1 evo 3 tire, as it seems to be a rare Euro-only spec. I expected a minor net weight savings with the aftermarket setup (which would improve with summer tires), but alas was mistaken. Maybe the posted weight of the Roulette Spoke wheels is incorrect?

Second, I was surprised that the aftermarket wheels dropped a whopping 20 miles from the range. I remember noting a big improvement in my SE's range when the weather warmed up, but apparently most of that was due to swapping from the aftermarket wheels back to the stock wheels. Since my SE was delivered in late September last year, I only put 115 miles on the stock wheels before swapping to the RSe05s with all-season tires out of necessity.

The additional width of the wheel and tire plus larger offset really fills out the wheel well, pushing the outer face 20.4mm further out than stock. I love the aggressive look, but secretly had second thoughts about having that much poke. (And now maybe third thoughts, given the loss in efficiency.)

This setup provides an even more planted handling feel than the stock setup, with absurdly high corner-holding capability and reduced torque steer. Maximum grin factor. And the Michelins ride much quieter than the Hankooks, which tend to "thrum" on all road surfaces. Most of my driving is shorter trips on city streets, so highway range performance is only an occasional concern as I rarely take trips long enough to push the limit. But losing 20 miles of range in good weather gives me pause--doing a wheel swap would be wise before any planned long-distance driving.

Next Steps
I had planned to get all-seasons for the Roulette Spoke wheels once I wore down the Hankooks sufficiently, but I think I'm going to make that change this fall--likely with Michelin Pilot Sport All Season 4 in 205/45R17. (Then weigh and re-test the range.) Likewise, I had planned to replace the all-seasons on the RSe05 wheels with summer tires at the same time, but instead will resume my search for some light-weight wheels with better proportions/aerodynamics which I find visually pleasing.

I scored a used set of 16" Electric Revolite wheels (Spectre Grey) from eBay shod in lightly-used Hankook Ventus Prime3 tires. I plan to use them for my winter wheels (replacing the tires of course), but will perform a range test with them as-is first. I will update my chart and post an update here once that's done. I expect efficiency to be a bit better than the Roulettes.

 

I really appreciate this testing.

I wonder if the rolling resistance of the tires is coming into play here, causing such a big discrepancy in range.

 

It could be rolling resistance of the tires, possibly due to the larger contact patch. I also suspect the width and offset of these wheels are impacting aerodynamics, adding resistance and/or turbulence. I don't have the right education/research to gauge if/how much either factor is making the most impact, though.

 

I did realize drag could be another factor. I've got the Power Spoke, which are a closed design, so probably a lower drag coefficient than the other wheel styles. But sometimes you gotta go with what you like.

It's too bad there's no formal rolling resistance/aerodynamic testing yet for EVs (that I know of).

 

Great testing! I used the Pilot Sport A/S 4 with another EV and saw the same efficiency loss. They are really sticky!

 

This is a bit in depth but has some decent info on wheel design's effect on drag:
https://core.ac.uk/download/pdf/211225703.pdf

Some notable bits:

• 25% of a vehicle's aerodynamic drag is caused by the wheels
• Wheel coverage area had the most significant effect on the drag (more closed off = less drag)

Im curious how the wheel options for the SE affect range... There looks to be quite a difference in open area between the tentacle spoke wheels and the 16" revolite or the power spoke.

 

Ooh, thank you for sharing this! Downloaded for some quiet time reading tonight.

Great question and I'm curious about this, too. I look forward to making a test run with the Revolites, but will have to wait a week or two for the latest heat wave to pass (aiming to keep weather conditions similar for each run).

 

Interesting! I'm likely to put those on my Roulettes, so will definitely re-test to see the effect.

 

I just ran the numbers and my efficiency drop was 12%. However - I stuck with the same width tire on that car. 225 is really wide for a Mini (but I bet it's fun!)