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Can a new wheel style compete with the efficiency of the Tesla Model 3 'aero' wheels?
Posted on September 16, 2019 by Iqtidar Ali
Written by: Ian Pavelko
Way back in 2016 when I camped outside the Montreal Tesla store for two nights to reserve my Tesla Model 3 Performance, I can't say I had wheels on my mind. There were many other things, obviously excitement wondering what the car would actually look like, the experience of meeting so many amazing people from the Tesla community, staving off frostbite... but in that exact moment any impact about what this car would have on my work was pretty far down the list.
Above: Three Tesla Model 3s at Transport Canada's PMG Test Track (Source: Tesla Owners Online)
However it wasn't long after I returned from this expedition that Ryan MacDonald, in Product Development at Fast Wheels, came to me and said, “this whole EV thing seems to be seriously blowing up, maybe we ought to design a dedicated line for them?”
At that instant, I had a seriously hard time imagining what that would be. Lightweight? We already had tons of choices. Aerodynamic? Yes, that made more sense. But all the aero-optimized wheels I'd seen to date were OEM efforts and were, to be kind, not exactly stylish. I was dubious that an alternative could be developed with an efficiency advantage.
Fast forward a year later and the first pre-production Model 3s started to appear and a number of them were wearing what we now know as the ubiquitous “Aero wheel”, a modular system consisting of an attractive lightweight Y-spoke alloy wheel with a removable full plastic aerodynamic cover. The idea was genius. Want style? Run them naked. Want extra range? Snap the covers on.
Early tests by owners of the Aero covers showed that they did indeed boost range by about 4% to 5%. That seemed amazing to me and I felt it highly unlikely we could do better unless we just went for a straight-up Bonneville style solid disc cover, which would likely be a very small niche product at best. What if we were to design a wheel that could at least approach the Aero's benefits while offering a little more panache? And maybe try to even try to shave another pound or two off the weight?
With that target in mind, we started with a clean sheet. The debates with the design group raged. Full cap? Inserts? Full alloy? Round and round – literally – we went. Finally in early 2019 the design you see here started to emerge, a directional-looking lightweight flow-formed base alloy wheel with five removable plastic inserts. After lots of secret-sauce aero tweaking, we were ready to start tooling, casting and testing. The final weight with inserts for the 18x8.5 Model 3 application came in at 21.4 lbs, a handy 1.6 lbs less than the Tesla Aero with the cover installed.
Above: Fast EV01+ wheel (Source: Tesla Owners Online)
But how were we going to test the aerodynamic performance? We looked at doing computer simulations or wind tunnel tests, but, in the end, it had to be real world testing. To date, all of the comparative tests I'd ever seen on the OE Aero wheels had been done on public roads. The methodology was good, but there are still so many variables that you can't control such as traffic, different types of vehicles ahead causing various forms/speeds of wake turbulence, etc — therefore, it had to be a controlled environment.
Enter automotive engineer and fellow member of the local Quebec Tesla community Pierre Champoux. Pierre had spent nearly 20 years working at Transport Canada's automotive research and testing facility here in Quebec, much of that as Director of Test Operations. He insisted that their 4 miles / 6.2 km high-speed oval track was the absolute best place to get rock-solid data.
Fast-forward to August and I find myself standing trackside with three Tesla Model 3s; a white SR+ with stock aero wheels that will serve as our test car for the various configurations, my own Performance Model 3 “Magneto” running on a set of Fast FC04 competition wheels that will act as a fixed-configuration Control car to monitor any changes in weather and track conditions, and Pierre's own Dual Motor Model 3 that will serve as a camera car for some photo laps. I would drive the Test car and the inimitable Trevor Page, the man behind Tesla Owners Online, would drive the Control car.
Every variable that could be controlled was; the tires used on the different test sets were all identical OEM Tesla spec Michelin MXM4s, right down to all treadwear readings being within 7/32nds to 8/32nds (tread height affects energy consumption, with taller/newer tread consuming more), all inflation pressures carefully set to 42 PSI cold and climate controls locked to fan speed 3 and temperature of 22 degrees C. We even booked a 1:00 pm to 6:00 pm time slot to ensure the smallest amount of temperature change over all the runs, and that worked out nicely as it stayed consistently in the 25C to 27C range throughout. Of course, we couldn't control the wind, but being an oval track any changes there would largely be canceled out over the course of a lap.
I decided on a test speed of 120 km/h / 75 mph, high enough to make air resistance the overwhelming energy consumption factor for the cars, but not so high that it would be out of the realm of daily use. We calibrated the speedometer differences between the test and control cars to ensure they ran at truly identical speeds and also always ensured a half-lap separation between the two cars while running together so that there would be zero chance of wake turbulence effects.
Video: Fast EV01+ wheel efficiency testing (Source: Tesla Owners Online)
With everything finally in a place we set off on Test 1, the factory Aero wheels with no covers on. After just a few laps the tire pressures stabilized at 44 PSI front and 45 PSI rear and the energy consumption readout on the trip meter settled in and remained dead stable for the rest of the 30+ km run.
Test 1 – Tesla Aero, no cover: 182 Wh/km (baseline)
Back into the pits to set up for Test 2, factory Aero wheels again but now with Aero covers on. The same pattern emerged, within a few laps the consumption meter settled down and didn't move for the rest of the session.
Test 2 - Tesla Aero, with cover: 173 Wh/km (5.0% reduction)
A 5% reduction, based on all the tests/claims to date, is pretty much what we were expecting. And after running what I think is the most controlled independent test so far there can be no question about it, these caps really work. Kudos to the designers and engineers at Tesla.
Now for the moment I’d been losing sleep over for months, Test 3, with the Fast Wheels EV01+, inserts installed. After a 20 minute stop to swap wheels and re-calibrate cold pressures one last time on this set we were back out. At first, things weren't looking good, the consumption graph actually started to go UP. I stared in disbelief... could we have actually gotten this wrong? However, within two laps, it began to drop dramatically. In no time consumption dropped all the way down to 172 and settled in at reading between 173 and 174 Wh/km, staying right there for the next 25 kilometers worth of laps.
I couldn't believe it.
Within margin-of-error, we'd matched the performance of the Tesla Aero wheel. I was over the moon!
Test 3 – Fast EV01+, with inserts: 174 Wh/km (4.4% reduction)
We then ran the Fast EV01+ wheel without its aero inserts to see what that would do.
Test 4 - Fast EV01+, no inserts: 180 Wh/km (1.1% reduction)
So a slight reduction over the naked Tesla wheel, but realistically it's not enough of a difference for me to claim any sort of victory. Still interesting though.
Test 5 was a repeat of Test 2, that is the OE Tesla Aero wheels with aero covers reinstalled. As the temps had risen by 2 degrees C over the course of the afternoon we had seen a very slight (2 Wh/km) fluctuation in our Control car, so just to be sure we had consistent data, Pierre suggested we run this one again. Swap wheels hit the track for another 30 km.
Test 5 - Tesla Aero, with cover: 174 Wh/km (4.4% reduction)
That matched the high side of what we saw with the EV01+. Incredible.
So the average of the two runs with covers worked out to the Tesla Aero delivering a 4.7% reduction and the EV01+ delivered a 4.4% reduction. Considering the surface shape of the two wheels is quite different at the detail level we were thrilled!
To celebrate we decided to use the remaining time we had in the session to bolt the set EV01+ to my Performance Model 3 to perform, uh, high-speed durability tests. Because if you had access to a track like this, wouldn't you invent an excuse? Let me say that I've spent hours running the Autobahn at 240+ km/h and it's definitively fun, but there's absolutely NOTHING like doing those same speeds and hurtling into a 20 ft high, 180 degree banked turn. I have never been so happy to be a firm believer in physics. I'll let Trevor's video (see above) tell the rest of that story.