Figured I’d link this since there have been a ton of threads on wheels and efficiency in here. Gives a lot more detail on all the aspects that affect range with wheel changes.
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Engineering Explained- wheel size effects on electric cars
- Thread starter Sam1
- Start date
I like Jason, but he did a poor job of distinguishing the effects of wheel diameter, wheel aerodynamics, and tire rolling resistance in the comparison of the Tesla range data. He simplified it down to just wheel diameter with the conclusion that more sidewall is critical for range.
It’s obviously more complicated than that. The 18” wheel and tire option for the Model 3 is optimized for range using highly aero efficient wheels and low rolling resistance tires. The larger wheel and tire options are not as focused on range.
Nevertheless, it great to see this kind of analysis presented to his audience.
It’s obviously more complicated than that. The 18” wheel and tire option for the Model 3 is optimized for range using highly aero efficient wheels and low rolling resistance tires. The larger wheel and tire options are not as focused on range.
Nevertheless, it great to see this kind of analysis presented to his audience.
He addressed that issue in a comment at the top of the comments on the video:
*CLARIFICATION!* Why do bigger wheels mean worse efficiency, when the overall tire diameter remains the same? This comes down to aerodynamics. A 20" wheel will cause more of a disruption in airflow than an 18" wheel. That's why Tesla (and others) uses aero covers on their wheels (Car & Driver testing showed it gives about a 3% efficiency bonus at speed). The smaller the wheel, the more of the side profile of the wheel & tire is perfectly flat (the tire is flat, the wheel is open: more tire = more flat area, less open area). Ideally, you'd have just a plain, solid sheet for the wheel, but obviously that's not idea for brake cooling. Wheel covers are today's common compromise as they have some airflow, but minimal.
Personally, the range penalty and added running costs (and perhaps maintenance of broken wheels) on the Performance model are why I went with the Long Range. I wish Tesla offered the 18" aero wheels on the Performance model, but I'll settle for the LR with Acceleration Boost.
I like Jason too . . . at least in terms of his personality. But he's really kind of a tech wannabe. Sort of knows a little but definitely does not know a lot.
P-Lo801
Member
Yeah, I still don't quite understand how 18s (without the aero cover) are more efficient than 19s, and so forth, when they're all the same diameter overall, assuming they all have the same low rolling resistance tires across the board.
I remember reading how inertia has something to do with it, but that was not mentioned in this video.
I remember reading how inertia has something to do with it, but that was not mentioned in this video.
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Clivew
Member
Because most of the aerodynamic drag produced by the wheel is ventilation drag. This is where the high pressure air within the wheel well and inside the wheel flows out through openings in the rotating wheel to the low pressure area adjacent to the wheel face.
As the air flows past the wheel spokes it creates drag, and the larger the wheel diameter, the bigger the moment arm of the drag force, due to the longer spokes.
The smaller 18” wheel with aero cover reduces this drag further due to a smoother transition through the wheel which causes less turbulence when this air meets the air flowing across the wheel face.
P-Lo801
Member
So theoretically, a mesh wheel versus one with only five spokes, would be more efficient, right? All things being equal like size and tires?
Clivew
Member
It very much depends on the actual spoke design, and how smoothly the air flows past and around the spokes. You’d have to carry out proper aerodynamic testing in a wind tunnel to obtain a definitive answer.
Dolemite
is my name
I felt the same way after watching this video - it also wasn't crystal clear to me that the data that Tesla submits to the EPA purely focuses on wheel diameter changes. It's not like the 20" wheels comes with a 20" MXM4. That would be hilarious.
Additionally, why doesn't he discuss the fact that a car has 4 wheels and not 1? Shouldn't his conclusion for rolling resistance be multiplied by 4, for example?
Dolemite
is my name
Also the proselytizing about the "environmental benefits" of driving a smaller wheel was pretty lame. If you wanna "make a difference," go live among the Hmong in Sapa instead of buying a $50K+ 4,000+ lbs EV with 500+ hp/tq that consumes its own tires for breakfast. ffs
That's pretty much what I tell people when they say it's great for the environment... 'anything I contributed gets taken away with the copious amounts of rubber left at nearly every stop light.'
See above post by Clive as to why this is not really true. His resume in this area is professional. So he's not speculating as an amateur. And stickiness per se is not the problem it's probably more trade-offs between rolling resistance/hysteresis, traction, tread compounding , and other tread and belt variables. I suspect you could get a low hysteresis Tire with a super soft tread that would stick like crazy and still get great mileage. But they would wear like Gumball erasers
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Please advise on how you get wheel spin in the model 3 from a standing start?
XLR82XS
D M C
Watts_Up
Well-Known Member
every single time you launch the car you get wheel spin. How do you think the computer knows how to nerf the power or enable traction control? It’s not magic.
just because you don’t see large clouds of smoke doesn’t mean you’re not spinning.
Apone
Member
Care to provide any proof for these claims? Contradicts what everybody else has observed. So it's possible your car is doing this but maybe you should attach a video.
Additionally you're wrong on the issue of "the computer" (traction control system) dialing back power. The car simply does not have enough power from launch to spin the tires as this would require more than 1.2 G's of launch Force. Because of the problem of torque Ripple in the permanent magnet switched reluctance rear motor, most people believe that it's not capable of 1.2 G's of force.
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