How Wheel Size Impacts Tesla Model S, X Efficiency

3 days ago by Steven Loveday 24

Tesla Model S

Tesla Model S P100D

Wheel size impacts range on all vehicles, but it has a greater influence on Tesla vehicles than you may expect.

According to older documents just recently released by the Environmental Protection Agency (EPA), Tesla vehicle efficiency sees a measurable change dependent on wheel size. Electrek shared Teslike’s analysis of the newly acquired data, which was posted on Tesla’s Redditt. Being that range is one of the most important considerations when deciding to make the switch to an EV, and these results are so compelling, it’s surely worth mentioning.

Tesla

Tesla Model X

The EPA conducted these tests nearly a year ago (December 2016). However, results were just publicized. Teslike’s summary of the results are as follows:

  • 4.9% more consumption for Model S P100D with 21″ vs 19″ wheels.
  • 5.2% more consumption for Model S P90D with 21″ vs 19″ wheels.
  • 11.6% more consumption for Model S 60/75 with 21″ vs 19″ wheels.
  • 11.8% more consumption for Model S 60D/75D/90D with 21″ vs 19″ wheels.
  • 22.2% more consumption for Model X P90D with 22″ vs 20″ wheels.
  • 22.5% more consumption for Model X 60D/75D/90D with 22″ vs 20″ wheels.
  • 23.3% more consumption for Model X P100D with 22″ vs 20″ wheels.

A screenshot of the EPA data from Reddit is shown below. The reports for other Tesla vehicles are available by following the Reddit link at the bottom of the page:

EPA documents show how wheel size affects Model S/X consumption. from teslamotors

As Electrek points out, the EPA performed some of the tests using a dyno at slower speeds (50 mph). This is not representative of highway speeds, wind resistance, or road conditions. However, the results are still telling.

Sources: Reddit via Electrek

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24 responses to "How Wheel Size Impacts Tesla Model S, X Efficiency"

  1. Terawatt says:

    That bigger wheels are less efficient isn’t really news, but very interesting to see the numbers. The 22 vs 20 on the X is shocking!

    It’s also a little unintuitive. For steel to steel (think railways) the rolling resistance is inversely proportional to wheel diameter, so the bigger the wheel the less energy is lost to rolling it.

    I wonder if the reason is just aero alone or if there are any other major factors.

    There’s many reasons to choose smaller wheels. Efficiency is one. Cost is another – tires are much more expensive for the note exotic wheel sizes. And if smaller wheels are combined with higher profile tires you also get less noise and better ride comfort. In some circumstances it can even improve road holding and reduce stopping distances.

    But big wheels are sexy. And in a culture as sex-driven as the West, this apparently more than makes up for all their disadvantages.

    1. SparkEV says:

      I was also thinking if it’s something else. People report as much as 10% loss in SparkEV’s efficiency simply by using different compound tires. It’s not at all clear if this test was only the wheel diameter and nothing else.

    2. Electric Steve says:

      Bigger wheels which have the same tire-width (245 for example), also have an almost identical outer-diameter (statistically almost irrelevant). So if the same tire-compound is used, there should be no relevant difference in range.

      But the 19’s on my 85 where more “eco” oriented, while 21’s have pure sports-tires and the different, softer compound is what makes the difference.

      1. Tom says:

        The weight of the rim has a major effect. Rotational forces matter a bunch. Compounds and tread too obviously. Snow tires for instance are less efficient. Width matters too.

        1. arne-nl says:

          The weight of the rim has no measurable effect on consumption.

          Suppose it makes the car slightly heavier (maybe 1%), it increases rolling resistance by 1% (everything else remaining the same). And rolling resistance is a relatively small component in energy consumption compared to air resistance.

          The shape of the rim is another thing. It can make a measurable effect in air resistance.

          1. arne-nl says:

            Oh, and inertia is an even smaller component in energy consumption in an EV due to regenerative braking.

    3. DL says:

      A 3 ton SUV is going to be a pig no matter what. Big sexy wheels only make it more of a pig.

    4. Dav8or says:

      -“But big wheels are sexy. And in a culture as sex-driven as the West, this apparently more than makes up for all their disadvantages.”-

      But who decided this?? Why are they sexy? I’ve thought now for the last decade that they are ridiculous. Big Conestoga wagon wheels, that’s what we need!

      I’m too old I’m sure and that’s the problem. I’ve also resisted all my life to be a slave to fashion and just liked what I liked. I grew up in an era where tires were a good thing and covering the ugly bits that stop and suspend the car was considered good design. The obsession with ever bigger wheels baffles me, but it’s harmless I guess and it keeps the tire shops in business, so to each their own I guess.

      I just can’t see the “sexy” in big, overdone wheels. I believe in proportion.

      1. jimjfox says:

        Agree. What is more ridiculous than a wheel so big that it can only fit an ultra-low profile tyre?

        Harsh noisy ride, huge extra cost, rim damage almost inevitable… sure there are more drawbacks but hey, the male ego must be polished.

  2. John in AA says:

    Does the moment of inertia vary with wheel size? You’d think it might, and that it might contribute.

  3. carcus says:

    The way I understand it ….. Most of the underbody drag comes from the air that spills out through the front wheels. Bigger wheels (even if the tire diameter doesn’t change much) means there’s more space for the air to get by the brake discs and out through the wheels — that equals more drag.

  4. SteveSeattle says:

    This is not really about wheel size. It is about the effect on rolling resistance of the wheel/tire combinations that Tesla sells on their vehicles. It is possible to see large variations even while keeping the same wheel size if the tire performance varies significantly.
    Add in drag and acceleration profiles and the overall effect on efficiency and range may be much smaller.

    1. jimjfox says:

      You know for a fact that these tests were done with a bunch of different tyres? I would have thought not, being objective.

  5. Yogurt says:

    Larger diameter rims equals more weight and worse ride comfort since larger tire sidewalls equal more suspension…
    Wider tires equals more traction and more rolling resistance and more aerodynamic drag…
    Larger diameter rims and wider tires also ware out suspension parts quicker especialy if they were not designed for the car…
    In gas cars putting larger and wider aftermarket rims on cars can lower gas mileage by a couple miles per gallon…

  6. Scott Franco says:

    So based on this we should put little 8″ tricycle wheels on the car…

    1. Counterpoint says:

      While smaller wheels give better fuel economy, bigger wheels give better handling and traction. The wheel sizes offered are all in the range of the handling and traction that would allow for optimum use of the car.

      Of the options, go for smaller wheels for longer range and bigger wheels for better maneuverability and braking.

      1. DL says:

        Bigger wheels have nothing to do with traction. Tire choice makes all the difference here; soft and sticky or hard and durable being the two extremes.

  7. CR says:

    Tire and wheel size have less to do with fuel economy than weight. The overall weight of the tire/wheel combination has the greatest effect on economy. The lighter that combination, the less energy it takes to begin the movement of that mass (inertia). I didn’t see where the author mentioned this fact.

    1. alohart says:

      For EV’s, shouldn’t the greater inertia of heavier wheels and tires also result in greater energy recovery via regen? Because regen is much less than 100% efficient, heavier wheels and tires would still result in greater overall energy consumption, but the penalty for EV’s might not be as great as for ICE vehicles without regen.

      1. Pushmi-Pullyu says:

        Yes, but at least according to one source I’ve read, energy recovery from regen is at best about 35%.** So as you say, the amount recovered is dwarfed by by amount lost.

        **That may not be true for all vehicles. If I understand what Elon said at the Tesla Semi Truck reveal, he’s claiming much much better energy recovery with the Semi Truck’s regen.

  8. arne-nl says:

    The difference is in the tires and the rubber compounds used to manufacture them. The 19″ tires are geared more towards economy and favour low rolling resistance over traction. The 21″ tires are optimized for performance and sacrifice rolling resistance for better traction.

    Larger rims does not mean larger tires, since the 19″ and 21″ have the same tread circumference. Larger wheels do mean lower rolling resistance due to less deformation in the contact area, but the wheels aren’t larger. Only the rims are larger. A fact that escaped many people.

    The 21″ tires are wider, also increasing air resistance.

    There will be a weight difference, but likely not much more than 1%. Weight affects consumption in two ways: by increasing rolling resistance and inertia. Both are minor components in the overall energy consumption, where air resistance dominates. Especially in an EV that can get back much of the kinetic energy put in during acceleration. But that depends a lot on driving style.

    And everyone is overlooking another important difference between the 19″ and 21″ rims: they have different shapes and therefore different air resistance, a much larger component in the overall energy consumption.

  9. Martin Winlow says:

    “The 21″ tires are wider, also increasing air resistance.” They increase the vehicle’s effective frontal area and therefore drag. But I can’t see this adding much more than a percentage point or 2.

  10. Nix says:

    This is why the BMW i3 has the narrow wheels/tires that it has.

  11. Peter says:

    Yes next goal for BEV car should be 1kW per 10 km driving.

    BMW i3 is close to that.

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