Size matters is 18” the right size?

[Huntsman]

How does the size of the wheel affect efficiency?

Tesla has offered an 18” wheel on the single motor and 20” on the dual and tri motor.

Other manufactures do this and adjust the sidewall height so both wheels have the same circumference for software and hardware reasons. Assuming the tire circumferences are the same, there is likely a weight difference, the larger wheel being heavier would contribute greater centrifugal energy and tend to keep things in motion. Inversely it would require more energy to get things in motion on a larger wheel. It has been said that heavier wheels exponentially detract from efficiency and that is the reason auto makers went to aluminum wheels 2 decades ago. Today we are told the opposite, larger wheels are heavier and they make the vehicle remain in motion therefore contributing to efficiency.
Which is it? EV’s also have the dynamic of regen during deceleration to consider. On the Ford Lightning website the Platinum trim level has wheels 2” larger than the Lariat and a range reduction of 20 miles because of the larger, heavier rims, according to Ford.

If larger rims detract from overall range and efficiency, why does Ford mandate when you order the extended range battery on the XLT, you must also upgrade wheels from 18” to 20”? This seems to suggest if you order the bigger battery you should be handicapped with bigger wheels.

While Ford offers 18, 20, and 22” wheels, the question applies similarly to Tesla - rather than have the single motor with 18” wheels, dual and tri with 20” - why not have the most efficient size wheel on all models?

If 18” and 20” wheels have equal sidewall height and therefore different circumferences - one revolution of the 18” wheel would travel a lesser distance than one revolution of the 20” wheel suggesting all vehicles should have really large wheels except for the reality that a larger wheel requires more energy to rotate one revolution compared to a smaller lighter wheel.

Why have manufacturers gone to larger and larger wheels? Twenty years ago wheels were 15”, now they are 20-22” certainly heavier due to the increase in size Dealerships justify the wheel sizes saying the public has demanded this look.

Two decades ago manufacturers told us they went to aluminum wheels over steel wheels because they had to reduce the weight of the vehicle to achieve EPA mandated economy, that is, wheels need to be lighter.

So in 25,000 words or less, I have posed my question - what is the most efficient wheel size on an automobile - how does size affect efficiency?

Should we return to 15” wheels and have them all aluminum to reduce weight, do we need heavy steel 22” wheels to have the best range, or is the 5 lbs difference in wheel weight negligible on a 6000 pound vehicle?

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[Rutrow]

Why have manufacturers gone to larger and larger wheels? Twenty years ago wheels were 15”, now they are 20-22” certainly heavier due to the increase in size Dealerships justify the wheel sizes saying the public has demanded this look.

Larger brake rotors and calipers will only fit inside certain size wheels. Check me on this, but I read somewhere (on this forum?) that T Sportline said that 20" was the smallest wheel that would fit over the Foundation Series brake components. Might the RWD's brakes fit in smaller wheels? We'll see... I'd prefer smaller wheels with higher sidewall tires, better for airing down in sand, mud, etc.

 

[SolarWizard]

Larger brake rotors and calipers will only fit inside certain size wheels. Check me on this, but I read somewhere (on this forum?) that T Sportline said that 20" was the smallest wheel that would fit over the Foundation Series brake components.

That is what they stated. Whether thats accurate or they just dont have an 18” wheel to sell remains to be seen.

 

[CyberGus]

 

[Woodrick]

It truly is the million dollar question, but you are also leaving out things like the tire hardness. That's a big factor for Tesla's cars and why they run them at 42 psi. Rolling resistance is a big deal.
The difference between the Foundation's All-Terrain tires and the All-Weather ones is 20 miles of range.

I hadn't heard the Tesla had decided on much of anything for the RWD, there may be speculation, but it's over a year away. Cost will be a big driving factor for it.

But as an EV owner for 9+ years, range is overrated. It's not as important as most people think it is. It barely effects anything.

Now, on the early Nissan Leafs, with 88 mile range, range was indeed important. Once you pass 200 EPA blended, it's not that big of a deal.

In other words, many existing Tesla owners put various tires and wheels on the car for various reasons and don't really care what the range impact is.

 

[scottf200]

Brainstorming exercise using BARD. The unsprung weight is commonly discussed.

Question:
Consider these two related questions:
1) what is the most efficient wheel size on an automobile - how does size affect efficiency?
2) Should we return to 15” wheels and have them all aluminum to reduce weight, do we need heavy steel 22” wheels to have the best range, or is the 5 lbs difference in wheel weight negligible on a 6000 pound vehicle?

Answer:
Wheel Size and Efficiency: A Balancing Act
There's no one-size-fits-all answer to the most efficient wheel size for an automobile as it depends on a complex interplay of factors. Here's a breakdown:
How size affects efficiency:

• Larger wheels:
  • Pros:
    • Can potentially improve handling and performance.
    • May offer a smoother ride over bumps.
    • Sometimes allow for larger brakes, which can improve stopping power.
  • Cons:
    • Generally heavier, increasing unsprung weight, which reduces acceleration and fuel economy.
    • Require wider tires, which also have higher rolling resistance, further impacting fuel efficiency.
    • Can decrease ride height, affecting aerodynamics and potentially increasing drag.
• Smaller wheels:
  • Pros:
    • Lighter, reducing unsprung weight and improving acceleration and fuel economy.
    • Often require narrower tires with lower rolling resistance, further aiding fuel efficiency.
    • Can raise ride height, potentially improving aerodynamics and reducing drag.
  • Cons:
    • May compromise handling and performance, especially in high-performance vehicles.
    • May not accommodate larger brakes, limiting stopping power.
    • Offer a less smooth ride over bumps.

15" vs 22" wheels:

• Returning to 15" aluminum wheels: This could be a good option for prioritizing fuel efficiency on a large vehicle like a 6000-pound car. The weight reduction and lower rolling resistance of smaller wheels can potentially offer noticeable fuel savings.
• Heavy steel 22" wheels: These typically prioritize aesthetics and performance over efficiency. Their weight and wider tires will likely have a negative impact on fuel economy.
• 5 lbs difference negligible? It's not entirely negligible. While 5 lbs may seem small compared to a 6000-pound car, it's a significant increase in unsprung weight, which can directly impact acceleration and fuel consumption. Studies have shown that even small reductions in unsprung weight can improve fuel efficiency by 1-2%.

Ultimately, the best wheel size for efficiency depends on your priorities:

• Fuel efficiency: Prioritize smaller, lighter wheels with narrower tires.
• Performance and handling: Larger wheels may be beneficial, but consider compromising on fuel economy.
• Balance: A mid-size range (17"-18") with lightweight materials can offer a good balance between efficiency and performance.

Remember, other factors like driving style, tire pressure, and terrain can also impact fuel economy. Experiment and find the sweet spot for your vehicle and needs.

 

[Huntsman]

That is EXACTLY what I wanted to know. Thanks for sharing that link.
Now, can we get Tesla to sell a dual motor with 18” wheels? Ha!

 

[SolarWizard]

That is EXACTLY what I wanted to know. Thanks for sharing that link.
Now, can we get Tesla to sell a dual motor with 18” wheels? Ha!

There are nearly zero truck tires in 19”

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