Engineering Explained- wheel size effects on electric cars

[Let's Drive]

Understand but he can't say that a larger wheel will cause this. You can put a 19" eco wheel designed for EVs vs an 18" wheel, for example the Tesla Model 3 wheel without hub caps and the 19" wheel will be more efficient.

Jason didn't just say it, he also showed the numbers. @Clivew also explained the difference diameter makes, given the same wheel (and other variables being equal). If you change the wheel design, as you have in your scenario, you're now arguing outside the point.

 

[freeAgent]

Well I'm not disagreeing with Newtonian mechanics. But I think we might not agree on where wheel weight sits in a sequence of quantifiable efficiency losses. For sure it comes after general body aerodynamic losses, after wheel aerodynamic losses and also after rolling resistance losses. I'd describe it as minimal in that sense and almost academic. Would you agree?

No, we fully agree

 

[ianc]

You seem to be ignoring the phrase 'same design' which I have previously posted three times (shown below).

Not ignoring it, but it isn't relevant to the content of the video which this thread is predicated upon, which is the blanket statement that big wheels = BAD, small wheels = GOOD, which is just patently not true. In fact a larger wheel can be just as efficient as a smaller wheel if designed correctly.

Some clown over at Jalopnik watched this silly video and couldn't stop himself from writing an article about it:

Why Big Wheels Clobber Efficiency And Slash Your Car's Range

That's all i have to say on the matter...

P.S. thanks for the C&D link, I wouldn't have thought it was that significant...

 

[Let's Drive]

Not ignoring it, but it isn't relevant to the content of the video which this thread is predicated upon, which is the blanket statement that big wheels = BAD, small wheels = GOOD, which is just patently not true. In fact a larger wheel can be just as efficient as a smaller wheel if designed correctly.

Gotta say, that's not my takeaway from the video or finer points of the thread. From what I'm reading, the statement does serve as a general fact (I'd reword it, personally), followed by some people who seem focused on arguing the exception. In general, it's understood that larger wheels create a bigger efficiency hit, and you've reinforced this idea in an indirect way, by claiming the increased diameter can be compensated for if "designed correctly". However, logic would dictate that if you reduce the wheel diameter and utilize the same "designed correctly" approach, efficiency would improve.

All that to say, if you're designing primarily for efficiency, you steer away from a bigger wheel, on principle. In my experience, bigger wheels are primarily about aesthetics, brake clearance and tire sizing options. Engineering is about compromise, so we'll see a variety of wheels out there, which is a good thing. Otherwise, the video already discussed the effect of the tires contact patch and rolling resistance, which would be the other two main contributors.

 

[chinney]

[...]

There is consensus that range can be improved by using wheel covers that are designed for range efficiency.

Any ideas on how to find an aftermarket wheel cover that would improve range?

https://www.fastwheels.ca/productinfo.aspx?wn=ev01(+)&fn=titanium

 

[chinney]

The underlying question I have is if there are any advantages to having the larger wheels on a Model 3. The 18-inch wheels are already pretty big. Aside from the 'look' (which is subjective - I personally do not like the appearance of the larger wheels), do they actually do anything? Better handling maybe? Anything?

 

[Webeevdrivers]

The underlying question I have is if there are any advantages to having the larger wheels on a Model 3. The 18-inch wheels are already pretty big. Aside from the 'look' (which is subjective - I personally do not like the appearance of the larger wheels), do they actually do anything? Better handling maybe? Anything?

A bunch of you tube videos indicate the handling is better, and some suggest the acceleration is better although I’m not sure why that would be the case.

I don’t have the 19’s but I like the look better with the silver 19,s. Than the stock 18’s. I am tempted to buy a used set but am waiting to see if the new Orbital silver Aero covers go into production. If they do I’ll just get a set of those.

 

[dfwatt]

The underlying question I have is if there are any advantages to having the larger wheels on a Model 3. The 18-inch wheels are already pretty big. Aside from the 'look' (which is subjective - I personally do not like the appearance of the larger wheels), do they actually do anything? Better handling maybe? Anything?

Obviously beauty is in the eye of the beholder but your judgment of the Aesthetics is definitely the minority opinion. I'm not saying you're wrong I'm just saying most people like the look of larger Wheels although I think twenty ones are too big for the car. 20s look great, 19's look okay but I think the 18-inch wheel looks too small but again this is all just personal opinion. What is not personal opinion are the trade-offs which I'll enumerate below.

CONS of larger wheel size:

1) greater cost for wheel and also for tire because you are talking about radically low-profile (35 and even 30 series and Below)
2) greater vulnerability to road and curb impact damage again for both Wheel and Tire.
3) greater unsprung weight. Although tire might be slightly lighter due to smaller sidewall, wheel is definitely more heavier than tire is lighter(and difference in tire weight is often times minimal when you compare tires of same tread width).

PROS of larger wheel size:

1) Aesthetics (with the above caveats)
2) somewhat greater stability of tread contact patch under extreme load - although this is debated by many. But shorter sidewall does mean a somewhat more immediate steering response to transient inputs. This is not debated.

You would be absolutely correct if you scan this list of pros and cons and come to the conclusion that the cons mostly outweigh the pros. However and again this is worth emphasizing, all the manufacturers of elite Sports Sedans and Exotics have gone to increasingly larger wheel sizes and radically low profile tires. In other words this is kind of a dominant meme out there in the sports car world. Whether that Meme deserves its unequivocal acceptance is another question. It's likely that the dominance of this meme is coming simply from aesthetics and a certain look that has become 'de rigour'.

In any case there's tons of discussion on this forum about how the OEM 20 inch wheels which are cast and heavy are not very sturdy and prone to deformation and even fracture from curb and pothole impacts. I've had several aftermarket wheels some of which have deformed but several of which have not because they were better made. So if you get a forged wheel from a good manufacturer you can mitigate some of the vulnerability to impact damage. A lot of that is on the driver to minimize the risks re: Wheel and Tire Damage from impacts, and obviously no wheel is going to tolerate impacts with curbs.

 

[chinney]

Thanks for the replies. Interesting, although a lot of it does seem to come down to a subjective feeling about 'look'. For somebody like me who actually does not like the 'big wheel' look, would it be possible to run a Model 3 with 17-inch wheels with slightly bigger tire sidewalls? Would there be a further efficiency gain? Or is 18-inch the smallest wheel that the Model 3 ought to take for other reasons?

 

[dfwatt]

Thanks for the replies. Interesting, although a lot of it does seem to come down to a subjective feeling about 'look'. For somebody like me who actually does not like the 'big wheel' look, would it be possible to run a Model 3 with 17-inch wheels with slightly bigger tire sidewalls? Would there be a further efficiency gain? Or is 18-inch the smallest wheel that the Model 3 ought to take for other reasons?

If you have the performance brakes I don't believe there's a 17in wheel that will fit. And there may be a point of declining returns actually around smaller wheel sizes. The efficiency gains have to do more with wheel aerodynamics than wheel weight. Wheel and tire weight really don't have that much of an impact on efficiency especially when you factor in regen braking. Minimal effects of wheel weight on efficiency compared to aerodynamics and rolling resistance.

 

[chinney]

Thanks. I will probably stick with the 18-inch wheels then. I have always liked the look of a slightly bigger sidewall though and I think it gives a bit of a softer ride, so a smaller set of rims would have been an interesting option to consider, especially for winter driving, had it been available. I stepped down a size in rims for my previous ICE vehicle, compared to OEM, when it came time for winter and was just speculating about whether that was possible for the Model 3 (with OEM 18").

But overall, I have no complaints about how my Model 3 (with the 18-inch wheels) drives. Quite the opposite: nicest car I have ever driven, by far.

 

[XLR82XS]

FWIW: I find the vehicle handling much improved on 19" over 18". Difference is enough that I would never have the 18s.

 

[FlatSix911]

Here is a documented example of the positive effect of smaller wheels on vehicle EPA range...
2021 Porsche Taycan 4S gets 10% more EPA range. We tell you why (electrek.co)

Porsche simply did not use the monster 21-inch wheel option in its EPA calculation in which it chooses the worst case scenario to report. Apparently, the 2021 is the exact same car as the 2020 as far as the drivetrain is concerned. The only difference is that the high-drag 21-inch wheels were not reported from/to the EPA. That same source told us that almost no one buys those wheels, as most people stick with the 19s or 20s. Those huge wheels come standard on the Taycan Turbo S so the calculation stands there.

The 20-inch wheels apparently make the Taycan over 10% more efficient, which is seemingly a huge gain.
In the case of the Taycan 4S, it added 24 miles of range. The 19-inch wheels/tires are apparently even more efficient.

 

[Zoomit]

Here is a documented example of the positive effect of smaller wheels on vehicle EPA range...

It’s also a classic example of discounting the effects of different tires. There’s no mention of whether the tested tires are different between the two wheel sizes. A lot of people think in terms of the two digit number representing wheel size, whereas the tire can easily have a larger influence on range.

 

[felizf]

After doing extensive research I've come to the conclusion that the aerodynamic of the wheel plays a much bigger role than the weight. Don't believe me? Check out the efficiency comparison between a performance model y vs a long range with the 19" aero wheels done by i1tesla. They drive side by side same speed on the highway and get similar efficiency..... Weight of the wheels only really matters when city driving.... And yes the performance is lower than the awd so it will help with efficiency...

 

[mcbarnet007]

A larger diameter wheel produces more ventilation drag and thus reduces range compared to the same design wheel of a smaller diameter. This is a hard fact.

Air is not ‘sucked’ into the wheel well. The wheel well/wheel arch is an area of higher pressure* (when the car is moving) and this causes the air to flow out the wheel well, some of it through the wheel openings, creating drag.

*High performance vehicles such as the Porsche GT3 RS have louvres in the top of the front wheel arches which help reduce wheel well air pressure and thus increase front downforce and grip.

doesn't most modern car including Model 3 have some sort of wheel well pressure relief into the front windshield area?

 

[67King]

ONe thing I did not see mentioned is inertia (apologies if I overlooked it). It isn't so much the mass of the wheel, but the wheel's inertia. I=m*r^2 - an equation I'm sure anyone who has played around with turbos knows quite well! That's for a uniform disk. But wheels aren't uniform. So the inertia is proportional to the radius of the center of the wheel/tire combo's mass. In other words, as you get larger in wheel size, the increase in inertia goes up exponentially, not linearly.

Well that's all well and fine, but what does inertia have to do with anything? Steady state, nothing. Conservation of inertia. However, as you accelerate, it takes more energy to overcome the inertia of the larger wheel. Of course, when you decelerate, if you only use regen, it can be recovered (ignoring inefficiencies).

BTW......my 67GTO does not have traction control. At the various stages of its life (currently completely apart being restored) when it was on the road, it could absolutely roast tires. It is an automatic (well, was.....that has already started to change), so there wasn't any sort of clutch dumping. The 3 blows the doors off of it. And besides, doesn't the track mode give one the ability to disable traction control and do burnouts?