Wheel Size - Effect on Range and Comfort

[jsro]

We have an R1S and a Model S. I'm looking to get a new EV truck. In shopping, it seems that all the EV trucks are now coming with huge wheels. The R1T has 22s, and I think the Silverado and Sierra come with 24s. Does anyone know why? I thought these bigger wheels hurt range and decrease comfort. Why go to the expense of putting in air springs if the tires are so thin that the ride quality is subpar?

Sponsored

 

[DeafPug]

I'm not so sure that large tires (the rubber part) - the size of the wheels (the metal center) in the case of calling out 22" and 24" diameter - impacts the range of the vehicle that much. It matters more about the tread pattern and rubber compound on the tires chose as they change the wheel size. In the case of Tesla, as the wheel size goes up for a specific vehicle, they use more performance minded tires, so the range drops. In the case of Rivian, they put more aggressive all-terrain tires on the smaller wheels so the range goes down as the wheel size goes down.

 

[R1Thor]

We have an R1S and a Model S. I'm looking to get a new EV truck. In shopping, it seems that all the EV trucks are now coming with huge wheels. The R1T has 22s, and I think the Silverado and Sierra come with 24s. Does anyone know why? I thought these bigger wheels hurt range and decrease comfort. Why go to the expense of putting in air springs if the tires are so thin that the ride quality is subpar?

2 things, as was just mentioned above: rolling resistance is the biggest factor. Period. And that's going to be characteristic to combinations of tread depth, tread pattern, coefficient of friction, siping, and road conformance of the rubber (ie: how much distortion in the contact area under accelerations).

We can talk about Newtons laws and fundamental characteristics of tires that affect range and efficiency, but I've already covered that in another, very long, very detailed thread.

But, what's more important to recognize is that wheel sizing is mostly dependent upon:
1- clearance around the hubs and brakes (remember, you're driving a 7000+lb vehicle, which is rated to tow upwards of 11,000 more pounds-mass. YOU NEED big brakes, and I cannot lie...)
2- structure and strength of the wheels themselves (going to need more material to support more mass, especially for rotational and shock loads--unless you avoid every pothole you possibly can). Distributed force across those impacts is important. It may be potentially mitigated by distribution across a larger sidewall tire, but see #1, and also consider what then you'll be increasing your tire pressure to in order to accommodate larger (overall rubber to metal ratio) tires versus the wheels
3- there is some lateral force that you're going to have to compensate for. Too much sidewall = increased lateral shearing. Ever drive a vehicle where the tire popped off because you were cornering too hard? Me neither, but I know people who have (I used to be into the modified cars scene and people did some silly things...) and it's not fun for anybody!

But again, you have a VERY heavy vehicle with A LOT of torque, rotational mass, clearances to consider and a lot of forces to be able to manage. And that has to factor across different surface types (asphalt, cement, bridges, off-road, etc), weather and climate, environmental conditions, load variations (passengers, towing, payload, etc)...

And as an Engineer, I can tell you: we don't do that worst-case math and say "that oughta do it." We then assign a factor of safety to it, and it's going to be in the order of magnitude to prevent us from being wrong (and liable), and to accommodate for manufacturing variance.

 

[Kaiju]

You might come to find the answer is not really rooted in engineering. Smaller diameter wheels and tires are more efficient, but you won't ever find the most efficient answer on a production vehicle because it will look stupid. While you need a certain minimum size for the brake calipers to clear, most huge wheels/tires are to do with marketing and aesthetics because the vehicles don't actually need to be big as they are.

The bodies of trucks and SUVs in particular have been getting progressively taller and there's a ratio of the wheel to body size that people see as appropriate and/or cool. Aesthetic trends have been towards bigger rims vs tires, even though that's typically heavier and less efficient. You have 24" wheels on a Silverado EV for the same reason you can't reach over into the bed from the outside any more. A set of 20" wheels with similarly low profile tires will look comically undersized vs the body, and it seems your average consumer prefers rubber band tires with huge rims because that manifests in every 'upgrade' option despite the fact it's a range hit and not a range increase. You'll see the efficiency option occasionally on F-250 work trucks with the smallest stock tire option and it looks silly even if it's the commercially correct answer.

Thicker sidewalls also tend to ride and spring better on top of absorbing hits from things like potholes. For truck stuff and ride quality, more rubber is better. But better is not what consumers always want.

 

[LL75]

Effective diamter is what you would look for. Rivian's 20 effective diamters are larger than their 21" and 22". It doesn't help that 20" only comes in AT tires as well where 21" and 22" are AS.

 

[tps5352]

...it seems that all the EV trucks are now coming with huge wheels. The R1T has 22s, and I think the Silverado and Sierra come with 24s. Does anyone know why? I thought these bigger wheels hurt range and decrease comfort...

I authored this post about Rivian wheels & tires. My 2021 Tesla Model X came with 22-inch wheels and relatively low profile 30-inch tires. I immediately switched to (OEM) 20-inch wheels and (OEM) higher-profile 30-inch tires.

My understanding and belief is that large wheels and relatively low-profile tires are currently somewhat of an automotive fad. I.e., they are in fashion. Why?

I think that the basic idea/trend probably originated many years ago with high-performance, competition, and/or exotic sports and racing cars. Over time the look caught on and eventually spread to many (sporty) consumer vehicles.

There seems to be no doubt that large wheels (up to a point) and low-profile tires result in:

• Better handling at speed and when cornering.
• Better acceleration and overall performance.

But unfortunately they can also result in:

• Greater chance of tire damage.
• Greater chance of wheel damage (e.g., from potholes and road debris).
• Faster (unsafe?) deflation (if/when there is a leak).
• Noticeably poor ride comfort.
• Possibly more road noise.
• Less mileage/range.*
• Faster rate of tread wear.

Plus, being fashionable, they can often be more expensive.

So why do regular consumers (who are probably not active street racers) want to spend more for an arguably poorer tire choice? Simple; looks. It is what is in style, and a lot of manufacturers are jumping on the band wagon by giving consumers what they want (and not necessarily what they really need).

I wouldn't mind except that (possibly to reduce costs) Rivian is not offering arguably more-sensible wheel/tire choices (like a more comfortable and durable 20-inch wheel combo with with higher-profile all-season or touring tires).

That's my two-cents worth.
_____
* To be fair, I've seen reports that low-profile tires give better mileage/range. Such claims may stem from the typically more shallow tread design found on performance tires in comparison to deeper, more aggressive all-terrain tire treads.






Quote Reply

Report

 

[UnsungZero_OldTimeAdMan]

It’s not so much about the wheel size, but the wheels and the tires they are paired with, in totality—each combo selected to meet demands of different needs.

Sponsored