Why big wheels are a bad idea on electric cars - range impact!

[sockmeister]

To add onto this, a larger wheel is going to have more mass than a smaller wheel/fatter tire combo, and therefore more weight. Rotating mass has much more of a range and efficiency impact than stationary mass.

The larger a wheel gets, the more massive the overall tire/wheel weight combo gets.

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[agoldman]

I'll take the impact. The wheels make the car!

 

[dbsb3233]

This may be borderline heresy... But I wonder if there will be aero covers available for the 19" wheels. Depending on how easy they are to remove, it'd be a nice option to have for road trips.

Back in my day, those used to be called hubcaps!

Seriously though, if they really make that much difference in efficiency (range) at high speed, I'd GLADLY slap some smooth hubcaps on when heading out on a road trip (even if it taints the looks). Then I'll just take em off when I get home where I really don't give a damn about range.

 

[dbsb3233]

To add onto this, a larger wheel is going to have more mass than a smaller wheel/fatter tire combo, and therefore more weight. Rotating mass has much more of a range and efficiency impact than stationary mass.

The larger a wheel gets, the more massive the overall tire/wheel weight combo gets.

But also the more energy to get it up to speed to begin with. Seems like the laws of physics would suggest that you can't really come out ahead by adding total weight, unless that weight inherently adds more energy (like charged batteries), or is used to reduce drag.

 

[DBC]

Engineering Explained posted a comment on the video's YouTube page that clarifies his point in the last part of the video:

Thanks for the cite but I don't think the explanation is persuasive. For starters, increasing efficiency by 3% can't explain a claimed range difference of 8%-15%. Plus, unlike the original eco cars like the EV1 or Honda Insight, current BEVs don't use wheel covers. My understanding is that manufacturers don't use these because you don't need them if the tire fills the wheel well.

I think the bigger reason why smaller wheels are more efficient -- not arguing about that -- is the increase in mass and moment of inertia attributable to the larger wheels.

Interesting that the CA Route 1 with 18" tires has the same range as the Premium RWD with 19" tires. I wouldn't expect that to be the case. If it is then a rethinking of the idea that smaller tires mean more range would be in order.

 

[dbsb3233]

Thanks for the cite but I don't think the explanation is persuasive. For starters, increasing efficiency by 3% can't explain a claimed range difference of 8%-15%. Plus, unlike the original eco cars like the EV1 or Honda Insight, current BEVs don't use wheel covers. My understanding is that manufacturers don't use these because you don't need them if the tire fills the wheel well.

I think the bigger reason why smaller wheels are more efficient -- not arguing about that -- is the increase in mass and moment of inertia attributable to the larger wheels.

Interesting that the CA Route 1 with 18" tires has the same range as the Premium RWD with 19" tires. I wouldn't expect that to be the case. If it is then a rethinking of the idea that smaller tires mean more range would be in order.

The whole topic seems ripe with contradictions, and things that don't seem to make sense.

Wider tires being worse makes perfect sense (more rolling resistance and more air resistance). But tire & wheel height seems to conflict on multiple points. I'd like to see Jason do a Part II to that video to tie it all together.

 

[timbop]

Interesting that the CA Route 1 with 18" tires has the same range as the Premium RWD with 19" tires. I wouldn't expect that to be the case. If it is then a rethinking of the idea that smaller tires mean more range would be in order.

I am certain the Route 1 WILL get better efficiancy/range, but it probably isn't worth it to Ford to have to do a whole other set of tests for a car that only garners a small fraction of sales (at least based on the order database here). From an EPA rules perspective it is OK to underspecify the Rt1's efficiency by lumping it in with the 19" non-aero covered premium cousin.

 

[dtbaker61]

This may be borderline heresy... But I wonder if there will be aero covers available for the 19" wheels. Depending on how easy they are to remove, it'd be a nice option to have for road trips.

the DIY ev crowd has lots of solutions for hypermiling wheel covers, and skirts on the rear.... which make a pretty big difference at highway speed, but look like hell. Simplest is to find the right size pizza pan, and just drill thru and tek-Screw that baby right into your wheel spokes!

...probably not what many of us would do, but it works

Major factors of rolling resistance are the combination of rubber compound hardness, sidewall flex, belt weight (steel/kevlar, et), and width all determining the contact patch and deformation resulting in heat. Opposing considerations may be comfort depending on your local road conditions and whether you do mostly highway, urban, or suburban miles.

where I live, in Santa Fe, the City/County roads are crap.... pothole, storm grates, water valve covers, bridge joints not at-grade gravel, dirt roads, etc, etc... Low profile tires are a BAD idea, unless you can afford to replace wheels with bent rims.

 

[dbsb3233]

the DIY ev crowd has lots of solutions for hypermiling wheel covers, and skirts on the rear.... which make a pretty big difference at highway speed, but look like hell. Simplest is to find the right size pizza pan, and just drill thru and tek-Screw that baby right into your wheel spokes!

...probably not what many of us would do, but it works

Major factors of rolling resistance are the combination of rubber compound hardness, sidewall flex, belt weight (steel/kevlar, et), and width all determining the contact patch and deformation resulting in heat. Opposing considerations may be comfort depending on your local road conditions and whether you do mostly highway, urban, or suburban miles.

where I live, in Santa Fe, the City/County roads are crap.... pothole, storm grates, water valve covers, bridge joints not at-grade gravel, dirt roads, etc, etc... Low profile tires are a BAD idea, unless you can afford to replace wheels with bent rims.

If it's only gonna make 5 miles difference in range (based on the EPA rating of 305 for the Rt1 vs 300 for the regular), then I'm not gonna bother looking at aero covers. That's not enough to really make a difference on a handful of long road trips.

 

[timbop]

If it's only gonna make 5 miles difference in range (based on the EPA rating of 305 for the Rt1 vs 300 for the regular), then I'm not gonna bother looking at aero covers. That's not enough to really make a difference on a handful of long road trips.

The actual number is 14 miles (5%), at least according to the docs insideevs dug up. I'll agree that still isn't very much, and for that reason I'm going to see what the wheels look like under the aeros. But, for long trips I'll probably put them back on, depending upon how much of a PITA they are. I can't tell if the aeros just clip on, or if the lug nuts are also holding them in place.

 

[ChasingCoral]

Low profile tires are a BAD idea, unless you can afford to replace wheels with bent rims.

I've always thought low profile tires looked dumb anyway.

 

[sockmeister]

This may be borderline heresy... But I wonder if there will be aero covers available for the 19" wheels. Depending on how easy they are to remove, it'd be a nice option to have for road trips.

I was searching around to see if anyone had asked this question before, as I have the same one.
I'm interested in having removable aero covers for roadtrips.
Would be great if the 19" ones on the Ca Rt.1 fit onto the premium wheels. I'm waiting for the part to become available somewhere to take a look at.

 

[timbop]

I was searching around to see if anyone had asked this question before, as I have the same one.
I'm interested in having removable aero covers for roadtrips.
Would be great if the 19" ones on the Ca Rt.1 fit onto the premium wheels. I'm waiting for the part to become available somewhere to take a look at.

The route 1's wheels are 18", not 19". Also, if you look closely at how they're molded, they wouldn't line up properly with the spokes of the premium's wheels.

 

[woody]

Sooooo....... The Ford engineers know not what they do. What is a poor boy to do? Redesign the whole car? Methinks not.

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