Engineering Explained- wheel size effects on electric cars

[Sam1]

Care to provide any proof for these claims? Contradicts what everybody else has observed. So it's possible your car is doing this but maybe you should attach a video.

Additionally you're wrong on the issue of "the computer" (traction control system) dialing back power. The car simply does not have enough power from launch to spin the tires as this would require more than 1.2 G's of launch Force. Because of the problem of torque Ripple in the permanent magnet switched reluctance rear motor, most people believe that it's not capable of 1.2 G's of force.

My statement doesn’t contradict anyone, because that’s the way traction control systems work is that they detect wheel spin and then they adjust the either the power or apply to brake to the spinning wheel. Not that hard to understand

 

[dfwatt]

My statement doesn’t contradict anyone, because that’s the way traction control systems work is that they detect wheel spin and then they adjust the either the power or apply to brake to the spinning wheel. Not that hard to understand

Thanks for that excellent clarification Sam. I didn't know that until you explained it to me so cogently. There's only one problem with your analysis and that is the assumption that the available torque clearly exceeds Tire grip on dry pavement. It doesn't. So that means the system never comes into play. Move on to the next issue.

 

[Sam1]

Thanks for that excellent clarification Sam. I didn't know that until you explained it to me so cogently. There's only one problem with your analysis and that is the assumption that the available torque clearly exceeds Tire grip on dry pavement. It doesn't. So that means the system never comes into play. Move on to the next issue.

don’t be dumb dude, you’re suggesting that every surface you drive on has enough grip to dead hook on a launch. That’s not happening, and if it did, Tesla would see a slew of broken drivetrain components from the shock that occurs when it does happen.

 

[dfwatt]

don’t be dumb dude, you’re suggesting that every surface you drive on has enough grip to dead hook on a launch. That’s not happening, and if it did, Tesla would see a slew of broken drivetrain components from the shock that occurs when it does happen.

Never said anything about the traction control system except on dry pavement. Move on Sam. You're stuck on this issue. Since you don't believe me why don't you just consult with senior track guys on the form. They can clarify for you when the traction control system is likely in play and when it is not. Maybe you can listen to them.

 

[Sam1]

Never said anything about the traction control system except on dry pavement. Move on Sam. You're stuck on this issue. Since you don't believe me why don't you just consult with senior track guys on the form. They can clarify for you when the traction control system is likely in play and when it is not. Maybe you can listen to them.

it’s not that I don’t believe you, because I wasn’t even validating your assertion since you weren’t aware of the basic function of how a traction control system works.

 

[Gasaraki]

Figured I’d link this since there have been a ton of threads on wheels and efficiency in here. Gives a lot more detail on all the aspects that affect range with wheel changes.

Watched that also when it came out. For people who disagree, it's obviously not exact.

Also my main problem is that the title is how the size of the wheels affect EVs but it's not really the size of the wheels. It more the width of the contact patch and rolling resistance of the tire. You can technically go with a bigger wheel but have the same contact patch width. In that case the size of the wheel wouldn't matter besides the weight difference assuming the tires are the same and the wheel itself sucking more air in to its wheel well.

 

[Gasaraki]

I like Jason too . . . at least in terms of his personality. But he's really kind of a tech wannabe. Sort of knows a little but definitely does not know a lot.

Nobody can know everything

 

[Gasaraki]

So theoretically, a mesh wheel versus one with only five spokes, would be more efficient, right? All things being equal like size and tires?

A mesh wheel will just let all the air in to the wheel area... How would that be more efficient?

 

[P-Lo801]

A mesh wheel will just let all the air in to the wheel area... How would that be more efficient?

I was asking based on the previous response that I quoted, but they clarified it.

 

[XLR82XS]

Check out:
THESIS FOR THE DEGREE OF LICENTIATE OF ENGINEERING IN MACHINE AND VEHICLE SYSTEMS

Investigation of Aerodynamic Resistance of
Rotating Wheels on Passenger Cars
by ALEXEY VDOVIN

Can't paste the PDF here.

 

[Let's Drive]

Also my main problem is that the title is how the size of the wheels affect EVs but it's not really the size of the wheels. It more the width of the contact patch and rolling resistance of the tire. You can technically go with a bigger wheel but have the same contact patch width. In that case the size of the wheel wouldn't matter besides the weight difference assuming the tires are the same and the wheel itself sucking more air in to its wheel well.

He discussed the tire/contact patch, in his first example of a 205mm tire vs a 305mm. Given his numbers, the difference was minor. Point 2 discussed the rolling resistance, which had a greater impact than the first, but not massive. The wheel diameter definitely had a greater effect than both, due to the amount of open area. A flatter wheel, with less room for air to pass through spokes, is ideal.

 

[Dolemite]

I don't trust that the "numbers" submitted by Tesla to the EPA for different wheel diameters are "everything else held constant," though. Does anyone know? Wouldn't the EPA be interested in the spec that the car comes from the factory?

 

[Clivew]

Also my main problem is that the title is how the size of the wheels affect EVs but it's not really the size of the wheels. It more the width of the contact patch and rolling resistance of the tire. You can technically go with a bigger wheel but have the same contact patch width. In that case the size of the wheel wouldn't matter besides the weight difference assuming the tires are the same and the wheel itself sucking more air in to its wheel well.

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.

 

[Zoomit]

I don't trust that the "numbers" submitted by Tesla to the EPA for different wheel diameters are "everything else held constant," though. Does anyone know? Wouldn't the EPA be interested in the spec that the car comes from the factory?

The coastdown coefficients are absolutely not “everything else held constant” besides wheel diameter. Tesla provides the coefficients for the three wheel and tire options for Model 3. Each set includes the sum total of effects from tire size & rolling resistance, wheel width & diameter, wheel (and cap) aerodynamics, and even tire aerodynamics.

Auto manufacturers have to provide this data for any option that has a take rate greater than 33%.

 

[subieworx]

I like Jason too . . . at least in terms of his personality. But he's really kind of a tech wannabe. Sort of knows a little but definitely does not know a lot.

I would disagree. As someone who make a living in the automotive aftermarket engineering space I think he does a very good job to simplistically explain very complex subjects. He does the research needed to become well versed on topics.

 

[dfwatt]

I would disagree. As someone who make a living in the automotive aftermarket engineering space I think he does a very good job to simplistically explain very complex subjects. He does the research needed to become well versed on topics.

Yup

 

[subieworx]

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.

This guy gets it. I have been designing and working with designers of boutique aero components for a decade and have learned quite a lot about how air flows around and through a car. It's very interesting for sure.

 

[kailm]

Yeah, I still don't quite understand how 18s (without the aero cover) are more efficient than 19s, and so forth, when they're all the same diameter overall, assuming they all have the same low rolling resistance tires across the board.

I remember reading how inertia has something to do with it, but that was not mentioned in this video.

Less weight is important! Road friction is constantly stopping your rotation. Hence 18s are superior.

 

[RheesB]

My AWD M3 has never spun a wheel except when stopping on a transition from gravel to pavement or when I stomp it on snow. The front wheels stopping on the pavement have better grip but the rears back on gravel will skid a little.

 

[Roger61]

Well I bought the Performance Version. So I have stop more frequently on long trips. But it stands out more and is more fun. Extra cost for the extra electricity is peanuts - what 5% more?

I could have gone for performance without the bits, but hell the performance bits weren't that more considering the 19inch alloys were 1.5-2k more.

I will upgrade in a couple of years if I can get one with 400 or so miles. But have no desire to go to smaller tyres for longer range. There is no other EV other than Tesla that will give me the range the Mode 3 P