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

[dbsb3233]

Sponsored

 

[dbsb3233]

So, I think I followed most of that, until the wide sidewall comment. Wouldn't wide sidewalls just make the tire taller, creating the same effect as a big wheel?

 

[kdryden99]

So, I think I followed most of that, until the wide sidewall comment. Wouldn't wide sidewalls just make the tire taller, creating the same effect as a big wheel?

No because the bigger wheel requires more torque to rotate than the smaller wheel.

 

[GoGoGadgetMachE]

did someone say "Big Wheels"?

 

[dbsb3233]

No because the bigger wheel requires more torque to rotate than the smaller wheel.

But won't big sidewalls (on a smaller rim) still just result is the same diameter of tire, thus the same torque to rotate it?

Unless I'm misinterpreting what he means by "bring back big sidewalls and get rid of silly low profile tires".

 

[Ron Bonifas]

But won't big sidewalls (on a smaller rim) still just result is the same diameter of tire, thus the same torque to rotate it?

Unless I'm misinterpreting what he means by "bring back big sidewalls and get rid of silly low profile tires".

while it is true that both tire wheel combinations could have the same overall circumference the higher-profile tires flatten out more to the road surface causing the center line distance to the road to be slightly less resulting in less torque needed to rotate. Car andDriver has verified higher profile tires to be more efficient and the rt1 mach e is coming with 18in wheels, although not the best looking Aero covers, it is expected to have the highest range

 

[kdryden99]

But won't big sidewalls (on a smaller rim) still just result is the same diameter of tire, thus the same torque to rotate it?

Unless I'm misinterpreting what he means by "bring back big sidewalls and get rid of silly low profile tires".

He calls it rolling resistance. I believe that due to the fact tires are softer they allow for deformation thus having less rolling resistance than a larger wheel with rubber bands

 

[dbsb3233]

He calls it rolling resistance. I believe that due to the tires are softer tjey allow for defotmation thus having less rolling resistance than a larger wheel with rubber bands

This confuses me too because I thought softer tires were bad for mileage while harder tires were better. Aren't we supposed to get better mileage when we keep high PSI in the tires, rather than taking air out to soften the tires?

 

[JamieGeek]

This confuses me too because I thought softer tires were bad for mileage while harder tires were better. Aren't we supposed to get better mileage when we keep high PSI in the tires, rather than taking air out to soften the tires?

Yup conventional wisdom is that harder tires and more PSI reduces the amount the tire deforms and thus are more efficient.

Tire deformation takes energy generating heat in the tire.

Think about steel belted tires..takes quite a bit to bend those belts.

 

[DBC]

But won't big sidewalls (on a smaller rim) still just result is the same diameter of tire, thus the same torque to rotate it?

Unless I'm misinterpreting what he means by "bring back big sidewalls and get rid of silly low profile tires".

You understand the video but it's what @kdryden99 has explained. Larger rims with low profile tires produces a higher moment of inertia because more of the mass is pushed further from the center.

 

[timbop]

I was confused by why having more rubber was better as well - it seemed to me that the same circumference with less flexible rubber would be better, but then this

You understand the video but it's what @kdryden99 has explained. Larger rims with low profile tires produces a higher moment of inertia because more of the mass is pushed further from the center.

suggests that having shorter spokes to the rims is more important than the fact that a larger diameter of rubber flexes more. Is it also the case that the larger diameter of rubber flexing over bumps helps keep the center of gravity in a straight line?

 

[dbsb3233]

You understand the video but it's what @kdryden99 has explained. Larger rims with low profile tires produces a higher moment of inertia because more of the mass is pushed further from the center.

Does that mean it's because of more weight (metal) rotating out further from the axis creating more rotation inertia (once up to speed)?

 

[kdryden99]

I was confused by why having more rubber was better as well - it seemed to me that the same circumference with less flexible rubber would be better, but then this


suggests that having shorter spokes to the rims is more important than the fact that a larger diameter of rubber flexes more. Is it also the case that the larger diameter of rubber flexing over bumps helps keep the center of gravity in a straight line?

Conventional wisdom yes you are correct but i think in the case of the EV not only do the bigger sidewalls help keep it straight, there is less momentum loss when driving over higher friction surfaces, i.e. cracks, gravel, etc. And explained in the video the biggest part was the narrower tires also which i believe is the biggest contributor to the range increase.

 

[Tim_C]

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

*CLARIFICATION!* Why do bigger wheels mean worse efficiency, when the overall tire diameter remains the same? This comes down to aerodynamics. A 20" wheel will cause more of a disruption in airflow than an 18" wheel. That's why Tesla (and others) uses aero covers on their wheels (Car & Driver testing showed it gives about a 3% efficiency bonus at speed). The smaller the wheel, the more of the side profile of the wheel & tire is perfectly flat (the tire is flat, the wheel is open: more tire = more flat area, less open area). Ideally, you'd have just a plain, solid sheet for the wheel, but obviously that's not idea for brake cooling. Wheel covers are today's common compromise as they have some airflow, but minimal.

 

[Thevanin]

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.

Sponsored