19" vs 21" Tires: Ride Quality/Range Difference

[Demosthenes]

For steady-speed freeway range, wheel weight makes little difference. Tire type (tread design, structure and compounds) and wheel aerodynamics can affect range up to about 10-15%.

Indeed. But that’s not the state that many of us spend the majority of our driving time in. Stopping and starting as well as accelerating and decelerating may be more significant, especially with the Lucid on high regen mode where a slight variation in pedal pressure results in immediate acceleration or deceleration. Thus, rotational inertia (and therefore wheel weight) may have a larger role.

I swapped out my OEM wheels for completely non-aero wheels that where significantly lighter and kept the exact same size and tires on them and I’ve driven over 6k miles since the swap and have noticed no decrease in range. That made me curious about the impact of rotational inertia or other factors on range in normal driving. But I don’t have a clue about the physics. @Jeanwoodie seemed quite knowledgeable, so I asked

 

[Jeanwoodie]

Are you implying that the 21” GT wheel range reduction of approx 10% is due to tire type and wheel aerodynamic difference with the 19” M+S rated tire?
Rather than the greater rotational energy of the 21” tire? How do you discount wheel weight and radius of gyration increase of that larger wheel as a factor at highway speeds?
Remember it is the square of the speed that affects both vehicle drag and wheel rotational energy. Both factors nearly douple at 85mph vs 60mph.

 

[DeaneG]

Are you implying that the 21” GT wheel range reduction of approx 10% is due to tire type and wheel aerodynamic difference with the 19” M+S rated tire?
Rather than the greater rotational energy of the 21” tire? How do you discount wheel weight and radius of gyration increase of that larger wheel as a factor at highway speeds?
Remember it is the square of the speed that affects both vehicle drag and wheel rotational energy. Both factors nearly douple at 85mph vs 60mph.

Yes, tire type, and width, causing roiling friction/losses at freeway speeds. For mostly steady-speed freeway driving, the energy used to accelerate the car and wheels to 70mph occasionally is quite small compared to the energy lost over time in tire rolling losses and air drag.

Many Tesla owners have reported 10%-15% range loss in changing tire type alone - e.g. from Michelin's MXM4 to the PS4 - without changing wheels or tire size.

 

[Jeanwoodie]

Demosthenes:
My thoughts on your example is if the radius of gyration, tire pressure, tread compound/design, and wheel aerodynamics identical with your OEM takeoffs then range increase would be directly proportional to percent weight reduction -at any given speed. Of course rotational inertia also a factor, but unless you’re doing launches, negligible on normal acceleration and on decel, regen recaptures.
It’s us the square of the velocity which greatly impacts both aerodynamic drag and rotational energy. Energy requirements for both almost douple going from 60mph to 85mph.
At low speeds both become negligible.

 

[Demosthenes]

Demosthenes:
My thoughts on your example is if the radius of gyration, tire pressure, tread compound/design, and wheel aerodynamics identical with your OEM takeoffs then range increase would be directly proportional to percent weight reduction -at any given speed. Of course rotational inertia also a factor, but unless you’re doing launches, negligible on normal acceleration and on decel, regen recaptures.
It’s us the square of the velocity which greatly impacts both aerodynamic drag and rotational energy. Energy requirements for both almost douple going from 60mph to 85mph.
At low speeds both become negligible.

So the effect of 60 lbs weight difference in wheels should be fairly negligible then since the percentage change in the total weight of the vehicle is minuscule? I’m just trying to understand why I’m not experiencing significant range reduction since my new wheels are not aerodynamically designed

 

[Jeanwoodie]

It is not the vehicle weight factor, but reduction in wheel rotational energy we are trying factor in with your lighter wheels. However you mention your replacements not “aerodynamically designed”. Thus lack of possible aerodynamic efficiency a negative factor while lighter wheel weight a positive factor; both factors (plus and negative) directly impacted by the square of vehicle speed. Wheel rotation a linear function of vehicle speed.

 

[hellolucid]

There have been few attempts at swapping to non-oem at this point. Would be a great stickied topic for this forum, but you will need to account for the following:

-Bolt pattern (iirc, 5x120 on Air)
-Hub bore (this has yet to be confirmed online from my reading online, but can be overcome with hub rings)
-Diameter + width (would suggest keeping same as the factory 19" size)
-Tire size + load rating (would suggest keeping same as factory 19" size)
-Offset and brake caliper clearance
-TPMS sensors

You'd then need to have the TPMS programmed to the car and the tire size programmed. Lucid mobile service can do this. This sounds daunting but is far easier than one would imagine.
If anyone is enterprising enough to get the above information, I'd be happy to help vet out options, I've got lots of wheel / tire experience.

so i found this from velox wheels with a max load capacity of 2100lbs. any idea if this is good?

 

[DeaneG]

so i found this from velox wheels with a max load capacity of 2100lbs. any idea if this is good?

View attachment 5345

These won't work. You need a "PCD" of 5-120. Not sure about correct bore and offset. Some say that Tesla Model S wheels fit the Lucid - maybe start by looking for Velox wheels for the Model S.

 

[DeaneG]

If someone has a wheel off an Air in the SF south bay area, I'd be happy to measure the bore.

 

[windscar911]

Out of spec just posted this comparison of 19" vs 21"

 

[hydbob]

Out of spec just posted this comparison of 19" vs 21"

Wow, TLDR, 13.5% reduction from 19s to 21s

 

[DeaneG]

Wow, TLDR, 13.5% reduction from 21s to 19s

That's very similar to what several Tesla owners reported by just going from MXM4 low rolling resistance all season tires to Pilot Sport 4 summer-only tires, keeping tire size and wheel size the same.

 

[borski]

Wow, TLDR, 13.5% reduction from 21s to 19s

Other way around, to be clear.

 

[Demosthenes]

That's very similar to what several Tesla owners reported by just going from MXM4 low rolling resistance all season tires to Pilot Sport 4 summer-only tires, keeping tire size and wheel size the same.

So the MXM4 had better range than the PS4?

 

[DeaneG]

So the MXM4 had better range than the PS4?

Yes, 10-15% better range with the MXM4, but far less grip. It's mostly noticeable in cornering and braking. This comparison was against the summer-only Pilot Sport 4, not the all-season Pilot Sport 4 S.

 

[s55b30]

@hellolucid As pointed out above, those wheels are the incorrect PCD (bolt pattern) for Air. Air is 5x120.

To determine what you need to exceed for a load rating, take the heavier of the two gross vehicle ratings per axle (on the sticker in the doorjam) and divide it by 2.

 

[Tesla2.0]

Wow, TLDR, 13.5% reduction from 19s to 21s

21” range is acceptable for me for look and handling. How often does one go on road trip?

My current efficiency range
3.0 ~ 3.2 mi/kWh around city
3.5 ~ 3.8 mi/kWh on pure highway

Current Odometer at 3100 mi.

 

[hydbob]

21” range is acceptable for me for look and handling. How often does one go on road trip?

My current efficiency range
3.0 ~ 3.2 mi/kWh around city
3.5 ~ 3.8 mi/kWh on pure highway

Current Odometer at 3100 mi.

Well in his small efficiency loops he got

4.1-4.2 on 19s
3.5-3.6 on 21s

 

[Demosthenes]

Yes, 10-15% better range with the MXM4, but far less grip. It's mostly noticeable in cornering and braking. This comparison was against the summer-only Pilot Sport 4, not the all-season Pilot Sport 4 S.

Interesting. Both the PS4 summer and the pilot super sport are rated as 'low rolling resistance'. I wonder how they compare to the stock pirelli's on the AGT.

 

[DeaneG]

Interesting. Both the PS4 summer and the pilot super sport are rated as 'low rolling resistance'. I wonder how they compare to the stock pirelli's on the AGT.

I'l bet they are "low rolling resistance" within their max performance category, but not in comparison to an efficiency-optimized all-season GT tire.