OEM Wheel and Tire Widths vs. Model S

Bokonon

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#1
Here's a question for the wheel and tire gurus on the forum:

Why do the OEM wheel + tire setups for the Model 3 include 8.5" wheels paired with 235mm tires, while the base Model S features 8" wheels paired with 245mm tires? What factors may have influenced this design decision?

I started thinking about this recently, after repeatedly stumbling into the curb rash thread, where someone recently wondered whether switching to 245-wide tires would provide better protection. I get that Tesla is trying to engineer the Model 3 to a complex set of constraints -- e.g. rolling resistance, aerodynamics, traction and cornering performance -- but I keep wondering what it is about the Model 3 that required a different wheel and tire setup than the Model S.

For example, if one goal was to make the smaller Model 3 more efficiency-oriented than the larger, performance-oriented Model S, using slightly narrower 235mm tires would make sense. But then why increase the width of the wheels from 8" to 8.5"? What benefit does that provide?

Any insight on the factors that led to decisions like these would be most enlightening, even if they are largely speculative. Bonus points if your name is Franz.
 

SoFlaModel3

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#2
Here's a question for the wheel and tire gurus on the forum:

Why do the OEM wheel + tire setups for the Model 3 include 8.5" wheels paired with 235mm tires, while the base Model S features 8" wheels paired with 245mm tires? What factors may have influenced this design decision?

I started thinking about this recently, after repeatedly stumbling into the curb rash thread, where someone recently wondered whether switching to 245-wide tires would provide better protection. I get that Tesla is trying to engineer the Model 3 to a complex set of constraints -- e.g. rolling resistance, aerodynamics, traction and cornering performance -- but I keep wondering what it is about the Model 3 that required a different wheel and tire setup than the Model S.

For example, if one goal was to make the smaller Model 3 more efficiency-oriented than the larger, performance-oriented Model S, using slightly narrower 235mm tires would make sense. But then why increase the width of the wheels from 8" to 8.5"? What benefit does that provide?

Any insight on the factors that led to decisions like these would be most enlightening, even if they are largely speculative. Bonus points if your name is Franz.
Tracking this thread and pinging @Mad Hungarian

On a previous car I had 235 tires on 8” wide rims and it offered a little protection.
 

garsh

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#3
Why do the OEM wheel + tire setups for the Model 3 include 8.5" wheels paired with 235mm tires, while the base Model S features 8" wheels paired with 245mm tires? What factors may have influenced this design decision?
Plugging those into a tire size calculator, we get:

Model 3: 235/45R18
Diameter: 26.3", Width: 9.3", Sidewall: 4.2", Circum: 82.7", Revs/Mile: 766

Model S: 245/45R19
Diameter: 27.7", Width: 9.6", Sidewall: 4.3", Circum.: 86.9", Revs/Mile: 729

Difference (going from 3 to S):
Diameter: +5.3%, Width: +3.2%, Sidewall: +2.4%, Circum.: +5.3%, Revs/Mile: -37

Keep in mind that these measurements are all approximations. Different tires will differ slightly from these values. And the width of the wheel that the tire is mounted on will make a difference too.

My guess for why they went with a wider wheel on the 3: to improve handling. Less flex in the tire's sidewall when cornering. But that's only a guess.
 

Mad Hungarian

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#5
Paging @Mad Hungarian for any further insight into this question, before his P3D arrives and he loses the ability to think about anything else... :)
LOL!!
Sorry about the delay, it's been a bit of a crazy week and I knew one slipped through the cracks somewhere.
We may have to institute a "Beetlejuice" protocol where anyone requesting help must tag me three times :).

I did start making some inquiries and even went through the SAE online library to see if I could pull some research data on rolling
resistance vs. wheel width. This is because although I can say unequivocally that @garsh is correct, the 8.5" will improve handling over the 8.0", I suspect rolling resistance may have also played into this wider width choice.
Stretching the sidewalls out a little further ought to not only reduce flex during transitional manoeuvres but reduce hysteresis, that is the parasitic energy loss the tire experiences from the constant rolling sidewall flex that occurs in the "bulge" over the contact patch as the tire rotates. So far no luck on that data, news as it happens.
 

Bokonon

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#6
LOL!!
Sorry about the delay, it's been a bit of a crazy week and I knew one slipped through the cracks somewhere.
We may have to institute a "Beetlejuice" protocol where anyone requesting help must tag me three times :).
:tearsofjoy:

I did start making some inquiries and even went through the SAE online library to see if I could pull some research data on rolling
resistance vs. wheel width. This is because although I can say unequivocally that @garsh is correct, the 8.5" will improve handling over the 8.0", I suspect rolling resistance may have also played into this wider width choice.
Stretching the sidewalls out a little further ought to not only reduce flex during transitional manoeuvres but reduce hysteresis, that is the parasitic energy loss the tire experiences from the constant rolling sidewall flex that occurs in the "bulge" over the contact patch as the tire rotates. So far no luck on that data, news as it happens.
Fascinating... as a humble Lapchik University student still struggling to pass Wheels and Tires 101, I never would have guessed that you could improve handling *and* reduce rolling resistance with a wider wheel (but in hindsight, after falling down a Google rabbit hole filled with interesting primers on contact patch shapes and, yes, hysteresis, it makes sense to me now).

So then why not make the same change for the Model S and increase the width of the base slipstream wheels to 8.5" as well? Wouldn't improved handling and reduced rolling resistance be welcome on the Model 3's less efficient, more luxurious sibling? Or is there something about the Model S (e.g. 1000 lbs of extra weight) that makes 8" wheels + 245mm tires a better choice overall (e.g. to maintain a certain level of ride comfort)?

Thanks as always for your insight!
 

garsh

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#7
So then why not make the same change for the Model S and increase the width of the base slipstream wheels to 8.5" as well?
They may do so in the future. Tesla used the lessons learned from S and X development when developing the Model 3. I'm sure they'll see how these latest design decisions work out when they're deciding how the next version of the S should change.

In particular, I wonder if all of the curb rash incidences will convince them that the "wide wheel, narrow tire" approach isn't worth the headaches for the S.
 

CleanEV

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#8
I have been reading this and other threads and am finding this information quite interesting. I have 18 Aeros as I was exceeding my budget at the time.

Out of curiosity I was looking at the pricing of 18” vs 19” on tire rack and to my surprise Michelin’s are more expensive on 18” vs 19”. All other brands have 19” tires that are more expensive. I had to choose different sizing for front and rear to see pricing for both tires at a time. See snapshot I took from tire rack

Is there a reason why Michelin’s will be more expensive for 18”?

upload_2018-7-23_15-14-54.jpeg