Anybody had the chance to test drive 18 vs 19 inch wheels on M3?

NJturtlePower

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#41
Assume you saw the Edmunds testing of 19" vs 18" wheels?

Too many inconsistencies to make any true comparison of strictly wheel size in my book...
  • Different Tires
  • Different Test Conditions (Temperature/Humidity/Track Section/)
  • Battery Status Variables (Full Charge or Warmed up?)
This was more a test of tires than it was wheels IMO.

If somebody can run the same tests WITH the same tires on the same day back-to-back we can put a fair end to this debate.
 

John

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#42
Too many inconsistencies to make any true comparison of strictly wheel size in my book...
  • Different Tires
  • Different Test Conditions (Temperature/Humidity/Track Section/)
  • Battery Status Variables (Full Charge or Warmed up?)
This was more a test of tires than it was wheels IMO.

If somebody can run the same tests WITH the same tires on the same day back-to-back we can put a fair end to this debate.

Both stock wheels have the same traction rating, which I realize is a bit of a broad range ("A"). Which part of the test are you most skeptical about? The cornering or the acceleration/braking?

I was most surprised by the acceleration/braking result. The cornering one I thought was expected, though it was nice to see numbers.
 

NJturtlePower

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#43
Both stock wheels have the same traction rating, which I realize is a bit of a broad range ("A"). Which part of the test are you most skeptical about? The cornering or the acceleration/braking?

I was most surprised by the acceleration/braking result. The cornering one I thought was expected, though it was nice to see numbers.
Both stock TIRES may have the same traction rating but come from different brands, which most would agree is not an apples-to-apples comparison.

I guess my main point is if we are comparing wheel/rim sizes and its effects on performance then all other variables should be the same.

Given that the 19" are heavier and of a shorter sidewall ratio they should be slower 0-60 mph, should reduce range, demonstrate a harsher ride and take longer to stop, but likey corner better and improve steering response.
 

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#44
I was going to do the same thing but when I saw that the tire offered was not something I wanted I figured that I might as well punt the decision until more data is available. So 19" staggered is 1200$ given I need to buy new tires anyway it is like 300$ cheaper to wait out. If I go for better looking 18inch it is 1K and 500$ less given I wan to go with Michelin Super Sport.
Yup. My Golf was delivered with the world's ugliest 19" wheels and some Continental 7p (or something) tires.
Saved 5lbs per corner with a set of nice 18" wheels and Michelin Pilot SuperSport tires for $2k all in.
Sold the ugly factory wheels for $1700 on eBay, got better braking, acceleration, cornering, ride quality, AND looks!

Selling and shipping stuff sucks, but $1500 for an "upgrade" is a racket considering you don't get to choose your wheel and they're keeping the 18s the car would have come with. At least it's not some insane $5000 upgrade like Porsche charges you, but still, I hate when an upgrade replaces existing parts but the cost doesn't reflect that.

Regardless, I'd go with the 18s though the aero covers are not exactly attractive.
 

Thom Moore

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#45
Yup, I saw that, and wondered how it could be. The outer diameter of the tires is exactly the same either way, and I don't think the 19s are any wider (?), just lower in profile. So it seem that the difference is mainly in the ratio of metal to rubber in the diameter, and perhaps the larger wheels are heavier. Certainly, there is less give in the lower profile tires, and better transmission of road noise to the wheel and axle and car. Perhaps the tread and tire design also affects that as well as the grip? The tires are Michelin in one case and Continental in the other, so that could be important.

This is a nice comparison since the same car was tested with a swap of the wheels (I think), and there is no "sport suspension" difference between the cars to muddy the water as there would be in comparing a Model S P100D with a 100D. Can anyone explain the physics of why the wheel size should make a difference, or do you think it's all about the tires?
 

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#46
The tires are Michelin in one case and Continental in the other, so that could be important.
The tire difference is of utmost importance. The 18" option comes with LRR Michelin MXM4, the 19" with Conti ProContact RX non-LRR tires. There is little doubt that the performance differences in the Edmunds tests were mostly due to tread compound and construction differences in the tires. The Michelin LRR tires prioritize range over other performance characteristics.

18": Michelin Primacy MXM4, 235/45-18, 98W
19": Continental ProContact RX, 235/40-19, 96W
 

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#47
The tire difference is of utmost importance. The 18" option comes with LRR Michelin MXM4, the 19" with Conti ProContact RX non-LRR tires. There is little doubt that the performance differences in the Edmunds tests were mostly due to tread compound and construction differences in the tires. The Michelin LRR tires prioritize range over other performance characteristics.

18": Michelin Primacy MXM4, 235/45-18, 98W
19": Continental ProContact RX, 235/40-19, 96W
And ride quality is most likely due to the higher pressures used on the LRR tires.

Agree 100% it’s all about tire choice when dealing with such a small difference in aspect ratios between the two.
 

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#48
Yup, I saw that, and wondered how it could be. The outer diameter of the tires is exactly the same either way, and I don't think the 19s are any wider (?), just lower in profile. So it seem that the difference is mainly in the ratio of metal to rubber in the diameter, and perhaps the larger wheels are heavier. Certainly, there is less give in the lower profile tires, and better transmission of road noise to the wheel and axle and car. Perhaps the tread and tire design also affects that as well as the grip? The tires are Michelin in one case and Continental in the other, so that could be important.

This is a nice comparison since the same car was tested with a swap of the wheels (I think), and there is no "sport suspension" difference between the cars to muddy the water as there would be in comparing a Model S P100D with a 100D. Can anyone explain the physics of why the wheel size should make a difference, or do you think it's all about the tires?
The tread on the 19" wheels is about 1/2" wider.
 

Thom Moore

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#49
The tread on the 19" wheels is about 1/2" wider.
Why would it be, if the tire has same dimensions except the lower profile? Are the 19 in rims wider? If so, wouldn't a wider 18 in rim do just as well and survive potholes a lot better?
 

DR61

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#50
Why would it be, if the tire has same dimensions except the lower profile? Are the 19 in rims wider? If so, wouldn't a wider 18 in rim do just as well and survive potholes a lot better?
The nominal widths of tire and wheel are the same, but the actual tread width that contacts the road is different. These are different makes and models of tire. Take a look at tirerack.com and compare same nominal size tire across different tire models for actual tread width.
 

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#51
Why would it be, if the tire has same dimensions except the lower profile? Are the 19 in rims wider? If so, wouldn't a wider 18 in rim do just as well and survive potholes a lot better?
Yep, what @DR61 said. Tires aren't shaped like an ideal hollow cylindar that is even with the sides of the rim, they have a shape as designed by the manufacturer. And it just so happens that for these two particular tires the 19" ones have a slightly wider tread width.

Note: that's not to say that the tire patch is larger; for the same weight vehicle and tire pressure, a wider tread will result in a shorter front-back tire patch to support the same amount of weight.
 

Thom Moore

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#53
I'm thinking that tread compounds (low rolling resistance vs high stickiness) may be a bigger factor than a slight difference in tread design, but of course both could be significant.
 

Thom Moore

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#54
I don't buy this explanation. The tire tread has an essentially identical radius from the center of the axle in this comparison, because the 19 in wheels use a tire that is about 0.5 in thinner than the 18 in wheels, compensating the wheel radius change. The contact patch cannot differ significantly for identical tire pressures. If the width is the same, the length of the patch must also be the same, for the tire pressure to support the same car. If the patch is slightly wider, then the length must be correspondingly shorter, to achieve the same force supporting the car.

The dynamics of the tire over bumps and in corners do vary. Over bumps, the sidewall flex is smaller per unit change of contact force in the bump. In corners, the lateral distortion of the tire is smaller per unit of G-force.
The low profile tire is a stiffer springy object than the higher profile tire, in both dimensions.

But these dynamic effects would not seem to affect straight-line braking results very much, would they?
 

John

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#55
I don't buy this explanation. The tire tread has an essentially identical radius from the center of the axle in this comparison, because the 19 in wheels use a tire that is about 0.5 in thinner than the 18 in wheels, compensating the wheel radius change. The contact patch cannot differ significantly for identical tire pressures. If the width is the same, the length of the patch must also be the same, for the tire pressure to support the same car. If the patch is slightly wider, then the length must be correspondingly shorter, to achieve the same force supporting the car.

The dynamics of the tire over bumps and in corners do vary. Over bumps, the sidewall flex is smaller per unit change of contact force in the bump. In corners, the lateral distortion of the tire is smaller per unit of G-force.
The low profile tire is a stiffer springy object than the higher profile tire, in both dimensions.

But these dynamic effects would not seem to affect straight-line braking results very much, would they?

The widths of the tread that touches the ground is NOT the same:
18" tires tread width = 7.8". Link here
19" tires tread width = 8.2" Link here

So for the same tire pressure, the 19" tires will have a wider but shorter front-to-back tire patch.
Understand now?

And though both tires have a "A" traction rating, the fact that the 18" tires have a wear rating of 500 versus the 400 of the 19" suggests that the 19" wheels may be softer.
 

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#56
Ordered 18s and ran with them for 8k miles. No complaints about the ride quality, they were just fine.

Switched to the stock 19s just a few weeks ago and I can feel the ride is a bit harsher, definitely feel the bumps in the road more but it’s not terrible. Handling seems tighter. I did give up on some efficiency as the car seems to use ~240-245kWh vs ~235-240kWh during my daily commute tracking. Looks prettier though. :)
@Maevra can you update us and confirm you are still receiving ~240-245kWh (19”) vs ~235-240kWh (18”)? If there is only 2% loss this makes the decision a little easier.
 

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#57
@Maevra can you update us and confirm you are still receiving ~240-245kWh (19”) vs ~235-240kWh (18”)? If there is only 2% loss this makes the decision a little easier.
Yep holding at 240-245 for daily drives.

We've also tracked the usage of the 18s vs. 19s over a longer period and it's been pretty cool to see the difference (or lack thereof, lol!)

Aero 18" usage stats:
1923 miles
480 kWh used
249 wH/mi

Stiletto 19" usage stats:
1505 miles
364 kWh used
242 wH/mi
 

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#58
Yep holding at 240-245 for daily drives.

We've also tracked the usage of the 18s vs. 19s over a longer period and it's been pretty cool to see the difference (or lack thereof, lol!)

Aero 18" usage stats:
1923 miles
480 kWh used
249 wH/mi

Stiletto 19" usage stats:
1505 miles
364 kWh used
242 wH/mi
Thanks for keeping us updated on these stats!

Question: does weather factor into this comparison? In other words, were most of the miles you racked up with the 18s during the fall/winter months, before you switched to the 19s in the spring? I realize SFO winters are fairly mild, but I'm wondering to what extent usage of the heating system may be a factor here.
 

Maevra

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#59
Thanks for keeping us updated on these stats!

Question: does weather factor into this comparison? In other words, were most of the miles you racked up with the 18s during the fall/winter months, before you switched to the 19s in the spring? I realize SFO winters are fairly mild, but I'm wondering to what extent usage of the heating system may be a factor here.
No prob! Yeah we started tracking around Feb, but weather’s been pretty mild and we rarely ever used the seat heaters or HVAC for a long time, so i don’t think they really played a big part. I’m thinking using the AC now will equalize it.
 
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#60
Do you have the stats reversed? I'm confused why the 18" wheels have a higher energy requirement than the 19" wheels...

Also for the sake of the comparison, it's helpful to know if you have the aero wheel covers on or off of your 18" wheels routinely.

Thanks!