19" vs 21" Wheels Pros and Cons

[smorgasbord]

It hasn't been talked about in this thread, but sidewall height seems like the thing we should be comparing if we're worried about tire and rim damage from the likes of potholes. Sidewall height is a function of aspect ratio and rim diameter, so Model S's large rims help.

For instance, on Model S,
The 19's with a 45 aspect ratio have a sidewall height of 4.34"
Rhe 21's with a 35 aspect ratio have a sidewall height of 3.37". almost an inch less. But, is that worrisome?

Since I drive a Roadster every day without issues and I haven't read about tire/wheel damage on Roadster as being a problem for other drivers, I thought that might be a good comparison.

For Roadster (stock sizes):
The rear 225/45-17's have a sidewall height of 3.98"
The front 175/55-16's have a sidewall height of 3.78"

So, Roadster's front tire sidewall height is about 0.4" more than Model S's 21s. That's about 13/32", which to help you get a feel for the difference is 1/16" deeper than the tread depth on new tires. Or, about a 10% reduction in sidewall height for Model S compared to Roadster fronts.

I don't know if that 13/32" reduction in sidewall height is killer or not, but it sure doesn't seem as bad when looked at this way.

 

[jerry33]

It hasn't been talked about in this thread, but sidewall height seems like the thing we should be comparing if we're worried about tire and rim damage from the likes of potholes. Sidewall height is a function of aspect ratio and rim diameter, so Model S's large rims help.

For instance, on Model S,
The 19's with a 45 aspect ratio have a sidewall height of 4.34"
Rhe 21's with a 35 aspect ratio have a sidewall height of 3.37". almost an inch less. But, is that worrisome?

It's about 22% less sidewall height. I'd say 22% is significant.

For Roadster (stock sizes):
The rear 225/45-17's have a sidewall height of 3.98"
The front 175/55-16's have a sidewall height of 3.78"

That's about 5% less sidewall height. (front to rear)

Or 8% less sidewall height between the front Roadster and the 45% Model S tires.

 

[AndyM]

Given how Portlanders drive in the snow (poorly) I would just leave the Model S in the garage for the two snow days per year!

I agree!

 

[jerry33]

Given how Portlanders drive in the snow (poorly) I would just leave the Model S in the garage for the two snow days per year!

That's what I would do too.

 

[smorgasbord]

Or 8% less sidewall height between the front Roadster and the 45% Model S tires.

10.8466% (1.0 - 3.37/3.78 * 100)

Is 11% significant? That is, if after tens of millions of miles almost no Roadster owner reports damaging rims or getting blowouts from potholes or bad roads, will an 11% decrease in sidewall height suddenly make it a real problem? Especially considering the air suspension?

 

[jerry33]

10.8466% (1.0 - 3.37/3.78 * 100)

Is 11% significant? That is, if after tens of millions of miles almost no Roadster owner reports damaging rims or getting blowouts from potholes or bad roads, will an 11% decrease in sidewall height suddenly make it a real problem? Especially considering the air suspension?

Jury is out. The Model S is significantly heavier than the Roadster. The only significant difference for me was the difference between the Model S' 19" and 21" tires. The difference between the weight of the two vehicles could (stressing the could) mean that the Roadster and the 19" Model S are more identical than the Roadster and the 21" Model S.

 

[Mycroft]

Given how Portlanders drive in the snow (poorly) I would just leave the Model S in the garage for the two snow days per year!

That's a good plan, the problem is that the 21" summer tires lose serious traction when the temps get below 45 degrees. As you know, this happens quite a bit Nov-Mar in the NorthWet.

 

[smorgasbord]

The Model S is significantly heavier than the Roadster.

Surely that's factored into the tire size and load rating.

 

[jerry33]

Surely that's factored into the tire size and load rating.

Certainly, but the forces when hitting a pothole are much greater if there is more mass. So the "effective" cushioning provided by the 19" tire may be the equivalent of the Roadster tire and the 21" tire could have a lower amount. For sure the 21" has less cushioning than the 19" tire.

 

[smorgasbord]

For sure the 21" has less cushioning than the 19" tire.

That's not the point at all. At least, that's not my point.

My point is that the 21" with 35 aspect tires may not find potholes the Achilles Heel many of us have assumed. With about 90% of the sidewall height of Roadster - a car in which no-one is complaining about potholes ruining tires/rims - they may be just fine for many people.

 

[stopcrazypp]

Jury is out. The Model S is significantly heavier than the Roadster. The only significant difference for me was the difference between the Model S' 19" and 21" tires. The difference between the weight of the two vehicles could (stressing the could) mean that the Roadster and the 19" Model S are more identical than the Roadster and the 21" Model S.

Looking at the BMW 7 series forums (a car weighing 5000+lbs or 300-400lbs heavier than the 85kWh Model S) people have not experienced issues with bent wheels using essentially the same size 21" wheels with 35 aspect ratio (stock: 245/35R21 front, same as Model S, 285/30ZR21 rear).

22" and 25 or 30 aspect ratio has been a recipe for bend wheels though.
http://www.bimmerfest.com/forums/archive/index.php/t-563320.html
http://www.bimmerfest.com/forums/archive/index.php/t-514218.html

I don't think bent wheels should be a huge issue.

 

[SCW-Greg]

Given how Portlanders drive in the snow (poorly) I would just leave the Model S in the garage for the two snow days per year!

Yeah, hope I don't offend, but Real Oregonians drive in the snow like Real Californians drive in the rain! It's all good.

Californian transplants to here, are at least smart (terrified) enough when it snows, to stay home. Oregonians aren't. And I am one, but have learned, also have secret AWD weapon.

 

[SCW-Greg]

I know this has been re-hashed, but I'll add my own minor epiphany today.
I was worried that the Continental 21" wheels that will ship on my Model S Performance would not work will in the Oregon winters here. (read: rain, rain, and rain again, with about 2 weeks of snow).
I called a friend of mine, who teaches autocross and runs a custom auto shop in the area. He assured me it's not the size of the tires, its the specs, and how they channel away water that counts.

When I checked the specs, and compared them to my current tires (which I feel were a great improvement from my previous ones), the new 21" Continentals are rated even better for traction.
When I looked at the tread on the Continentals in the store, with another friend, without even asking him this friend (a well-experienced auto mechanic) told me those would work very well in the rain.

In short, I am no longer worried about running the Performance 21"s year round in Oregon. If winter gets gnarly, I'll just drive like they do in the Minnesota lake test video.

This is good to know, as this has been a major concern of mine too. Thanks!

 

[AndyM]

Yeah, hope I don't offend, but Real Oregonians drive in the snow like Real Californians drive in the rain! It's all good.

Californian transplants to here, are at least smart (terrified) enough when it snows, to stay home. Oregonians aren't. And I am one, but have learned, also have secret AWD weapon.

So as not to sling insults: any driving condition in which one has little practice means one will tend to suck at it. It's not personal.

 

[ckessel]

Yea, we Oregonians are pretty bad in snow. In our defense:

1) We get very little of it so people don't get much practice.
2) It's not the dry, blowing snow you get in mountains or Colorado or some such. It's nasty, wet stuff that often ices over, melts, ices, etc. It's really treacherous.

That doesn't excuse folks going out in it though, that's just not smart.

I simply don't drive in it. I'm horrible in the snow. My wife is pretty good at it though, she did a lot of skiing in her youth and drove snow covered roads.

 

[Lyon]

Yea, we Oregonians are pretty bad in snow. In our defense:

1) We get very little of it so people don't get much practice.
2) It's not the dry, blowing snow you get in mountains or Colorado or some such. It's nasty, wet stuff that often ices over, melts, ices, etc. It's really treacherous.

That doesn't excuse folks going out in it though, that's just not smart.

I simply don't drive in it. I'm horrible in the snow. My wife is pretty good at it though, she did a lot of skiing in her youth and drove snow covered roads.

Indeed. It's mostly the cities in the Valley that end up with people stranded all over the place with 2 inches of snow on the ground.

While a grew up in Eugene I've skied my whole life and have driven in the snow a lot.

The biggest mistakes I see when it snows in the Valley:

1) AWD is great to get you going and to keep to in line around corner but it doesn't help you stop.

2) The vast majority of"all-season" tires aren't. (If they don't have the Severe Service logo on them they're not really all-season)

3) slow down before you want to turn. You may have enough traction to corner and you may have enough to slow down but you don't have enough to do both at the same time.

I'm sure that this list could be expanded, but these are the big ones, IMHO.

 

[Doug_G]

10.8466% (1.0 - 3.37/3.78 * 100)

Is 11% significant? That is, if after tens of millions of miles almost no Roadster owner reports damaging rims or getting blowouts from potholes or bad roads, will an 11% decrease in sidewall height suddenly make it a real problem? Especially considering the air suspension?

I've bent a rim. Pothole.

 

[smorgasbord]

I've bent a rim. Pothole.

Is this the exception that proves the rule - or something to make us avoid 21" if our roads ain't so great?

How many miles do you think TMC posters have on their Roadsters, and how many damaged rims?

 

[SCW-Greg]

Is this the exception that proves the rule - or something to make us avoid 21" if our roads ain't so great?

How many miles do you think TMC posters have on their Roadsters, and how many damaged rims?

Quality of rim barrel might be at play as well here.

 

[Ken Edwards]

One more important factor to consider: range. Tesla engineers I spoke with all said the 19 inch wheels would get about 5% more range. If range (and economy) is important to you, and you want to save money and have more choice of tires and manufacturers, then the 19s are best for you. Overall this was enough of a factor to persuade me to go to the 19s even though I'm giving up an included $3,500 more expensive wheel (included in performance and signature cars).