Real World Range Questions (Winter)

[jerry33]

As far as I know larger tires have greater rolling resistance?

Wider tires have greater rolling resistance all things being equal. My bad for not defining "larger". I meant larger in diameter--not tread width.

Yes, I know. However, many of the more science oriented and uncontroversial articles are quite good. Also, I think the last few posts are about the efficiency difference between two cars that are identical except for mass and battery power (MS40 vs MS85).

I apologize for throwing wikipedia references at you, however. I didn't mean to be dismissive. Sorry.

I'm a bit sensitive to Wikipedia because there are some topics where people change them every day depending upon their leanings. Sorry about that.

According to the wikipedia article, though, rolling resistance depends on the rolling resistance coefficient C_rr multiplied by weight. The relationship is not linear despite seeming to be, because C_rr can depend on weight. In this case, though, where everything but mass and power is identical, I don't think it does.

That's the way I understand it. There are a lot of variables. The issue I had was with "the tire rubber is deformed more with higher vehicle weight". My assumption is that as vehicle weight increases tires with greater carrying capacity are installed.

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We're talking about the same car with the same wheels and tires aren't we. In that case, the energy loss from the tires goes up linearly with loading for a reasonable range.

That wasn't what I was thinking. I was thinking vehicle size increase = tires with more carrying capacity. If we're talking about the same vehicle with the same tires, then you are supposed to increase pressure to compensate for the weight. This will increase the pressure on the rubber but it won't increase the rolling resistance. If you don't increase the tire pressure than, of course rolling resistance will go up.

If you don't believe Wikipedia, how about NHTSA? Here's a reference to one of their papers on rolling resistance: http://deepblue.lib.umich.edu/bitstr...3.0001.001.pdf

And that's actually a pretty good paper. But I believe the basic problem here was my reading of the original post. Sorry about that.

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Something to think about though is this rolling resistance table. It's a bit out of date because tire manufacturers don't like to give out rolling resistance information but it does have the numbers for a variety of real tires. One of the interesting points is that one of the lower rolling resistance value tires is the 40 lb. Michelin Diamairs 285/60R18 with a value of 0.00889 and an overall diameter of ~31". One of the highest rolling resistance tires is the 10 lb. BFG Turanza LS-T P205/65R15 with a value of 0.01200 and an overall diameter of ~25.5". Now there's no doubt that the 18" tire will actually use more fuel, especially in the city, because it's a lot more mass to get going, but the rolling resistance part is actually smaller.

[eledille]

I'm a bit sensitive to Wikipedia because there are some topics where people change them every day depending upon their leanings. Sorry about that.

I agree that is a problem, but it mostly appears in articles dealing with highly controversial and politicized issues. See every article about nuclear power, for example... I think things have improved somewhat, though - articles are locked for editing except for recognized editors and users get banned. I have improved some of those articles a bit, and as long as I reference properly, my edits stay, but there's plenty of tendentious stuff and outright lies left. The problem is that digging up good references takes a lot of time. But unsubstantiated drivel can be deleted - if it's completely unreferenced and you know it's untrue, or if the referenced source is biased or does not cite properly (e.g. ref to unsubstantiated article by known anti-nuke campaigner in a nuclear-related article), just delete it.

Ahem. Back to topic...

That's the way I understand it. There are a lot of variables. The issue I had was with "the tire rubber is deformed more with higher vehicle weight". My assumption is that as vehicle weight increases tires with greater carrying capacity are installed.

Yes, but increasing weight still plugs right into the formula F_{r r} = C_{r r} * N.

Compare a 2 ton car with the best tires you listed to a 1 ton car with the worst ones:

0.00889 * 20 kN = 178 N
0.012 * 10 kN = 120 N.

The heavier car still has the highest rolling resistance.

[Keystone S]

I am a new member to Tesla Motors Club. This is my first post. Can more of you post actual watt-hours per mile you are experiencing in cold weather driving? I am taking delivery of my model S in a little over a week, and plan to take a trip (Philadelphia PA to Springfield MA - 265 MI) over the Christmas Holidays. I am planning one stop to recharge but I am not sure how much of a charge I will need. For planning purposes, I am figuring on expending 350 to 400 watt-hours per mile but after reading a little about what others are getting in warm and sunny California, I think that I should be expecting a much higher energy usage. Can you share your cold weather energy usage with me? Is 350-400 watt-hours per mile in the ball park for cold weather?

[brianman]

Welcome a-board.

Can you share your cold weather energy usage with me? Is 350-400 watt-hours per mile in the ball park for cold weather?

If your landscape is relatively flat (Texas/Florida) you'll likely easily stay below 350 Wh/mi. at <= 65 mph. If you're in hilly areas (Seattle), it's relatively easy to keep it under 415 Wh/mi. at <= 65 mph. This is for 40-45 F temperature outside.

This is with 85 Perf and the 12" wheels and stock tires.


Going uphill towards my house and flooring it, I've seen ~1500 Wh/mi. to give you an idea of the extreme. The "instant" projected range was 20 mi. (while the rated was 99 mi.), but it rose quickly by the time I took the picture.


Edit:
Some low quality camera shots:

Uphill


Downhill

[Keystone S]

Brianman,
I can plainly see the energy usage spikes on your graph. I just took delivery of my car and have put 86 miles on it so far. I am not very efficient with energy management yet. Once I learn the settings, controls, and get a feel for the road and the car response to terrain, I will get my watt hours down. after 86 miles (and a few rocket starts for my guest passengers, I am averaging just under 400 watt-hours/mi. So I think as you say, I should be able to lower that as I get used to the car and consciously try to conserve. Thanks again.

[AnOutsider]

Brianman,
I can plainly see the energy usage spikes on your graph. I just took delivery of my car and have put 86 miles on it so far. I am not very efficient with energy management yet. Once I learn the settings, controls, and get a feel for the road and the car response to terrain, I will get my watt hours down. after 86 miles (and a few rocket starts for my guest passengers, I am averaging just under 400 watt-hours/mi. So I think as you say, I should be able to lower that as I get used to the car and consciously try to conserve. Thanks again.

Heh... A week later and I'm still around 360!

[Brian H]

For max contrast, floor it halfway into a hard 60-0 braking run!

If you dare...

[cinergi]

So if you're really curious you can spend 16 minutes watching my video (hah!) here: Tesla Model S Energy Usage - YouTube (ETA 15 minutes from time of this post)
It's completely unedited and definitely boring in many spots but if you're really interested in energy usage, I think it'll serve you well. This is me in some nasty traffic with the heat on.
At the end of the drive:
183 miles rated range left (started at 206 I think ... I should have made note of that)
Drove 37.7 miles for the day (so 18.9 miles each way) using 14.3 kWh for an average of 380 Wh/mi
And the final graph