jackmott
Member
lighter wheels have no impact on highway range. tires can have a big impact though.
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MASTER THREAD: 2021 Model 3 - Charge data, battery discussion etc
- Thread starter EV Promoter
- Start date
So why the difference between M3 range with 18” vs 19” when tyre width is the same ?
AlanSubie4Life
Efficiency Obsessed Member
They’re different tires aren’t they? Also the 18” has the aero wheels which do make a difference. They’re aero.
It’s not the weight to first order though. Theoretically weight makes nearly zero difference. Energy taken to spin them up (which is fairly small component of overall kinetic energy) is nearly completely reclaimed.
Steve446
Dusty Crophopper, M3 LR 2021 Midnight Silver
Doesn't the design of the tires make a difference too? I understood that was a problem for energy economy since there's a sidewall energy burden more or less important as a function of tire design and driving style?
Just something interesting to add to the tire discussion...
www.bbc.com
Could flat tyres soon be a thing of the past?
Airless tyres that do not puncture are getting close to market but some remain sceptical about them.
www.bbc.com
jackmott
Member
jackmott
Member
Tweels are neat, but it is probably impossible for a non pneumatic tire to ever have rolling resistance as good as a pneumatic one. I know the tweel guys once a year come out claiming it will have better rolling resistance but so far they haven't achieved that and I don't think physics would allow it even in principle.Just something interesting to add to the tire discussion...
Could flat tyres soon be a thing of the past?
Airless tyres that do not puncture are getting close to market but some remain sceptical about them.
So they would be very bad for range (and comfort, and handling) but can work great on certain lower speed equipment (mowers, industrial/farm equiment, etc)
I’m not so sure either... I think it’s all going to depend on material science coming up with a material that can mimic a pneumatic tire. I also don’t like the exposed ‘spokes’...i would worry about twigs getting stuck in there...or worse, a malicious person putting a piece of rebar between the spokes... I prefer a pneumatic tire that is filled with some kind of closed cell foam
It seems that every year or two these air-less tires make a splash in the news, but then quickly go back into hiding until the cycle repeats itself. As far as I can tell, they never get any closer to commercial production except in specialized use cases.
AlanSubie4Life
Efficiency Obsessed Member
Eventually. Happens more at high SOC, and in fact at high enough SOC you’ll see the line get shorter without dots which indicates it is fundamentally limited.
Temp and SOC related. Depending on the temperature and driving you do 30 minutes may not be enough.
And 15C is COLD. 59F. Definitely cold enough to have regen limitations.
Shouldn't be that much in it as the LR with 18" have performance tyres not efficiency ones, and even with the aero covers off the 18s are better.
jackmott
Member
The LR with 18" tires usually comes with Michelin MXM4 which is very much not a performance tire and is very much is a range optimized tire.
I'd agree there if you MXM4, but in Europe (and possibly all MiC) the LR comes with Michelin PS4. Granted not the ultra high performance PS4S but still higher performing that the Hankooks they put in the 19" rims.
jackmott
Member
And it looks like the European range difference is only ~14 miles vs ~24 miles in the USA with the lower rolling resistance tires. So the difference is likely just from the ~5% savings of the aero covers. (which, works out to about 15 miles)
My battery is 15C or colder most days of the year, I do not se regen limitation above about 7C (give or take a few degres).
Caviat that they changed anything in a recent firmware…
Batt temp 14.3C as I write this, no regen dots.
AlanSubie4Life
Efficiency Obsessed Member
You run low SOC though.
If my SOC is over 70-75%, it is quite common to see the dots. Even in spring in Southern California. Basically if it feels slightly cool you may see limited regen. Especially on a significant downhill, the regen limit builds up, and the regen limitations get worse as you drive. But eventually all is well of course.
gergelyricsike
Member
Hello guys i was wondering what was the 100% displayed range of the 2021 MIC SR+ when brand new? Anyone has the info? Thank you!
Good evening and nice to meet you.
My first post in TMC since I own my 2021 M3 LFP 55kWh
Today I've played a simple experiment when going to my office since I'm able to charge there. I lowered SOC to a minimum value (10%) in order to check battery capacity and some questions have arisen.
I've loaded 50 kWh at 95% efficiency or 47.56 kWh. With this load I've risen my SOC from 10% to 100%. By applying a simple rule of three my battery pack is 52.8 kWh that is exactly what SMT tells me (52.9 kWh). However, SMT does include battery buffer and this is 2.4 kWh. So, something is not good here. My calculation should have given 50.4 kWh and not 52.8 kWh since buffer should be substracted.
Summarizing:
- SMT tells me battery full pack is 52.9 kWh.
- SMT tells me buffer is 2.4 kWh
- I've loaded 47,56 kWh from 10% to 100%. So, full battery pack should be 52.8 kWh WITHOUT buffer.
Theories?
a) 100% does indeed includes buffer. This should not be the case because buffer is just that... buffer "just in case..."
b) SMT does not include buffer in Nominal Full Pack. But this is not what I've read in documentation.
c) Tesla has changed CANBUS protocol in later updates and now does not include buffer in Nominal Full Pack readings.
d) Tesla decrease buffer in order to deal with battery degradation.
e) I don't know how to calculate a rule of three.
By the way, I've seen a video from Bjorn Nyland where he takes a 2021 M3 with 100km and 52.5kWh Nominal Full Pack and a previous one with a 55 kWh Nominal Full pack (not the same car).
Just curiosity.
My first post in TMC since I own my 2021 M3 LFP 55kWh
Today I've played a simple experiment when going to my office since I'm able to charge there. I lowered SOC to a minimum value (10%) in order to check battery capacity and some questions have arisen.
I've loaded 50 kWh at 95% efficiency or 47.56 kWh. With this load I've risen my SOC from 10% to 100%. By applying a simple rule of three my battery pack is 52.8 kWh that is exactly what SMT tells me (52.9 kWh). However, SMT does include battery buffer and this is 2.4 kWh. So, something is not good here. My calculation should have given 50.4 kWh and not 52.8 kWh since buffer should be substracted.
Summarizing:
- SMT tells me battery full pack is 52.9 kWh.
- SMT tells me buffer is 2.4 kWh
- I've loaded 47,56 kWh from 10% to 100%. So, full battery pack should be 52.8 kWh WITHOUT buffer.
Theories?
a) 100% does indeed includes buffer. This should not be the case because buffer is just that... buffer "just in case..."
b) SMT does not include buffer in Nominal Full Pack. But this is not what I've read in documentation.
c) Tesla has changed CANBUS protocol in later updates and now does not include buffer in Nominal Full Pack readings.
d) Tesla decrease buffer in order to deal with battery degradation.
e) I don't know how to calculate a rule of three.
By the way, I've seen a video from Bjorn Nyland where he takes a 2021 M3 with 100km and 52.5kWh Nominal Full Pack and a previous one with a 55 kWh Nominal Full pack (not the same car).
Just curiosity.
AlanSubie4Life
Efficiency Obsessed Member
How did you measure this?
95% efficiency is too high - it's actually not possible. Tesla clearly documents that charging efficiency on Model 3 is about 88-89%. Basic Search | Document Index System | US EPA
Anyway, I suspect this is the root of your discrepancy.
The right way to determine how much energy you added to your pack is to take the delta on the SMT numbers for your pack energy content before and after the charge. Since you have SMT this makes it easy!
For your vehicle, the car will display (on the screen in the car) from a 10% to 100% charge that you have added (I'm going to assume 55kWh for the degradation threshold, I think it may be actually slightly lower - someone needs to check the data - I think it has been posted here before) ~55kWh/263mi * (0.9 * 52.9/55*263) = 47.6kWh. (Obviously a lot of numbers cancel here - it simplifies to 0.9*52.9kWh - but I write it this way to show the separate factors.) This is because the car does not display the actual energy added to the vehicle battery pack - it displays the number of miles added (in your case 90% of ~253mi (407km), which is 228mi (367km) ), multiplied by the charging constant which is (roughly) 55kWh/263mi = 209Wh/mi (130Wh/km).
But on SMT you'll see the delta is 0.955 of that, which is 45.5kWh (you started at 2.4kWh+5kWh ("10%" SOC with 0% being 2.4kWh) and ended at 52.9kWh). Because that's the actual energy added. Also gives roughly 90% charging efficiency if the EVSE (charging station screen) said it added 50kWh.
SMT includes the buffer in NFP.
It's a very common point of confusion, because people naturally think the car is displaying the energy added to the vehicle when it displays that number after a charge event. Unfortunately it is not - it's displaying the result of a calculation based on BMS estimates, which is then scaled up by 4.5% for inexplicable reasons (it boils down to the discrepancy between the charging constant and the actual energy content of each displayed rated mile, which of course differs by 4.5% due to the buffer of 4.5%). (I guess it is scaled up by 4.7% since 1/0.955 = 1.047 but you get the idea.)
This issue and the similarly inexplicable position of the rated line (which is 5Wh/mi or 3Wh/km higher than the actual charging constant) cause no end of confusion here. That and the degradation threshold (but that's a transient issue). And also the behavior of the Energy Consumption screen confuses people because it suffers from related issues.
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