Do P85Ds and S85Ds have inaccurate odometers that overstate distance traveled?

[NOLA_Mike]

I think Tesla is probably just using a bad calculation somewhere.

Or, for the conspiracy theorists among us they did it on purpose to show slightly better range on the Dual Motor cars than you're actually achieving...

(Note, I'm not included in the conspiracy theorist group and think this is just within the allowable margin of error.)

Mike

 

[EarlyAdopter]

This may all be true.

But that doesn't explain why people who have owned the Model S before are seeing an issue now when they didn't have one before. For example:




I think Tesla is probably just using a bad calculation somewhere.

Did both cars have the same wheels and tires, with roughly the same wear on them?

 

[Andyw2100]

Did both cars have the same wheels and tires, with roughly the same wear on them?

He said he made a dozen trips, and on the first trip with the P85D noticed a huge difference. I would have to assume that those dozen trips were made over enough of a time span that the tire wear wasn't the same on all 12 trips. The first trip with the P85D, however, was certainly on very new tires, so any overstating of distance due to tires being worn would not apply. If anything, the mileage should have come up short on that first trip, with new tires, as compared to other trips with worn tires.

To help answer those who are suggesting that this is normal, could some of you who have had Teslas before please confirm that they did not exhibit this issue?

Thanks.

 

[wk057]

He said he made a dozen trips, and on the first trip with the P85D noticed a huge difference. I would have to assume that those dozen trips were made over enough of a time span that the tire wear wasn't the same on all 12 trips. The first trip with the P85D, however, was certainly on very new tires, so any overstating of distance due to tires being worn would not apply. If anything, the mileage should have come up short on that first trip, with new tires, as compared to other trips with worn tires.

To help answer those who are suggesting that this is normal, could some of you who have had Teslas before please confirm that they did not exhibit this issue?

Thanks.

This is a trip I've done pretty close to 100 times since I got my driver's license when I was 16. The main portion of the trip has remained the same with minor changes over the years. With the Model S, an obvious change is different fuel stops, but the distance difference is pretty negligible.

I've done the trip about a dozen times in a Model S (in both my old P85 and my fiance's P85) and once so far in the P85D at < 1k miles. In both P85's I always got within +/- 1 mile of expected distance door-to-door. I don't really deviate from my route, and +/- 1 mile seems pretty good accounting for other variables (like being in a different lane around a bend and such).

I'll be doing the trip again in the P85D soon now that the range issue is somewhat sorted out.

 

[eco5280]

This is a trip I've done pretty close to 100 times since I got my driver's license when I was 16. The main portion of the trip has remained the same with minor changes over the years. With the Model S, an obvious change is different fuel stops, but the distance difference is pretty negligible.

I've done the trip about a dozen times in a Model S (in both my old P85 and my fiance's P85) and once so far in the P85D at < 1k miles. In both P85's I always got within +/- 1 mile of expected distance door-to-door. I don't really deviate from my route, and +/- 1 mile seems pretty good accounting for other variables (like being in a different lane around a bend and such).

I'll be doing the trip again in the P85D soon now that the range issue is somewhat sorted out.

Go measure your tires diameter - are they the same?

 

[wk057]

Go measure your tires diameter - are they the same?

I don't really have any way to accurately measure the tires to within the ~1/8" tolerance needed to check this for the 0.8% discrepancy.

If the discrepancy were from calibration being for the average tire size through a wear cycle, the reading on the P85D should technically be *lower* in the early stages of tire life and higher in the last moments of tire life (with the average across tire life being close to actual), not the other way around with a higher reading at < 1k miles. I'm almost going to have to throw out all tire-related theories based on that alone, personally.

Edit: I'm half tempted to adopt the tin-foil-hat theory of purposely inflating efficiency numbers per mile by 0.8% for dual motor setups. Applying this to efficiency numbers would result in a 2 to 3 Wh/mi bias (showing slightly less usage per mile than actual). However, since the gap is/was so extreme (more than 1%) I'm thinking this wouldn't make much sense to do on purpose, especially since 2 to 3 Wh/mi would be well within a margin of error on such a test.

 

[eco5280]

I don't really have any way to accurately measure the tires to within the ~1/8" tolerance needed to check this for the 0.8% discrepancy.

If that's all that's needed to cause this discrepancy can't we agree that it could just be tire wear causing this issue? Or tire variance from the mfr?

 

[wk057]

If that's all that's needed to cause this discrepancy can't we agree that it could just be tire wear causing this issue? Or tire variance from the mfr?

If the discrepancy were from calibration being for the average tire size through a wear cycle, the reading on the P85D should technically be *lower* in the early stages of tire life and higher in the last moments of tire life (with the average across tire life being close to actual), not the other way around with a higher reading at < 1k miles. I'm almost going to have to throw out all tire-related theories based on that alone, personally.

See my post above on why I don't think that makes sense.

 

[Danal]

Just measured 37 mile run. Car showed .7957% further than GPS.

Two week old P85D on .179

 

[gpetti]

For reference, I'm driving on 19" blizzaks. I did set the car to 19"

 

[jerry33]

Go measure your tires diameter - are they the same?

You can't use the diameter (or the circumference) of the tire. Use the RPM from the tire manufacturer's tables. Note that the number is an average so very new tires and very worn tires will show differences from the stated RPM. Tesla would use the RPM value supplied by the tire manufacturer to calculate the miles traveled.

- - - Updated - - -

For reference, I'm driving on 19" blizzaks. I did set the car to 19"

Go the the Bridgestone site and get the RPM, then go to the Michelin site and get the RPM for the OE tire.

 

[Andyw2100]

Just measured 37 mile run. Car showed .7957% further than GPS.

One week old P85D on .179

Thanks, Danal. That's some pretty precise data there, and awfully close to the .8% number being bandied about.

Edit: With this additional piece of information I decided that there was enough evidence to bring this to Tesla's attention. I just sent the e-mail message below to the head of engineering, with a copy to Jerome Guillen.

---
Hi <first name>. We’ve corresponded a bit before.

I’m writing now to alert you to an issue that you should definitely be aware of if you aren’t already. That issue is that the P85Ds and perhaps the S85Ds as well seem to be overstating the actual distance traveled by a fairly significant amount in a way that other Tesla Model S vehicles have never done in the past.

I started a thread about this on the TMC forums, to seek input from other Model S owners. I wanted to make sure that this was a real issue before bringing it to your attention. At this point the evidence is pretty compelling that there is something wrong. Perhaps it is just a simple programming error that can be easily corrected.

I’ll include a link to the thread below, as well as my opening post in that thread. I’d urge you to either read through the thread or to have someone on your staff do so if there is any doubt in your mind that this problem exists. Of course if you are already aware of the issue I trust that you and your staff are already working on correcting it.

Thanks very much!

 

[eco5280]

Fair enough, I'm no expert. Just thinking "out loud". But - over a 4-yr mileage of say 60,000 miles, we're talking about a discrepancy of 480 miles. That doesn't affect the value of the car - it's not as if a car with 60,223 is worth more than one with 60,705 miles. I don't understand why this is a big deal exactly. Are we saying that other mfr's odometers are so much more accurate that Tesla is not within the standard of the industry? I've had so many speedometers be off by ~ 5-10%, and always faster than I was actually going.

 

[Andyw2100]

Fair enough, I'm no expert. Just thinking "out loud". But - over a 4-yr mileage of say 60,000 miles, we're talking about a discrepancy of 480 miles. That doesn't affect the value of the car - it's not as if a car with 60,223 is worth more than one with 60,705 miles. I don't understand why this is a big deal exactly. Are we saying that other mfr's odometers are so much more accurate that Tesla is not within the standard of the industry? I've had so many speedometers be off by ~ 5-10%, and always faster than I was actually going.

I'm not sure anyone is saying it's a "Big Deal." But if all it's going to take to get our cars' odometers to be as accurate as other Model S odometers have been in the past is an engineer tweaking some software, why not alert Tesla to the issue, to allow them to begin the process of looking into it?

 

[billarnett]

You can't use the diameter (or the circumference) of the tire...

Why not?

 

[ACVolt]

Why not?

When a tire rolls down the road there is a deformation where the tire interacts with the pavement. The deformation changes the diameter of the tire and can change with speed and tire wear.

 

[eco5280]

When a tire rolls down the road there is a deformation where the tire interacts with the pavement. The deformation changes the diameter of the tire and can change with speed and tire wear.

But isn't the tire size / tire wear is going to affect true mileage vs. odometer readings regardless where the data comes from to calculate it? I understand one may be more accurate as a rule, but tires aren't all identical and neither is wear.

 

[Danal]

New trip, new data point: When the car clicked over 100.0 exactly, the GPS Odometer read 99.19. Even my mental math can see that's right on the 0.8%.

I did several other intermediate calcs, and they were all in the range of 0.79 to 0.81 error with the car always showing the larger (longer distance traveled) miles.

Danal

 

[Danal]

And, here is everything you never wanted to know about calculating odo/speedo meter errors and tire diameters. In short, 0.8% is WELL within the differences cause by tread wear. At the same time, it is in the exact wrong direction for a new tire. Therefore, as wear increases, the problem will get worse. Therefore, Tesla still should take a look.

Anyway, here's the math. Let me know if I slipped up somewhere:

P85D Odometer and Tire Calculations

 

[eco5280]

0.8% is WELL within the differences cause by tread wear.

I thought it would be, thanks.

At the same time, it is in the exact wrong direction for a new tire. Therefore, as wear increases, the problem will get worse.

Totally true, great point.