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no i mean the speed could have been recorded via ups, not what was on his dash.

But.

If the problem was 19 inch tires instead of the configured 21 inch, his actual ground speed would be LESS than reported. Meaning if he thought the speedometer said 45, and the tire size was configured wrong, any GPS measurement would read LESS than 45mph, not greater.

That's backwards, I think. The cars speedometer will report that it's traveling slightly faster than it's actually going. It thinks each rotation of the tire is X distance, when it's really traveling slightly less than X (cause of a smaller circumference). So the actual ground speed will be GREATER than that reported by the speedometer, not less. So if the speedometer says 45 mph, you might actually be traveling 47 mph. So an external measuring system (assuming it's accurate, which GPS isn't really) would show you traveling faster than what's reported on the dash.

The problem is that it assumes that Tesla is using speed data calculated via GPS (which they could, but I'd doubt it). Also, even if they were, it cannot possibly account for the vast differences between what the reporter claimed he was doing while "limping along", and how fast they measured him going. Oh. And we also don't know what the actual difference in total tire/wheel diameter is. The tire size is the inner diameter of the tire (the size of the actual wheel). The other numbers tell us how tall the sidewall is, and how wide the tire is (which is why when you see larger diameter wheels, they're usually accompanied with lower profile tires. The actual total diameter is unchanged). Most folks use offset calculations when changing to different wheel sizes so that the actual total diameter of the outer edge of the tire is very close to what it was with the original wheel size. Usually, when going to a smaller size, you get better performance and mph because while the total diameter doesn't change much, the weight of the wheel itself differs dramatically. That's weight that's pushed around with every rotation and has a bigger impact than the total diameter as the reporter seems to be trying to claim.


But then the reporter probably has no clue about the actual effect of changing out wheel and tire sizes. And of course, all of this assumes that Tesla didn't calibrate their speedometer to the size wheel that they themselves put on the car. Which seems unlikely to begin with.

Edited, Feb 15th 2013 4:16pm by gbaji

"I want to get a refund on my computer."

"Okay, can you describe your problem?"

"The cup holder was too flimsy and broke right off. Now my computer won't turn on."

".... Excuse me?"

"You know, the little cup holder tray. You push the button and it comes out. It's too weak for a Big Gulp. It snapped right off and spilled soda all over my computer. Now it won't turn on. None of the lights are working and it makes no noises."

"Sir, your computer doesn't come with a 'cup holder.'"

"Don't you tell me what my computer did and did not come with! I picked this model specifically because it had the cup holder."

"Yes, it has a tray that slides out, but -"

"You guys really need to design these things better."

"Sir, that's the CD tray."

"The - the what?"

"The CD tray. Your computer plays CDs. You put them in the tray and it reads them."

*click*

"Sir?"

Edited, Feb 16th 2013 1:10am by catwho

God I rated gbaji up to excellent. I feel dirty.