Passion/Brabus Odometer Accuracy?

[Brabus]

The speedometer is known to be 1.5% too fast on a Passion if I read DIY odometer thread correctly.

Can someone tell me how mileage is calculated on the smart?

After I read that I then wondered if the Brabus odometer is the same as the Passion. Then I'm wondering about the speedometer. Is the speed calculated base on the front or rear axle?

Here's what I used to do the calculations based on this tire calculator. I've been using this same calculator for years, yet I've never used it for a car with different size tires so I'm not sure whether to use the front or rear.

Tire Calculator
Tire size calculator

According to the calculator and tire sizes.

Passion front 155/60/15
Passion Rear 175/55/15
Brabus front 175/55/15
Brabus Rear 215/35/17

The Brabus front wheel would spin a complete rotation 1.1% slower than the Passion (yet the Passion is 1.5% faster making a net 0.4% faster).

The rear would spin 7.3% too fast! Meaning my odometer if the same as a Passion would be getting CONSIDERABLY more miles racked on it, 8.9%

(7.3 + 1.5) = 8.9

For example, approx 22k miles would read 24k miles.

My sister got a check from Honda a year or two ago. She leased an Accord and had went way over her mileage. Long story short she paid for the overage and to her surprise there was a class action lawsuit that people had filed claiming the odometer was wrong. She got a check in the mail without even knowing about it. I mention this because I was surprised Honda couldn't do something very basic (produce an accurate odometer), but apparently it's a more common problem than I thought.

The Passion odometer going 1.5% too fast is disappointing but not that big of a deal. If the odo measured by the front then the Brabus odo is pretty accurate (0.4% too fast). If it is calculated for the rear tires at 8.9% too fast, then this is a problem with warranty, lease and to some degree resale value.

[smcnally]

You've got your math backwards. A larger tire results in less rotations per mile so your odometer would read lower than it should if you have the larger Brabus wheels. Odometers are based on standard factory tire size for the car.

[Brabus]

Originally Posted by smcnally

You've got your math backwards. A larger tire results in less rotations per mile so your odometer would read lower than it should if you have the larger Brabus wheels. Odometers are based on standard factory tire size for the car.

You're right. Too fast on the speedometer means lower odometer. That's what I get for trying to think at odd hours.

[jetfuel]

Originally Posted by Brabus

You're right. Too fast on the speedometer means lower odometer. That's what I get for trying to think at odd hours.

...I think you should give up while you're ahead....

jetfuel....in Ziahuatanejo Mexico

[gbryers]

Actually, when I am traveling at highway speeds, with both the GPS and the ScanGauge on, I get the following:

Speedometer shows: 75
Scangauge shows: 73
GPS shows : 73

Since the odometer is driven by the computer (the same device, BTW, that reports to the Scangauge), I doubt that it is mis-reporting mileage. It is more-likely a mis-calibrated analog device reporting somewhat inaccurately the signal provided to it.

[Brabus]

Originally Posted by jetfuel

...I think you should give up while you're ahead....

jetfuel....in Ziahuatanejo Mexico

LMAO, you know I had a totally blond moment there. I could tell you some really funny (sad) blond moments I've had that I wonder where my brain is at times. I mean math was a minor of mine, too. I made str8 As through the highest levels of Calculus in college, but I swear I can be a complete idiot at times. lol Maybe I had too many lead chips as a kid. My elementary school was discovered to have lead.

Originally Posted by gbryers

Actually, when I am traveling at highway speeds, with both the GPS and the ScanGauge on, I get the following:

Speedometer shows: 75
Scangauge shows: 73
GPS shows : 73

Since the odometer is driven by the computer (the same device, BTW, that reports to the Scangauge), I doubt that it is mis-reporting mileage. It is more-likely a mis-calibrated analog device reporting somewhat inaccurately the signal provided to it.

Ah, another gadget I don't need but want. Thanks for the information. That makes sense. Especially people who put ridiculously big tires on their vehicles would get getting substantially free miles. I'm going to experiment with 4x 17" wheels since I have two sets of Brabus wheels. I bought tbone28's wheels. This makes me feel better about doing it. They just arrived today!

[Wdhitch]

Yes the speedo is off... I only use the Scan Guage for my speed now.

[John_H]

But is it always 2mph off? If so, adding a small grommet around the 0mph backstop would change the offset since the needle is reset to "zero" mechanically.

[Wdhitch]

No... over 70mph it's almost 5mph off... it says your doing 80 and you're only doing 75... it's ok up to around 45mph....

[gbryers]

And that is typical of most analog speedometers - I don't care what year or make of car. They may be tweaked to be more accurate at the "optimal" driving speed of the car, or not, but typically, they will be more accurate at lower speeds, then the gap widens as the speed increases.