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Old 04-06-2010, 09:40 PM   #1 (permalink)
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Question Speedo Accuracy with MPGuino :-(

I have a Honda City (Which is Honda Fit Aria elsewhere), and I have an MPGuino, that I managed to put on, and calibrate with values for Honda Fit, as available on MPGuino Wiki pages

I have the values scaled to show me KM/L readings, so my us/gal value is scaled down by a gal:L ratio, and VSS pulses/mile is also scaled down by mile:km ratio.

With that, I am generally happy, and the gizmo is helping me achieve new heights in FE. The figures shown are also plausible, so I guess the calibration values are accurate. No worries on that count.

What bothers me is there is a distinct difference between the speed indicated by the MPGuino, and the speed on the analog speedometer. The MPGuino appears to indicate slightly lower speed.

Is that because the MPGuino, or the speedo are out of calibration? Is it true that speedometers are calibrated with an error on the positive side, and the speed indicated on the dial is always slightly more than the absolute speed?

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Old 04-06-2010, 09:49 PM   #2 (permalink)
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hummingbird -

Sounds like a job for a GPS cross-reference test?!?!?!

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Old 04-06-2010, 10:27 PM   #3 (permalink)
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Car speedos can vary quite a bit, but the odometer should be accurate. I would synch the mpguino distance calibration up with the cars odometer and call it good.
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Old 04-06-2010, 11:25 PM   #4 (permalink)
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If the odometer is consistent with the MPGuino's reported distance, then the MPGuino speed is probably the more accurate one. Analog speedometers can be off, especially if your viewing angle is not the same as the intended one.

Our Yaris, for example, has the gauge cluster in the middle of the dashboard, not right in front of the driver. So, when the needle is straight up, at around 60MPH, it looks like it's around 64MPH for the driver, but 56MPH for the passenger.

We just took a trip with a GPS, and I ended up using that as the speedometer for dialing in highway speeds. If I had an MPGuino or SGII in that car, I would use that as the speedometer. In my Tercel, I use the MPGuino, but that's because I know the gauge is off anyway.
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Old 04-07-2010, 12:26 AM   #5 (permalink)
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GPS outta question, as of now. (Waiting for the next best sexiest GPS phone, which will be cost effective - it's like chasing a mirage!)

Cross-check with odo is a good idea, I'll do that over the weekend where I travel at least 30 miles in one go, so as to bring out small differences if any.

OT: My regular trips are 5 miles one way, which are a big let down for FE - the engine is barely warm by the time I pull up in my office parking lot. And that makes me realize hypermiling can mess you up in the head - making you yearn your average trip length were more so as to score better on FE

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