If the RX-8's speedo is not 100% correct from the factory....
05-14-2009, 04:26 PM
#27
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Also, do you know if there is a way to make the digital speedo to read the speed smoothly? Cause, I don't like it when it skips 2 or 3 mph, I find it pretty annoying. It's nowhere near as bad as an s2000 or a civic, but it would be great if it read as fast as the Chrysler 300's digi speedo.
05-14-2009, 05:06 PM
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I've noticed that as my tires wear the speedometer becomes a little more optimistic. I think it was very accurate when new but now that the tires are about 2/3rds worn down the speedometer reads about 3 to 4 MPH fast.
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05-16-2009, 12:22 PM
#30
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There's a difference between the vehicle speed sensor and the wheel speed sensors. I'm assuming the RX8 uses the same setup as most cars I've had...
Wheel speed sensors are used for ABS and traction control and measure each wheel's rotational speed. The vehicle speed sensor on the output shaft of the transmission generates electrical pulses that are read by the microcomputer in the instrument cluster. The pulses are used by the odometer to calculate distance travelled and the speedometer to determine velocity. Wheels speed sensors are not used by the speedometer or the odometer.
If you change either the differential gearing or the overall diameter of the wheels, you will introduce EQUAL error into both the odometer and speedometer readings.
There is no way for the car to "self-calibrate" the speedometer. Going back to the original post, it's one of the reasons why using the speedometer to measure 0-60 is ridiculous. The magazines use an expensive and sophisticated version of the G-tech to do their measurements, which contains multi-axis accelerometers to accurately read acceleration and derive quarter mile, skidpad and braking performance numbers.
Ok. Tell me where I'm wrong.
Wheel speed sensors are used for ABS and traction control and measure each wheel's rotational speed. The vehicle speed sensor on the output shaft of the transmission generates electrical pulses that are read by the microcomputer in the instrument cluster. The pulses are used by the odometer to calculate distance travelled and the speedometer to determine velocity. Wheels speed sensors are not used by the speedometer or the odometer.
If you change either the differential gearing or the overall diameter of the wheels, you will introduce EQUAL error into both the odometer and speedometer readings.
There is no way for the car to "self-calibrate" the speedometer. Going back to the original post, it's one of the reasons why using the speedometer to measure 0-60 is ridiculous. The magazines use an expensive and sophisticated version of the G-tech to do their measurements, which contains multi-axis accelerometers to accurately read acceleration and derive quarter mile, skidpad and braking performance numbers.
Ok. Tell me where I'm wrong.
Oh duh. haha. You're definitely right. I totally neglected to realize the fact that the wheels are rotationally connected to the shaft haha. (I'm an engineer, and I should have realized that). Thanks for pointing that out.
(The wheel speed sensor btw I mixed up bc of semantics, I wasn't even taking those systems into consideration.)
Now since that is in fact how it's calculated, maybe I'll make my millions debunking odometer fraud.
05-16-2009, 01:53 PM
#31
It's a Cavalier
iPhone does work well to measure acceleration and skidpdad. In a Road and Track article, the Dynolicious app was tested against a Gtech Pro, a professional accelerometer called the VBOX, and an onboard computer in an SRT8.
The iPhone was accurate to within a couple of tenths of a second in each test run.
To read about it, check here
http://www.bunsentech.com/2009/dynol...oad-and-track/
Here's the results chart... doesn't translate too well, but it's readable. VBOX is the control (by far the most accurate)
VBOX | Charger SRT8 | G-Tech Pro SS | Dynolicious
0-60 mph, sec
Run 1 5.44 5.59 5.66 5.52
Run 2 5.51 5.70 5.73 5.63
Run 3 5.56 5.74 5.77 5.87
1/4-mile, sec @ mph
Run 1 13.93@103.8 14.01@103.9 14.15@101.8 14.11@102.9
Run 2 13.85@103.7 14.06@104.6 14.09@101.5 14.15@102.9
Run 3 13.91@103.7 13.99@104.4 14.13@101.7 14.15@105.8
The iPhone was accurate to within a couple of tenths of a second in each test run.
To read about it, check here
http://www.bunsentech.com/2009/dynol...oad-and-track/
Here's the results chart... doesn't translate too well, but it's readable. VBOX is the control (by far the most accurate)
VBOX | Charger SRT8 | G-Tech Pro SS | Dynolicious
0-60 mph, sec
Run 1 5.44 5.59 5.66 5.52
Run 2 5.51 5.70 5.73 5.63
Run 3 5.56 5.74 5.77 5.87
1/4-mile, sec @ mph
Run 1 13.93@103.8 14.01@103.9 14.15@101.8 14.11@102.9
Run 2 13.85@103.7 14.06@104.6 14.09@101.5 14.15@102.9
Run 3 13.91@103.7 13.99@104.4 14.13@101.7 14.15@105.8
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