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Discussion Starter · #1 ·
Is the speed shown on your speedometer measured by the front wheels or the rear wheels? Anyone know? My guess would be the front wheels.


[Modified by adsl_keeki, 9:21 AM 1-29-2003]
 

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Re: Speedometer measures speed of the front wheels or rear wheels? (Max Rebo)

quote:[HR][/HR]Off the transmission
Yep. The tranny has a speedo gear.[HR][/HR]​
Interesting, perhaps I'm retarded. Or is it because I have an autotragic?
 

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Re: Speedometer measures speed of the front wheels or rear wheels? (grue)

quote:[HR][/HR]Off the transmission
Yep. The tranny has a speedo gear.
Interesting, perhaps I'm retarded. Or is it because I have an autotragic?
[HR][/HR]​
No, no, you're OK!

The speedo drive gear is attached to the final drive subsystem of the drivetrain - that is, the output shaft of the transmission. Since the output shaft is directly attached to the wheels via the CV joints and hard halfshafts what the output shaft reads, once math is added to account for the circumference difference of the output shaft versus the tires, is directly readable as road speed.
This is why you get a different, inaccurate speedo reading if you oversize the wheel / tire combination greater than the 'plus' system figures. If you change the outer tire circumference over what was computed by the car manufacturer when the speedo system was created the speedo will not read right, as the output shaft is still spinning at the same speed but the tires will be traveliing a different distance per revolution of that output shaft.
 

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Re: Speedometer measures speed of the front wheels or rear wheels? (CBJ)

quote:[HR][/HR]Off the transmission[HR][/HR]​
That's right. That's why when you change your wheel diameter you get an inaccurate speed reading.
 

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Re: Speedometer measures speed of the front wheels or rear wheels? (dinosnake)

My previously clear-as-mud statement: "Yep. The tranny has a speedo gear,"
Should have been translated easily into dinosnake's description below.

(Thanks for the additional info!) http://****************.com/smile/emthup.gif
quote:[HR][/HR]
No, no, you're OK!

The speedo drive gear is attached to the final drive subsystem of the drivetrain - that is, the output shaft of the transmission. Since the output shaft is directly attached to the wheels via the CV joints and hard halfshafts what the output shaft reads, once math is added to account for the circumference difference of the output shaft versus the tires, is directly readable as road speed.
This is why you get a different, inaccurate speedo reading if you oversize the wheel / tire combination greater than the 'plus' system figures. If you change the outer tire circumference over what was computed by the car manufacturer when the speedo system was created the speedo will not read right, as the output shaft is still spinning at the same speed but the tires will be traveliing a different distance per revolution of that output shaft.[HR][/HR]​


[Modified by Max Rebo, 7:31 PM 1-29-2003]
 
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