Speedometer Question

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Jan 20, 2002 | 12:58 PM

Mr. C's 5

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Burning Brakes

Joined: Feb 2001

Posts: 936

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From: Reston VA

Speedometer Question

Does anyone know how the VSS translates drive shaft rpm into mph and if it can be adjusted to compensate for diffferent tire diameters? - C.

Jan 20, 2002 | 01:36 PM

Godspeed

Melting Slicks

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From: DFW TX

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Re: Speedometer Question (Mr. C's 5)

I believe the VSS reads MPH directly from the rearend, not the drive shaft (actually the torque tunnel.) If you change either rear end ratio or tire size you need to adjust the PCM, not the VSS. A custom PCM program can be done to correct it or you can use someing like a Hypertech to do it too. Good luck.

-Jeremy

Jan 20, 2002 | 02:29 PM

Mike Mercury

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Joined: Apr 2001

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From: S.W. Ohio. . . . . . NRA Life Member

Re: Speedometer Question (Godspeed)

Quote:

If you change either rear end ratio or tire size you need to adjust the PCM, not the VSS.

Actually, not correct. The VSS reads the ring gear in the carrier... which does not change with rear end axle ratio upgrades. But, tire size changes will indeed cause a speedo error. The Hypertech can correct for this.
Best to call them with your specifics before ordering.

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