location of speedometer reading
Thread Starter
Melting Slicks
Joined: Feb 2005
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From: Springfield VA,
location of speedometer reading
Does anyone know whether the computer speedometer reads off the front or rear wheels? I am changing wheels and my have to go with rear wheels/tire package that will be slightly different stock than stock. So my question is, if I keep the front wheel/tire package the same height, will I need to recalibrate the speedometer? Not sure how the computer figures out the speed and odometer readings, does it measure it by the rotations of the front, back or combination of the wheels? Thanks, Jeff
Racer
Joined: Nov 2004
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It measures it at a senson in the rear axle, changing the outer diameter of the rear tires will make speedometer inaccurate, not sure what it will do for stabiliy control/abs that use each wheels speed to take actions. I don't know if it compares the wheel speed to other wheels or to the speedo...
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 3,372
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From: Springfield VA,
Thanks. So the next question is how do I recalibrate the computer? The outer diameter will only change slightly, but it will change so I'm sure it will throw the calibration of by 4-5 mph.
Burning Brakes
Joined: Mar 2003
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From: Pittsburgh PA
Recalibration is done at the PCM. A hand held programmer or a professional edit is necessary. if the ratio of the front and rear diameters is changed the AH and ABS will be effected. I experienced this on my C5. The ABS kicked in too soon as did the AH. I think that if you keep the overall diameters within 1 inch of each other you'll be alright.
Heel & Toe
Joined: Nov 2005
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Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 3,372
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From: Springfield VA,
Originally Posted by aaaaa
Recalibration is done at the PCM. A hand held programmer or a professional edit is necessary. if the ratio of the front and rear diameters is changed the AH and ABS will be effected. I experienced this on my C5. The ABS kicked in too soon as did the AH. I think that if you keep the overall diameters within 1 inch of each other you'll be alright.
