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Old Feb 8, 2009 | 01:48 PM
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dduckie88
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does anyone know where the computer reads the speed if the ar and the mileage? i want to put on some 17s on my 86 to accomodate the C5 brake upgrade i plan on putting on but want to make sure i adjust everything properly if needed. ive heard two different stories, 1. that it is measured on the axle, and 2 that it is measured in the rear diff. also, im planning on putting CCW Classics on as the new rims. anyone have any suggestions on new widths? stock or wider? any performance increases? Thanks!
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Old Feb 8, 2009 | 02:05 PM
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Originally Posted by dduckie88
does anyone know where the computer reads the speed if the ar and the mileage? i want to put on some 17s on my 86 to accomodate the C5 brake upgrade i plan on putting on but want to make sure i adjust everything properly if needed. ive heard two different stories, 1. that it is measured on the axle, and 2 that it is measured in the rear diff. also, im planning on putting CCW Classics on as the new rims. anyone have any suggestions on new widths? stock or wider? any performance increases? Thanks!
Speed is measured by the VSS system (vehicle speed sensor) at the back of the transmission. There is a gear that slides onto the output shaft and is read by another gear that is wired to the car's computer. When you change your rear-end diff. ratio, you change the gears. I don't know how to change them for increase tire height though.
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Old Feb 8, 2009 | 03:07 PM
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If you keep the tire dimensions (diameter/RPM-revolutions per mile) equal or similar your speedometer/odometer calibration is usually not a problem. It's likely accommodated with only a change of the "driven" gear on the speed sensor which is transmission mounted. If you start changing the tire dimensions "dramatically" it can get more complicated.

I would suggest you "confirm" the accuracy of what you have before you start doing your replacements.
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Old Feb 8, 2009 | 03:50 PM
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I don't think you'll be off too far with the new rims and tires bolted up. A couple of the Corvette catalog companies sell an electronic calibrator box that you hook up to the car and adjust the VSS signal. The module stays in the car once installed. Price was ~ $200 if I remember right.

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