Speedometer calibration question (non-GN)

[John84GN]

I recently bought an 85 Chevy Silverado with 32x11.50x15 tires on it, and the speedometer is NO WHERE NEAR correct...I was wondering if there was a calibration chart to punch in the numbers, and see what my actual speed was at...lets say...60 mph...is there any?!? I already looked at the TCI website, but I don't know what teeth are it it, and the axle ratio is, so thats not much of a help...I just what to know about how much it is off, so I don't get into any trouble

Thanks

 

[MeanBuicks]

If you don't know what rear gear or what speedo gears you have, what numbers are you going to punch in? Even if you knew the size of the original tires there's no guarantee that comparing srictly tire diameter differences will yield accurate results because you're not sure if the previous owner swapped rear gears too.

You could do some investigative work and obtain your rear gear ratio and speedo gear tooth counts, or you could figure your speedo error by traveling an indicated 60 mph between two highway mile markers, timing the vehicle and calculating the error.