Speedo Calabration

My 1981 K-20 had 9.50 x 16.5 tires that were 30" tall I replaced them with BFG 12.50 x 16.5 that are 33" tall I used SnoMan's web site to see how far the speedo was off at 85 it was 93.5 see

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witch is A great siteThanks SnoMan I know that I can replace the speedo gear in the tranny this is A simple swap any ideas on the gear size or GM part #

Thanks Dave Las Vegas NV.

Reply to
Dave
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Try using two less teeth on the driven gear (one on the cable) and that should put you real close. Also for what it is worth, if you plan to regear sometime, one step deeper with current spedo gear would about be dead on too. Gears are color coded and I have about a half dozen of them here somewhere that I will have to dig out sometime and list the on my site by color and tooth count.

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Reply to
TheSnoMan

You know, that is something the vast majority of people don't know. Even people that work in drive line & speedometer calibration shops. Heck even when switching from one GM gear ratio to another the countermen don't know what speedometer drive gears go with what tire size and rear axle ratio. Charles

Reply to
Charles Bendig

Reply to
David Johnson

Borrow a Garmin GPS & read your speedometer every 10 mph on a flat road

vs. the true GPS speed... GPS reading is accurate to 0.1 mph...

This will put you in the ballpark as to the gear change needed...

Reply to
Dennis Mayer

Reply to
TheSnoMan

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