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Correcting Speed-o for larger tires

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Z3PR, Jun 21, 2002.

  1. Z3PR

    Z3PR Banned

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    Okay, I'm planning on 35" tires and lower gears. How will I correct the speed-o ???? Don't like tickets-o. /forums/images/icons/grin.gif /forums/images/icons/confused.gif /forums/images/icons/confused.gif
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Best way I know of is to get an electric speedo converter and run an autometer speedo that you can adjust no matter how many times you change gears/tires.
     
  3. shane74

    shane74 1/2 ton status

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    Take it to a local speed shop. They can fix you up pretty cheap. At least cheaper than a ticket! /forums/images/icons/wink.gif
     
  4. Blue85

    Blue85 Troll Premium Member

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    An electronic speedo calibrator is worthless in a '76 Blazer since it has no electronic speed signal. You could always regear and retire in the same proportion so that you speedo ends up still being correct (fat chance) OR you can just change the plastic speedo gears. Do a search and you will find a lot of information here. Basically, you will find out what color your gears are now, find the rolling radius of your new tires and use a chart (you'll find links in your search) calculate what speedo gear(s) you need and pick that up from a local dealer or speedo shop for cheap.
     
  5. Diesel Dan

    Diesel Dan 1/2 ton status

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    No need to even get inside the case to change speedo gears.

    Just figure out the percentage you are off, have someone drive at 60mph and you pace them to figure out what yours is reading. Then a speedo shop can built a reduction box with that ratio, it screws onto the 'case and your cable screws onto it.

    Had a friend that worked at a semi shop and we used something better. It was an electronic unit that went onto the speedo out put of the 'case. Rolled the truck a set distance and it gave off a ratio code say 1.036 or so. Looked up on the chart and it told what gears to use in the ratio box. We used factory ratio boxes and just regeared.
     

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