pete8717

Hey guys. Does anyone know anything about calibrating the speedometer on the 81 non turbo ZX's? Mine is about 5-6 mph's fast and I have no idea how to fix it. Some help would be appreciated. Thanks guys. L8rZ

Pete

NismoPick

You match the speedo cog w/ the diff ratio. Do you know which color speedo cog you have? Do you know what diff ratio you have?

pete8717

I don't know the color of the cog but i'm pretty sure i have the 3:90 gear ratio.

NismoPick

Okay, is it the orig tranny, rear end, and speedo? Are you using the stock tire size?

pete8717

Original tranny, rear end and speedo. I think i'm using smaller tires though. P195/60R14

NismoPick

Smaller tires = faster speedo reading.

lww

http://www.miata.net/garage/tirecalc.html

pete8717

I knew my speedo was about 5 off but does anyone know how to actually change the speedo calibration so it reads accurate?

NismoPick

Well... you have to calculate how many revolutions off it is from stock. Using that website L-Dub posted is probably the easiest way. Then you could either take the speedo to a shop willing to re-calibrate it for you (they will likely charge a nice bit of $$$cash$$$), or get a speedo tranny cog that will bring it closer to the real reading...

pete8717

How could I tell which cog to get?

NismoPick

Well, the smaller tires are acting as a higher ratio diff (If I'm thinking this out correctly). So... you could try to find a 4.11:1 cog (pretty rare actually). I think the easiest solution would be to get the right size tires.

pete8717

I did not know that. Ok thanks. In december i'm puttin on my new rims and according to that lil conversion page my speedo will still be a little off. It will only be about .1 off so I ain't worried about it. I'm going with P205/ 65R15 and that is the closest I will get

260zturbo

http://atlanticz.ca/zclub/techtips/d...tial/index.htm

4.11:1

* 720 4X4 6/83 to 12/85 - R180
* 200SX Turbo 1985 to 1986 - R200
* 200SX Turbo 1985-1998 -R200 (Canada)
* 200SX Non-Turbo's 1984 to 1988 - R180
* Ring gear is stamped with 37:9

also found this pretty cool website
http://www.nicoclub.com/Greg/ratios.html