anyway to get accurate speedo readings with 3.90s?

[Foxfan88]

I have a 3.90 gear and a Zspec t5, not sure on the gear drive and my speedo gear is the white one for a 4.10 gear.

my speedo is sorta right, at lower speeds its pretty close. but once you start getting up in speed, like past 40 it starts getting more off the faster you go.

when i am cruising 65 mph, the speedo only says 55 and the faster you get the more gap you have.


is there any write ups on getting accurate readings?

 

[jrichker]

The stock range of speedo gears work correctly with a limited range of tire sizes. The 23 tooth white gear works good for some guys, but self destructs in a few months for others.

See http://www.corral.net/tech/gearcalc.html for more help

Check to see if there is a speedometer shop in your area. If there is, ask about the Stewart-Warner speedometer gearbox. I believe it is either a 777 Series Drive Joint Kits and Parts or 666 Series Drive Joint Kits and Parts. It is a small gear box that fits between the speedo pickup gear on the transmission and the speedometer. It has quick change gears that allow you to choose almost any tire size and rear end gear ratio you want. This will allow you to get the accuracy with within 1%-3%. The drawback is that it isn't cheap.
Please excuse the typo (their's, not mine) in the following picture - it should read Custom ratio adapters, not Custom radio adapters.

See http://www.gaugeguys.com/ratioadapt.htm for more info.