Aftermarket Tach reads a little odd

[bikes&bowties]

Originally Posted by ToughBowtieTruck

Not really. It is cable operated, and is lubricated by either grease or transmission fluid. Difference in lubrication temps means the difference in the resistance for the shaft running the speedometer.

I have had trucks do that, and have had ones that will have a jumpy speedometer when they were warmed up too.

I guess that makes sense. Maybe never noticed the speed difference while going down the road... 5mph isnt that much i guess to notice going down the highway.