Speedo Error, Adjustments other than tire size? Options

[Van B]

So, compared to GPS, my Speedo is consistently 5mph too optimistic. My tires are 195/65-15. I’ve read in other threads that has shown to be a good size for correcting error.

So, not really wanting to go taller still, is there any other way to calibrate the Speedo?

Thanks,
Van

[Dave_Darling]

I only know of a few options correct your speedometer reading.

- Get tires with a rolling diameter that gives the reading you want.
- Get a cable-driven speedometer that gives you the reading you want.
- Use a GPS-based speedometer.
- Get ahold of an an old-fashioned rally odometer gearbox. You can change the number of rotations in versus the number of rotations out using different gears in the box. Change them until you get the reading you want.
- Have the speedometer recalibrated.

I don't think I would want to try recalibrating the speedo on my own. The speedo works by having the input spin a magnet, which induces eddy currents and therefore magnetism in an aluminum cup that is attached to the spring-loaded needle on the gauge. You either have to change how the magnet and cup interact (possibly changing the position or size of either or both) or change the tension of the clock-spring on the needle. Those are waaaaaay too fiddly for me to mess with, so I would probably take my gauge to Palo Alto Speedometer (who are local to me) and have them deal with it. Which would probably be expensive.

--DD