Is there a formula or something to figure out what kind of speedo gear you need for a tire size change so your speedometer is accurate?

 

there are some interesting calculators at www.4lo.com that will help with tire size,gear ratio etc, but nothing about speedo gear size calculation. When I went to bigger tires my Ford dealer figures it out for me---there have been some threads on several sites on the internet also regarding speedo gears.

 

mbuechler,

If this is for your 2002 truck, then you need to have a dealership reprogram the PCM. There is no mechanical speedo gear on the 4R70W after 1998.

This caculator will tell you how far off your speedometer is, or will be.

 

Thanks for the info, yes it is for my 2002!