Quick question about speedo...

does my speedo read higher speed or lower speed than actual now that I have put 30in tires on my otherwise stock XJ?

Answer = Lower

Imagine a small tire the size of a donut - it would be spinning so fast that your speedometer would be off the scale.

Now imagine a tire about the size of your aunt Betsy after the Thanksgiving dinner. One revolution of the tire would take a lot longer than normal and your speedometer would show a lower than actual speed.

hit the "search" button, do a search for "speedometer correction" about the third or fourth post down will have a link to what you are looking for.

thanks!