I was wondering how I can figure out what speedo gear I'll need for my car. All of the math I've found either in magazines or online use the default driven gear as a basis for the math, but I have no idea what my speedo gear's teeth are or if it's even a stock gear. Right now, I'm running an M20 transmission with a 3.73 rear end and 245/50/14's on the back. I'll be upgrading the tires to 255/60/14's later this week, so I'll need a speedo gear to match that.