Speedometer settings missing info?

[BlackWS6LS1]

Ok well the first time and everytime I've read the VCM, I've never seen any info in Previous (Saved) Tire Size and Gear so when I put in new Tire Size and Gear, it says no old data. But the real problem is that I put in the new tire size and gear and guessed what the old size was now its off by about 5-6 mph. I'm not sure what to do, I know they are 373's and I've measured the tire about 20 times. Let me know if any one has an idea. I've figured that it should of bought the size and gear into those blanks automatically.

Tom

[P_Mack]

Just scale your tire size the same amount your speedometer is off. For example, if your speedometer is reading 10% too high and you have 26" tires, put 26" in the new tire size box and put 28.6" in old tire size (because 26*1.10 = 28.6). This will scale the speedometer reading down ten percent.