Hey JMD, no offense taken on this end! I really shouldn't have said it'd be "dead nuts" accurate. That's taking it a bit too far on my part because you're actually right in the fact that the factory usually uses a gear that's at least one tooth different from the answers I get from Jam's calculator. What's interesting though, is I've ran the gear Jam recommended and also have ran the gear the factory used, and neither of them were right on the money. For example, 3.23 ratio with 245/50/16, the factory combo was 17/44, and Jam recommended 17/43. Just to see which combo was more accurate, my city set up one of those flashing speed things that tells you how fast you're going, and I decided to see what their gadget said with either gear combo. Well, with one combo, my speed was actually higher than what my speedometer said, and with the other combo my speed was lower than what my speedo said. So in other words, neither combo was dead on the money. With Jam's calculator, you actually end up having to round up or down to the nearest match, because it'll say something like 43.2 or 43.7 for the number of teeth required on the driven gear. It's almost never a perfectly even number, so you end up having to round either up or down to the nearest whole number.
Lol. Sometimes I wonder if the newest cars out there that use an electric, pulse type speedo and a more powerful PCM have the capability to make the speedo read perfect? This simply isn't possible with a mechanical, or cable-driven speedo, but maybe it is possible with the electric ones. Whatever the case, whether I use the factory gear combo, or the Jam calculator combo, either of them comes out close enough to where I don't get busted for speeding!