Bob,
I'm pretty sure the rear on an SM is 42 also...
I have an '03 TA, and I went to an 18 front. That was early on before I rejetted and removed the snorkel, installed TBS needles, and TBike pipes. I definitely noticed a difference starting out with the 18 tooth sprocket. You had to get the revs up a bit.
After the other mods, however, the bike runs a lot stronger, even at idle, and the 18t is no longer an issue when I start out.
In all the sprocket discussions on here, it has never been mentioned that the results are quite different between stock and an engine that has been tweaked a bit....
