2009 DRZ400sm I bought this bike with a little less then 600 miles. I have since put down more 60000 miles on the bike. I thought I would share a little about my bike and the modes i have been able to do.
1. Gearing I Run a 16 tooth front sprocket and a 37 tooth rear. And you can go all the way down to 35 tooth if you wanted to slightly modify the rear hub. I would advise against this. My opinion, a with mildly modified DRZ(exhaust and 3x3 mod) I would not go with taller gearing than 16-39 or 15-37.
2. Rear Tire, You can run up to 160/60 R17, My opinion 150/70 R17 is the best handling.
3. Rewiring Charging cable, by shortening and using a thicker gauge wire that is routed from the battery over to the starter relay and then back into the loom. As well as bringing down the Fuse AMP down to 15amp. 15amp is enough to operate 100 watts of light.
4. 4mm Stroker, Can be installed using the stalk piston and 91 pump gas. 5mm stroker needs to modify the crank case and replace the piston.