Hi from BC Canada

Just got a 2009 WR250R on Thursday (7000 km). What a blast on the road (paved and gravel). I have been riding a 2007 XT225, (16/45 road - 14/51 trail) but have also owned XT350, XR400, MR 175, TY 250, TR32 and IT 175. Currently also have a 1997 Scorpa Easy trials bike. Have not done a lot of research on gearing for the WR beside knowing not to go to a 12 tooth front. The current gearing sucks for the single track here. How would running a 13/14 with a 48 work? Use 13 for tight trail and 14 for road.
Will a 15 fit?

Great bike!

Welcome to the pack!

The 15 isn't going to fit without hitting the case, sadly. There is no problem putting a 12 on...hopefully you aren't going on the 'ZOMG NO!! The 12 will wear thru your chain slider and into the swingarm!' bullshit... It WILL NOT chew into the swingarm unless you are a complete idiot and never check your chain tension. Myself as well as quite a few others have run the 12 with no troubles (I still have the stock chain slider and wore out the 12t already, new chain etc...so you CAN run the 12). It's definitely the easiest fix for gearing the bike so it's more single-track worthy. I ran the 12/43 combo, on a ton of single track and it was awesome. I could still hit the highway and pass ppl and have throttle left to spare.