you need at least 108, 106 is stock and won't work- trust me. order front sprocket for xr650L or ninja 250. there ya go.

 

you'll still need a longer chain. that's my point- it's ignorant to waste a perfectly good probably new oem chain when just going to 45 in the rear. you have to buy a new chain and sprocket. the same ratio can be had by lowering the front to 13 and keeping the stockrear. the oem chain obviously works with this setup and the mod can be had for $12 or so. 13/42 is exactly the same as 14/45. but if you want tractor climbing low end if you can say that about 20 horse or so, go 13/45. with a pipe and jetting, it's quite a wheelie machine with help and finesse, did i say help? yeah, you gotta clutch it to wheelie it. but it's easier with this ratio.