If it fit I would be interested to see how it would do. My old 09 did great with 15/42, rode from rasor rd. CA (about 30 miles past Barstow towards Vegas) to Huntington Beach at about 80 the whole way (so actually 72 ish) got up to 100 (so 90 or so) for a second, the bike was screaming but it actually handled really well. That ride was a bit long but I enjoy hour long rides on the freeway. I only weigh 150 so maybe that helps. I like to imagine what people think when there getting past by a 20hp dirtbike on the freeway =P

 

I have a 2010 KLX 250S. I ran 15/42 on stock motor with no problems. Yeah I had to down shift on big hills and I'm 225 pounds. Bike pulled that gearing just fine. I did use 14 for all day offroading. I ordered 330 kit , DG R-series slip-on , kdx 220 air box mods with jet kit. I found with the 15/42 gear that it is under geared again with all the new power. I do more hwy riding then offroad. So I don't want the engine in the high rpm range. Since the 16 won't fit. That leaves dropping the rear to a 39. If your not happy with the power then get a big bore kit. Wish I done it first thing. If anybody has any questions about my setup , I'll be happy to answer them.

 

I used 15/39 combo on my 2007 (351) when I did a SS1000/BB1500. I "almost" had to shift down into 5th on a couple of long mountain grades.

I don't think a stock 250 would be very happy with gearing that tall.

Ron