I am super interested to hear your feedback.

I’m running 13/50 sprocket combination and I think a properly uncorked 250cc bike with this combination and your wide ratio gear box, especially with a pumper carb, would be an absolute beast. Nice and low in 1st and yet adequate to run 60+ at relatively relaxed RPMs for somewhat extended periods of time between the trails.

 

This is a game-changer! Unlike some of you guys, I'm not sure hardcore so I'm contemplating on just running a 15T front sprocket to lower RPM's between trails but this might be the solution for everything!

 

Be careful running a 15 tooth counter sprocket. I did for about 1,000 miles and I had a bit of wear against the cases wear the chain was rubbing into the aluminum. I swapped back to the 14 tooth with a 39 tooth rear since I have a 351 big bore and it's able to pull that gearing.

 

Any updates on this swap? Do you have the part numbers of the gears that need to be replaced? I'm really interested in what you did here with this swap. I have a 2006 and I love the extra overdrive 6th gear with the 351 big bore, but having a lower first gear would be great especially since I'm running a 14/39 sprocket combination.

 

Gotcha yeah that's smart. Do you think a KLX250 would be able to pull a 39 tooth rear sprocket? If not, what count would you recommend for a stock KLX for it has a slightly higher road bias and less technical dirt riding?

 

I ran a 15/38 or 39, forget exactly which one. I didn't shift to 6th until over 4000 rpm, which was near 60 if I remember right. It requires downshifting to hold speed at times when hitting smaller grades. It is just pushing a lot of wind at that point and needs to rev to use the power between 6000-8000 rpm to do it.

 

I'm not sure a stock klx 250 could pull a 14/39 tooth sprocket combination. I have that setup with my 351 big bore and although my 06 klx has a 6th: 0.904 vs 0.952 for the 09+ klx I still don't shift into 6th gear until almost 60 mph. I haven't found a 40 or 41 tooth rear sprocket, but jt sprockets offer rear sprocket sizes: 39, 42, 43, 44, 45, 46, 47, 48, 49, 50, 52, 53. The stock 14/42 sprocket combination is actually decent for the klx. If you do decide to go with a 39 tooth rear sprocket to drop the rpms while cruising on the road let us know how you like it.

 

Good stuff. Yeah I have a JT 15T for my '18 KLX250 just haven't swapped it in yet. It's dipping into the 10's tonight after the blizzard storm we had here in Virginia. For most of my riding here it's mostly road and to be honest, I'm about 177 lbs and it's out of steam around 65 mph and starts to get kinda buzzy. Don't need much just a little more up top just to keep up with traffic here at 70 mph is all I'm really looking for. So I'll swap in the 15T front sprocket but be cautious of the rubbing (hopefully not) of the casing and see how I like that. I read on the forums that the ratio is an increase in +1 tooth to the front is about the equiv of -3 tooth in the rear. I just wish they made something like a 40 tooth rear sprocket incase the +1 tooth front sprocket is way too much for the KLX to handle.

 

Well, only have had a couple short rides so far, no trail riding but it is so much better IMO, it does NOT seem too wide at all, I did ride around on the street and running my 14/45, love it. So comparing to a new 2021 bike with the same sprocket combo, I have a lower first and my 5th gear is just a hair lower than a 2021 6th gear so my 6th is another 8 to 10 MPH @ same RPM higher. I ride mostly off road so the option of the stock 42 or even worse a 39 rear would never see the light of day on my bike, when in riding in Colorado ST I would run either a 13/47 or for real steep tight ST 13/50, I have three Chains to accommodate my sprocket options , as I have a 12/13/14/15 for the front, and 42/45/47/49/50 for the rear, This is the Transmission Kawasaki should have put in the DS version of the 250/300's.
As weather permits, I will post actual GPS speed RPM's later as my 07 Speedo reads about 5 MPH higher than actual.

 

I would like to see the max top speed on level ground with same wind comparisons with sprocket options. I'll put money the stock gearset is faster top speed. NO CHEATING!