I use 13 or 14 depending on the ride. 45 Rear. (longer chain required) snail cams end up at 5.5 or 7 on my 06.

don't use a klx300 sprocket unless you swap to a klx300 collar. The 250s 13t is common with the mohave quad sprocket

 

Having the supermoto version with a taller tire, my 13/39 is slighly taller than the klx250s' (avon distanzia 130/80/17) 13/42, however it really made the bike more enjoyable on the street, I never see more than 60-65mph on the street, and if I do, my 6th gear is closer to the sweet spot of the rpm range just to give it throttle and go a bit easier when passing cars. I plan on doing the 42 in the back to = your 45 in the rear then swap 13 or 15 front depending if I am going to city ride or plan a long trip.

 

i probably couldn't have done my san francisco to san diego, and back along the 5 highway if i didn't have 15/39 gearing on my klx250sf....since flow of traffic was roughly 80+ mph along the long flat stretch along central california....i also have a lifted klx250sf with taller tires which puts me on my tip toes at stops....

13/39 is enough to lift the front up....13/42 seems like overkill....15/42 would feel similar to the stock 14/39...i switch between 13/39 and 15/39...if i wanted it perfect..i think 13/40 and 15/40 would be my two combinations....but, i've only been able to find aluminum rear sprocket in a 40t for the klx250s/sf...

 

I meant 16 front not 15 haha so shorter than stock and then taller when i chose. But i never go past 65 mph in vegas

 

I just recently put a 15t up front
only one size larger then stock

it saved me 800 rpm on the freeway, and my speedo is now calibrated dead on
so at 65 mph im at 7000 rpm
I dont think I can even hit 75 mph but never tried since adjusting the speedo

I dont know who posted you can hit 100, maybe if the speedo is way off like how it comes from the factory

or who posted you can gain top speed from going 1 tooth smaller I would think if I lost 800 rpm going one bigger then you would add 800 rpm going one smaller
so at 65 mph your now at 8600 rpm, you would be screaming in 6th gear
and thats with the calibrated speedo
non calibrated I think you may be reading 75mph at 8600 rpm

unless the bike is used only for roads and trails then who cares

 

16? I think 15 the largest available/that will fit.

 

Jt sprockets makes as large as a 16 for the klx

 

But will/does it fit?

 

I figured since they manufactured it for the bike it would fit, but who knows haha, I've never heard anyone try it before

 

I've never yet heard of anyone fitting a 16T. The sprocket fits other applications. If you fit a 16, let us know how it goes. I have doubts though...