I just posted this on a similar thread and then I realized the thread was dead since 2015. Here it is:


I have a 09 KLX 250s with only 400 miles and am planning on changing the gearing as well. I bought it years ago from a family member for a deal I couldn't pass. I bought it exclusively to use off road. I actually stripped it down and registered it as OHV only to not have insurance.

I was looking at changing the gears but mine, stock, is 15/42. I counted it 3 times to make sure it really was 15. I want it for OHV only, basically just narrow trails. I have zero need for top end speed. I tow the bike to where we ride from. I was thinking of going 13/49 but thought that might be too much coming from 15/42. Everything says add a tooth at a time but I don't have the money to buy that many gears. If im just going trails and want it to ride like a dedicated OHV dirt bike, should I go 13/45 or 13/49, or something else? Anyone else notice their stock sprocket was a 15? I originally planned on only changing the rear sprocket until I found out the front was 15.

Lastly, should I just sell it and buy a dedicated dirt bike instead of changing the gears to make it more like a dedicated dirt bike? Didn't want to run into more things I want to change down the road.

 

Tony, Welcome to KF.

Stock is 14/42. Someone put a 15 on there, most likely.
Get a 13 front and see what that does for you. It should work with the current chain and should be around $15. If that isn't enough, get a nice large rear sprocket that works with both the 13 and 15 so you'll have a good range of gearing to play with. Going up one at a time on the rear sprocket may make sense for racers and very experience dirt bikers, but for someone just wanting to see what the differences are, changing the front down a tooth or even two at a time is much more economical.

see this: https://www.kawasakiforums.com/forum...-length-42553/

I've played with quite a few combinations and currently run a 13/51, which is pretty darned low. One tooth up front is roughly equal to three in the back, so 13/42 is about the same as 14/45 or 15/48. You could also likely go as low as a 12 up front with the current chain and rear sprocket, saving some funds over buying a new chain and larger rear. You should be able to find reasonably priced sprockets from Sunstar and JT Sprockets.

edit: The KLX is a bit heavy for a dedicated dirt bike. A lot of us ride them in the dirt and with the beauty of having a plate and being street legal. It may be heresy around here, but I don't think selling the KLX and picking up a lighter, dedicated dirt bike is necessarily a bad idea.

 

I recently swapped mine to 13/42 and am thrilled with it. It now has a light front end, and cost me all of $10. Fantastic upgrade. For your description of riding, I'd suggest a 12.
Report back, I'll be anxious to hear your thoughts.

 

Thanks for the responses. I could not find any manufacturer that made a 12T front sprocket for the 09 KLX250s, which sounded like the best option. Guess I'm going to have to go with the 13 for now and test it out, see if I want to change rear too. I'm an absolute novice at working on dirt bikes, with a 13T front from a 15T will I need to take out links in the stock chain? Ill peruse and find a thread on how to deal with chains.

EDIT:

JT, Sunstar, Renthal could only find 13-15 for 09 KLX 250s. Found a PBI steel 12t on that allegedly works. Gonna give that a shot. Will the 12T be too much strain on the chain?

 

The 13 is going to be a big change from a 15. Regarding chain, did you look at the link I posted above? It should be helpful. The 12T shouldn't be too much strain as others have done it and many dirt bikes run a 12T. As I look at it, if you really want to gear down you'll eventually be getting a larger rear sprocket and longer chain to go with it. May as well hammer on the stock chain and get some life out of it.

Don't limit yourself to 09KLX. Also check the '06/'07 and I'm going to guess that KLX300 and maybe even '96+ KDX200 share the same front sprocket design (the rears are the same).

 

12t klx250 2009 | eBay

 

Spend the money and go for a 49T rear sprocket and leave the 15. Less chain wear because of less chain wrap and load spread over more teeth. It's a 3.26 ratio, 13/42 is 3.23. Go to a 14 or 13 for stupid low, I did a 13/47 and the bike would pull sand like no problem. I planned on doing a 13/47 for off road then 15/47 for road, but cut the chain 2 links short... bummer.

 

meh
use two master links

 

Didn't have two at the time... Maybe another day. I like the idea of a front sprocket change going from close to stock to really low off road.

 

I do too, which is why I thought the sprocket combo thread linked above would be helpful. The giant 51-tooth rear sprocket doesn't play well with all 13/14/15 CT combinations.