Hi all!!
Just purchased a 2010 KLX250S and am STOKED. Question: It is currently stock geared. The original owner gave me (still new in packages) a 13tooth front and 50tooth rear gear set. Otherwise, gears are stock.

Questions - I think that if I only replace the front gear with the 13, it gears lower, better for trails. But what if I do both (front to 13 and rear to 50)? What will result, and will I need new chain?

I'll spend some more time researching such, but thought to introduce myself with this post. I'll be doing some town riding to/from work at around 55 and mostly Alaska trail riding.

Advice solicited and appreciated.

Thanks all - Matthew

 

I think that the gearing using both sprockets will be too low for the street. Sure, you might be able to climb a tree, but your top speed will be low and your revs high on the street.
I suggest that you try the 13T only as the 50T may require a new chain.

Craig

 

Matthew, welcome to KF!

I have a 51 rear on now and run either the 13 or 14 up front. fzrcraig is right, this isn't for street riding, its for trail use. If you go with the 50, you should be able to use any of the 13, 14, or 15 front sprockets with the right chain. Check out this thread:

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

 

I run my 351 with a 13 CS sprocket, which I had before the 351 kit. It will make 1st pretty low with the ablilty to ride on pretty slow sections without slipping the clutch and give you good punch out of slow sections. It will not change the top speed.
If you put the 50 on I would imagine that you will be shifting a lot more and the top speed would be reduced & rpms be quite a bit higher.
I would just do the CS sprocket and see how you like it. You will probably need a new chain if you put the 50 on, maybe some others can answer that issue.

 

I run a 14/50 setup on mine which is what the off-road-only KLX300 runs. I weigh close to 200 pounds, and first gear is still capable of climbing just about any loose, steep, nasty incline with excellent traction and without fanning the clutch with any abuse. I don't know...going to lower gearing than this would seem to make even a lot of dirt roads be a strain on top gear rpm much less pavement. Even at 14/50, I hate to run over 50 mph for very long due to the higher rpm on pavement.

 

Here is some food for thought. Lots of simple math.

If you are replacing the chain or if it is long enough I'd recommend you do the 50 with a 15 front. The bigger the sprockets the less the chain has to wrap, which is less rotation of the chain joint, less pin wear. Plus the load is spread over more teeth, meaning less chain pin wear and less wear on the sprockets. Too often riders jump on the small front sprocket when replacing the sprockets and chain without thinking about this. You also gain range possibilties when using the larger rear sprocket. Granted only buying a front sprocket, while not replacing the chain and rear sprocket, it is worth doing the 13, but if replacing sprockets and chain, the larger set just makes sense and is marginally more expensive. There is one other thing - the bigger sprockets will not have the chain hitting the slider on the swing arm as often. Yamahas have a real problem with the chain sawing the slider and even the swing arm.

The stock 42/14 is 3.00, the 42/13 is a 3.23 ratio, a bit lower. The 50/15 is a 3.33 ratio, 50/14 is 3.57, and 50/13 is 3.84, so you can go three ratios lower than stock and two levels or pretty much match the 42/13 and have two ratios lower. I set up to run a 47/15 which was 3.13, but giving the option of a 47/14 at 3.35, or a 47/13 at 3.61. I ended up cutting my chain too short to use the 15, I got in too much a hurry and set it up for the 47/13, the chain was one link too short to do the 15. I'm running the 14 now.

The 47/13 was really low, enabling me to pull through deeper sand without bogging. It would rev high on the freeway, but I don't do freeway. Still it was too low in general. Had I cut the chain right I'd have quite a broad range of gearing possible with only a front sprocket change.

 

Thank you everyone. Its pretty cool how much you can learn when you are delving into something new. I think I'll just stick the 13 on the front and leave the rear alone and see how it goes. Mostly off road for me, but I'll drive her through the city from time to time.

Now off to dx the battery, - it is cranking slow and not starting as quickly/predictably as I'd like.

 

I currently run a 13/49 on my 09 250s. It is awesome on the trails I love the low gearing. It is about 7000 rpm at 55 mph. I mostly ride in the woods and don't ride it much on the highway. I might ride it more in the highway if it wasn't so low. I haven't tried putting the 14 back on the front and trying that.