Front Vs Rear Sprocket Swap (KLX 250)

Discussion in 'Technical' started by Satonic, Aug 12, 2012.

  1. Satonic

    Satonic Ol'Timer


    I was chatting with a Thai mechanic mate of mine over a few beers last night and I told him I was planning to use a 13t front sprocket on the KLX. He told me this wasn't the best choice and I should swap the rear sprocket instead.

    Any views or ideas on this? (I'll be using the bike 70% dirt so not worried at all about top/cruising speed)

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  3. mudboots

    mudboots Ol'Timer

    If your gearing your bike down for more off road use i would agree with your mechanic friend, you may have to modify your chain guide if you go up to many teeth on your back sprocket.

  4. Satonic

    Satonic Ol'Timer

    Thanks mudboots, I'm new to this and please excuse my stupidity but why would it make a difference front vs rear if your ending up with the same gearing ratio?
  5. mudboots

    mudboots Ol'Timer

    Dropping one tooth on your front sproket is like going up 3 teeth on your back but puts a lot more stress on your chain and front sproket you will be changing gears more as 1st and 2 will no longer have the legs, and off road where you are changing gear a lot and under load up hills or in mud it will put a lot more stress in chain and front sproket they will ware out a lot faster! Some say you should try going up or down 1 tooth at a time to see how the bike gos but who can buy 3 sprokets at one time if you go up 3 teeth on your back sproket your chain guide should still be okay but will ware more from the chain slapping it on exit you will need a new chain as well at least 3 links longer do not just add a bit to it thats a no no.
    hope this helps.

  6. Maha

    Maha Ol'Timer

    As a first modification, changing the 13t sprockets is one of the easiest and simplest thing you can do. The benefit is that you can use the original chain and in case you plan some longer on road trip, you can easily swap the 14t back if you want (but you don't want after trying the 13t). I used the 13/42 gearing for few thousand km and there was no problmes. Of course for real dual sport you want faster shorter gearing than this, I used 13/47 which is very good for on/off road use unless you plan Bangkok-Chiang Mai trips with the bike. With 13/47 the highway speeds for longer trips are 80km/h to keep the rpm down, but the bike still goes 130km/h @ 10000rpm if you need to overtake or something (and have de-restricted the bike so the rpm limiter won't cut you).

    You can see from the below that changing the rear sprocket means new chain. If you need to change the chain, you buy Er-6 chain and cut it shorter (that's what I did).

    This info is from Ho Watanatham Nithat

    Gearing Links
    =============== ========
    14/42 106
    13/42 106
    13/45 108
    14/45 108
    13/47 110
    14/47 ???
    14/48 110
    14/49 110
    13/49 110

    Go and change the 13t sprocket and enjoy!
  7. Satonic

    Satonic Ol'Timer

    Thank you both very much for the replies. That clears up the questions I had in my mind.


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