Chain/Tires on 89 KX125, what was stock?


Apr 28, 2000
Ok, I am considering getting back into riding and have found a 1989 KX125 that appears to be in very nice shape in the pictures I have seen. The current owner says it needs a front tire, and a new front sprocket. Before I go look at the bike, I would like to get a good idea of what I am going to have to spend on parts.

Now, for some reason I recall being told that it is generally a good idea to change both sprockets along with the chain all at once. Is that true most of the time? Also, what kind of chain did it come with from the factory? All I have been able to find is that it needs a 520 chain with 112 links. From what I have read it says if a bike came stock with an o-ring chain that you should only replace it with an o-ring chain. Did this bike come with an o-ring chain?

Also, what size front tire did this bike come with? Again,the information I have found is less than I need (it has a 21" rim).

Once I have all the information I need I can price the stuff out and hopefully have a good idea of what I will be getting into if I buy it......

Thanks in advance for any answers to my questions.


Apprentice Goon
Mar 16, 2001
Charlestown, IN
Your bike could have a 47t-48t-49t rear, and a 12t front stock.
Chain is a 520, but don't trust that the 112 links is sufficient.
Get a chain with plenty of links (120) and break it as needed when you mount it.
I would definately change out both sprockets and chain.
No need to worry about a ring chain. The thing about needing a ring chain if the bike came with one is total bologna. BUT, if you don't like taking care of your chain, a ring chain will probably last a bit longer.
It's no big deal if you run a ring chain or standard. Keep both cleaned, lubed, and properly adjusted and you will be fine.
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