I put a 43 tooth rear sprocket on last week. I decided that the 13 tooth front sprocket was either to much gearing or not enough for the conditions that I ride in around here. Browsing through the Dennis Kirk catalog, I found that a KX500 came with 43 tooth rear sprocket from the factory. I went to my local bike shop and ordered one. I got the cheapest one I could find. It ended up being a Parts Unlimited steel sprocket and the cost was $20. Here is what was on the sticker:

Part #: K22-3917
REAR SPROCKET KAW 520 43T
OEM # 42041-1127

This is a real nice upgrade for me, as the stock gearing is nice on the highway but not enough for technical trails. The 43 tooth makes the bike feel like it is a bigger cc bike without sacrificing highway cruising. I am using the stock 14T on the front and I am using the stock chain.

Just thought I would pass this info on.[sm=shades.gif]

 

Excellent. That is a much better way to go than the 13T front. Using a smaller front sprocket really increases your chain wear as it has to move more per revolution to make the tighter turn around the radius of the smaller sprocket. I will say though, now that you know the 43 works for you, buying a lightweight aluminum cog will increase your benefit also. But that can wait until you wear out the steel one!

 

No need for a different length chain, huh??? hmmm....

 

ARE you sure its 43 tooth because thats higher gearing.

 

Isn't stock 42 tooth on the rear and 14 on the front?

 

42 is stock gearing but a 13 front is equal to a 45 rear

 

Yeah, but I think what dazjr is saying is that he removed the 13T front and went back to stock 14.
Then he changed the 42T rear to a 43... the net effect being a very slightly lower gearing.

Sounds like a great compromise to get just a wee bit more torque without loosing any highway speed. (I wonder just how true that is though - you've gotta loose something and I don't want to give up any top speed at all).

 

So you went from a 14-42, to a 13-42 to a 14-43? I have to be honest with you, you won't really notice the difference. In order to see a difference one way or another, you have to go up or down at least 1 tooth on the front or 3 on the back respectively. JMO. What riding are you doing? I am on everything from tight trails, to gravel roads, to 60 mph down the highway, I went from a 14-42, to a 13-42 to a 13-45. With the Muzzy and the jetting and of course running with the air box cover off, the setup is perfect. If I decide to go back to the 14 on the front to lessen the chain wear, then to keep the same gearing I would have to bump the rear up to a 48.

 

Im running 14-49 and could still be a little lower in the trails,A stock klx 300 is 14-51 and is just about perfect the only downfall is top speed around 72 mph.With 14-49 i can still run around 75 at 8000 rpms

 

Going from stock 14/42 to 14/43 is only about a 2.4 % difference - very small, but it still might be noticeable.

I originally went from stock to 14/49 which was, IMO, a bit too much. I loved what it did down low, but I did not like losing the top end. It essentially gave a whole new gear down low, at the expense of losing 6th gear. Since I ride a good bit on the roads commuting as well as getting to the trails, losing 6th was a bit too high of a price for me. The bike can certainly maintain the speeds and go fast enough so it wasn't a matter of losing top speed for me. Rather, it was the comfort of riding 55 MPH at relatively low RPM just wasn't there. It took 1000 more RPM to go the same speed after that change.

Just for comparison, the ratios are:

42:14 = 3.000 0.00 % % diff from stock
43:14 = 3.071 2.38 %
42:13 = 3.231 7.69 %
48:14 = 3.429 14.29 %
45:13 = 3.462 15.38 %
49:14 = 3.500 16.67 %
48:13 = 3.692 23.08 %

One of the reasons I chose to do the 300cc upgrade was because I wanted the extra torque, but did not want to lose 6th gear up high.