Replacing chain and sprockets on TTR 125E

I'm replacing the chain and sprockets on my 2006 TTR125 E, as the title says, because the chain is wicked worn and stretched and the sprockets come with the replacement kit. I looked on the bike and right now the back sprocket has 49 teeth and the front sprocket has 13 teeth. I have a couple questions. The smaller the rear sprocket is and the larger the front sprocket is, the faster the bike is geared to top out at correct? If this is true, if I replace the front sprocket with a 15 tooth sprocket, the bike would have a higher top speed correct? If I did that would I have to get a longer chain or would the chain be the same length? Also, the website I am looking at lists a bunch of different chains and chain lengths. If I got the DID 428 Standard/ 120 link is that ok to replace the chain with? I'm not sure which type of chain is on the bike at the moment. Also, would there be any worth in getting the Renthal R1 428 gold/ 120 link instead? Is one better than the other? Thank you all for all the help

IMO, your better off staying at stock. You will have a higher top speed, but the higher you gear that front sprocket, the less torque you will have, which means it will take a lot longer to get to that speed. If you want any real speed, get some head work with some re jetting, and then change your sprockets.

lets say your bike has 10 hp (im not sure so im just using this number), and you have your 15 tooth sprocket, then it will be putting more strain on your motor. and you could top out at 70 mph.

But with your 13, you will have a lower gear, less strain and you can still top out at 70mph.

Its all about rpms, if your engine doesnt have the guts it needs to get up to an rpm, then its useless to change your gears any higher.

When I hit top speed the engine is probably pretty near red line. At least I'm guessing it is by the noise and the feel. And what type of head work and rejetting would I need to do to give it some extra speed? Would I just switch out the main jet for a larger jet? Cause I'm looking to make the bike street legal and right now it tops out at 51mph. I'm looking to be able to make the bike top out around 60 or so so I could run it at the 55 needed for highway speeds without hurting the engine for a continuous time because it wouldn't be at its redline, you know?

you could go up one tooth on the front sprocket and still use the stock chain

My prefered final drive gear ratio would be 14T front /48 T back so it still has a bit of bottom end (torque) whilst raising your top speed

Rethal 0-link chain or Volar o-ring chain would be my decision on brands.

Edited by Barra8

a piece of advice. put some blue loctite on your retainer screws on the front sprocket. Just had my screws back out and dropped the sprocket, so i will loctite the new one.

I wanted to increase my comfortable cruising speed (I do a lot of trail riding at high speeds) so changed from a 13T front and 51T rear to a 13T front and 49T rear. It didn't seem to make much difference to the lower gears (good for very steep hills and thick mud) but it increased my cruising speed by 3 to 4mph. I now have to take a few links out of the chain to make it fit properly though. The smaller the rear sprocket is the faster you'll be able to go. I've found shops that sell rear sprockets as small as 44T. Good luck in getting it road legal. I'm slowly going down that route. Would be great to see a few pictures of the final road legal version!

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