Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Sprocket change

Discussion in 'Maintenance and Servicing' at netrider.net.au started by adjustedpete, Mar 9, 2013.

  1. Im looking at changing my sprockets on my NSR 150 and can't decide which way to go. Im thinking 1 down on the front sprocket and 1 up on the rear, or just 1 up on the rear. I have beeen using this sprocket calculator http://web.singnet.com.sg/~ivant08/NSR150SP.htm but still cant make an informed decision. My other dilemma is, will I run a 120/80/17 tyre on the rear or a 130/80/17 ? . I use the bike primarily as a fast commuter but love to give her a workout on the weekends.

  2. I would go down one on the front to begin. I take it you want more grunt but don't want to loose top end speed. Front's are a third of the cost of a rear.
    And stick to the original tyre spec. A wider rear will make the bike turn in a bit slower. And you not going to spin up a 150. So stick to the original size.
  3. problem with the nsr150 is that 1st gear is quite short. Shortening your final drive ratio will only make that worse....although 2 second little monos off the lights will get easier...:)
  4. I would increase the rear instead of dropping teeth off the front, that way you're not making the chain turn sharper around the front sprocket.

    1 up on the rear won't make a big difference, 2-3 up on the rear would equal 1 down on the front, depending upon sprocket sizes of course.

    My TRX is currently running +6 on the rear, drops the top speed from 210 ish to 200 ish, but much easier around town & first gear is much better.
  5. Lol..That is the problem Im trying to deal with. 1st gear is a biatch, so inconvenient.

    Ok, that works for me. I get to save some money too. Thanks.

    Is that a problem, cos I havent even thought about that. I assume you mean more stress on the sprocket and chain wear. Would that be a prob on a 150?
  6. Not a problem per se, but by most accounts will increase chain wear... You probably get pretty good chain life out of a 150, but I have got as little as 10K out of a set of chain & sprockets before.
  7. Standard gearing is 2.857:1 (40/14)
    Your choice of gearing, -1F +1R would be 3.154:1, will make the problem of a short 1st gear worse.
    The alternate choice of std F +1R would be 2.928:1, will still be worse than standard as far as 1st gear goes, but not as much.
    If you wanted to stretch 1st you would go down 1 or 2 teeth on the rear,

    BUT ......

    The reason 1st is short on the NSR150 is that it makes getting off the line and low speed riding ( think heavy traffic, filtering, stop start.... ) easier. It is after all a learner / commuter bike.
    If you wanted a 2 stroke rocket ship you should have bought an Aprilia RS125 ( the older 2 stroke version, not todays 4 stroke joke )

    Have you noticed that 2nd - 6th gear are nicely spaced and work comfortably with the engines' power charateristics.
    If you change the final drive ratio to give 1st gear a bit more "legs" you will compromise the rest of the gears and overall performance will suffer.
  8. Yep, thats the crux of my dilemma. This is my first attempt at doing mods to a bike, so Im a little in the dark as to what's possible. So ideally I want a longer 1st gear. Can I do that?..
  9. #9 mike8863, Mar 10, 2013
    Last edited: Mar 10, 2013
    Not without changing the gearbox internal ratios....err too hard...

    Another possibility, thinking outside the square for a moment, might be to alter the final drive ratio so that you forget about using 1st gear altogether and only use 2nd - 6th.
  10. Ok, so thats possible. Where can I find info on changing internal ratios?, remembering I have not alot of engineering knowledge. The good thing is I have a spare motor, so I am going to pull that down and use the gearbox to play with.

    With the short 1st gear I find on a right hand turn Im changing in the turn . And short shifting drops the revs too much. Its just a dull area in an otherwise great little bike. And Im hoping I can do something about it.
  11. Not sure...a thought, maybe, if the gearbox internals are the same as the Honda 125GP bike or CR125. I know the GP bike has alternate gearings available...but rare as hens teeth.

    Are you running a standard exhaust ? if you are, replace with a Tyga or Jolly Moto pipe and muffler, remove the snorkel from the air box and re jet the carb....makes a big difference to the mid range and top end.
  12. #12 adjustedpete, Mar 11, 2013
    Last edited: Mar 11, 2013
    Mmmm if I could find out some spec's of what I needed, maybe someone could knock one up. Ok I have alot of searching to do.

    Already there,Im running a tyga pipe, 155 jet, with yss gas shock, racing steps for clearance( i found that out the hard way) I have been a busy boy...lol. Im thinking of replacing the carb with an older cr 125 one. There is some benefit from the larger intake Im told. I nearly bought an nsr 250 carb but I realised that I wouldn't be able to cut it up (sin).
  13. Just an update on the 1st gear issue.. I have done some research, and for my application its probably not worth it. I dont plan on racing it, so I will just adapt myself to its idiosyncrasy's. But in the mean time I have found a nsr 250 carb already cut with adapter plate and cable...Wooohooo. Thanks Mike for you input. Rare as hens teeth isnt the word for it. Just getting info was bad enough.
  14. They race the NSR150 in England as a one series. And a company I cant quite recall now does gearboxes. But yeah quite a lot of bux you wont get back, and something that you could quite easily work around
  15. Yep that killed it dead. Anyway with the mods i have and a bit of tweeking Im hoping for about 33/34hp. That'll do for now.
  16. hey pete, not to hijack the thread but I'd be interested to see how your NSR looks especially with your gas shocks. Did you get them from Tyga? Were they easy to install?

  17.  Top
  18. Cheers. Only if it was easy to fit that PHAT rear wheel too!