Jump to content

Chain and Sprockets change


Recommended Posts

Hi All, I've got a Honda CBR125R (2017).

Currently doing quite a long commute (80 miles a day) on one dual carriageway, sitting at about 70mph (8.5k revs) for about an hour.

I've heard that a sprocket change of 1 less tooth? Could help lower the revs at high speed and preserve the bike better. I don't know much at all on this, can anyone give me some advice on a good chain and sprocket for me to buy, and any opinions on the matter.

Any help is appreciated.

Link to comment
Share on other sites

You want one tooth more, that will give you "longer" gearing requiring lower revs to do the same speed at the cost of acceleration. The real question here is can you afford to lose that acceleration, essentially the power at the rear wheel? You may find your top speed actually decreases, especially if the bike is struggling to top out already.

Link to comment
Share on other sites

Let's be sure we know which sprockets we're talking about.

Going up one tooth on the gearbox (front) sprocket will raise your gearing. If your current sprocket has (for example) 14 teeth, then fitting a 15 tooth sprocket will raise your gearing by around 7%. That's not huge, but will be noticeable. You probably won't notice the very slight decrease in acceleration but you should appreciate the reduced revs at 70 mph. If your bike currently slows on uphill sections this might become more noticeable, but dropping down a gear will give you more speed than it used to. I think for what you want it's worth a try.

If you want to change the rear wheel sprocket, changing from, say, a 43 tooth sprocket to a 40 tooth would have a similar effect to the 14/15 change.

Given that increasing sprocket size at the front may require a slightly longer chain and decreasing the rear may require a slightly shorter chain, I would suggest you find a supplier who can advise on the chain length best for the sprockets you choose - the standard length may, or may not, be ideal. It's a long time since I did any of this, so I can't advise on a supplier - sorry.

Link to comment
Share on other sites

Appreciate the quick replies on this.

As for the decrease in top speed, I'm not too fussed, as currently know the bike can get around 82mph+, but I solely sit at 70 just to try keep the bike from being worn.

As for hills there are relatively none on the a13, so that shouldn't be an issue.

Thanks guys I will contact my mechanic and see which he would recommend.

As for chain and sprockets brands, can you recommend a good safe brand? Just done the silly option of budget on eBay. But the thing is stretching very quickly.

Link to comment
Share on other sites


As for chain and sprockets brands, can you recommend a good safe brand? Just done the silly option of budget on eBay. But the thing is stretching very quickly.


As I say, I haven't bought chains or sprockets for several years now, but you might try : https://www.wemoto.com/bikes/honda/cbr_125_r/17/picture/did_heavy_duty_chain_and_jt_sprocket_kit

I don't know if they can supply alternative sprockets, but a phone call or email should get you a quick answer.

Or these people might help : https://www.chainkit.co.uk/chains-sprockets-HONDA/

Tsubaki or DID o-ring 428 chain and JT sprockets seem to be the current leaders.

I wouldn't advise shopping on eBay or Amazon for chains or sprockets.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Sign up now

    Registration is quick and easy 

  • Create New...

Important Information

Terms of Use Privacy Policy Guidelines We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.

Please Sign In or Sign Up