Down Gearing

[NS125RK]

Hi,

I was just interested to see if down gearing my bike would be a good idea. I don't think the bike is restricted as its an Iitalianimport NSR125RK. At the moment the bike is capable on a road which is called the mad mile to get to 150 - 155 kmph and just red lining at 11000rpm but it takes a long time to get there.

Do you think by slightly down gearing the bike I could roughly keep the same speed by going further into the redline but also improve acceleration.

Thanks,

Shaun.

[Ste]

Nope, as it being down geared will mean that for the same amount of revs it is doing a lower speed, so you'll drop your top speed as it can redline in 6th already.

[NS125RK]

OK, just thinking as well i'd be at higher revs just cruising anyway and I'd like to try and stay away from that hair dryer sound as much as possible.

Thanks,

Shaun.

[ts50x0]

i think these bikes have got a rev restrictor anyway to stop you going into the red line so down gearing would definatly lower top end speed. but it sound fast enough anyway for a 125 why dont you do it and get the better acceleration. i mean how often do you get a long enough road with no traffic to reach that speed anyway? and this would make it more fun around town and on the twisties !!!!

[Dusty]

[Frost]

He said he barely got it into the red on that massive runup, so he suggested downgearing to give better acceloration, and allow the bike to go futher into the red.
Downgear it a bit, perhaps 1 down on the front?

[NS125RK]

Hi,

I know what you mean, I very rarely get chance to max it out and the acceleration would be great. But on dual carriage ways when i'm doing about 70 its at about 7500 - 8000rpm if I down geared it would probably go up to 8500 - 9000rpm and for long stretches i'd of thought this could be a bit close to red line.

It does red line in 6th, but I mean barely just on 11000rpm. I'm not positive but I don't think it has a rev restrictor in as i've had it up to 12000rpm in 5th.

One thing is to get it to red line in 6th I have the revs high enough in 5th so that when I go into 6th it's in its powerband at 7500rpm if I go into 6th under that it will struggle to get into its powerband. So down gearing may be able to solve this.

Shaun.

[Flywheel]

hi

i have the same bike as u but mine aint an import and i have the same problem trying to use 6th gear so was thinking bout down gearing it to.

[ts50x0]

thats interestin cause mine reved to exacly 11,00rpm even in nutral. maybe somepne had fitted a rev limiter or maybe it was faulty. mine had trouble to get past 3rd gear if you didnt powerband it.
And id say that sitting at those revs all the time was probably what blew it up. i wish id have changed the gearing now!!!!

[NS125RK]

Hi,

think I will see what down gearing my bike will be like, i've had a quick look on the internet but am having trouble finding a smaller front sprocket. Can anyone tell me a good place to get one and also the number of teeth on the standard sprocket.

By the way when I say red line I mean getting into the red, is this the wrong terminology?

Thanks,

Shaun.

[Frost]

Typically you can't just go buy a sprocket for your bike with more of less teeth. as the standard ones are normally only available you have to get one off a different bike, or a different model of bike.

The NS125RK has a 13 tooth front sprocket, so you would need a 12, which no NSR has, so dropping 1 on the front doesnt seem likely to work.

13:33
Is the standard ratio
12:33 is about what you want but isnt possible
13:36 gives exactly the same drop in gearing, but there is no 36 rear Sprocket, so you shall have to go for a 13:35 ratio, dropping your top speed by 6% and giving better acceloration.

https://www.gear4bikes.com/acatalog/Honda_Rear_Sprockets.html

279 - 35

[Flywheel]

hi

there is away to stop the bike redlining and gain more acceleration without changing the gearing.On the right hand side of the bike next to the exhaust manafold is a large nut, remove the nut to sind a cast iron rod with a plate atached to it.You can cut the plate off to give u better acceleration but lower top speed.But be carefull if u dont like it you can put it back in but make sure you put a spacer or spring in aswell to keep in in place just incase.

The reason this gives you more acceleration is cause it opens up a chamber which on european models has a power valve in place of the metal rod.

Sice your is an import it may already have the ATAC system valve.If so the just leave it the way it is and change the gearing.


good luck

[NS125RK]

Hi,

thanks for the link DaFrostyOne and as for the ATAC system valve I was under the impression that it was already on my bike.

Sorry if this sounds a bit dumb but is the first number the type of fitting or something along those lines? as the NS starts with 279 but the NSR is 604.

Thanks,

Shaun.

[NS125RK]

Hi,

I've just had some pretty good luck. Just bought my self a spare rear wheel and picked it up from the posty. As well as it being in incredibly good nick its also got a decent tyre on it but i've just counted the teeth on the sprocket, which is also in good nick, and it only has 35 teeth.

Think i'll get them changed over tomorrow and see whats it's like.

Shaun.

[Ste]

Hope it wasn't from gear4bikes!! FInd out more about them on Google (hint, the third link down ).

[NS125RK]

Hi,

no got it from good old ebay managed to pick up a spare front wheel and tyre and two spare foot pegs as well its not very often they pop up so I thought I might as well get them just in case.

Shaun.

[Kickstart]

Hi

Your bike is an NSR125RK so the standard gearing is 13/36 not 13/33 which is for the NS125RK (and unfortunatly the sprockets are not interchangeable). Also it does not have an ATAC system. Having that chamber open on an ATAC equiped bike will increase low down power at the expense of top end power.

All the best

Keith
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