Hi all,

My trusty GN is due a new set of sprockets and chain, and as i plan to be doing a fair bit of longish distance travel this summer i was thinking that going with a different number of teeth on the sprockets may make the sustained high speeds (i wish) a little easier on the engine by bringing the revs down

i generally cruise at about 50mph with a top speed of about 60 so bringing those figures up a little would be nice too, but my main motivation is bringing the revs down so my engine doesnt get too stressed out.

I know a sprocket change can in theory do this, but i figure since the the speeds on a GN are so low a small % change may not really make a difference to my speed or that the engine , do you think the revs may come down much though?

im also concerned about a loss of torque, hills are already a bit of a nemesis, do you think gearing for higher speeds would make them a massive issue, or would it just be a case of shifting to a lower gear than at the moment?

As the bike is, 1st and 2nd dont see any use outside of pulling away so im hoping she can accomodate having the gears spaced out a little more.

One other thing was that its commonly said that sprocket changes should always coincide with a chain change so the three can wear together, it wouldnt be too pricey to just have two front sprockets and to change the gearing depending on use, but is this going to muller my chain? even if its a sexy new DID bad boy on such a low power machine?

Any ideas are greatly appreciated

I wouldn't do it, as you said you'd be losing out on pulling power in the lower gears and that would probably put more strain on the engine than cruising at 60.

Better still, get a 2-stroke - made to be thrashed! (not an Aprilia tho!). I used to cruise at 70 on my RXS100, fully loaded with camping gear too. Except for hills of course.

Yeah i think your right, ive been to london and back once already now and much of the time i cant even make use of 5th gear due do hills and wind.

I think i will get a reasonably powerful 250 and hopefully it will hold 70 all day without much fuss

Your profile says you have an SR250 - not on the road then?

We used to put a smaller front sprocket (one tooth) on RD250LC's which used to shorten the horrid flat spot in mid range and make them accelerate faster, but you lost the top end speed, although it would reach the max every time

Putting one tooth bigger or less on a 125 would probably make things worse for you, if it won't redline in top gear one tooth less would make this happen but it'll rev its tits off in every other gear, one tooth more and top gear would be even worse.. unless your going down a big hill!
plus your chain will end up either shorter or longer, its better to change the chain and rear sprocket as well etc

I agree with BG on 4 strokes 125's its more hassle than its worth

Yeah i dont think i will bother now, i think it would be a bit pointless trying to turn the 125 into a long distance bike, when what i really need is a bigger motor; and the reason im not on the 250 is that its on SORN and i still have mod2 to pass, i picked up the SR for peanuts just to learn some bike mechanics on before i even did my CBT and doubt i will ever even use it.

Im just going to get my mod 2 out of the way and get a 400 to 650 cc bike i think, ive been a CBT rider for 3 years now so its about time i did

That's the best way to go!

Well, mind your CBT is only valid for 3 years. If it expires you'll have to do it again or you're not licensed to be on the road (and all the mess that entails).

So i finally changed the the chain and sprockets on my GN125 yesterday in preperation for its MOT and in the process noticed that the rear sprocket was larger than stock (3 extra teeth), which would explain my bikes wimpy performance at higher speeds it never occured to me that someone else would have previously been messing with them. Now im running with stock sized sprockets, it will be interesting to see if acceleration is noticably worsened.

And as far as CBT's are concerned im already on my second one so i have a little over a year to get mod2 out of the way, i already took a shot at it and failed due to speeding of all things, but as that was all i slipped up on im confident i will finally have my full lisence in the next few weeks, hopefully my passing will coincide with me finishing work on a some what tatty honda cm400 i just picked up to replace my 125!