fitting new sprockets...

[myk1979]

G'day guys and gals,

I picked myself up a new sprocket and chain set today (from Con at House of Speed, thank you very much) for my ZXR250 C. The original rear sprocket is a 48 tooth and the new is 41 tooth. I'm just wondering if anyone could tell me how much of a difference this will make to the bike ie: will it be very noticable, and for the better or worse? also will it throw out my speedo or is that supposed to run off the front wheel....

Cheers, Mick.

P.S. I realise i should have asked Con when i picked up the parts but i was in a rush and didnt pay much attention at the time

[robracer]

Put simply, less go from start but more top end, your speedo is off the front wheel so no drama there.

[myk1979]

Cheers Rob. Thats what i thought, just figured i'd get an educated opinion before tearing into it.

[robracer]

Cheers Rob. Thats what i thought, just figured i'd get an educated opinion before tearing into it.

Hint ...Do the front sprocket before taking the chain off.... you might need to use the back brake to help get the sprocket off

[myk1979]

Will do, thanks again Rob!

[photomike666]

Put simply, less go from start but more top end, your speedo is off the front wheel so no drama there.

I might have to disagree with this (sorry).

Slower off the mark, yes. Higher top end, probably not. I tried going down teeth on my CBR600 a few years ago, and it made the ratio too hard on the motor. Fuel economy went out the window and it struggled to rev in top gear (I only dropped two teeth). 7 teeth on the rear is a huge difference, and with out a front sprocket change will seriously affect the performance.

[robracer]

Put simply, less go from start but more top end, your speedo is off the front wheel so no drama there.

I might have to disagree with this (sorry).

Slower off the mark, yes. Higher top end, probably not. I tried going down teeth on my CBR600 a few years ago, and it made the ratio too hard on the motor. Fuel economy went out the window and it struggled to rev in top gear (I only dropped two teeth). 7 teeth on the rear is a huge difference, and with out a front sprocket change will seriously affect the performance.

Be interesting to hear what happens with such a large jump in teeth, sounds like you are right mike, after thinking about it a bit more, I am used to incremental changes.

[mick_dundee]

I was thinking less pick up more top speed to but yeah, that's a massive drop... we await with baited breath waht happens, what made you go so small on the rear sprocket incidentally?

[timmyrocks]

thats a huge drop!!! i went 1 tooth up on the rear and noticed it :O lolz
you will have to shorten the chain id say to account for the smaller sprocket,
let me know how it goes

[myk1979]

I was thinking less pick up more top speed to but yeah, that's a massive drop... we await with baited breath waht happens, what made you go so small on the rear sprocket incidentally?

Well to be honest with you i was after an original sprocket set but when i got home and checked them thats when i noticed the difference. I haven't got it apart to check the front yet. Thought about taking it back but then i got curious about the result of fitting the smaller one and i'm thinking i'll give it a shot
I was speaking with a bloke a little while back and i'm pretty sure he went down several teeth on his ZXR250 but of course i can't remember the exact number I'll see how it goes and if all else fails i can always go back to the 48 as its still in good nick! Was actually mainly worried about replacing the front sprocket cos the center has been chewed out pretty severely, but figured i might as well go the set and new chain also seeing as i have no idea how old the whole set up is. But judging by the condition of the front sprocket i'm assuming it's probably original!

I won't be getting stuck into it until next week sometime, but i'll be sure to let you know how it turns out. No harm in trying.............i hope!

[robracer]

Might want to speak to the guy who sold you this sprocket & see what he say's, he is the one that has sold it to you & one would assume he would know what he is doing, but question him anyway ... that will possibly give you recourse if it is way wrong which it sounds like

[Bogan]

You might not get more top end but you definitely will get less revs for a given road speed in a given gear, you'll be cruising at 110km/h in top at 5300rpm where you used to be at 6000 or something like that (guessed numbers).

I doubt many of us use the top of the top end to notice a change in sprocket sizes.

[myk1979]

Ok so the new sprockets and chain where put on the bike on friday night with the much appreciated help of Phil and Shaun, i'd have been really struggling without your help guys so thanks again!
As well as the drop in teeth on the rear sprocket the front was also down a tooth. Basically the major difference to the performance is a drop in revs at any given speed as Bogan suggested. As it was originally, in top gear at 100 - 110km it was sitting on around 11-12,000rpm and now its down around 7000 - 8000rpm, so basically i'm not having to rev the tits off the old girl all the time. I was a bit concerned that it might suffer a bit in terms of acceleration but to be honest i didn't really notice a big difference and actually found 1st gear in particular to be alot more user friendly, and up high in the rev range i found it still had plenty of pull. I found myself cruising along quite comfortably in 5th without realising that i still had 6th to go until i double checked what gear i was in.

My thoughts on it so far after riding down to Macquaries Pass via the Nasho today is this:
I'm pretty happy with it at the moment and will leave it as is and see how if i have any issues with it over the next couple of months. Now i've just got to service it and get it running a bit better..........but thats another story!

Cheers, Mick

[IsleofNinja]

I've seen a few 1/4 bangers with huge rear cogs over standard.

It seems to be a mentality to make it accelerate like a bigger bike

But as you have found it doesn't really tend to do much. More likely have you looking for gears all the time in reality.

ie Putting a 41 instead of the the 48!! on a VTR 2fiddy recently mean't you could get to sixty quicker and not be in 6th!!!!

[photomike666]

That's an excellent result. From your comments, "in top gear at 100 - 110km it was sitting on around 11-12,000rpm" I would say that someone put an unusually large sprocket on the back to aid monos, and that you are now back at a standard ratio. I'm glad it's worked out ok. Let us know what the difference in fuel economy is.