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Changing front sprocket from 13t to 15t?

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Alastairmcc
Two Stroke Sniffer



Joined: 21 Jun 2013
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PostPosted: 22:38 - 16 Aug 2013    Post subject: Changing front sprocket from 13t to 15t? Reply with quote

I have a hyosung 07 gv 125 aquila, it has 6000 miles or so, gonna change the chain, but i was wondering what would happen if i changed front sprocket to 15t from 13t??
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Pigeon
World Chat Champion



Joined: 27 Sep 2012
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PostPosted: 22:45 - 16 Aug 2013    Post subject: Reply with quote

Very roughly, slower acceleration in each gear, but higher top speed in each gear.

You have no more power, your just gearing it differently.

+2t on front sprocket might require more link(s) in chain, might not.
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Teflon-Mike
tl;dr



Joined: 01 Jun 2010
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PostPosted: 22:52 - 16 Aug 2013    Post subject: Re: Changing front sprocket from 13t to 15t? Reply with quote

Alastairmcc wrote:
I have a hyosung 07 gv 125 aquila, it has 6000 miles or so, gonna change the chain, but i was wondering what would happen if i changed front sprocket to 15t from 13t??


You would increase over all drive line ratio by 2/13 or aprox 15%.

It would make first gear almost as tall as 2nd for pulling away.
It would make forth gear about as tall as fifth - possibly making top gear almost 'redundant'.

It almost certainly wont make the bike any faster.

Speed = Power / Drag.

If you ent got no more power to pull taller gearing, it will still top out when the drag force matches whatever power you have.

Might mean that you actually cant go 'as' fast, 4th gear being still a tad low to get max speed at max power revs; but top too tall to let you get at the power to go that fast.

Would possibly make for more relaxed cruising, at lower speeds.

MIGHT find you a little more ecconomy. Mainly from going slower, or at least from lower acceleration in given gear, less time going as fast.

Might as easy loose you some ecconomy; thrashing it harder in lower gears, due to lesser force from taller ratio.
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SteveZZR
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Joined: 12 Jul 2013
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PostPosted: 23:54 - 16 Aug 2013    Post subject: Re: Changing front sprocket from 13t to 15t? Reply with quote

Alastairmcc wrote:
I have a hyosung 07 gv 125 aquila, it has 6000 miles or so, gonna change the chain, but i was wondering what would happen if i changed front sprocket to 15t from 13t??

in b4 edit


You've worded ambiguously OP! Evil or Very Mad


I'm surprised the grammatical might of BCF has not smote you already for this!

Your title says you're going one way on the gearing, your post the other!

+2 teeth means you'll have less acceleration and more top end, but as Teffers has said: if you don't have the power to pull the higher gearing you might actually lose top speed.

-2 teeth means you'll accelerate much more quickly and lose some top speed


Taller gearing (bigger front, or smaller rear) is often associated with better economy due to lower revs but as Teffers has said, with a 125cc machine you'll just end up ragging the shit out of it and getting no better MPG. That said, I had a -3 rear (same as +1 front) and got a pretty constant 45mpg out of my ZZR 600, now with a stock rear and a -3 front I get between 38mpg and 52mpg depending on how I ride it so gearing tall for economy doesn't always work.


My bike 'should' be good for almost 160mph as standard, but geared down like mine will only do approximately 135mph as it hits redline in top gear (at Cadwell officer) at that speed. If I geared it stupidly tall it might pull to a higher top speed than standard, but chances are the power won't be there to take it to the higher speeds.

With a 125 you're best off leaving it standard gearing, unless it's a daft quick 2 stroke in which case I have no idea and it might be worthwhile.
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Pete.
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Joined: 22 Aug 2006
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PostPosted: 09:57 - 17 Aug 2013    Post subject: Re: Changing front sprocket from 13t to 15t? Reply with quote

Teflon-Mike wrote:
Alastairmcc wrote:
I have a hyosung 07 gv 125 aquila, it has 6000 miles or so, gonna change the chain, but i was wondering what would happen if i changed front sprocket to 15t from 13t??


You would increase over all drive line ratio by 2/13 or aprox 15%.


Err, no you won't. You change the front sprocket size by 15% but the original ratio of 1:3.2 (15/48) will be changed to 1:3.7 (13/48), a 4% change. And that's just final-drive ratio, not overall.
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