gear ratio - which sprocket to change first?

[jpcjguy]

Hi all,

So I have a kandi spyder - KD-150GKA-2 and it is slow and has no torque. Not to beat this aspect of the topic as it has been already covered in this thread: http://www.diygokarts.com/vb/showthread.php?t=26814 - Apparently, this seems common to this buggy.

My question is which sprocket to change first? or both?
Here is what is has currently:
GY6 150cc - with new top end.
22x11.00-10 rear tire size
31 teeth on the axle sprocket and 16 or 17 on the small (have to double check).

Looking at buggydepot.com - for the kandi, they offer a 39 tooth axle sprocket that is "verified fit" with this description: "High quality 39 tooth sprocket. Replaces the stock 31 tooth sprocket for a large increase in climbing and takeoff power!"

However, when talking with a support tech at another large parts provider, the advice was to start with the small sprocket.

I want to get this buggy so it good all around - Don't need a speed demon, not racing and being in VA we have decent hills - not Texas/Oklahoma flat - but not Colorado either, so decent torque would help.
It is a heavy buggy and my 240lbs does not help.

Can anyone provide clarification on the best course of action? What effect does changing the upper vs. axle sprocket do, in terms of motor stress, etc.

Thanks!

 

[Joe-405]

It is impossible to gain speed and torque with gear changes. You lose one and gain the other.

The gy6 I fixed and rode around for awhile would do 40mph with 2 adults and climb steep hills with one 180lb adult so you might have other issues it sounds like.

 

[itsid]

While I have to agree with Joe here mostly..

there are indeed some cases where you gain both by fixing the ratio..
especially on CVT engines like your gy6 or engines with a TC setup..

namely, when you are geared so terribly high,
that the TC is unable to shift up to it's full extend,
then lowering the gear ratio to a "good" value will increase torque enough to fix the incabality to shift up as well, hence you might end up with more torque and that causes a higher speed (thanks to the now fully functional CVT or TC)

COULD.. doesn't mean it will be the case for you though.. but chances are (with a gear ratio that bad) you might be lucky *shrugs*

Aanyways.. as you can see in the thread you linked there's plenty of confusion regarding the original gear ratio for kandi mini buggie like yours.
Unfortunately nearly no two gy6es are created equal (all beautiful snowflakes)
So where he original engine with a matching internal gearing might be okay with such insane final chain ratio, another one (optimised for a different setup) might not.

Tough to tell!

IMHO.. the larger the sprockets you use the better..
so as long as you have room to mount a bigger axle sprocket that'd be the way to go.
Simple reason:
the more teeth are engaged the better.
Sprockets and chain will last longer.

'sid

 

[jpcjguy]

Ok, so it sounds like trying the 39 tooth on the axle is the best place to start.....

 

[Joe-405]

That shall be more torque for sure. And if your belt is slipping any because your current gearing is off then you shall gain both.

 

[@Josh]

You have some real common issues with the kart and hopefully I can offer a couple of things to try based on my experience with GY6 buggies.

The same simple things that you would do for a Predator work wonders for these motors... Upgrade the air filter. Change the carburetor to a mild upgrade... like in the 28mm-30mm range. Upgrade the intake from the carb... you can buy a billet one from The Ruck Shop for under $30 Upgrade the CDI to provide better spark. Upgrade the spark plug to an NKG BP5ES 7832. Upgrade the variator weights with a kit

These easy DIY upgrades will provide you with a lot more torque. Not a ton more speed, but a ton more fun. The upgrades will average about $20 each with the spark plug's lower cost offsetting the carburetors higher cost. Try those before tearing too deep into it. I think you'll be pleasantly surprised.