Gearing options

[Scott.A86]

I have a Carters go kart similar to a yerf dog with suspension. It has a predator 212, govenor and oil sensor removed. It also has a 30 series CVT and a chineese mikuni 22mm carb. Gear ratio is currently 6:1. It had a top speed of aprox. 21 mph before the carb and aprox. 31 mph after. It got alot quicker too.

This ratio and speed is perfect for my yard track. I may not even reach top speed in my yard but, when I am trying to get top speed I feel like it should and could have more. Besides upgrades I am thinking about changing the gear ratio. I am thinking a 3T difference on the jackshaft so I can swap the sprokets for a higher or lower ratio.

Currently - 300lbs Kart, 16" tires, prabobly 3800 - 4000 rpm
CVT - <JS - JS> - DRIVE
10T- <15T-15T> -60T 6:1 @ 4000rmp 31.7 mph

I am thinking.
10- <12-15> -60 4.8:1 - 39.6 mph
10- <15-12> -60 7.5:1 - 25.3 mph
Or
10- <15-18> -60 5:1 - 38 mph
10- <18-15> -60 7.2:1 - 26.4 mph

[Edited to fix gear ratios]

Are these ratios and speeds achievable? Are my calculations wrong? I am happy doing weelies or 45 mph as well as wheelies at 45 mph. I just dont want to burn out my clutch and belt or mess up my motor experimenting.
All my reasearch and googling tells me how to calculate gear ratio but now how to apply it. I'm sure one or more of you may have some insight to this.

 

[itsid]

series 30 TCs have 10% overdrive, I think those are missing in your calculation

I'd say you shouldn't gear higher than 5.5:1 at all.. (maybe even lower 5.7:1 .. 6:1 is already almost perfect)

I'd say 4.8:1 will only shred your belt rather quickly and you won't find any noteworthy increase in top speed.
(lacking the torque to make use of the 'faster' gear ratio)

'sid

 

[Scott.A86]

Thanks sid, I just noticed I wrote my ratios wrong... early morning. So I should keep the 6:1 and either get a bigger motor or continue upgrading the 212 for more RPMs? Also, I was just thinking, would it be beneficial to get rid of the TC motor mount plate and move the driven pully to the JS in... reducing friction and less moving parts from motor to tire. The only reason I did not do that to begin with is the kart came with a 1" bore JS and I believe driven is ⅝".

 

[itsid]

without seing the kart I can't tell what would make the msot sense to me
(and much less what makes the most sense for you)

generally.. if a kart has a jackshaft installed it's most likely (very few exceptions) meant to take the driven of the TC
and one sprocket for the chain.
You can of course decide to have a TC with backplate and use the jackshaft for just sprockets.
but most of the time that only causes additional drag and worse additional noise.
And since most of the time you have to swap the chain with it anyways it's not less effort to swap ratios ..
tough call tbh.
it can certainly be set up that way and if everything's aligned it's just a bit of drag, weight and noise as a downside,
nothing to worry too much about.

I'd say you can try to push the engine to 5500 rpms with some more minor tweaks,
I wouldn't bother to try and install high performance high dollar mods since they are mostly more expensive than actually usefull
unles you are trying to compete in a racing class that requires a specific engine.
(which is unlikely with a full suspended kart )

'sid