Go-kart sprocket help

[Jm88]

What size sprocket should I use? I have a Go-Kart with 20” tires on the rear, the motor is a Predator 212cc which I think has about 3600 rpm. The clutch has a 10T sprocket. Thanks in advance for the help.

 

[Oldguy1951]

Offroad 80 teeth, grass/yard 70 teeth, pavement only 60 teeth.

 

[Jm88]

Offroad 80 teeth, grass/yard 70 teeth, pavement only 60 teeth.

Okay thank you, I’ll try it out. The guy I got it from said it kept burning up the clutch, but I noticed it only had a 28T sprocket. Would that be the reason it kept burning it up?

 

[Oldguy1951]

With 20" tall tires, absolutely! Even with 10" tires I wouldn't go less than 40 teeth (and even that would be hard on the clutch)! Gear it lower and it will run great and the clutch will last.

 

[Kent]

28T sprocket is really high geared with a 10T up front and 20" tires. That will almost guarantee burning up clutches. The sprocket you want will depend on how your going to use your kart. While changing out the sprocket you might look into upgrading into a torque converter. That kart looks like it would be well worth the money to do so.

 

[jamyers]

Yup, 70 or so teeth should work fine. Check out the speed calculator on the home home page, shooting for 30mph

 

[Jm88]

Thank you guys. I’ve been looking, and can’t seem to find a 70T sprocket for a #420 chain. Im only seeing it for #35 chain, do I need to change the clutch?

 

[Oldguy1951]

This #4170 tooth sprocket will work fine with #420 chain (I am currently using the same sprocket and chain). You will need a SK hub for 1" shaft (the SK hubs are far superior to the hubs on standard kart sprockets.

Or just get a #35 clutch (won't be near a strong as #420)!

 

[Jm88]

Thank you again.

 

[itsid]

Jeez...
nope.. with 20" wheels and just a centrifugal clutch that thing won't move at all at a 7:1 ratio
it's a heavy two seater (assuming at least 215kg with one passenger)
gearing higher than 15:1 won't cut it! ( so we're talking 150 teeth ABSOLUTE MINIMUM)
the cent clutch will certainly NOT work at all (that sprocket would be ~ 24" in diameter )

So you need a Torque converter (series 30 6" driven will do fine)
then the 7:1 will almost be possible (if you stick with one person only and stay below 450 lbs!)

if you crack the 650 lbs in total weight (two adults seated)
you will need 8:1 at the very least still (even with the tc)
and another tooth for every ten lbs above that
(750 lbs 9:1, 800 lbs 9.5:1... and so on and so forth)

anything less and you will just burn out clutches / belts like crazy and won't move much at all.. especially not up the slightest incline.



'sid

 

[Oldguy1951]

Heavy buggy, 212 Predator, 30 series torque converter, 22" tires, 7 to 1 gearing. Will climb 30° grades with ease!

30° hill coming up!

 

[itsid]

Heavy buggy, 212 Predator, 30 series torque converter, 22" tires, 7 to 1 gearing. Will climb 30° grades with ease!

modified predator.. and most of all TORQUE CONVERTER!!
(Jm88 has a centrifugal clutch installed if you take a look at his pic!)
So apples and oranges!
(also you are using an additional fnr gearbox, IDK what internal reduction it has if any..
and this: View attachment 122901 is NOT a 70T sprocket at all )
Sooo *cough* excuse me but I assume you are actually closer to 8.5:1 judging by that sprocket there.

As I said.. 7:1 might work with an unmodified predator but it's far from gentle on the belt
and certainly you will burn your belt if you don't have a run-up to climb that hill..
since the poor tc needs time to fully engage before you hit the incline or it just fails to do so

So yeah.. your advice above was still TERRIBLE I'm afraid

'sid

 

[Oldguy1951]

Not going to argue with you Sid! Definitely needs torque converter. I can park my front tires on the bottom of that hill, punch it and spin those big mud tires all the way up (engine is only stage1)

 

[itsid]

Not going to argue with you Sid! Definitely needs torque converter. I can park my front tires on the bottom of that hill, punch it and spin those big mud tires all the way up (engine is only stage1)

that is indeed impressive that you can spin up quick enough for the belt to fully engage..
with a 7:1 ratio that's ~7mph for the belt to stay rotationally relatively fixed with the driven pulley (6.93 @2k rpms)
or you just live the moment and risk the belt to push through

without a tc that'd compare to 189 teeth on the axle sprocket with a cent clutch btw...
which is the sole reason I was complaining about your earlier post.
but you said it yourself:
"Definitely needs a torque converter"
And with those few words we're on the same side of the pulling cord

'sid

 

[Oldguy1951]

Maybe I'm luckier than most, my hour meter says I have 28.3 hours on the same belt (and my Grandson and I don't baby it)! A torque converter and 70/80 tooth sprocket and he will be ready to rip!

 

[Joe-405]

Maybe I'm luckier than most, my hour meter says I have 28.3 hours on the same belt (and my Grandson and I don't baby it)! A torque converter and 70/80 tooth sprocket and he will be ready to rip!

Your not. I have a built box stock project engine about 15-18 hp and I’ve been in the same belt since I built it in the build off from 2016 or so. And it’s a Chinese knockoff 30 series.

 

[Oldguy1951]

I think a lot of belt life is due to good driving skills which you obviously have!

 

[Jm88]

Thank you guys. I got the torque converter, and sprocket ordered can’t wait to get it going.

 

[madprofessor]

My own sprocket guard set was ordered larger than my ordered split sprocket just for the possible future need to up-ratio from 5:1 with a 60-tooth to 6:1 with a 72-tooth, so it wouldn't cost me any ground clearance at all with my little 4.10x3.50/6 tires.
You however might want to consider the clearance issue of a huge rear sprocket, even with 20" tires. Looks like you have real nice clearance all the way around right now. Hate to see you eating up chains and sprockets with sand and dirt from dragging along with only a couple of inches from the sprocket to the ground.
Picture that rear end with its weight and yours plowing through some sugar sand.