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Old 03-19-2020, 08:54 PM
djtuttiman djtuttiman is offline
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Default 13HP Gear Ratio HELP!?!

Hey Im a newbie to the go kart seen and just started by first budget go kart. Im have a lot of trouble finding a good gear ratio for the kart.

Because its a budget go kart, I would like to use a centrifugal clutch and found a 14t one for pretty cheap. Not looking to add a TC yet and trying to avoid using a jackshaft unless I absolutely have to. Kart weights about 350-400lbs with someone in it. It has a 13hp 390cc engine with a governor delete. I currently have 13" wheels but am open to changing them if needed. Kart will mainly be on asphalt and packed dirt. Would like to reach up 40mph but its not a must.

So with all that, what would be a good gear ratio set up; what is a good axle sprocket size and wheel size ?
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Old 03-19-2020, 11:00 PM
Smerft85 Smerft85 is offline
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Post pictures, easiest way for us to help.
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Old 03-19-2020, 11:09 PM
djtuttiman djtuttiman is offline
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Post pictures, easiest way for us to help.
hey, its hasn't been assembled yet. Its in a bunch of pieces.
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Old 03-19-2020, 11:56 PM
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Unfortunately I think you are going to have major problems doing what you want to do if you keep that 14T clutch. For a kart that weighs as much as yours does, you are going to need at least about an 8:1 ratio. With a 14T clutch, that means that your axle sprocket would have to be 112T. That is a pretty big heavy sprocket, and I am sure you are not going to have the height clearance for the sprocket to not drag in the dirt. Even with a 10T clutch, you are still going to need an 80T sprocket in the rear.

This is why you are probably going to need a jackshaft for compound gear reduction and space saving.

If you are desperate not to use a jackshaft, you could maybe get a 10T clutch and 72T sprocket and see if that works for you. You never know....with the larger engine it could maybe be ok.

Others will probably be around to give you some more advice
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Old 03-20-2020, 01:50 AM
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Originally Posted by landuse View Post
Unfortunately I think you are going to have major problems doing what you want to do if you keep that 14T clutch. For a kart that weighs as much as yours does, you are going to need at least about an 8:1 ratio. With a 14T clutch, that means that your axle sprocket would have to be 112T. That is a pretty big heavy sprocket, and I am sure you are not going to have the height clearance for the sprocket to not drag in the dirt. Even with a 10T clutch, you are still going to need an 80T sprocket in the rear.

This is why you are probably going to need a jackshaft for compound gear reduction and space saving.

If you are desperate not to use a jackshaft, you could maybe get a 10T clutch and 72T sprocket and see if that works for you. You never know....with the larger engine it could maybe be ok.

Others will probably be around to give you some more advice
If i could some how get the weight to be under 300lbs. In your opinion, what combination of tire size, clutch size and sprocket size would allow me to reach that 40mph mark? If that means using a jackshaft, how would i go about setting it up?
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Old 03-20-2020, 03:53 AM
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while I though the same thing as landuse..

13" wheels, not 13" rims right?
since if the wheel diameter gets bigger the ratio needs to be adjusted.
And other users came with a similar question had misinterpreted the tyre designation before
... but if it IS 13" wheel diameter (4 or 5" rims)

the calculator says you get away with 6:1 ratio up to 330 lbs
and 6.5:1 ratio up to 440 lbs

but that still makes a huuuge sprocket
for #35 chain 10" for 6:1 (84 teeth)
and 11" for 6.5:1 (91 Teeth)

And now the bad part: chances are you have a #40 sprocket
in which case you simply can't
because the sprocket diameter is 13.5" for 85 Teeth and 14.4" for 91 Teeth
bigger than the rear wheel diameter of 13", no way it fits.

So you indeed need a jackshaft either way.. and then.. you better get rid of the sprocket and buy a series 40 clone TC instead.

Since frankly even in best case you cannot reach 40mph (33 mph on 6:1 perhaps.. )
with a clutch.. but you can easily with a TC...
KartInfo by kartcalc.net:
Code:

KART
RW diameter: 33.02 cm | 13 in Total weight: 200 kg | 440.92 lbs
ENGINE
Original HP: 13 Asummed HP: ~14.46 Torque: 25.71 Nm | 18.97 ft lbf RPM: 5200
TRANSMISSION
Final ratio: 4:1 TC type: series 40 Lowest ratio: 9.72:1 Highest ratio: 4:1
PERFORMANCE
Max Wheel Torque: 249.9 Nm | 184.32 ft lbf Min Wheel Torque: 102.84 Nm | 75.85 ft lbf Acceleration: 4.6 m/sē | 15.09 ft/sē Top Speed: 80.91 km/h | 50.28 mph
if you want to play with numbers and calculate yourself..
get the phone out and browse to app.kartcalc.net yourself

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Old 03-20-2020, 08:17 AM
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I do agree with sid, the 40 series t/c is your best bet. However I have the 14t cc on my scrap rod and it does over 40mph. You are almost forced into using a Jack shaft weather you use a t/c or a cc. I have 18" tires, 14t cc, 9t sprocket on one side of the Jack shaft, a 13t on the other, and I believe my axle sprocket is 72t. It won't do burn outside or wheelies, but does 40mph pretty easy. Its geared too high so the cc is already getting worn and that kart weighs maybe 200 pounds powered by a gx270.

Reason I asked for pictures is because we are guessing at the simple things such as actual tire size. Doesn't matter that it's all in pieces, it will still help us determine what exactly you are working with. You may also exaggerate the weight of the kart, or may not. There is just too much guess work without seeing what it is you have, and 40mph isn't that unreasonable of a goal with a gx390, my dingo with a 212 does 40mph on a cc and 18" tires.
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Old 03-20-2020, 10:51 AM
djtuttiman djtuttiman is offline
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Thanks for the input guys.
I took an hour and assembled as much as the kart as i could. pictures are attached. I was planning to shorten the length which would take care of some of the weight. I think I will be able to get right under 300lbs including a driver when Im done.

The full wheel diameter is 13", but im planning on changing them out so i am open to new sizes. Looks like i will need a jackshaft either way. So what would be the best set up for me?

Chances are, I will be getting a TC sooner or later. I know that comet is usually the way to go in terms of TC but whats your take on ebay 40 series TC? What issues do they usually have?

link to ebay TC: https://www.ebay.ca/itm/Go-kart-torq...sAAOSwRSBdulhv


btw: that calculator is pretty cool
Attached Thumbnails
IMG_2289.jpg   IMG_3831.jpg  

IMG_2037.jpg  
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Old 03-20-2020, 11:05 AM
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I have never seen a gx390 clone with a 4 bolt valve cover,

from the looks it seems like a 196ish cc , 6hp engine , 3/4 shaft?

The 40 series would be overkill for such an engine, id recommend the 30 series kit.
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Old 03-20-2020, 11:11 AM
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Quote:
Originally Posted by karl View Post
I have never seen a gx390 clone with a 4 bolt valve cover,

from the looks it seems like a 196ish cc , 6hp engine , 3/4 shaft?

The 40 series would be overkill for such an engine, id recommend the 30 series kit.

Sorry thats not the engine im running. I sold that one, i now have a 13hp 389cc clone
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Old 03-20-2020, 11:14 AM
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is that diamond plate steel? maybe try and replace it, that is a ton of weight.
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Old 03-20-2020, 11:17 AM
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is that diamond plate steel? maybe try and replace it, that is a ton of weight.
I think it is. Good idea, thanks
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Old 03-20-2020, 11:30 AM
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jeez that mower saddle looks uncomfortable as can be..
but man I like the idea

Now, small wheels checked..
large axle sprocket even more of a problem I'm afraid..
so yeah.. jackshaft is mandatory to not cut a slit in the road wherever you go.
and with that.. I still vote pro series 40

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Old 03-20-2020, 11:48 AM
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Quote:
Originally Posted by itsid View Post
jeez that mower saddle looks uncomfortable as can be..
but man I like the idea

Now, small wheels checked..
large axle sprocket even more of a problem I'm afraid..
so yeah.. jackshaft is mandatory to not cut a slit in the road wherever you go.
and with that.. I still vote pro series 40

'sid
Thanks, hopefully I can take out soon.
What’s your take on eBay TCs ? I want a good kart but I’m not trying to break the bank for one
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Old 03-20-2020, 11:58 AM
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we have had ONE user with a bad experience on a chinese clone TC
(from ebay or amazon.. can't remember.. same same anyways)
And several dozens with no issue whatsoever,

Stay away from the backplate thingies
and you have a really good chance of not having any troubles with it.

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Old 03-20-2020, 07:02 PM
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Alright guys,
After some research and everything you guys said, I've decided to go on the TC route. Because this is a budget kart, im going to try my luck with a TC clone. Im looking at ordering this one (https://www.ebay.ca/itm/Go-kart-torq...sAAOSwRSBdulhv). Its a 30 series TC but has it can handle a 8-18hp motor. I would probably try to run the 12t sprocket using a #35 chain to a 60t axle sprocket. I somehow arrived at 18" tires.

Now that KartInfo app doesn't say I would have an issue with running this setup. but what do you guys think. Will i be okay to run this?
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Old 03-20-2020, 07:59 PM
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If you bump up to 18" rear tires you could fit a bigger sprocket, something like a 72t, and on the t/c a 9t, possibly avoiding a Jack shaft still maintaining a low enough ratio to set you back in the seat.

Btw I say 72t, but not sure what is available in that range for a #40 chain, could be 70t, could be 8?t, but check the diameter of the sprockets before purchasing. I can get a tooth count on both of mine that run 18" rears tomorrow so you know it'll fit for sure. Even off road I don't ever hit the sprockets on the ground with the 18" tires.
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Old 03-20-2020, 08:26 PM
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Quote:
Originally Posted by Smerft85 View Post
If you bump up to 18" rear tires you could fit a bigger sprocket, something like a 72t, and on the t/c a 9t, possibly avoiding a Jack shaft still maintaining a low enough ratio to set you back in the seat.

Btw I say 72t, but not sure what is available in that range for a #40 chain, could be 70t, could be 8?t, but check the diameter of the sprockets before purchasing. I can get a tooth count on both of mine that run 18" rears tomorrow so you know it'll fit for sure. Even off road I don't ever hit the sprockets on the ground with the 18" tires.
Yea, if you get a chance let me know what your running. Only reason why im running a 12t with a #35 chain is because it comes with the kit and the manufacture recommends it. Does that sound okay though?? I am debating between a 60t or 72t axle sprocket
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Old 03-20-2020, 10:23 PM
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Id say get the engine/tc and the proper fitting seat desired first, then look at where things are going to fit.. Off hand..Its looking that the engine isnt goint to fit well if not at all...
Big blocks are big and wide....
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Old 03-20-2020, 10:57 PM
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no a series 30 will NOT work (not well that is)
you will go through belts like crazy (25 a pop.. sooo not a cheap idea)

a series 40 is much more suitable for your engine.

THAT:
https://www.ebay.ca/itm/40-Series-To...t/391386757260


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