9hp 2:1 reduction gearing.

[jakeofalltradz]

Hi guys.
I've finally joined the group. I've had a few projects over the last 2 years and I have gleaned so much from these forums. Pretty useful stuff. I'm from New Zealand.
I'm trying to work out the gearing for my current project. Any advice greatly appreciated.
I've bought a new 9hp 2:1 reduction with wet clutch. It has a 22mm output shaft. So sprocket options are limited.
The go kart has a 34t sprocket welded to axle. What's the advice on number of teeth for engine drive sprocket. And best gear ratio for a wet clutch?
Cheers, Jake

 

[Denny]

10 tooth on the engine is about the smallest you’ll find. Maybe 8 tooth if you’re lucky. Use only on paved surfaces and wide open throttle if you want the clutch to live.

 

[jakeofalltradz]

A 10t makes it 3.4/1 gear ratio. Doesn't a 2:1 reduction in gearbox help mitigate this? So shouldn't the clutch be just fine?

 

[anderkart]

How tall your rear tires?

 

[ezcome-ezgo]

A 10t makes it 3.4/1 gear ratio. Doesn't a 2:1 reduction in gearbox help mitigate this? So shouldn't the clutch be just fine?

Yes

 

[jakeofalltradz]

How tall your rear tires?

They are 15 in tall

 

[anderkart]

They are 15 in tall

Ok, looks like a very heavy Go kart...

Have you've already shopped around for 22mm-bore drive gears available for you to buy in your country?
If so, what was the engine/drive gear with the fewest number of teeth, and what pitch#/size chain was it made to fit?

How many pounds will the driver(s) weigh?

Where will you be riding this kart?
Just on flat paved roads, parking lots or hard-packed, flat off-road type terrain?
Or off-road in sand and/or expect to be climbing up steep hills or mountains?

What top speeds are you expecting?

And, would you prefer gearing it for lower top speeds to achieve better acceleration ability? (you cant have both...)

Or, higher top speeds with Less-acceleration ability?

Or, would you prefer us to just calculate the best overall gearing compromise of top speeds & acceleration ability? (this is what I would recomend...)

 

[jakeofalltradz]

Ok, looks like a very heavy Go kart...

Have you've already shopped around for 22mm-bore drive gears available for you to buy in your country?
If so, what was the engine/drive gear with the fewest number of teeth, and what pitch#/size chain was it made to fit?

How many pounds will the driver(s) weigh?

Where will you be riding this kart?
Just on flat paved roads, parking lots or hard-packed, flat off-road type terrain?
Or off-road in sand and/or expect to be climbing up steep hills or mountains?

What top speeds are you expecting?

And, would you prefer gearing it for lower top speeds to achieve better acceleration ability? (you cant have both...)

Or, higher top speeds with Less-acceleration ability?

Or, would you prefer us to just calculate the best overall gearing compromise of top speeds & acceleration ability? (this is what I would recomend...)

Hi anderkart
My guess is the kart would weigh about 80kg engine is another 30kg. I'm 65kg maybe a bit more if I've had too many pies.
I've only found one sprocket in nz with #428 pitch (this is the pitch of axle sprocket welded in place) it was a 13tooth. I've got a local parts guy who can machine a sprocket for a pretty similar price. So I can choose how many teeth.
Most driving would be flat paved road or hard packed gravel. Ideally I would like to cruise at 50km/hour (32miles/h). That's the speed limit for streets in town.
I would gear for middle of the road between speed and acceleration

 

[anderkart]

Hi anderkart
My guess is the kart would weigh about 80kg engine is another 30kg. I'm 65kg maybe a bit more if I've had too many pies.
I've only found one sprocket in nz with #428 pitch (this is the pitch of axle sprocket welded in place) it was a 13tooth. I've got a local parts guy who can machine a sprocket for a pretty similar price. So I can choose how many teeth.
Most driving would be flat paved road or hard packed gravel. Ideally I would like to cruise at 50km/hour (32miles/h). That's the speed limit for streets in town.
I would gear for middle of the road between speed and acceleration

Ok, we can use this forums speed calculator to estimate top speeds, but we'll simply need to compensate for your engines 2:1 gearing reduction, by doubling the tooth count of the axle sprocket entered into the speed calculator...

Here's the link to our forums speed calculator if you'd like to calculate other gearing options:

Speed Calculator For Go Karts and Mini Bikes

Use this easy tool to find the optimum sprocket combinations and top speeds of your project.

www.diygokarts.com

I preformed 2 different speed calculations for you:

#1 ~ With entering a 13 tooth engine sprocket, 15" tall tires and entering a 68-tooth axle sprocket, your estimated top speed @3600 rpm
calculated out to a 28 mph.

#2 ~ But by simply entering a 15- tooth engine sprocket, (instead of 13-tooth) your estimated top speed calculated out to a 35mph estimated top speed.


My Disclaimer:
I'll be honest and tell you that I have absolutely no experience using Kart engines with a 2:1 gear reduction, so I don't know if these gear ratio's would be putting excessive stress on your engine Wet Clutch & Gear Box or not... But these are simply the gearing combinations that would be required to achieve the estimated top speeds of 28mph or 35mph.

Here's a screen shot of that estimated 35mph top speed gearing calculation i preformed for you: