Need advice on gear ratio

[gguuyy]

Ok I've been rebuilding my old go-kart and I've almost got it done. It has a 10T driver and 55T driven so that's a 5.5/1 ratio right? The tire size is 4.10/3.50-5. Should this be ok? It pulls me around good. I weigh 160 and it has no problem on take off. It will spin in gravels. The top speed is ok but not the best. The problem is that the clutch is smoking after about 10 minutes of riding. The clutch is brand new and the old clutch didn't smoke with the same set-up. Maybe it's just burning off the excess oil? It slung out some oil so maybe that's it. Anyways everyone's advice will be appreciated.

 

[itsid]

Maybe it's the clutch, maybe not *shrugs*
Maybe the clutch you now have has a different engagement speed, and your engine doesn't reach that speed fast enough to fully engage the clutch.

what engine do you have HP wise?
and what clutch you got?

'sid

 

[gguuyy]

The engine is a gx200 6.5hp, the clutch came from tractor supply I don't remember the brand but I will find out tomorrow. It is different than the old clutch though.

 

[itsid]

So, you have a ratio of 5.5:1 on 13" wheels.. (They're 13" righ?)

that'd be 30.4mph top speed... (for a governed engine @3600 rpm)
You sure your take off is good and you didn't skipped teeth on your axle sprocket by mistake?
Or is there a jackshaft in between?

Anyways..
the important part is at what rpm does the clutch fully engage?
For a engine like this that should be closer to 2000 rpm than to 2500 rpm but well above 1500 rpm

Say you got a clutch that engages at ... say 2200 (but JUST) instead of one that engages at 1800... now you shift the clutch full lock speed accordingly up from say 2100 to 2500 rpm

Now you're sitting on a kart at about 20mph and the clutch cannot fully engage, because the engine isn't capable of delivering enough power through the slipping clutch to get to 22mph...
And that's it, the clutch will burn (and glaze) and the more it does the less power it can transfer..

I don't know if that's the case here, but it might;
so please check which clutch you got and at what rpm it fully engages.

'sid

 

[gguuyy]

The tires are 11 inches tall. Here's a pic of the old clutch. It has springs inside and the new one has c clips instead of springs.

 

[gguuyy]

Here's the new clutch.

 

[gguuyy]

I think I'm gonna look into putting a torque converter on it. I can fly around on it and the clutch doesn't get overly hot but the kids can putt around on it for 5 minutes and it gets so hot it smokes. They ride to slow to fully engage the clutch so its just causing to much friction. I may try the old clutch and see if it can do any better but I doubt it will.

 

[itsid]

Wait what?

the kids are slower???

So... you do NOT LIMIT the throttle do you?
You should never do something like that (because it'll almost always kills your clutch! AND it WILL kill your Torque converter too)

'sid

 

[gguuyy]

No I don't limit the throttle but the kids drive it slow because they can't control it well enough yet. It went sideways on my oldest one (6) and it scared her so she just drives around slowly now. Ill just have to work with them on how to drive it properly for awhile or just have to ride them around on it until they get a little older. Any advice on this is appreciated. I want them to be able to drive it but not if its unsafe. If I have to sacrifice a few clutches then so be it.

It's got quite a bit of torque I can whip the fish tail on pavement and cut nice donuts in grass and dirt. Maybe I could change the gearing so it wouldn't take off so fast?

 

[itsid]

No need to sacrifice a clutch, get split sprockets and a sprocket holder..
or a jackshaft with different sizes for the jackshaft for that matter.

If your kids drive the kart use a different ratio (9:1 instead of 6:1 for example) it'll be quicker at take off, so dont get too low, since that can be scary as well...
but it'll reduce the top speed at full throttle and your kids will push the pedal fearlessly

'sid

PS I can't recall your drive setup, so maybe you want to let us know again so we can help you figuring a good ratio set for that purpose

 

[OzFab]

That would be the best idea, however, lowering the gear ratio will lower speed but, it will increase torque so, it won't take off fast, it'll take off hard & will be more inclined to break traction

5.5:1 ratio, read post #1 sid...

 

[gguuyy]

Yea Its got a 10T driver and 55T driven so if I figured it right its a 5.5:1 ratio.

I like the torque but I rebuilt it mostly for my kids to enjoy and the hard take off is what turns them against it. I think getting a jack shaft is the way I will go with it and get a few different sprockets like Sid was saying.

 

[Half-breeder]

That would be the best idea, however, lowering the gear ratio will lower speed but, it will increase torque so, it won't take off fast, it'll take off hard & will be more inclined to break traction

5.5:1 ratio, read post #1 sid...

... yea the higher the ratio the better chance tires WILL spin... but TOP speed is lessened, and the 'load' on your motor is lessened as well.
I have the same size motor and wheels(in this vid) as you... this vid is w/ a 7.5:1 ratio...tops out at 14-15mph...
http://www.youtube.com/watch?v=8tYT3UTIKzc

 

[gguuyy]

Yea my kart seems to handle similar to that but I thnk it tops out at 17 or 18 mph. So the larger the sprocket the higher the top speed and vice versa?

 

[Half-breeder]

Yea my kart seems to handle similar to that but I thnk it tops out at 17 or 18 mph. So the larger the sprocket the higher the top speed and vice versa?

I use a JShaft on this kart... I can run a 7.5:1 ratio w/ a 12T clutch->15T JS in->12T JS out->72T axle. On 10" wheels 14-15mph(above vid)... w/ 16" 22-23mph(below video). If I swap the JS gears (15T and 12T) Ill be running a 4.8:1, which I run w/ my 10"s, which comes out to 22-23mph(same as the other ratio on 16").

This is the same kart/gear ratio/motor... just bigger tires(16"=22-23mph)...
http://www.youtube.com/watch?v=R93-jkdNP10

So yes/no its all a matter of gear size... but placement as well. I use this link to calculate the ratios... then I use this to calculate speed.

You are correct in saying that a 10T clutch n 55T axle = 5.5:1 ratio... but you 'should' be doin 19-20mph(depends on weight/drag/elevation/surface grade).

 

[itsid]

..
5.5:1 ratio, read post #1 sid...

Oh boy.. of course.. I'm sorry, Not my day...

'sid

 

[OzFab]

Yea my kart seems to handle similar to that but I thnk it tops out at 17 or 18 mph. So the larger the sprocket the higher the top speed and vice versa?

Well, that depends on which sprocket; a larger engine sprocket will give you a higher top speed but, a larger axle sprocket will give you a lower top speed:

High ratio numbers = low gear = low top speed/good acceleration
Low ratio numbers = high gear = high top speed/poor acceleration

So, 4:1 is a high gear which will give you a high top speed
8:1 is a low gear which will give you a low top speed