Teeth??

[DavidPorvaz]

I'm new to this, so please excuse my lack of knowledge. I was giving a go kart frame and engine. I only need a clutch. it is a centrifugal clutch, but what is the difference between the number of teeth and what are the purpose of different teeth numbers?

 

[Poboy kartman]

Number of teeth on clutch and wheel sprocket determine gear ratio. Count both and include tire diameter and engine size if you want a suggestion for tooth count for the new clutch. Keep in mind that chains and clutches also have different sizes- #35,#40 and #41 most likely.

While you're at it- fill out your profile so we know where you are from.

 

[landuse]

You want to get a ratio as close to 6:1 or lower (which means a higher number). If you have a 72T axle sprocket, you would want to get a 12T clutch to give you at least 6:1. Getting a 14T clutch wouldn't really work well for you with a 72T sprocket.

This all depends on tyre diameter though. If you have tall tyres, you will need to gear lower (a higher number in the ratio eg 8:1)

 

[DavidPorvaz]

Tires are kinda small. This go kart is for my kids.(2-10 year old boys) .So I don't want it to have too fast of a take off and I can govern the engine so the top end speed isn't too high as well, but I also don't want too slow of a start that 1 year daughter can beat them off the line...lol. I have a 5 horse honda engine , it's a two seater frame. It's my first as well as theirs. I have a feeling that this might the beginning of a great thing. Do I still want to go with a 6:1 ratio? I will count the teeth on the sprocket on the tire.

 

[itsid]

Tires are kinda small. This go kart is for my kids.(2-10 year old boys) .So I don't want it to have too fast of a take off and I can govern the engine so the top end speed isn't too high as well, but I also don't want too slow of a start that 1 year daughter can beat them off the line...lol. I have a 5 horse honda engine , it's a two seater frame. It's my first as well as theirs. I have a feeling that this might the beginning of a great thing. Do I still want to go with a 6:1 ratio? I will count the teeth on the sprocket on the tire.

yes.. maybe even 7:1! (you might need a jackshaft then)

because
a) the lower the ratio (higher the numbers) the lower the speed
b) you do not want to govern the engine too much (maybe 300-500 rpm) to not rev too low for the clutch to fully lock.
(that'll burn clutches pretty fast)
c) the lower the ratio the quicker the takeoff

Just let us know what kind of top speed you have in mind for your boys, and what exact tire diameter you have,
we can give you a starting point for you
to play with some numbers here:
http://www.diygokarts.com/speed-calculator.html
to achieve that

'sid

 

[OzFab]

I can govern the engine so the top end speed isn't too high as well

No you can't, that will cause problems with the clutch, it need to reach a certain RPM (usually around 2500) before it locks, before that it's slipping. If you govern the engine down too far, the clutch will never lock, causing premature wear...

The best way to slow a kart down is with gearing. The problem is, what may be too fast for one, may be too slow for another...

Do I still want to go with a 6:1 ratio?

At 6:1, top speed will be around 23mph; at 8:1, it comes down to 17mph. The problem there is, with 13" tyres, you'll most likely need to resort to a jackshaft.

My daughters kart will do around 12mph. When she first got it, she was very tentative but, was shown how to control the speed by feathering (on & off) the throttle; now, a year later, she guns it & has a blast

 

[Poboy kartman]

No you can't, it need to reach a certain RPM

Hmmm- me not know that that Kimosabee, but me needs more school.

 

[Half-breeder]

I dont have 13" wheels(yet)... but I run 10's and 16's I 'can' run both at 7.5:1 ratio. W/ the 10"s, the kart will do about 14mph(but if ya gotta lead foot youd be buying rear tires alot).
7.5:1 w/ 10"

W/ 16"s w/ the same ratio I do 23mph...
7.5:1 w/ 16"

I have a jackshaft and I bought certain gears just so that I can do/go 23mph w/ 10"s just by swapping the JShaft gears around to produce a 4.8:1 ratio. But that's for when a 1wheel wonder race happens.

Just remember... more torq= fast takeoffs/acceleration, but slow speeds(like running a 10 speed bike in 1st gear always)... less torq=slower takeoffs/acceleration, but top speed it higher(just takes longer to get there, and you risk cooking your clutch, and it 'does' put a strain on your motor).

IMO ones ratio is a matter of 'personal' favoritism/opinion/driving characteristics...

 

[landuse]

I can govern the engine so the top end speed isn't too high as well.

Unfortunately we see this question waaay too often, and I can understand why if the member is new to karting. When you are new, you just don't understand how things work

Some people think they can limit the travel of the pedal so that the engine doesn't reach wide open throttle (WOT). Some people even put some limiter on the throttle lever on the engine. All this will do (as Fabroman said) is to cause the clutch not to engage properly, therefor wearing out at a rapid pace. It is important not to do this more for centrifugal clutches thatn for torque converters, as TC's have variable gear ratios, and can handle lower RPM's a lot better

 

[DavidPorvaz]

I looked at the sprocket that is attached to one of the back wheels. It has a 54 tooth count . The tire is 13 x 5.00 -6 nhs. That's what it reads on the side. So I guess I'll go with a quick start so the top end isn't too fast....is that right.? And I won't govern the engine! So back to the original question, what size/ tooth count do I want to use on the clutch to get the right ratio with out burning it out or having a quick wear down on it. I can't even get my wheels spinning!!! And yes, the pun was intended

 

[DavidPorvaz]

And what is a jack shaft? And why do I need it?

 

[mckutzy]

A jack shaft is used to change the gear ratio, drive line adaption to rear wheel, structural components and other parts like sprockets; ( on a bike like mine) to have a right side drive.

Look at my thread of my ride, halfway down on the first page, check my sig line. there is a good example.

 

[OzFab]

And what is a jack shaft? And why do I need it?

With your current axle sprocket of 54t, let's say you buy a 10t clutch, that gives you a drive ratio of 5.4:1; you need to go lower than that

Low numbers = high speed = high gear/ratio
High numbers = low speed = low gear/ratio

To attain a drive ratio of (let's say) 7:1, you would use a jackshaft which is, literally, a shaft with two sprockets on it.

So, if you have a jackshaft with a 17t & a 13t, you would end up with a final drive ratio of 7.06:1

10t clutch to 17t J/S sprocket
13t J/S sprocket to 54t axle sprocket

You can use this jackshaft calculator to play around with the numbers...

One last question: Do you know the pitch the axle sprocket (distance between teeth)

 

[Oxymoron]

If you don't know how to determine the pitch, check here. You'll then know what #chain you have, and what type of sprocket to buy.

 

[Scout]

http://gokartsusa.com/jackshaft-kit-gokart-minibike.aspx

Look on the side of the chain links, they usually have the pitch number stamped on them.