gearing a gokart general questions...

[MidNightIllusions]

So from what I've seen on here but haven't really played with is the gearing.

From what I've seen and was wondering was can you over or under the gearing???

My karts front clutch gear is either a 10 or 12T and rear is a 67T #35. Engine is a 6hp Intek briggs OHV. 11" tires on the front.

My kart is snake as **** on take off but max speed is 50km/hr.

My friends Kart is the same but his engine is a flat head 5hp briggs with a 60T #35 and his kart does 71.1km/hr.

What are my gearing limits to kick his ***? Lol

 

[OzFab]

The difference is the 7 teeth difference in your axle sprockets...

If you have #35 chain, it's most likely you have a 12t clutch; all other variables being the same you have 5.58:1 gearing where your buddy has 5:1...

Also, you didn't mention the tyre size of either kart, that can make a big difference...

 

[landuse]

.... 11" tires on the front.

Also, you didn't mention the tyre size of either kart, that can make a big difference...

He did mention the front tyres, but for us that means nothing. What we have to have is the REAR tyre size.

 

[MidNightIllusions]

Sorry guys that was a typo. I meant to say rear not front lol
11" tall tires on REAR.

But the main thing I'm really wondering is can the kart be over or under geared. Till the point on damage??
If so how can you tell you've gone to far? Lol

Thanks for the reply guys

 

[landuse]

But the main thing I'm really wondering is can the kart be over or under geared. Till the point on damage??
If so how can you tell you've gone to far? Lol

Yes it can . If you gear too low, you will be popping wheelies and frying your tyres tring to take off. You will have a stump puller though with all the torque.

If you gear too high your clutch will slip (centrifugal) and get fried. If you have a TC your belts will shred

 

[MidNightIllusions]

Sorry that sounded backwards. Did you mean if you gear too HIGH you'll pop wheelies? As in small front huge rear sprockets?

Low gearing as in small front small rear sprockets?
Maybe it's me that has it all messed up lol

But either way if you had 12T on front and let's say you wanted to do a 120km/hr so you went with let's say a very small rear 40T, your saying it could burn up your clutch...how so?

Thanks.

 

[landuse]

Sorry that sounded backwards. Did you mean if you gear too HIGH you'll pop wheelies? As in small front huge rear sprockets?

Low gearing as in small front small rear sprockets?
Maybe it's me that has it all messed up lol

But either way if you had 12T on front and let's say you wanted to do a 120km/hr so you went with let's say a very small rear 40T, your saying it could burn up your clutch...how so?

Thanks.

No....you have it the wrong way around. When you gear high, you have a small ratio, like 4:1. This means you have a small axle sprocket. Gearing hight gives you more speed and less torque. The problem with less torque is that the engine cannot spin the clutch fast enough to engage, and the clutch will then slip.

Gearing low means that you have a higher number, like 10:1. This gives you more torque and less speed.

If you have a 12T and a 40T sprocket, your gear ration would be 3.33:1. Your kart probably wouldn't even move because the clutch would not be able to engage. It will slip like crazy and fry your clutch

 

[itsid]

first of all.. you can never HIT 100km/h with 6HP!
that's impossible.

then, low gear is high number ratio (rear sprocket toothcount divided by front sprocket toothcount)
high gear is low number ratio

And the clutch will burn because you cannot provide the power you need to take off, thus, the chain will lock the clutch drum in place and the fast turning enigine accelerates the shoes which are unable to grab the fixed drum and slip
even above full engagement speeds.
slipping means creating heat, burning up the shoes and drum... toast!

'sid

 

[OzFab]

So, in short:

Low gear = high number = low speed
High gear = low number = high speed

first of all.. you can never HIT 100km/h with 6HP!
that's impossible.

Well, nothing's impossible but, it would cost a fortune...

 

[Poboy kartman]

first of all.. you can never HIT 100km/h with 6HP!
that's impossible.

then, low gear is high number ratio (rear sprocket toothcount divided by front sprocket toothcount)
high gear is low number ratio

And the clutch will burn because you cannot provide the power you need to take off, thus, the chain will lock the clutch drum in place and the fast turning enigine accelerates the shoes which are unable to grab the fixed drum and slip
even above full engagement speeds.
slipping means creating heat, burning up the shoes and drum... toast!

'sid

Nothing is impossible. ....HIGHLY HIGHLY unlikely. ....yes ......but NEVER say never. ...'sid...you ought to know better. ......blanket statements are virtually doomed to be proven untrue....... eventually.........

 

[mckutzy]

Sid.... Virtually impossible. But....
Here is a high speed racing bicycle. 100mph+
http://www.donhoubicycles.com/land-speed-bike/


So get a big enough sprocket, it will go as fast as you want, eventually...

 

[itsid]

....
Well, nothing's impossible but, it would cost a fortune...

Nothing is impossible. ....HIGHLY HIGHLY unlikely. ....yes ......but NEVER say never. ...'sid...you ought to know better. ......blanket statements are virtually doomed to be proven untrue....... eventually.........

It IS impossible..
mind you I said "with 6HP"

I never said it's impossible to mod a 6.5HP engine to the HP you need to hit 100 km/h
(that'd be 12.1 Hp for a 150kg kart incl driver btw )

but with stock 6HP.. IMPOSSIBLE!

Sid.... Virtually impossible. But....
Here is a high speed racing bicycle. 100mph+
http://www.donhoubicycles.com/land-speed-bike/


So get a big enough sprocket, it will go as fast as you want, eventually...

it wont move from a full stop at all just pushing the pedals
but yes..I'd have to punch in the numbers for fun... but I guess that's doable.
IIRC a well trained biker can push up to 7W/kg body mass
so a 70kg biker can provide roughly 490W,
100 km/h should work since I believe that's somewhere in the 300W region needed..
100 mph I highly doubt it that'd be more in the 550W region!
(okay I just estimated the wattage needed here, so yeah *shrugs* I might be off)

but a go kart...
it's physics, I can't help it
150kg @ 100km/h -> ~9kW of power needed

'sid

 

[MidNightIllusions]

Lmao....Omg you guys are just too funny. I'm so glad I joined!

So currently my friends Kart has a 12T front and 60T rear on a stock 5hp briggs flat head. And current top speed using GPS is 71.1. He is determined to hit 100Km/hr. So ill keep you guys up to date on this epic fail hahaha!
I have a feeling this is gonna be all bad, but hey it should be interesting lol.

Btw you guys are awesome, with excellent answers. Good job everyone! Cheers.

 

[itsid]

now that's interesting stock 5HP briggs... 71.1 km/h.. that means
mathematically he's running on 21" wheels..

with 11" wheels.. the engine must turn ~6700rpms to hit 71.1 km/h...
pretty nasty for a engine without mods.
Also.. @ 6700 rpm that engine has about 9HP
So there goes the 5hp stock ....

Only other possibility: GPS failure...
last time I checked my GPS calculator I've hit 25m/s (~90km/h)...
sitting in front of my computer on a wheelless deskchair
only for a split second, but enough to trigger the update routine *shrugs*

that's why the code isn't public yet

'sid