To say I'm unsure about the engineering aspects and what to do about it, is a major understatement. I appreciate your comprehensive analysis. Perhaps answers to you questions will narrow the options:
1) The engine is a Lifan 168F-2R, with Lifan Owners manual specs of 196cc and 6.5hp. The gokart manufacturer specs say 200cc.
2) The tires on the driven axle are 16x8-7 and 145/70-6 on the front.
3) Although the capacity is rated by the cart supplier as 375lbs, I cannot conceive of ever carrying that with small youths, probably maxing out at less than 200lbs. The usage however would include some unpaved with a slight grade.
Not to worry,
we try our best to answer all your questions and
help you fix your kart,
for you to have some happy kids tearing up your back yard
So,
yes, thank you, having more exact information indeed helps to narrow down onto possible solutions.
So we have a gx200 clone (and a good one at that) with 16" rears
that with the weight is all I need to know at this point
let's take your weight assumption
(275 lbs kart plus 200 lbs worth of passengers)
475 lbs..
6.5 horse 5.73:1 ratio 16" rear wheels
Tha kart calculator takes those infos and calculates the
required wheel torque
(getting to move from a dead stop and climbing up a 5% inclination)
and compares that to the assumed wheeltorque
you get with your engine and gear ratio at 2200 rpm.
(2200 rpm is the speed most clutches fully lock at... thus don't have unwanted slip and do not "burn up" in the process)
and in case it sees an issue
it checks at which point the "available" torque matches or exceeds the "needed torque" to suggest a viable gear ratio.
THAT however is calclated for a drum-shoe dry clutch
of just decent quality, just to make sure even cheaper setups will work.
an with the given values
it spits out this Warning:
Code:
[FONT="Verdana"]
...
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 73.69 Nm | 54.35 ft lbf[/B]
[I]Top Speed[/I]: [B] 48.13 km/h | 29.91 mph[/B]
[/INDENT]
[B][U]PROBLEMS[/U][/B]
[INDENT][B]You might burn your clutch/belt![/B]
[B]Gear ratio too high![/B]
[I]Suggested final ratio[/I]: [B] at least 11.43:1[/B]
[/INDENT]
[/FONT]
11.43:1 that is the Number we care about now..
since you do have a 2:1 reduction wet clutch,
the first and most obvious thing to find your needed chain ratio
is to divide ratio by 2
giving us a rounded 5.72:1
means with the clutch output sprocket fixed,
you'll need a 86Tooth axle sprocket to achieve that.
changing the axle sprocket to 10T a 57T axle sprocket should do
with the owners manual total weight of 650 lbs that suggestion would be 13.43:1 so 6.72:1 chain ratio [clutch to axle] so a 101 tooth axle sprocket with 15T on the clutch or 67T with 10T on the clutch
But not only is it a disc clutch it's also a wet clutch
so it can take quite a bit more abuse..
unfortunately my calculator can't take that into account (thermal capacity of the oil would be one of many factors to make a proper suggestion for example)
Anywhoo..
a working wet clutch should be able to compensate for around 0.3:1
chain ratio mising (this is just a guts value without any scientific calculation or observation backing it)
giving us 5.4:1 with @ 475lbs
or 6.4:1 @ 650 lbs
and that's where the TC came in essentially..
when your kids get older (and therefor bigger) you might need to readjust the gear ratio if we take the numbers close to the weight borders..
And readjusting does two things:
while the kart still moves with the higher weight it naturally gets slowed down when gearing lower
which is odd if you think about it,
the younger version of your kids being less trained in using a kart have a faster kart than the more experienced older versions of themselves.
here's a comparision of a wet clutch (precompensated.. ignore the warning)
against a TC
WETCLUTCH:
KartInfo by kartcalc.net:
Code:
[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 40.64 cm | 16 in[/B]
[I]Total weight[/I]: [B] 294.84 kg | 650 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 12.8:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 164.61 Nm | 121.41 ft lbf[/B]
[I]Top Speed[/I]: [B] 21.54 km/h | 13.39 mph[/B]
[/INDENT]
[B][U]PROBLEMS[/U][/B]
[INDENT][B]You might burn your clutch/belt![/B]
[B]Gear ratio too high![/B]
[I]Suggested final ratio[/I]: [B] at least 13.4:1[/B]
[/INDENT]
[/FONT]
And TC:
KartInfo by kartcalc.net:
Code:
[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 40.64 cm | 16 in[/B]
[I]Total weight[/I]: [B] 294.84 kg | 650 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 6.6:1[/B]
[I]TC type[/I]: [B] series 30 6" driven[/B]
[I]Lowest ratio[/I]: [B] 17.82:1[/B]
[I]Highest ratio[/I]: [B] 5.94:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 229.17 Nm | 169.03 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 76.39 Nm | 56.34 ft lbf[/B]
[I]Top Speed[/I]: [B] 46.43 km/h | 28.85 mph[/B]
[/INDENT]
[/FONT]
As you can see I had to lower the chain ratio a notch (6.6:1 [final ratio] instead of 6.4:1 [*2 for the wet clutch internals] ) since a TC is a dry clutch and belt system.
So as much as I like the wet clutches since they're really reliable and beefy.
in this particular case.. I'm not sure if it's the best way to go.
especially not if -as you can see- the original top speed can almost be met with a TC and would be cut in half with a working setup wet clutch.
'sid
PS Oh and yes there's an adjustable speed limiting weight for the series 30 to slow your kids down at younger ages if want to..
Clutch Plate.jpg