Build a Go-Kart: Calculations & Planning

[JOHN daruwala]

so i am planning to build a go kart
i have purchased the engine with following specs:
power =8.2 KW (11.1 Ps) @8000 rpm
torque= 11N-m @5000 rpm
Calculations:
rolling force=221 N
drag force=26 N
total tractive force=221+26=247N
torque at wheel= 247 X 0.1 ( 20 cm wheels)
= 24.7
then i calculated power =Ft X vmax
=247 X 23/1000 =5.68 KW (23m/s is limit at my track)
the i calculated wheel rpm=2100 by power rpm torque relation
found out the gear ratio =engine rpm/wheel rpm
=3.7
14X3.7=axle teeth
52=axle teeth i am at planning stage i want to know if iam right uptill now or wrong
all so want to know how to calculate pitch of teeth if i want to cast the sprocket

 

[Ranger Mike]

good effort and you are on the right track
how much do you weigh?
what is the estimated weight of the kart?
is final drive live axle or dead axle?
i would worry about final sprocket selection at the last. go with number 35 or 41 roller chain.
it would help me if i knew horsepower and torque in ft. lbs

 

[JOHN daruwala]

i have taken gokart+my weight as 330 lb (150kg)
i would be using dead axle
Engine- torque 8.79 ft-lbs
power - 11 hp
is there a criteria for selecting roller chain ?

 

[Ranger Mike]

#35 roller chain is typical for your HP application. wheelbase around 41" and 41" track width is good. big sprocket on axle 72 tooth.
the clutch could be 10 tooth or 12 tooth. Kart should weigh 130 to 150 pounds. you need to consider live axle to get max performance.

 

[JOHN daruwala]

i would agree with you on live axle,
but increasing tooth on axle sprocket would reduce my top speed

 

[jack action]

big sprocket on axle 72 tooth.
the clutch could be 10 tooth or 12 tooth.

If his top speed is 23 m/s (51 mph) and his tire diameter is 20 cm (7.875"), that would give an engine rpm between 13200 & 15800 rpm. I don't think it will work with his 8000 rpm engine.

 

[JOHN daruwala]

i was thinking 14 tooth clutch and 56 rear sprocket clutch with 1:4 ratio
what time will my clutch survive if i use this ratio

 

[Ranger Mike]

jack as usual is right.
i did not do the math...from stricktly experience and what common final ratios are around here
i was referring to typical 6:1 or 7:1 final ratio most karts run..5:1 is getting too high and i think 4:1 will be real slow from the start. 7:1 is a stump puller gear and 6:1 is a good happy balance

 

[JOHN daruwala]

if i were to cast the sprocket , could you tell me something about the pitch ratio of the teeth ?
TY.

 

[Ranger Mike]

#35 roller chain is fastest but # 40 or 41 is heavy duty for your weight kart..i don't trust cast parts , forged is much stronger for racing