Build a Go-Kart: Calculations & Planning

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Discussion Overview

The discussion revolves around the planning and calculations involved in building a go-kart, focusing on engine specifications, torque, power, gear ratios, and chain selection. Participants explore various technical aspects, including weight considerations, axle types, and sprocket design.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant outlines their engine specifications and initial calculations for rolling force, drag force, total tractive force, torque at the wheel, and gear ratio, seeking validation of their approach.
  • Another participant asks for the weight of the kart and the individual, suggesting that final sprocket selection should be considered later and recommending a specific roller chain size.
  • A participant provides their combined weight with the kart and converts engine torque and power into different units, inquiring about criteria for roller chain selection.
  • Discussion includes recommendations for sprocket sizes and axle types, with one participant suggesting a live axle for better performance.
  • Concerns are raised about the impact of increasing the axle sprocket size on top speed, with a participant questioning the feasibility of achieving the desired engine RPM with the specified engine limits.
  • Another participant shares their experience with common final ratios used in go-karts, suggesting that a 6:1 or 7:1 ratio is more typical, while a 5:1 ratio might be too high and a 4:1 ratio too slow.
  • Questions about the pitch ratio of sprocket teeth are posed, indicating interest in casting the sprocket.
  • Concerns about the strength of cast parts versus forged parts for racing applications are mentioned, with a recommendation for a heavier-duty roller chain for the kart's weight.

Areas of Agreement / Disagreement

Participants express differing views on the optimal axle type and sprocket sizes, with no consensus on the best approach for achieving desired performance metrics. The discussion remains unresolved regarding the ideal gear ratios and the implications of various design choices.

Contextual Notes

Participants express uncertainty about the calculations and assumptions made regarding engine performance and gear ratios, highlighting the need for further clarification on roller chain selection criteria and sprocket design.

JOHN daruwala
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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
 
Last edited:
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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
 
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 ?
 
#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.
 
i would agree with you on live axle,
but increasing tooth on axle sprocket would reduce my top speed
 
Ranger Mike said:
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.
 
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
 
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
 
Last edited:
if i were to cast the sprocket , could you tell me something about the pitch ratio of the teeth ?
TY.
 
  • #10
#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
 

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