Gear ratio
- Thread starter trekklee
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KartFab
Active member
I heard that it depends.
We have got to know what sort of gearing and kart you have now. Tyre diameter is important, so what have you got now?
Gearing depends on many factors, but you can work on the common gear ratio of 6:1. This should give you a balance of power and speed. This depends on tyre diameter and weight though.
With a centrifugal clutch, if you gear too high (eg 4:1) you will burn your clutch out. With a low gear ratio (eg. 8:1), you will have loads of torque, but not a whole lot of speed.
What are you looking for?
Gearing depends on many factors, but you can work on the common gear ratio of 6:1. This should give you a balance of power and speed. This depends on tyre diameter and weight though.
With a centrifugal clutch, if you gear too high (eg 4:1) you will burn your clutch out. With a low gear ratio (eg. 8:1), you will have loads of torque, but not a whole lot of speed.
What are you looking for?
falcon52
New member
Landuse, could you explain of refer me to a place that does explain how a lower gear ratio correlates to those number you have in your example versus a higher head ratio being a lower number of drive driven? And the ratio is input to output/drive to driven correct?
Well I have a comet torque converter 30 series and it is connected to chains and I have a giant sprocket on the axle I don't know how to figure out the wheel diameter
mckutzy
Well-known member
Take a tape measure, hold oneside roughly where the edge is, measur across, that's the diameter. Measure on center.
Doc Sprocket
*********
The much more accurate way-
Put the end of the tape measure on the ground, and measure straight up to the very highest point of the tire. This will give you the static loaded diameter, and about as accurate as you're going to get. Much better than trying to eyeball both sides of the tread at the same time, and unloaded.
Put the end of the tape measure on the ground, and measure straight up to the very highest point of the tire. This will give you the static loaded diameter, and about as accurate as you're going to get. Much better than trying to eyeball both sides of the tread at the same time, and unloaded.
That's what I did the end of tape measure touching the ground up to top
17 inches
A high ratio is a low number like 3:1. This will give you greater speed and less torque, but will fry your clutch really fast
A low ratio is a high number like 8:1. This will give you more torque than speed
You can hink of it like a bicycle. When you go up hills, you put it into low gear. If its low gear ratio is EG 8:1, this will mean that you will have to pedal 8 revolutions to move the wheel 1 revolution. The same goies for an engine. The sprocket on the PTO shaft will turn 8 times to turn the sprocket on the axle (or the wheel itself) 1 time. This gives you lots of torque to get up the hills
If you left you bike on a high gear ratio going up that hill (eg 3:1), you will only be pedaling 3 times to move the wheel once. That is going to be real hard, but if you get it right, you are going to be going a lot faster.
To calculate your gear ratio on a straight clutch to axle setup, you use this formula. You can do the same for a TC:
(Axle sprocket tooth count/clutch sprocket tooth count)
If you have a jackshaft you do the following:
(JS in Tooth count/clutch tooth count)*(axle sprockt tooth count/JS out tooth count)
Here are some calculators you can use
Tire, gear ratio, RPM & Speed Formulas
http://www.diygokarts.com/vb/showthread.php?t=9591
http://www.csgnetwork.com/gearratcalc.html
http://www.4lo.com/calc/gearratio.htm
Jackshaft ratio calculator
http://www.fasttrackraceway.com/calc/index.php
http://www.compgoparts.com/TechnicalResources/JackshaftRatioCalculator.asp
http://www.affordablegokarts.com/GearCalc.php
Doc Sprocket
*********
And then, for the really accurate numbers-
Plop your butt in the kart with all your regular gear and a full tank of gas. Have somebody else measure from the ground up to dead centre of the rear axle. That gives you the Static Loaded Radius. Multiply that number by 2, and enter it into your calculator as the diameter (or just use the SLR as-is for calcs that use radius).
For perfection, you'd use the Dynamic Loaded Radius, but that measurement is near impossible to get. At speed, your tire can actually expand a bit, effectively increasing the radius. To get an inflated example (pun intended) watch videos of dragsters taking off, and watch the rear tires carefully...
Plop your butt in the kart with all your regular gear and a full tank of gas. Have somebody else measure from the ground up to dead centre of the rear axle. That gives you the Static Loaded Radius. Multiply that number by 2, and enter it into your calculator as the diameter (or just use the SLR as-is for calcs that use radius).
For perfection, you'd use the Dynamic Loaded Radius, but that measurement is near impossible to get. At speed, your tire can actually expand a bit, effectively increasing the radius. To get an inflated example (pun intended) watch videos of dragsters taking off, and watch the rear tires carefully...
falcon52
New member
Thank you landuse! I have always been told and taught however that a low ratio was a low number like 3:1 versus the 8:1 in your example.
I have the same spec but I don know about how many tooth mine has but same engine
I got a Tecumseh 6.5 ohh60 and its in a yerf dog.
.
OzFab
Well-known member
falcon52
New member
O, well that's bass ackwards to what one would think lol. I guess I have always thought of it the other way but knew that low gear number meant high "gear" ratio, as in 4th or 5th. And vice versa.
OzFab
Well-known member
That's absolutely correct &, if you find some specs, you notice that the numbers for 1st gear are higher than those of 5th gear 
Eg: 1st gear in a car gearbox is usually somewhere around 3:1
4th gear is usually 1:1
Eg: 1st gear in a car gearbox is usually somewhere around 3:1
4th gear is usually 1:1
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