and ran the numbers through based on a 3600 rpm engine with 14 tooth front 20 tooth jackshaft in, 17 tooth jackshaft out, 40 tooth final and 24 inch tall tires.
It says I should be able to hit 75 mph. Yikes
assuming a 13 hp clone can reach full rpms with that gearing. I may have to play with sprockets to slow it down some.
If I went to a 30 tooth on the jackshaft i could knock it down to 50 or so. Or switching out to 18 inch tires will get it down around 60 depending on how much they grow.
Junkstarbuilds Administrator
Age : 47 Join date : 2012-07-03 Points : 4634 Posts : 236 Location : Fort Stewart Georgia
Thanks for the link - itll come in handy when i get around to finish building my mod tractors - 3 in the works are my trail/offroad GT murray, my wizard go kart and rat rod wheelhorse.
The GT will be the slowest, the wizard and wheelhorse will be the fast ones.
Junkstarbuilds Administrator
Age : 47 Join date : 2012-07-03 Points : 4634 Posts : 236 Location : Fort Stewart Georgia
I don't know if this site is already on here somewhere, but diygokarts.com has a calculator based on drive wheel diameter, total drive ratio, and engine rpm.
This calculator is handy for single speed things like go karts and minibikes. Also, the site has some plans for minibikes and go karts for those who are interested. "Teeth on axle" and "teeth on clutch" can be any number. I usually leave clutch as 1 and change the axle number to match my final ratio on the tractor/minibike/go kart/etc. The ratio can be calculated for every gear, even reverse.
For those who don't know how to find the total drive ratio on their tractor: • Find out the max rpm of the input shaft on the trans [for 1:1 pulley setups, it's the same as the engine, usually 3600rpm] • Put the trans in it's highest gear and count the number of turns it takes to turn the wheel once. • Example: if the input shaft spins 14 times per 1 revolution of the drive axle, you've got a 14:1 final drive ratio • So if you have 23" rear tires, and the input shaft runs at 3600rpm, and your ratio is 14:1 in 6th, your tractor will go 18mph [IF your engine is strong enough to spin up to 3600rpm under that load [anything over 10hp should have no problem]]
• RATIO = [trans turns]:1 [wheel rotation]
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Age : 45 Join date : 2019-07-02 Points : 4337 Posts : 2383 Location : Ontario, Canada
I know this is a very old thread but I found a really good and basic lawn tractor speed calculator. Unfortunately pulleys sizes are in millimeters but with the"T drive" field you can check your theoretical top speed or even for each individual gear!
Subject: 
November 21st 2012, 1:43 pm
