I need help on deciding what gears to run on my jackshaft thers a 60 sprocket on a 15 inch rim the kid i bought it from used it for the trails. he said it only did 20 and would rev out real fast .ther was a 20 tooth gear that went to a 8 tooth gear then to the 60 tooth sprocket im not sure how many teeth he had on the clutch ...i have a hemi predator id like to put on this bike. id l Iike to put a tav on this bike but money is tight for Christmas so a max tourqe will have to do i have plenty laying around .any help would be appreciated
Motown, what are you aiming for? MPH? Torque? Any computation will require the engine RPM, (I use governed 3600 RPM) as well as OD of rear tire. Pardue here had a neat .xls calculator on line, but I can't find it here anymore. I do have one on my machine here at home.
You can do some searches on line for a Jackshaft calculator, but the one from Pardue was excellent. Max torque is fine for this application, though I'd gear on the low side to keep it happy.
IF your outside tire dimension is 15", your Max Torque clutch is 12 tooth, and you're running at 3600 RPM, your maximum speed calculates out to just under 13 MPH with the sprockets you described.
IF your outside tire dimension is 15", your Max Torque clutch is 12 tooth, and you're running at 3600 RPM, to attain 24 MPH, you should swap your 8 tooth sprocket for a 15 tooth.
My Rule of thumb is that I want a 5:1 ratio or higher. (Depends on total weight of rider and machine)
Lastly, all this ratio and speed computation is pure bull crap, because none of it take into account the engine's torque curve, which may or may not be at max RPM. It doesn't take horsepower or torque into account at all, just spinning RPM's. So the numbers for a 50 HP engine at 3600 RPM and the numbers for a 2 HP engine at 3600 RPM are going to look the same. But obviously, the 50 HP engine is going to do fine at higher gear ratios, while the 2 HP wouldn't even move the bike at those higher ratios.
You can do some searches on line for a Jackshaft calculator, but the one from Pardue was excellent. Max torque is fine for this application, though I'd gear on the low side to keep it happy.
IF your outside tire dimension is 15", your Max Torque clutch is 12 tooth, and you're running at 3600 RPM, your maximum speed calculates out to just under 13 MPH with the sprockets you described.
IF your outside tire dimension is 15", your Max Torque clutch is 12 tooth, and you're running at 3600 RPM, to attain 24 MPH, you should swap your 8 tooth sprocket for a 15 tooth.
My Rule of thumb is that I want a 5:1 ratio or higher. (Depends on total weight of rider and machine)
Lastly, all this ratio and speed computation is pure bull crap, because none of it take into account the engine's torque curve, which may or may not be at max RPM. It doesn't take horsepower or torque into account at all, just spinning RPM's. So the numbers for a 50 HP engine at 3600 RPM and the numbers for a 2 HP engine at 3600 RPM are going to look the same. But obviously, the 50 HP engine is going to do fine at higher gear ratios, while the 2 HP wouldn't even move the bike at those higher ratios.
It will probably be more for him to cruise around on threw the trails hes 100 lbs .i was thinking about the tav but i wont be able to run it straight back to the sprocket because the rim has hub breaks . And i cant just turn it around because it locks into a little tab on the swing arm. Iv been reading alot on the motor bicycle pages because they deal with taller rim and tire setups for the predator motors but havent found a good jackshaft calculator
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Here is a link to an excellent calculator- the one I refered to in my post above. Download it, and you can play around with the numbers to see various outcomes. http://www.oldminibikes.com/forum/e...-speed-calculators-post810737.html#post810737
I'm doing a project now, where I am installing a jack shaft and turning the wheel around. Also has hub brakes, and I will weld on a brake tab for it on the other side.
I'm doing a project now, where I am installing a jack shaft and turning the wheel around. Also has hub brakes, and I will weld on a brake tab for it on the other side.