Gearing question

If I were to put a 6-inch gear sproket on the motor shaft, and put a 2 inch sprocket on the drive shaft, would that provide a better high end speed? Would the acceleration from a dead stop suffer? Would the chain break? Anything else I haven’t mentioned?


[QUOTE=Joe_Oh;4716]If I were to put a 6-inch gear sproket on the motor shaft, and put a 2 inch sprocket on the drive shaft, would that provide a better high end speed?[/QUOTE]

[QUOTE=Joe_Oh;4716]Would the acceleration from a dead stop suffer? [/QUOTE]

[QUOTE=Joe_Oh;4716]Would the chain break? [/QUOTE]
possible , you could use motercycle chain and sprockets for better results

Well, yea, I want to use what would usually go on a motorcycle. Heavier duty would be better if I can find it.

there’s lots of chain (like for the Hyabusa) that is rated for some really high torque.

whats this going in?

A lightweight street legal vehicle with a 10hp D&D motor.

you don’t NEED anything bigger than 520 or 530 if you gear it like that.

Lets say you put out 50 ftlbs (if I remember correctly for that motor) at a dead stop. The gear ratio you chose would actually DECREASE the torque at the rear wheel. This isn’t good.

circumference of the front sprocket is 3*3.14159 = 9.42inches, 3.15 inches for the front.

thats a 1:3 ratio. you’d only get about 17 ftlbs of torque at the rear wheel axle. Lets say you’re 150lbs, and the vehicle is 400lbs (550 total), that’d take a really long time to accelerate a 550lb vehicle to speed only using 17 ftlbs of torque. You should be using at LEAST a 3:1 (not 1:3) ratio.

My motorcycle (calculated) will put 50ftlbs of torque at 300A, with a 5.45:1 ratio, for about 270ftlbs pushing against the road to push a 600lbs vehicle/rider.

How fast do you want this thing to go? whats the weight of the vehicle? do you want this to be “fun” or just “practical”. having a rear torque value of 1/2 the weight of the vehicle would be FUN, 1/4 of the weight would be usable, anything less would be a waste of time.

Also, at 1:3 you’d be sucking the amps out of the batteries for quite a while, which would be very hard on the batteries.

I would like to get a small 3 speed transmission (clutchless?) to solve this problem. Perhaps rigging up some sort of centripital clutch to expand the faster I go on the motor shaft and have the drive shaft at a fixed gear size.


I’m hoping for decent acceleration at a top speed of 50+ mph?

Here’s a picture of what I came up with. It should work as long as I find the right kind of centrifugal clutch to expand the motor pully ratio…

When the motor runs the clutch will expand causing the tensioner pully to rise up and keep the belt taught. The tensioner spring will be just strong enough to keep the tensioner pully in check. Hopefully this will allow for a starting 1:3 ratio and top out at a 1:1 ratio allowing for faster speeds.

Looks good no?

one question…


HOW FAST do you need to go… seriously. Series wound motors are good for 5-6000RPM, AC is good for even MORE RPM. 1:1 ratio running 5000RPM on an 24" motorcycle tire (thats the total diameter) would give you 356 miles per hour… and that’s just not even possible (or remotely realistic). Even above 60-70mph would be hard due to wind resistance.

I think you need to do some gear calcs.

Be a little more realistic. You’ll need more HP than that to overcome wind resistance. It comes into play above 40-50mph. 10hp (~25 max) might get you to 60-70… my K91-4003 (almost the same motor), gets 63mph on my motorcycle with a 4:1 ratio. Takes a while, but gets there.

I just don’t see the point in having an adjustable gear ratio, motors have a flat power curve, and you START with 100% torque. There isn’t a power curve like an ICE. As the RPM’s increase, voltage increases and the Amps decrease, but the power stays fairly constant. If you want an adjustable ratio, use a CVT… thats basically what you’ve explained.

For the time being I’ll work with a single gear ratio. From what you are saying, my 800lb (curb weight) ride will need a 1:8 ratio (50*8=400ft lbs of tourqe) not to be out-ran by everyone else on the road.

Is that right?

well, thats for a motorcycle, but 400ftlbs sounds like it’d be FUN to 50-60mph. I think you’d be happy with a 6:1 though, somewhere around 300ftlbs. It won’t accelerate like a crotch rocket, but 1/4-1/2 is going to be great.

Reccomend any websites that sell good quality gears? I tried to do a websearch with mixed results. I’d like to know what you’d reccomend.

for front sprockets (hardened steel) go to
they’ve got tons of different sprockets for all sorts of different shaft sizes for about 4-5 bucks a piece. They’ve also got some machine chain (cheap way to test some ratios) for under 20 bucks. Get yourself a chain break too. Get 2-3 different ones to test out. THats what I did, and I’m glad I did. You can get some good chain later, but this helps the experimental process… its not an exact science.

For the rear sprocket, I’d go with a known good manufacturer and safe yourself some time and trouble. is where I got mine. I got a 60tooth rear sprocket, for 530 chain, that was made for my motorcycle, with a Titan tough coating.

Instead of fooling with a chain that could break, I found a speed increaser gearbox at this site. It looks great for what I need but they dont list the price. I wonder if that means it’s gonna cost $1000+…

you don’t want a speed increaser gearbox, you want something to take the 5000+RPM from the motor, and decrease that to the wheel.

Have fun, but I think you’re overcomplicating it.

The CHAIN WILL NOT BREAK! I said cheap, because its machine chain, its just going to wear more than o-ring chain. o-ring chain is 150-200 bucks, this machine chain is 20 bucks for 10 feet. If you break the chain, your motor is NOT 10hp, it’d have to be something like 30 or 40 continuous.

66 rear sprocket and 12 front (5.5:1) with an RPM of 5000 with a rear tire diameter (edge to edge) of 24 inches (just a guess) would give you 64mph. The acceleration would be good, and do what you want.

Gearboxes are NOT cheap. has some too, and they’re all over 150-200 bucks, just for the transmission. then you have to figure out how to get that to the rear wheel.