correct me if im wrong...chain drive

chain drive is when you use chains and bike sprockets if so then thats what im doing. as i said on my previous thread i was using 2 1 inch diameter sprckets and a 10 inch diameter sprocket i also want to know if the ratios are done in the sprocket diameter if so with my rear wheel being about 5 inches the gear ratio would be 16:1

please i need help is it possable to make a multi gear motorized bike

so you are using a weedwacker motor and its right hand drive. a sprocket on your engine and a chain to run down to a sprocket near your peddals and back threw your derailer to the gears on bike.

The diameter of your sprockets will give you a rough idea of the ratio, but if you want to be more accurate, count the number of teeth on each sprocket to get your actual ratio. Say you have 8 teeth on your one inch and 56 on your ten inch sprocket. Your ratio is 56 to 8, or 7:1 (56/8 = 7, 8/8 = 1). Remember, I'm pulling these numbers out of my...err, out of thin air. You need to count yours if you want to be accurate.

Pretending for a moment that your measurements are accurate. You are going from 1 inch on your motor to a ten inch on your jack shaft (from what I read). So your first ratio is 10:1. Your jack shaft spin's at 1/10th the speed of the engine. On the other end of your jack shaft, you have another 1 inch sprocket, this time going to a 5 inch sprocket on your wheel, so you have a 5:1 ratio this time. Your rear wheel will spin at 1/5th the speed the jack shaft is spinning. And if your jack shaft is spinning at 1/10th the speed of your engine, then the rear wheel is spinning at 1/50th of your engine's speed.

To make it simple, when using a jackshaft, you're multiplying the ratios. 10 x 5 = 50 and 1 x 1 = 1. so you have 50:1. You're not adding ratios, as in 10 + 5 = 15, or what I think you did to get 16, which was probably 10 + 1 + 5 = 16. Remember, multiply.

If you're using a little weed-eater engine, you probably want 25 to 1, not 50 to 1, though you might want to check with the guys who've actually done it. You can get that by having the small sprocket on your jack shaft be a 2 inch sprocket (now the ratio from the jack shaft to the rear wheel is 5:2, aka 2.5:1), or you can leave the 1 inch on the jack shaft and use a 5" as the large sprocket on the jack shaft(now you have a 5:1 ratio between the jackshaft and the engine, the jack shaft will spin twice as fast as at 10:1).

You can use this link to fiddle around with your gear ratios to see how fast what ratio will get you. Use the "transmission gear ratio" as your engine-to-jack-shaft ratio, and the "differential gear ratio" as your jack shaft to wheel ratio, and remember your tire radius is half of your tire diameter, so a 26" tire's radius is 13". Oh and estimate your engine RPM to be at least 7,000 at top speed. These little weed whacker engines can easily do 10,000rpm under no load, but pushing a bike is a big load for such a little engine.

Phew. Good luck!

ok ive changed my game plan alot so im gonna have a 1.5 inch sprocket with 10 teeth mounted on the engine(also before i go into detail i was told to do a 16:1 ratio with a weed eater) an maybe a 50 tooth sprocket on the jackshaft, another 10 tooth on the other side of the jackshaft and then a 30 tooth sprocket on the rear wheel(that ten inch sprocket wasn't going to work out because i couldn't find one of that size so im gonna have to find a way to take the stock sprockets off the rear wheel can some one explane how to do that or do i have to explore my bike)so i multiplied 3 and 5 and got 15 so it should be about 15 to 1 but im gonna go as close as i can to 16:1

Also i wish to know what i can sub for a jackshaft also what i can put to hold the sprockets to the jackshaft or i would just love a whole totoriol on how to do the whole bicycle transmission system

I'm glad you've got down how the jackshaft/gearing bit works.

16:1, if the engine is powerful enough to reach 7000rpm while pushing you along on your bike (it probably won't be strong enough) will mean you're doing 33mph. You'll probably only see that on a long downhill.

The higher your ratio, the lower your top speed and lower your gas mileage, but also the faster your take-off and the steeper the hill it will climb at top speed.
50:1 would probably be good if you were on a mountain bike on a dirt road, climbing up a mountain. You'd have a top speed of about 10mph, but the engine could take you up a stupidly steep slope. Your gas mileage would be poor though.
At 25:1, it'll take you up average hills on paved roads with little or no pedal assistance and top out at about 20 mph. Great if you want the engine to do all the work all the time. You'd have a half decent gas mileage.
At 16:1, your engine is going to be there for "assistance". It'll keep you going on the flats, but you'll have to pedal on hills steep/long enough to lose your momentum. You'll get really good gas mileage, though, and have a high top speed, if you have long level stretches to ride on.
Of course, this is just my view of it, and is dependent on the size of your engine and the terrain you're riding on. Around here, and because I don't mind pedaling, I'd go for 16 to 1. There are few hills that can't be avoided. If I lived in Seattle, with all those hills, I'd probably want a ratio twice as high as that (32:1) for good hill climbing. To start with, anyway, and I'd "tune" the gearing thereafter.

Have fun!

Well i live in maryland and truthfully i dont know the displacement of my motor, ive been trying to find out but cant. Its a poulan pro 114 (very old) but pretty powerful i hope the horsepower is good because like i said i didn't know.
i will go for 20:1 because i want speed and fuel efficiency but i also want to go up hills and maintain a good speed.
The bike i have is a stiff mountain bike but i don't ride mountains with is so i put thin street tires on it(which i really need to change)
if you could help me find the displacement of the weed eater that would be nice. also how would i put it so at points i could pedal and at other points i wouldn't need to pedal but the motor would still do the work because that almost seems illogical to me

Lastly how would i take the sprockets off the rear wheel... wait a second i just thought of something front wheel drive but i would still need some sort of jackshaft to put the sprockets to i also want to know how i would do that is it a special jackshaft i can buy or do i have to build it myself because i barely have any tools

i change my mind i want rear wheel so i just want to stick torear wheel just tell me how i would go along having pedals and a drive at the same time because i was just thinking have the motor do all the work all the time i also thought of multiple gears.

You're right about it being illogical with the setup you are intending. I wasn't actually thinking about how you were intending to set it up when I made the comments about maximum speed and gear ratios and such. Most people put a sprocket on the opposite side of their wheel from their derailleur. If you don't, the engine will spin the pedals at the same time, which is hazardous and you'll never be able to go any faster than you can pump your legs...unless you lift your feet completely clear of the pedals or something else silly like that. I can't recommend hooking your engine up on the same side as your crank. Putting a sprocket on the opposite side of the wheel is your best bet.

Your idea of putting the engine on the front is one way to get around that, since it won't be on the same wheel that your pedals connect to. And there's a potential bonus...if you sap out your front wheel for a free-wheel (Rear wheel) off another bike, you won't have any added drag of having to spin a second chain and sprockets when you are under pedal power alone. Done right, you would be able to shift gears on the go on the front/engine wheel.

Mounting a sprocket on the opposite side of your rear wheel or setting up the mechanics to shift gears on the front wheel is probably getting a bit too complicated for a first build, or at least for someone without many tools on hand. This is most likely why friction drive is the more popular choice for a first build. They're simple, effective, and don't require any special tools.

You could buy the kind of sprocket that come with the engine kits. They bolt through the spokes, sandwiching the spokes between rubber and steel plates and only require simple wrenches to put on. But then you need the right kind of chain to go with it and another sprocket that goes with that same chain to go on your jack shaft, unless someone out there sells these bolt-through-the-spokes sprockets that uses regular bicycle chain.

I couldn't find the displacement of your engine (probably 20 to 25cc) but I did find out that it has a clutch on it. That's a very good thing, in my opinion. Much more practical. If it didn't, you'd probably have no choice but to use a friction drive with it.

i've heard of some people completly getting rid of there pedals and putting something on there bike to hold there feet while (since the pedals were gone) they ran some sort of shaftthrough there and put sprockets on both sides and thats what i want to know how to do. that way i dont have to rig anything to my wheel or much. wow at this rate of complications i might have to save up and try to get a kit which my mother would have to pay for from her credit card then i'd have to pay her or i'd have to ask for it as a x-mas present or something