Is this gear ratio okay?

[zzirrgrizz]

On the motorized bike I am building here are the gear specs:

Ratio: 4:1
Clutch- 11 teeth
Sprocket- 44 teeth
Rear wheel- 22"
RPM for engine- 3600

will this work out or this a bad gear ratio? Sorry I am very new and want to make sure I am doing this right. I assume it should be okay since a lot of motorized bike kits use this ratio but I just wanna make sure.

EDIT
I also have a 62 toothed sprocket as well that I could probably get to work, so let me know which one you would recommend I use

 

[BirdFanatic]

Depends on what clutch your using. When i was running that low i was using a 150$ clutch

 

[KartFab]

Mopeds have cvts(automatic transmission), if your running just a 'clutch' you will have almost no power and will burn up your clutch in no time.

What kind of engine will you be using? Hp?

My brother used to have a little scooter. Topped out at 40 mph down hill. We both were thinking we were going to die with 400 lbs of us on it, and then the death wobble starts. Good times!

 

[zzirrgrizz]

Mopeds have cvts(automatic transmission), if your running just a 'clutch' you will have almost no power and will burn up your clutch in no time.

What kind of engine will you be using? Hp?

My brother used to have a little scooter. Topped out at 40 mph down hill. We both were thinking we were going to die with 400 lbs of us on it, and then the death wobble starts. Good times!

What do you mean just a 'clutch'? What would be a possible solution? And are you sure this ratio wouldn't work because I am using pretty much the same gear ratio and same power as the motorized bike kits

 

[zzirrgrizz]

Mopeds have cvts(automatic transmission), if your running just a 'clutch' you will have almost no power and will burn up your clutch in no time.

What kind of engine will you be using? Hp?

My brother used to have a little scooter. Topped out at 40 mph down hill. We both were thinking we were going to die with 400 lbs of us on it, and then the death wobble starts. Good times!

And sorry I forgot to answer your questions but I have a 2hp Briggs and Stratton

 

[landuse]

And sorry I forgot to answer your questions but I have a 2hp Briggs and Stratton

There is ABSOLUTELY NO WAY that a 2HP briggs is going to push a bike with 22" tyres anywhere at all. Your clutch will be toast before you can say "jiminy cricket". I build my minibike with a 3HP Briggs, and I had 20" tyres. The thing would not move until I had changed to a ratio of 11:1. Yours will be no different. As a matter of fact it will be worse because the tyres are bigger.

You are going to have to use a jackshaft to achive compound gear reduction. You will not get a ratio of 11:1 with a standard clutch to axle setup (unless you have a 110 tooth rear sprocket).

I am assuming that you are running a standard centrifugal clutch.

 

[zzirrgrizz]

There is ABSOLUTELY NO WAY that a 2HP briggs is going to push a bike with 22" tyres anywhere at all. Your clutch will be toast before you can say "jiminy cricket". I build my minibike with a 3HP Briggs, and I had 20" tyres. The thing would not move until I had changed to a ratio of 11:1. Yours will be no different. As a matter of fact it will be worse because the tyres are bigger.

You are going to have to use a jackshaft to achive compound gear reduction. You will not get a ratio of 11:1 with a standard clutch to axle setup (unless you have a 110 tooth rear sprocket).

I am assuming that you are running a standard centrifugal clutch.

Hmmm alright, but just out of curiosity, how do little 40cc bike kits with a lower ratio pull this off? (With no jack shaft)

And also (excuse my ignorance) but is a 4:1 gear ratio the same thing as a 4.0 gear ratio?

And lastly I also have a 62 toothed sprocket that could probably fabricate and make some modification to, to fit on the sprocket mount kit. Would you recommend I use this?

 

[KartFab]

Gear ratio is only part of the equation. If you have 12" tires and a 4:1 gear ratio you will have more torque than the same set up gear ratio of 4:1 with 22" tires. Weight also comes into play as well. Light=faster acceleration.

So a "normal" clutch is just a centrifugal clutch.

What we are trying to say is that if you gear it wrong, that clutch will constantly be trying to engage but won't move the bike forward fast enough. The weights in the centrifugal clutch will rub against the clutch and cause a lot of friction and heat. If you drive around long enough or try to climb any hills, the heat will literally "fry" the clutch.

The 2hp briggs will just not work well. It just doesn't have enough torque anyway. It's perfect for edging a lawn though.

About those mini pocket bikes, they are powered by 2 stroke engines, have small tires, and weigh next to nothing. They really don't have that much torque (like a 4 stroke does) at low rpms, but are capable of revving like 2x higher than a 4 stroke, producing most of their torque at the higher rpm range. Additionally, I just did a quick search and it looks like those mini/pocket bikes run an 8:1 or 9:1 ratio. Don't quote me on that lol.

Hope that helps!

If you are really wanting to use the 2hp and move any serious weight around, then you will need to follow what landuse said.

 

[landuse]

Hmmm alright, but just out of curiosity, how do little 40cc bike kits with a lower ratio pull this off? (With no jack shaft)

You just said it!! They will have a lower ratio....just what I recommended. High numbers = low ratio = more torque

 

[zzirrgrizz]

You just said it!! They will have a lower ratio....just what I recommended. High numbers = low ratio = more torque

Oops sorry I didn't mean a low ratio lol I meant a high ratio, on a lot of the motor bike kits they run a ratio of like 3:1 or lower. (Sorry for the bad communication lol)

 

[zzirrgrizz]

Gear ratio is only part of the equation. If you have 12" tires and a 4:1 gear ratio you will have more torque than the same set up gear ratio of 4:1 with 22" tires. Weight also comes into play as well. Light=faster acceleration.

So a "normal" clutch is just a centrifugal clutch.

What we are trying to say is that if you gear it wrong, that clutch will constantly be trying to engage but won't move the bike forward fast enough. The weights in the centrifugal clutch will rub against the clutch and cause a lot of friction and heat. If you drive around long enough or try to climb any hills, the heat will literally "fry" the clutch.

The 2hp briggs will just not work well. It just doesn't have enough torque anyway. It's perfect for edging a lawn though.

About those mini pocket bikes, they are powered by 2 stroke engines, have small tires, and weigh next to nothing. They really don't have that much torque (like a 4 stroke does) at low rpms, but are capable of revving like 2x higher than a 4 stroke, producing most of their torque at the higher rpm range. Additionally, I just did a quick search and it looks like those mini/pocket bikes run an 8:1 or 9:1 ratio. Don't quote me on that lol.

Hope that helps!

If you are really wanting to use the 2hp and move any serious weight around, then you will need to follow what landuse said.

I see what you're saying haha I probably wall have to look into a jack shaft. But btw I was not referring to pocket bikes I was referring to little motorized bike kits that people put on mountain bikes (which have tall tires as well). These things use ratios lower like 3:1 with little 49cc engines and no jackshaft . How does this work?

And yeah I am kinda rethinking this 2hp motor but I read and watch videos online and saw a lot of motor bikes with equally sized engines if not smaller and they pulled just fine. I would prefer not to get a bigger engine though because in my state if your motor is 2hp or less you can be any age and ride the bike in the bike lane (Which I would like to do)

 

[OzFab]

I was referring to little motorized bike kits that people put on mountain bikes (which have tall tires as well). These things use ratios lower like 3:1 with little 49cc engines and no jackshaft . How does this work?

Have you ever seen on of those take off from a standing start? In just about every case I've seen, the rider needs to start pedalling before releasing the clutch to engage the engine; releasing the clutch too early (at too low a speed) will not start the engine...

 

[landuse]

Have you ever seen on of those take off from a standing start? In just about every case I've seen, the rider needs to start pedalling before releasing the clutch to engage the engine; releasing the clutch too early (at too low a speed) will not start the engine...

Yeah. You cannot get your bike moving from a dead stop. The gear ratio is too high for it to work

 

[itsid]

I see what you're saying haha I probably wall have to look into a jack shaft. But btw I was not referring to pocket bikes I was referring to little motorized bike kits that people put on mountain bikes (which have tall tires as well). These things use ratios lower like 3:1 with little 49cc engines and no jackshaft . How does this work?

Let's take a fairly common 80cc bike Kit:
2-4kw @ 6000rpm (depending on the kit, that's 2.7 - 5.4 HP btw)
no matter what kit I look at though, it's always the same engine style (4.5:1 internal reduction) and all Kits come with a 18:1 gear reduction..

see the internal reduction?
otherwise the bike would be pushed around at ~100 mph
(well it wouldn't but that's a different topic)

but you're right, it has a 4:1 CHAIN ratio... that doesn't mean anything though I'm afraid.
it's still a 18:1 ratio from the crankshaft to the rear wheel.
let's look inside the teardrop clutch..
that is the clutch with it's bevel gear:

and that's what's driving it


'sid

 

[zzirrgrizz]

Let's take a fairly common 80cc bike Kit:
2-4kw @ 6000rpm (depending on the kit, that's 2.7 - 5.4 HP btw)
no matter what kit I look at though, it's always the same engine style (4.5:1 internal reduction) and all Kits come with a 18:1 gear reduction..
View attachment 53372
see the internal reduction?
otherwise the bike would be pushed around at ~100 mph
(well it wouldn't but that's a different topic)

but you're right, it has a 4:1 CHAIN ratio... that doesn't mean anything though I'm afraid.
it's still a 18:1 ratio from the crankshaft to the rear wheel.
let's look inside the teardrop clutch..
that is the clutch with it's bevel gear:
View attachment 53371
and that's what's driving it
View attachment 53373

'sid

I know it's been a while since I have been on here but tell me what you think about using a back sprocket instead with 62 teeth? I had one and made some adjustments to it so that it can adapt onto the back wheel. Or will this still not work?

I really do not want to have to use a jack shaft and I cannot increase the power of the motor or else it isn't street legal Could I use a 7 tooth clutch with my 62 sprocket (gear ratio of 8.857)?
I don't mind changing out clutches on the shaft, that's easy. But drilling 9 holes through another solid sprocket to get it to fit with the adapter kit, that's another story.

 

[itsid]

Well, a 62T axle sprocket and a 7T clutch would indeed be much closer to what makes you move,
but I'm not sure the clutch would survive...

-May I ask what 7T clutch you're talking about?? that doesn't sound plausible for any std chainsize &engine PTO *shrugs*-

even with just 100kg of weight (bike, engine and you)
that's quite a stretch.. I'm not even sure 11:1 would do the trick for just two horses I'm afraid.
Think about it this way.. with that (8.86:1) ratio you have a maxtorque of 35Nm roughly..
to get you moving at all you need 27 the very least;
and while that seams to match, keep in mind that the max torque is NOT necessarily available when your clutch engages. (depends on the torque curve of the engine)
So you might end up with no more than 25Nm and your clutch will burn in an instant,
even if you have 27Nm you might start moving but too slowly to prevent the clutch from overheating.
It's a real pain I'm afraid.. with wheels that big and an engine that small...

Sorry, you may give it a shot;
but be aware that you might render your clutch useless within no time
and have to buy a new one directly after failing with that ratio.

'sid