Sprocket sizes VS speed

Np02

New Member
#1
My bike has an ungoverned 212 harbor freight engine on it with a 12 tooth clutch and a 60 tooth rear sprocket. The displacement is quite a bit large for a bike so small that the gas tank wont fit on the engine. The power it produces does not get used to its full potential as I am almost always keeping it at a somewhat maintained speed and I am not too aggressive with the throttle. If I wanted to get some more speed without having to rev the engine higher than I would like it to, then could it be as simple as changing the sprocket sizes? I'm assuming so but I usually don't know the strings attached that come along with doing so. Would the more common thing to do be changing the 12 tooth clutch to a 15, or would it be taking the 60 tooth rear down to a 48 or even less? I'm sure I'd lose some acceleration speed but i am more concerned with having a higher overall speed so that I can ride it faster without something in the engine going wild.
 
#5
My bike has an ungoverned 212 harbor freight engine on it with a 12 tooth clutch and a 60 tooth rear sprocket. The displacement is quite a bit large for a bike so small that the gas tank wont fit on the engine. The power it produces does not get used to its full potential as I am almost always keeping it at a somewhat maintained speed and I am not too aggressive with the throttle. If I wanted to get some more speed without having to rev the engine higher than I would like it to, then could it be as simple as changing the sprocket sizes? I'm assuming so but I usually don't know the strings attached that come along with doing so. Would the more common thing to do be changing the 12 tooth clutch to a 15, or would it be taking the 60 tooth rear down to a 48 or even less? I'm sure I'd lose some acceleration speed but i am more concerned with having a higher overall speed so that I can ride it faster without something in the engine going wild.
if i were you, i would go 53-55t on the rear and leave the front. how fast do you want to go? a predator will float valves at 5300ish.
thats kind of your secondary governor (i dont have this problem, i upgrade my 196 with a stage one kit, ive revved it to 6500 before!)
keep in mind, your going to be losing torque, lots of it. also, if your going to run the higher gearing, your going to be burning out clutches (thats if your going with a smaller rear sprocket) so, dont go too high. again 53-55 should be the perfect.
also, what bike do you have?
 

Np02

New Member
#9
if i were you, i would go 53-55t on the rear and leave the front. how fast do you want to go? a predator will float valves at 5300ish.
thats kind of your secondary governor (i dont have this problem, i upgrade my 196 with a stage one kit, ive revved it to 6500 before!)
keep in mind, your going to be losing torque, lots of it. also, if your going to run the higher gearing, your going to be burning out clutches (thats if your going with a smaller rear sprocket) so, dont go too high. again 53-55 should be the perfect.
also, what bike do you have?
'69 ruttman wild goose
 
#11
I run a 10 front 72 rear on my Murray fast track. I like that it can carry me over a levee if need be. If your looking for hill climbing power and 50mph get a 30 series
 
#12
I would bump the clutch driver up to a 14 or 15 tooth and leave the back gear alone . 15:60 sprocket sizes would give a ratio of 4.1 to 1 …..and a 12:50 sprocket sizes would be a ratio of 4.1 that's a pretty tall gear ratio . I would try the 14:60 sprocket sizes it is 4.3 to 1 ratio . Taller the gear is the more heat you will build up in your clutch .
 

Np02

New Member
#13
I would bump the clutch driver up to a 14 or 15 tooth and leave the back gear alone . 15:60 sprocket sizes would give a ratio of 4.1 to 1 …..and a 12:50 sprocket sizes would be a ratio of 4.1 that's a pretty tall gear ratio . I would try the 14:60 sprocket sizes it is 4.3 to 1 ratio . Taller the gear is the more heat you will build up in your clutch .
Most of my rides aren't that long, say maybe 3 or 4 miles at a time. It is also on flat roads with very few points where I need to slow down or give it more gas. If Im not going on and off of the throttle or giving it so much gas that Im lifting up the front wheel off of the ground every time I take off, then could I run a 44 or 46 tooth rear sprocket (keeping the 12 tooth for the driver) without cooking the clutch?
 
#14
OND is right...change the clutch out. You'll want a clutch that's not a China knock off. However, I do think anything less than 5:1 final drive is a clutch killer. You can get away with mid 4s to 1 with a torque converter.
 

I74

Well-Known Member
#15
Max torque SS clutches are awesome.
Dr. shop teacher is right about anything less than a 5 - 1 ratio being a clutch killer.
I would stick with the 12 - 60, your clutch will last a lot longer...
Am guessing with your tire size, that puts your ratio around 5 - 1.
 

Np02

New Member
#16
Max torque SS clutches are awesome.
Dr. shop teacher is right about anything less than a 5 - 1 ratio being a clutch killer.
I would stick with the 12 - 60, your clutch will last a lot longer...
Am guessing with your tire size, that puts your ratio around 5 - 1.
I have a 4.10/3.50-6 for the rear - is that smaller than most? Seems like I'm pretty limited in my options then for changing sprocket sizes as all my options lead up to the same price point as well as all wearing down the clutch. For the same price I could get the "max torque" clutch. Are the max torques actually different than the regular ones I can buy at the hardware store? if so I would just go that route and buy a brand new 15 tooth clutch instead of replacing the drive sprocket. I'm assuming this is what your'e talking about.
 

I74

Well-Known Member
#17
I have a 4.10/3.50-6 for the rear - is that smaller than most? Seems like I'm pretty limited in my options then for changing sprocket sizes as all my options lead up to the same price point as well as all wearing down the clutch. For the same price I could get the "max torque" clutch. Are the max torques actually different than the regular ones I can buy at the hardware store? if so I would just go that route and buy a brand new 15 tooth clutch instead of replacing the drive sprocket. I'm assuming this is what your'e talking about.
That's the dimensions of the rim.
You need to measure the O.D. / Outside diameter of the rear tire to calculate the ratio.
I would measure it with where you run the air pressure for that tire, & for where it's at with including tread wear, for the most accurate ratio's.
Get that measured & est. RPM of your engine, & I will tell you where you are at now ,, & also give you your est. top speed.

A lot of the hardware store clutches these days are made in China.
The metal's ''especially the drum - shoe faces'', generally get worn out pretty quick, because of the low quality of steel used.
The Max torque SS clutch is a ''very stout'' 6 shoe set up,''for the money'',, & are made in the USA.
Make sure when buying a 6 shoe clutch, that it say's made in the USA.
Have seen some knock off ones on Amazon ect. that say Maxi torque,,, ect. ect. Those are the ones that are usually 15 - 20 bucks.
OldMiniBikes warehouse here, pretty much has the best prices on the genuine article's.
If it costs 35 - 50 bucks, it's probably the real deal.
 

I74

Well-Known Member
#19
That's the dimensions of the rim.
You need to measure the O.D. / Outside diameter of the rear tire to calculate the ratio.
I would measure it with where you run the air pressure for that tire, & for where it's at with including tread wear, for the most accurate ratio's.
Get that measured & est. RPM of your engine, & I will tell you where you are at now ,, & also give you your est. top speed.

A lot of the hardware store clutches these days are made in China.
The metal's ''especially the drum - shoe faces'', generally get worn out pretty quick, because of the low quality of steel used.
The Max torque SS clutch is a ''very stout'' 6 shoe set up,''for the money'',, & are made in the USA.
Make sure when buying a 6 shoe clutch, that it say's made in the USA.
Have seen some knock off ones on Amazon ect. that say Maxi torque,,, ect. ect. Those are the ones that are usually 15 - 20 bucks.
OldMiniBikes warehouse here, pretty much has the best prices on the genuine article's.
If it costs 35 - 50 bucks, it's probably the real deal.
Added,,
Was browsing around looking for pics of your 69' Ruttman Wild goose, & noticed that it probably has a jack shaft.
I would need both sprocket sizes on that also, for the ratio calculator.
I
 

Np02

New Member
#20
Added,,
Was browsing around looking for pics of your 69' Ruttman Wild goose, & noticed that it probably has a jack shaft.
I would need both sprocket sizes on that also, for the ratio calculator.
I
No jackshaft. Straight from the clutch to the sprocket attached to the hub and not an axle. I believe the diameter was just past 12 inches on the rear wheel. Taking a look at some pictures I had it turns out the clutch on it is a max torque so I might be able to get away with having a 46 or 48 without it pooping out just yet.
 
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