sprocket/chain sizes

Greybeard

Greybeard

New Member
I've been looking at some pieces I have, and trying to mate them in the best way possible. The easy part is I need to use a 10 tooth jackshaft sprocket, and there are a few choices.
The tougher part for me is that I'm not very smart about these things, and I want the jackshaft sprocket/chain to mate up with a bicycle hub that has a hub sprocket with three tangs on inside that mate with groves in the hub. The sprocket is held onto the hub with spacers and a snap ring.
The goal is to get a reliable combo, and to get a hub sprocket with about 30 teeth. I've thought about welding a 30 tooth onto the 18 tooth to get there, but still want all these things in one chain size.

anyone up to helping me problem solve?
 
Need more input, Greybeard.

Would you like pedals with that, sir? Will it be a single speed sprocket on the right-side hub? What kind of engine, and which side of the bike is the engine sprocket? Are you thinking of using just the 10-tooth and the 30-tooth sprockets?
 
No pedals, no brakes. Single sprocket on the hub. Hub is a Sturmey archer BTW, and will be not be used as a wheel hub. The engine is a GX35. Will be using only 10 and 30 tooth.
 
HI,

I recently made a sprocket for a coaster brake hub (has 3 small prongs on the inside bore to mate the sprocket to the hub assembly....I'm not sure how that sprocket was held on since the owner of that sprocket just sent us his to get mounting dimensions off of)...

If I had a sprocket to go by, we could probably make a custom sprocket for your Sturmey Archer hub as well.

Andrew
 
Andrew,
Thanks. I think that's what I'll need to do. The 10 tooth sprocket is available in several chain sizes. What size would you prefer to do?
 
Greybeard said:
No pedals, no brakes. Single sprocket on the hub. Hub is a Sturmey archer BTW, and will be not be used as a wheel hub. The engine is a GX35. Will be using only 10 and 30 tooth.
Click to expand...

With only 10t/30t sprockets, your gear ratio will be 3:1. Your clutch will burn out and your engine will not move the bike. Even if you are rolling downhill and you went to wide-open throttle, the engine will not propel the bike.

You need at least 15:1 for fair performance.

You need 18.75:1 for "not bad" performance.

"Hub is a Sturmey archer BTW, and will be not be used as a wheel hub".

What does that mean?
 
azbill said:
sounds like he is using the hub as a jackshaft ;)
Click to expand...

Gearing, yay!drn2

Okay, so the SA hub might have gears like 1.277:1, 1:1 and .616:1

At 14.18, the 7th speed on my shift kit is usable for cruising. To attain 14.18 @ .616:1 SA third gear, your first gear needs to be 29.4:1 and second gear will be 23.02:1. This will provide excellent low speed and acceleration. Third gear will allow the engine to cruise without strain.

Are you using the chainring sprockets? If so, it'd be easier to create an effective gear ratio.

If not using a 5:1 gearbox or multiple jackshafts, it will not be easy.

Need more input.
 
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The bike will only move forward 9.5" per revolution of the SA hub. I'm just trying to find a dependable chain/sprocket size that won't be the weak link. The engine only puts out about 1.5ft lbs of torque, so that's really all the chain needs to put up with, but it'll moving quite rapidly as the 10 tooth will be turning engine revs. #35 or a 40 series? The chain will be quite short, and alignment will be ajustable so I don't need a sprocket chain combo that makes up for minor misalignment.
 
Greybeard said:
The bike will only move forward 9.5" per revolution of the SA hub. I'm just trying to find a dependable chain/sprocket size that won't be the weak link. The engine only puts out about 1.5ft lbs of torque, so that's really all the chain needs to put up with, but it'll moving quite rapidly as the 10 tooth will be turning engine revs. #35 or a 40 series? The chain will be quite short, and alignment will be ajustable so I don't need a sprocket chain combo that makes up for minor misalignment.
Click to expand...

Need more input.

Chain strength or engine torque are not issues yet. You need to calculate an effective gear ratio, so you can choose correctly sprockets the first time out.

I don't know how simple I can ask this.
Which side of the bike is the clutch?
Are you using a gearbox?
How many sprockets will be on the bike?
Will there be chainring sprockets?
 
I've done all the calcs. With what I'm doing, the speeds @8000rpm are 18mph in 1st, 24mph in 2nd, and 32 mph in 3rd with the sprockets I'm trying to come up with. An 11 tooth primary will raise the speed per gear 10%, and a 12 tooth 20%. These are the ranges that I'm trying to work with a GX.
The only chains on this bike will be the original right side with derailer, and a short chain between the 10tooth and the 30tooth, which is what I'm trying to ascertain would be the best considering it has to round a 10tooth sprocket at high RPM.
Enough clues?

5-7 HEAVEN
Did you used to hang around Chevy Talk or Chevelles years ago?
 
Greybeard said:
I've done all the calcs. With what I'm doing, the speeds @8000rpm are 18mph in 1st, 24mph in 2nd, and 32 mph in 3rd with the sprockets I'm trying to come up with. An 11 tooth primary will raise the speed per gear 10%, and a 12 tooth 20%. These are the ranges that I'm trying to work with a GX.
The only chains on this bike will be the original right side with derailer, and a short chain between the 10tooth and the 30tooth, which is what I'm trying to ascertain would be the best considering it has to round a 10tooth sprocket at high RPM.
Enough clues?

Okay, now I get it, friction drive with the SA hub as the roller. Interesting concept, for sure. Thanks for the PM. I never would've guessed it.

Since you mentioned a short chain, I'm presuming that this is a rack-mount project, which brings up major issues.

If the clutch faces the bicycle chain side (right side), the SA hub/roller rotates clockwise, but the engine turns counter-clockwise.

If the clutch faces the left side, the engine turns the wrong way to spin the hub, which spins the tire. Besides, the SA hub cannot be flopped to the other side anyway, because it will freewheel and not turn.

However, if you install a 5:1 pocketbike tranny onto the engine, then you'd be able to face the tranny sprocket to the right side and chain up to the SA hub. You will have 5:1 gearing, which will cause a problem of turning the roller too slowly. A friction roller turns the same rpm as the engine. If the engine is spinning 8,000rpm, the roller is also spinning @ 8000rpm. HOWEVER, at 8000rpm, a 5:1 gearbox reduces engine output to 1600 rpm. This is less than idle speed on the Honda engine.

Couple this issue with the super-sized 3" roller. This large spindle will also reduce tire rpms.

My recommendation would be not to fabricate any custom sprocket or buy chain until you resolve your gearing issues.....on paper.

Lemme go look for the friction roller/mph calculator and return with more statistics.
Click to expand...
 
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Okay, I found the formula for friction drive calculations:

mph = diameter x rpm x .002975

mph = 3" roller x 8000rpm x .002975

71.4 mph = 3" x 8000rpm x .002975

That's IFFF your drive sprocket was spinning @ 8000rpm, and both drive and driven sprockets had the same tooth count (10t/10t, 11t/11t, 12t/12t etc.). And of course, the Honda 35 does not have enough power to reach 71.4mph.

If you installed the 5:1 gearbox to correct the engine rotation, 8000 engine rpm would drop to 1600rpm @ the gearbox spline. If you were to use the 10t/30t sprockets, that would lower your gear ratio to 15:1 in second gear. Rpms would drop from 8000rpm to 533rpm @ the SA hub. Using the formula above:

mph = 3" x 533rpm x .002975

4.76mph = 3" x 533 (8000rpm/15) x .002975

To reduce the negative effects of the tranny's gear reduction, you would have to place a 50-tooth sprocket on the drive sprocket and a 10-tooth sprocket on the SA hub. Since the 10t sprocket won't fit on the hub, you'd have to ru maybe a 14t SA hub sprocket and a 70t sprocket at the gearbox. Even if you could fit that monstrous 70t sprocket on the gearbox, you'd still have bad performance from that oversized roller.

JMO, there is no way you can effectively use a 3" roller on the Honda 35, especially with a 5:1 tranny or even a 10t/30t combination. However, if you installed a powerful 96cc four-stroke engine, it might work.

How did you get your calculations?
 
You need to think a little outside the box.
The 1" roller is the norm for a friction bike that needs to be able to climb hills. It driven directly off the clutch hub and rotates at engine speed. The SA hub, with a bolt-on knurled friction sleave is 3". 3 times as much. Hense, I'm looking to reduce it by 3-1. 10tooth to 30 tooth.
Since the roller runs backwards, if the SA is turned around and driven on the left side, where the engine will be mounted as in most friction drives, the SA's rotation is correct. Instead of a shaft coming directly off the engine clutch and containing a friction drive spool, it will have only the 10 tooth sprocket on the left side, driving a chain to the 30 tooth SA. The SA hub will be rotating in it's designed rotation, at 2666rpm (with the engine @8000)driving the wheel. No gearbox is necessary. The 71.4mph was 1-1 and did not take into consideration the 10tooth to 30tooth reduction, which brings it to 24mph.

Can we go back to chain and sprocket?
 
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Greybeard said:
You need to think a little outside the box.
The 1" roller is the norm for a friction bike that needs to be able to climb hills. It driven directly off the clutch hub and rotates at engine speed. The SA hub, with a bolt-on knurled friction sleave is 3". 3 times as much. Hense, I'm looking to reduce it by 3-1. 10tooth to 30 tooth.
Since the roller runs backwards, if the SA is turned around and driven on the left side, where the engine will be mounted as in most friction drives, the SA's rotation is correct. Instead of a shaft coming directly off the engine clutch and containing a friction drive spool, it will have only the 10 tooth sprocket on the left side, driving a chain to the 30 tooth SA. The SA hub will be rotating in it's designed rotation, at 2666rpm (with the engine @8000)driving the wheel. No gearbox is necessary. The 71.4mph was 1-1 and did not take into consideration the 10tooth to 30tooth reduction, which brings it to 24mph.

Can we go back to chain and sprocket?
Click to expand...

LOL, I LIVE outside of the box.

Are you sure you can turn the SA hub and drive it on the left side? I don't think so. That's why you have left-hand threaded freewheels for pocket bikes and Staton hub sprockets. That's also why an 8-speed casssette will not work, if you try to drive it on the left side.

Of course, you can go back to chain and sprocket. This is your project.

Just saying.....
 
Here's an option:

Find or build a platform ala Titan/Dax rear-mount setup. However, mount the engine with the clutch facing the left side of the bike. Install a bellhousing w/6-tooth pocketbike sprocket. Mount a jackshaft directly below the engine and platform, using a 12-tooth sprocket and chain. On the SA hub side of the bike, install another 12t jackshaft sprocket and chain it to the original 18-tooth SA hub sprocket. Mount the SA hub under the Titan/Dax platform.

There you have it, thinking outside the box.dance1

Your SA hub will now work as a 3" friction roller. A 6t/12t jackshaft = 2:1, and a 12t/18t combination = 1.5:1. Total gearing is 3:1. No need for fabricating a special 30t hub sprocket. 6t/12t/18t sprockets make for a tighter, inexpensive package. No custom sprockets necessary.
 
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And here's Plan B:

Fabricate a drive housing similar to BMP's last innovation (before they went outa business). Either that, or find that BMP housing and weld the clutch drum hole, then drill to accept another .5" x 1.375" jackshaft bearing. Mount the left-facing engine ATOP the BMP housing, above the front jackshaft holes. Install and chain the 6t/12t sprockets on the left side, using a jackshaft and .5" x 1.375" bearings. Mount a 12t jackshaft sprocket, outside the housing, on the right side. Chain up to the SA hub'S 18T sprocket. The SA hub will mount in the rear jackshaft position of BMP's latest drive housing.

The SA hub will not clear the ceiling of the BMP drive housing, so you will have to cut a "sunroof/skylight" in the drive housing above the SA hub. You should be able to find two 1.375" bearings that will accept either side of the SA hub's axle. This way, the SA hub will bolt directly into the drive housing. You will then be able to easily adjust the hub/roller for correct downward pressure.

Again, a tight, inexpensive package, with no custom components necessary, except for that 3" friction sleeve.

There it is.xct2
 
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