40 pitch sprockets skip from 60-72?

[crazyman]

Every source I've seen just totally jumps from 60T straight to 72T.

I really need something in the range of 62-64 teeth for my motorized bicycle set up for an X hub (2" center hole) or a 5/8" bore. That would put me smack dab in the powerband at 20-25mph.. I'm currently a 51T @41xx rpm @25mph, a 60T would be 47xx rpm at 25, and a 64T would be 5100 rpm at 25. The law says 20 is the top speed, so I need torque at legal speed, and 5-10 extra mph out in the country on a road trip.

Has anyone found a supplier for something like this?

 

[landuse]

You could always get one made for you, but that might be costly. Have you thought of using a jackshaft instead.

I am not too sure what sprocket pitch you are looking at, but here are some PDF's from Azusa on sprockets

http://www.azusaeng.com/Sprockets/AzSDno35.pdf
http://www.azusaeng.com/Sprockets/AzSDno40.pdf

They might have others as well. Give them a ring

 

[augidog]

if you'll post a basic pic of your drivetrain, i'll maybe have some ideas for you.

 

[crazyman]

r_chez_08 alerted me to the fact that some here may need 72T sprockets in 40 pitch. Here is a source.
"http://www.surpluscenter.com/item.asp?item=1-1979-72&catname=powerTrans"

Anyways, I do have a jackshaft and this bike is almost 175 lbs..

Today was my first big ride. I have only taken it to town and back since motorizing it. I live in mixed rural and busy territory. I got a call from a customer wanting his heater fan fixed on his farm tractor, so I told him I'd be there in an hour and a half, and I was. It was a 15 mile one way backroad trip. The wind was at my back roughly half the journey, so it wasn't that bad. But, when I went perpendicular to the wind, it was like the motor wasn't even there and I could barely pedal. It's just a bit underpowered at 20 mph on level wind free days. It could stand like another 1000 rpm, but I don't want it maxed out at 20...

My primary sprocket is an 11T. It's welded to the clutch. My secondary sprocket is this thread you are reading. My primary pulley is the smallest I can get. My secondary pulley is roughly 5.25" and it's welded to the axle.

To the nerds like me that want to know the numbers side of this, the secondary drive ratio is 2.625:1. At 25 mph my wheel is spinning 333 rpm by my calcs.

Does anyone have a tach you could check wide open throttle on a string trimmer for me? That would be awesome, because it would help determining my target rpm for my engine.

 

[augidog]

engine size is what matters, so much power will pull so much weight only so fast and no more.

based on what i see, i'll guess you can get about 6000-7000 rpm no-load. back off to about 80% and that's what you have to work with loaded, which is just about where your numbers land. so far so good. that's how fast your engine will turn under load, now we have to give it enough reduction to be of use.

i like numbers too...this is only rough and approximate guesswork:

most (2-stroke) 50cc/30mph (26") MaB's max out at a final-total ratio of about 18:1 to 20:1...my opinion is that you're geared way too high at approx 13:1.

personally, i'd go straight to the 72T sprocket*:

primary drive ratio = 6.55
secondary ratio = 2.625:1

and this (approx total = 17:1) may still be too high for that engine to be of much help. my guesswork leads me to believe you need about 22:1 for a 20-25mph MaB.

*if possible, i'd first consider using a larger lower pulley.

 

[Jake.B]

I dont know if this helps but, have a chainsaw engine thats 40 cc mounted on a bike with 16 inch wheels and a 16:1 gear ratio it does roughly 34 MPH and it has a decent take off on flat asphalt from a dead stop. With 26 inch wheels i would go with a 20-24:1. 13:1 with those tires i feel bad for that clutch.

 

[crazyman]

I feel bad for the clutch too.

 

[augidog]

EDIT: i haven't found any reference to your engine size or make.


Motorized Bicycle Laws Link-List

would you show me details on your headlight? and please install a front brake before you get this drivetrain rocked out, you'll need it. a coaster brake works fine, but it's hazardous to rely on it alone at speeds.

 

[crazyman]

The law I found was 625 ilcs 5/1-140.1 and it states no license, 20 mph, and under 1 hp. Sure I'll share details. The bike has suicide throttle on the frame, so a coaster brake doesn't scare me.

 

[augidog]

i found that statute, thanks for the correction.

 

[crazyman]

I'm just going to install the 72T sprocket. It dawned on me that if it's too much, I can upsize the primary pulley....

Thanks for the help, everyone. And augidog.

 

[crazyman]

I got the 72 awhile back. It's a good match for the bike.

I messed up in another area though. When replacing the clutch shoes, I used a screwdriver to stop the engine from spinning, and when getting the shoe plates to unscrew, I broke off some flywheel cooling fins. No big deal. A month or so later, the motor barely runs. It turns out that the imbalance ruined the crank bearing, forcing me to buy another motor. Luckily I found one on ebay today.

The moral of the story is, if you break a fin off a flywheel, it is infact a big deal. Replace it.

 

[r_chez_08]

Glad you got your bike working well! Looks great fun.
Unfortunately the UK laws restrict me to a 200w motor and 15mph IIRC.

Are you still looking for a tach? You can pick them up on eBay for about $10. search 'hour meter tachometer' and they come up.

 

[OzFab]

I got the 72 awhile back. It's a good match for the bike.

I messed up in another area though. When replacing the clutch shoes, I used a screwdriver to stop the engine from spinning, and when getting the shoe plates to unscrew, I broke off some flywheel cooling fins. No big deal. A month or so later, the motor barely runs. It turns out that the imbalance ruined the crank bearing, forcing me to buy another motor. Luckily I found one on ebay today.

The moral of the story is, if you break a fin off a flywheel, it is infact a big deal. Replace it.

Next time, use the rope trick

 

[oldbikerarlo]

The reason that sprockets go from 60 to 72 tooth is, the number of degrees between the tooth count. 60 tooth is 6*, 72 tooth is 5*, it is realy hard to engineer a sprocket that is not a whole number degree seperation between the teeth. it must be a tooth count that is also divisable evenly into 360* IE: 360* divided by 7* would equal 51.425 tooth count. but 360* divided by 8* would be 45 tooth. Does this make sense.

 

[crazyman]

I won my second engine for $23 shipped. Can't beat getting 600 miles out of a free weedeater.

 

[anderkart]

The reason that sprockets go from 60 to 72 tooth is, the number of degrees between the tooth count. 60 tooth is 6*, 72 tooth is 5*, it is realy hard to engineer a sprocket that is not a whole number degree seperation between the teeth. it must be a tooth count that is also divisable evenly into 360* IE: 360* divided by 7* would equal 51.425 tooth count. but 360* divided by 8* would be 45 tooth. Does this make sense.

What? The only reason some shops only stock 60 or 72 tooth axle sprockets is because those are the 2 most common sizes used on funkarts. You can buy most any tooth-count/pitch sprocket you want here at this online store: http://gokartgalaxy.com/sprockets_&_sprocket_hubs.htm