10:1 gear ratio too high?

[kra]

I have a 25cc weed eater engine with a little clutch and an 8 tooth sprocket. I ran this on a bike using a 25:1 gear ratio, and it had a lot of low end torque and could take off from a standstill and climb steep hills, and even go through a foot of snow, but it was slow, only topping out at 10 mph.

I was wondering if anyone has any experience with chain drive and gear ratios for engines this small before I waste my time rigging it up only to find out that 10:1 is too high of a gear ratio.

 

[devino246]

I have a 25cc weed eater engine with a little clutch and an 8 tooth sprocket. I ran this on a bike using a 25:1 gear ratio, and it had a lot of low end torque and could take off from a standstill and climb steep hills, and even go through a foot of snow, but it was slow, only topping out at 10 mph.

I was wondering if anyone has any experience with chain drive and gear ratios for engines this small before I waste my time rigging it up only to find out that 10:1 is too high of a gear ratio.

25:1 is an extremely low ratio. Many of us use 6:1, but thats for 4-stroke industrial engines. I wouldnt see any problem with 10:1

 

[Doc Sprocket]

I dunno. Small engine, not much torque, weak clutch. Maybe 15-20:1.
Do we have any idea what the maximum available RPM is?

 

[r97]

tire size?
weight of frame and rider?
and any engine specs, HP, RPM?
where will you ride?
sprocket sizes?
a lot of torque and 10mph doesn't sound to bad to me for a weed eater engine.

 

[Bluethunder3320]

tire size?

normally 12:1 ratios are used on pedal bikes with weed wacker engines.

 

[kra]

Tire is 20" I believe, the bike is a schwinn stingray chopper bike thats all set up for my 3.5 briggs, except the briggs needs work or a new starter clutch because it squeals like crazy. So I was thinking of throwing the weed eater engine on and riding that around until I can fix the briggs or find another engine. I'll probably be riding on pavement and the occasional gravel or dirt road. I think the engine is around 3/4 - 1 hp and 7k rpms, but I could be wrong. The pedals have been removed so it's not a pedal bike anymore, so it will have to be able to start from a standstill. I know that now its a homemade, unregistered, uninsured, and unlicensed motorcycle now, but thats half the fun!

 

[devino246]

Tire is 20" I believe, the bike is a schwinn stingray chopper bike thats all set up for my 3.5 briggs, except the briggs needs work or a new starter clutch because it squeals like crazy. So I was thinking of throwing the weed eater engine on and riding that around until I can fix the briggs or find another engine. I'll probably be riding on pavement and the occasional gravel or dirt road. I think the engine is around 3/4 - 1 hp and 7k rpms, but I could be wrong. The pedals have been removed so it's not a pedal bike anymore, so it will have to be able to start from a standstill. I know that now its a homemade, unregistered, uninsured, and unlicensed motorcycle now, but thats half the fun!

You need to oil the starter clutch. Relatively simple, just use the search feature on the site for how-to. With tires that big, i wouldnt go below 15:1, if that.

 

[kra]

Well I tried the little weed eater engine while the 3.5 is off the bike, and it's just too small with that gear ratio. So looks like I need to fix the starter clutch on the briggs or find a centrifugal clutch for my other tecumseh 3.5.