How do you determine the right ratio for gearing?

M

MCope

New Member
#1
#1
I have a 6.5 HP engine and wheels and tires are 6 inch wheels with 4.10x3.50x6 tires. I figure I will have a lot of tork with the 6.5 engine. So I am trying to determine the amount of teeth for the clutch and rear sprocket. It seems for most applications the #35 chain is typically used. That is what I used the last time I had the bike running.

Any suggestions will be appreciated.
Thanks,
Mike
 
Txpowdercoater

Txpowdercoater

New Member
#2
#2
depends on what type of rear rim you have, hub mounts are limited in choices.
also how I determine what I want for gearing :
race bike
1. track type, soil, sandy, pavement etc etc
2. track length, distance from holeshot to turn 1.
3. tire I'm choosing, diameter and tread type matters.
4. what rpm's I wanna be at when I get to turn 1.

street bike
1. tire diameter
2. speed wanted
3. rpm's I wanna be at to reach #2
 
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M

MCope

New Member
#3
#3
Tire Wheel Sprocket.jpg

As I previously mentioned I am working with 6 inch wheels with 4.10x3.50x6 tires running a 6.5 HP engine. I have no clue to some of the items you mentioned. Just looking for good performance and nothing radical. The old 3.5 HP engine running with a 60 tooth rear sprocket and clutch with a 12 tooth sprocket did 30 mph. I suppose keeping it the same would be about the same speed but with more tork. Make sense?
 
M

MCope

New Member
#4
#4
One more thing the engine specs is as follows...
196cc
Speed 3600+ / 150 rpm.
Interesting is the docs for the engine specifies 91+ octane. First time I have seen a spec for gasoline with that high of octane. Normally in my other engines I always run at least 86.
 
Txpowdercoater

Txpowdercoater

New Member
#7
#7
MCope said:
View attachment 72814

As I previously mentioned I am working with 6 inch wheels with 4.10x3.50x6 tires running a 6.5 HP engine. I have no clue to some of the items you mentioned. Just looking for good performance and nothing radical. The old 3.5 HP engine running with a 60 tooth rear sprocket and clutch with a 12 tooth sprocket did 30 mph. I suppose keeping it the same would be about the same speed but with more tork. Make sense?
Click to expand...
yes, you will get to your 30 mph max speed faster / easier with bigger motor, but the new motor will allow for more top speed if you have higher gears. if no jackshaft, you can switch to a 13 or 14 tooth clutch driver and get more top speed. the bigger motor will still pull well low end as well.

I have a stock honda 5 hp with 11 tooth driver and 60 tooth rear and it was a wheelie machine, I switched to a 38 rear /13" diameter tire and was clocked at 50 mph the other day. the stock 5 still takes off easily and pulls to 50.
 
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M

MCope

New Member
#8
#8
That is great info and will help with a baseline. 50 MPH is more than enough on a mini bike. LOL
My son used a handheld GPS to see how fast he was going all the time. :)
I appreciate your response and thanks a bunch.
Mike
 
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