Gear ratios vs tire size?

J

Jpar

Member
#1
#1
So I have my MX Bonanza up and running with a 6 horsepower Briggs & Stratton.
This is going to sound odd but it almost seems too fast as in it doesn't want to cruise at slow speeds whatsoever. I'm looking at the gear ratio here and it looks like I have a 40 on the back in about a 9 on the front with a one-to-one off the drive on the jackshaft. It's got eight inch wheels and tires. I'm thinking this should have a much much bigger rear sprocket? I mean when it gets going I can't even get it up to full blast before it gets too scary and when I want to go slow it just chugs along at way too fast of a speed... Almost seeming to give me low speed performance problems?..
Any help or experience that anybody has would sure be appreciated. Thank you..
 
J

Jpar

Member
#3
#3
So it looks like I have a 12 tooth clutch and a 13 tooth jackshaft Drive sprocket. So I ordered an 18 and see if that doesn't help things.. of course a longer piece of chain as well...
 
SAS289

SAS289

Well-Known Member
#4
#4
The 18 would help as long as it is the first sprocket on the jackshaft. Clutch chain attaches to it.

To get to 6/1 you will need the 18 after the clutch and a 10 tooth in front of the rear sprocket. If both of your jackshaft sprockets are 13 tooth your current numeric ratio is 3.3/1. This is not a good gear ratio for any mini bike or go kart.
 
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J

Jpar

Member
#5
#5
SAS289 said:
The 18 would help as long as it is the first sprocket on the jackshaft. Clutch chain attaches to it.

To get to 6/1 you will need the 18 after the clutch and a 10 tooth in front of the rear sprocket. If both of your jackshaft sprockets are 13 tooth your current numeric ratio is 3.3/1. This is not a good gear ratio for any mini bike or go kart.
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As it sets I believe I have a 12 to 13 running the 9 to 40. I plan to change the 13 to an 18?..
 
J

Jpar

Member
#7
#7
SAS289 said:
Oooh.. So just adding only the 18 will get you to 6.6/1. Try that I guess.
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I'm trying to go that route as it would be just easy to pop that little gear off the outside then having to get the drum/sprocket and the whole assembly gizmo off. To change that's not a big of a deal but I notice from when I was a kid if the rear sprocket was too big I'd start riding on it around corners??
 
SAS289

SAS289

Well-Known Member
#8
#8
Jpar said:
I'm trying to go that route as it would be just easy to pop that little gear off the outside then having to get the drum/sprocket and the whole assembly gizmo off. To change that's not a big of a deal but I notice from when I was a kid if the rear sprocket was too big I'd start riding on it around corners??
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Yeah you wouldn't want too big on the rear sprocket. That's what is nice about the jackshaft. You can fine tune the gearing there, if the sprocket sizes you want are available. Hopefully that 18 tooth isn't too much of a change.

My preference on mini bike gearing is the same as it is on a classic car. I'm not interested in the highest top speed possible. Better acceleration is my preference big engine power or not. For example, I knew that 2.80/1 gearing wasn't going to fly with my 289 with a 4 speed. So I just hit the easy button and got a Granada 8 inch third member with 3.50/1 gears. Much more fun to drive even with the mildly built 289.

In my opinion you could have a very fun mini bike with a bone stock engine Just gear it to your preference.
 
J

Jpar

Member
#9
#9
SAS289 said:
Yeah you wouldn't want too big on the rear sprocket. That's what is nice about the jackshaft. You can fine tune the gearing there, if the sprocket sizes you want are available. Hopefully that 18 tooth isn't too much of a change.

My preference on mini bike gearing is the same as it is on a classic car. I'm not interested in the highest top speed possible. Better acceleration is my preference big engine power or not. For example, I knew that 2.80/1 gearing wasn't going to fly with my 289 with a 4 speed. So I just hit the easy button and got a Granada 8 inch third member with 3.50/1 gears. Much more fun to drive even with the mildly built 289.

In my opinion you could have a very fun mini bike with a bone stock engine Just gear it to your preference.
Click to expand...
this is supposed to go to the grandkids at some point and I was originally considering a three or three and a half horsepower engine. That's what I had for my boys and I enjoyed it and it was just about right. Plenty of torque for playing around in the yard and not too damn fast... My neighbor gave me this Motors so I'm working with it. The gear was only like $13 on Amazon and I bought $8 worth of chain and $6 worth of Master links so I can make a chain smaller or bigger...
I sure appreciate your response as I'm really not used to how long it takes to get one. Again I've been an active member of one of the car forums it seems like I've already gotten more response about this minibike there in the off topic discussion then here... Again thank you and I'll keep trying...
 
Rapidrob

Rapidrob

#10
#10
You may want to change the spring in your clutch to a stronger type that does not engage until a much higher RPM. You have to give it more throttle even to get it to move. This may also help.
 
J

Jpar

Member
#11
#11
Rapidrob said:
You may want to change the spring in your clutch to a stronger type that does not engage until a much higher RPM. You have to give it more throttle even to get it to move. This may also help.
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Yes I swear it's engaging way too fast as well.. even at a steady slow idle it's trying to pull a bit and anything off of idol it's definitely pulling hard...
I finally said the heck with it I'm going to see how damn fast this thing will go so I took it a couple blocks away down to a long stretch block which goes about four or five blocks with no side streets.. I got it up to what I think was at least 35 miles an hour if not more and it was still pulling hard! And I did finally have to let off of it before I felt it top out... I came back home with tears shot back to my ears.. !!... LOL.. for whatever reason I feel like I have the throttle hooked up wrong.. it's pulling the governor lever that's pulling the carb wide open? I don't feel like it's working correctly or that it's choking itself out or coming on too fast I don't know? Any help with that would sure be appreciated....
 
SAS289

SAS289

Well-Known Member
#12
#12
Change one thing at a time so you know what made what difference. Do the 18 tooth before you make any other change. I think initial engagement from a stop will be much nicer.

Your issue reminds me of another from a few months ago. They said once the clutch engages it takes off "like a bat outta hell". Pretty much poor slow speed rideability. Another way to describe it would be "the bike goes too fast when I'm trying to ride slow".

Once you put the 18 tooth on you will be able to ride at a slower speed with the clutch engaged. And the initial engagement will not be as harsh.
 
J

Jpar

Member
#13
#13
SAS289 said:
Change one thing at a time so you know what made what difference. Do the 18 tooth before you make any other change. I think initial engagement from a stop will be much nicer.

Your issue reminds me of another from a few months ago. They said once the clutch engages it takes off "like a bat outta hell". Pretty much poor slow speed rideability. Another way to describe it would be "the bike goes too fast when I'm trying to ride slow".

Once you put the 18 tooth on you will be able to ride at a slower speed with the clutch engaged. And the initial engagement will not be as harsh.
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Thank you for that reply! I should get the sprocket tomorrow from Amazon... We'll give that a shot first..:scooter:
 
J

Jpar

Member
#14
#14
Well I didn't have my gear yet this morning so I tried putting the old throttle configuration as in how it was when it was a pressure washer just taking the pressure off the lever hooking a throttle cable to it and the return spring.. look a little odd as if it was stuck full throttle? And then backs off?.. anyways I went ahead and start it with the tire up against my car trailer and sure enough it tried to take off full throttle I had to kill it... Pulled all that crap back off of it and put it back how it was. Then the gear got here and I put that on with a new piece of chain.... When it started up of course it had more torque and dug hole in my yard!.. LOL..
Low-speed drivability still completely sucks... I'm either wants to go like hell, chug real hard CHUG CHUG CHUG... Or just flat-out die...
I don't figure something out quick it's going to end up with a $99 Harbor Freight predator... And be done with it all... The slow-speed drivability is making it so I don't want to ride it it's just gets away too fast and when I slow down again chugging or dying..
 
SAS289

SAS289

Well-Known Member
#15
#15
Sorry to hear that the issue is still happening.

You may want to return to the original engine throttle arrangement and start over with where you connect the throttle cable. All this IF you want to continue with this engine.

Did you ever ride the bike with the Greyhound?
 
J

Jpar

Member
#16
#16
SAS289 said:
Sorry to hear that the issue is still happening.

You may want to return to the original engine throttle arrangement and start over with where you connect the throttle cable. All this IF you want to continue with this engine.

Did you ever ride the bike with the Greyhound?
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I guess that's what I was saying I did. When I said I put all the old stuff back on for the throttle and tried it that way..
No never tried to Greyhound...
 
J

Jpar

Member
#17
#17
Ok.. I had a little break through.. I bought a clutch for the cheeftah and tried it on the bananza.. BONGO!!... I knew right away it had a much higher stall.
Still having high idle problems.. I did notice when I leaned it to the left or right it would idle up or it would stall..? Seems like float bowl?..
 
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