Gearing setups?

#1
What is a good gear ratio to run for mini bike
Now is 14.5 tire 35chain 70th rear and 12th clutch. I topped it out today at about 39mph 5280rpm when valves floated, im running a 212 predator hemi with header rejeted and pod filter, have billet rod and flywheel on the way mod2 came and heavier springs. Any ways as it sits now it is alway wanting to lift the front wheel even at a good speed if i crack the throttle. I was thinking about putting a 53th on the back or a 18th for the clutch to try and tame it but im now sure if that would dog it down to much. What setup yall run with out having to flintstone it taking off and have a decent speed still.
 
#3
As of now i would have to just pull back wheel of and then swap sprocket, but looking to get an adaptor to run split sprockets to make it easier to swap out down the road
 
#4
I am running a jackshaft setup. I have 13T on my clutch, 13T jackshaft in, 13T jackshaft out, and a 67T on my rear wheel. My final gear ratio is 5.154 and it is about perfect, the wheelie popping is very minimal. I am running a 212 predator with a Mod 2 cam as well. Its pretty peppy.
 

Kob67

New Member
#5
I'm looking for some help doing the math on my sprocket, clutch and or engine if in fact that's my problem. I just picked up an old Manco that has a 6.5 Predator 212, 8" wheels, 10 tooth clutch, 72 tooth sprocket, with a #40 chain.. My very first test ride flipped me on my back with lots of road rash. Not interested in doing that anymore. I was riding on pavement and just easing on the throttle. I'm looking for a set up with less acceleration on take off but more at top end to avoid another back flip or wheelies? What combination clutch, sprocket, chain would work best? Would changing the wheel size help? Any suggestions will be appreciated.
 
#6
Changing the clutch sprocket would be the easiest and probably to most effective way of getting your front wheel down; I would got to a 12 tooth. (or 13 if it is available for #40 chain...)
 

Kob67

New Member
#7
Thanks CL I'm going take your advice and look for a 13t or get a 12t clutch. I found a 60t sprocket. Do you know if that would help any using it with my 10t clutch?
 

Latent

Active Member
#8
I was running a 12t clutch 59t rear with a 15" tire, but found the gear ratio of 4.9 was too low... So I went with a 12t clutch 64t rear with 15" tires @ 5.33 gear ratio, and has more responsive power band. Modified engine running black mamba senior with 26lb valve springs.. 8000+ rpm limit...
 
#9
I chatted with another member yesterday who recommended a 54t rear. I'm going to swap out my present 72t with a 60t and then try the 54t to see the difference. I'm still a little uncertain about the clutch size?? Is it best to use a 10t clutch with 54 or 60t rear or should I be using a 12t clutch? Or does it really matter?
 

Latent

Active Member
#10
It depends on your tire size as well. So you need to take that into consideration. If your tire is 13" or taller I would go with a 10t clutch.
 
#11
I have a baja warrior with 18-in tires and a 50 tooth rear sprocket what size clutch should i run with this it also is running a 212 predator modified with a 275 cam 26 lb valve springs chromoly push rods at stock length any advice
 

SAS289

Well-Known Member
#12
I have a baja warrior with 18-in tires and a 50 tooth rear sprocket what size clutch should i run with this it also is running a 212 predator modified with a 275 cam 26 lb valve springs chromoly push rods at stock length any advice
Depends on what RPM you want the engine to run at what certain road speed. You can use a speed calc to try to get an idea of what you want. But you can't use an unrealistic RPM number. As an example, if you used 7500 RPM and 10/50 gearing it may tell you 80 MPH. That's not going to happen. For your engine 5500 RPM would be a better example at 58 MPH. Speed calcs do not factor in available engine power and load.

Mini Bike Speed Calculator (MPH) (csgnetwork.com)

If you want to use all of the RPM you built the engine for one setup you could use is a torque converter with a Juggernaut driver. Start with 10/50 gearing. If you top out RPM too soon then switch to a 40 tooth.
 
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