Rear sprocket size for DB30S with Predator 212?

#1
New guy here, got the bike not running so I have no baseline. Going to just go ahead and put a 212 in. I've got a 12T clutch on order, how well will that play with the stock 70T rear? Should I change that or leave it as is?
 
#2
Do you still have the 14"+/- 145/70-6 tires on it? Tire OD will affect 'effective gear ratio' (search it). I would have gone with a larger odd number tooth count clutch sprocket for use with the 70T rear sprocket, probably a 13T or 15T Max-Torque, depending on other factors.. Odd number tooth count sprockets reduce wear on both the sprocket and chain for reasons I won't get into here. You will have a lot more torque (than stock engine) with a 212 (I recommend the Ducar) so you could use a larger clutch sprocket with the 70T rear sprocket instead of replacing the rear sprocket. If you do replace the rear sprocket, I suggest getting the DB sprocket adapter hub and split sprocket(s) from BMI Karts. Try the 12T - 70T combo (5.833:1 ratio) and see how you like it before spending more money.

https://www.bmikarts.com/Baja-Doodlebug-Sprocket-Adapter-Plate_p_7093.html

https://www.dynocams.com/item/212-1000/ducar212/
 
#3
Do you still have the 14"+/- 145/70-6 tires on it? Tire OD will affect 'effective gear ratio' (search it). I would have gone with a larger odd number tooth count clutch sprocket for use with the 70T rear sprocket, probably a 13T or 15T Max-Torque, depending on other factors.. Odd number tooth count sprockets reduce wear on both the sprocket and chain for reasons I won't get into here. You will have a lot more torque (than stock engine) with a 212 (I recommend the Ducar) so you could use a larger clutch sprocket with the 70T rear sprocket instead of replacing the rear sprocket. If you do replace the rear sprocket, I suggest getting the DB sprocket adapter hub and split sprocket(s) from BMI Karts. Try the 12T - 70T combo (5.833:1 ratio) and see how you like it before spending more money.

https://www.bmikarts.com/Baja-Doodlebug-Sprocket-Adapter-Plate_p_7093.html

https://www.dynocams.com/item/212-1000/ducar212/
Thanks for all the info! Yeah still on the stock 145/70-6, but on the hunt for new tires as we speak.
 
#5
Thanks for all the info! Yeah still on the stock 145/70-6, but on the hunt for new tires as we speak.
I went from the 145/70-6 tires to 13x5-6 and 13x6.5-6 pocket bike tires, which are actually only 11" or so OD (drastic change!), on a couple of Coleman CT100Us, which would have put the stock 75T sprocket and chain way to close to the ground.
 
#7
Use a high-quality name brand #35 chain such as RLV, EK, D.I.D., etc. Most of the no-name stuff will stretch quickly. Lots of members like RLV Gold, I don't like bling so I bought RLV Black in bulk, it's specs are the same as the gold other than the finish.
 
#8
Use a high-quality name brand #35 chain such as RLV, EK, D.I.D., etc. Most of the no-name stuff will stretch quickly. Lots of members like RLV Gold, I don't like bling so I bought RLV Black in bulk, it's specs are the same as the gold other than the finish.
You know... As a 15+ year motorcycle rider I should've known that, but silly me bought a cheap one on Amazon thinking low power wouldn't be an issue. I'll go on the hunt for a branded chain and return the no name.
 

Addicted 2 Minis

Well-Known Member
#10
You know... As a 15+ year motorcycle rider I should've known that, but silly me bought a cheap one on Amazon thinking low power wouldn't be an issue. I'll go on the hunt for a branded chain and return the no name.
I got some cheap chain from tractor supply once... once. If you like adjusting chain tension every other day until you have to start taking links out, go with the cheap stuff. The sad part was, it was #40 chain on the stock engine for my CT200U and it was still GARBAGE!.
 
#13
Couple important things to factor....
1. Rider weight
2. Riding terrain
3. Tire diameter as mentioned above

You will get various opinions on static gear ratio. If you're on flat ground/pavement, you can probably get away with a 12/60 at 180 pounds or so . Anything lower than that and you'll be cooking the clutch until it locks up. Heat is a clutch's enemy. 12/70 is just under 6:1. That's a good baseline in my experience. I prefer to spend the few bucks for the rear sprocket adapter and run split sprockets. A Split sprocket is much cheaper to change and swap out than a new clutch. Just my .02. Have fun!
 
#14
Couple important things to factor....
1. Rider weight
2. Riding terrain
3. Tire diameter as mentioned above

You will get various opinions on static gear ratio. If you're on flat ground/pavement, you can probably get away with a 12/60 at 180 pounds or so . Anything lower than that and you'll be cooking the clutch until it locks up. Heat is a clutch's enemy. 12/70 is just under 6:1. That's a good baseline in my experience. I prefer to spend the few bucks for the rear sprocket adapter and run split sprockets. A Split sprocket is much cheaper to change and swap out than a new clutch. Just my .02. Have fun!
Best explanation right there^^^^.
To The OP: Your original question cannot be properly answered w/o additional information as there is no "one size fits all". Add to that the fact that perceived performance is very much personal preference and quite subjective and will vary from individual to individual. Personally, (with the very limited information you have provided) I would say start with a 12/70 combination and experiment with different combinations (ratios) from there.
Michael
 
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