Help With Racing Pred 212/DB30

#1
Hi everyone, I'm looking for a few pointers on getting my minibike to its peak performance. The 212 is a hemi with billet rod, flywheel, mod2 cam, etc. and is built very well and runs great, if I had to guesstimate it has around 12hp. However, the top speed isn't quite were I expected it to be. I am having issues wrapping my head around the way gearing comes into play.

The bike is equipped with a TAV2 with blue/silver springs, aluminium weights, and the stock driven spring adjusted. It also has a 60T rear and 14" tire. With the way it is setup now it goes about 57mph in 1/8 mile, which as I've said, is not quite as fast as I would like it to be. It takes off like a mad man after the new springs but is only slightly faster than before. After watching the driven, it seems to engage at the same time as the driver; is this supposed to happen? Any other setting on the driven assembly causes the belt to melt.

Hopefully someone with much more experience than I can chime in with some tips. I plan on only taking this bike to the local track, but until I can really pull a run with the best of them, I'll keep building. I appreciate any help you may have.
 
#2
Hi everyone, I'm looking for a few pointers on getting my minibike to its peak performance. The 212 is a hemi with billet rod, flywheel, mod2 cam, etc. and is built very well and runs great, if I had to guesstimate it has around 12hp. However, the top speed isn't quite were I expected it to be. I am having issues wrapping my head around the way gearing comes into play.

The bike is equipped with a TAV2 with blue/silver springs, aluminium weights, and the stock driven spring adjusted. It also has a 60T rear and 14" tire. With the way it is setup now it goes about 57mph in 1/8 mile, which as I've said, is not quite as fast as I would like it to be. It takes off like a mad man after the new springs but is only slightly faster than before. After watching the driven, it seems to engage at the same time as the driver; is this supposed to happen? Any other setting on the driven assembly causes the belt to melt.

Hopefully someone with much more experience than I can chime in with some tips. I plan on only taking this bike to the local track, but until I can really pull a run with the best of them, I'll keep building. I appreciate any help you may have.
Not sure I understand what you mean by "driven seems to engage at the same time as the driver"? In order for the belt to move at all, the driver has to engage which in turn moves the belt engaging the driven. So, yeah, that's perfectly normal. It couldn't work any other way without burning up your belt. Not meaning to insult your intelligence, I just am not sure I understand what you are asking.

What size is the sprocket on your driven? What hole do you have the driven spring in?

Im sure some other guys with more experience will chime in but I think you might be asking too much of that TAV. If you are burning up belts, then either something is not assembled correctly, you have a defective part, you have a gearing ratio problem, or you have too much horsepower. Otherwise it shouldn't be melting belts
 
#4
Then definitely try going up to a 12 tooth sprocket on your driven. That will give you better top speed for sure. In fact, you might even consider going to a higher tooth count sprocket than that, especially if the diameter of your wheel is only 14 inches. I have the same 6 to 1 gear ratio as you, also using a torque converter with tires that are about 14 inches in diameter and its a wheelie machine. That's with a stock motor. So that's the first thing I would try if I were you.

My other question is about the belts. You said that any other setting on your driven is melting belts. That seems odd to me. With a 6 to 1 ratio, using the size of tires you are using, you shouldn't be having trouble melting belts. Premature belt failure is usually cause by misaligned sheeves, worn out or missing brass idler, improper belt installation, or gearing that is too high (by "high", I mean for example 3:1 is "higher" gear ratio than 6:1). If it is a gearing issue, belt life can be somewhat helped by moving the driven spring position from the 1st hole to the 2nd or 3rd. This in essence keeps the TAV in "low gear" longer giving better low end torque. But from what you are describing, using the #1 hole is the only setting that doesn't melt belts. If anything it should be opposite of that. This makes me wonder if something else is wrong with the TAV...
 
#6
Before you change anything. Do you have a tach? If so what rpm are you crossing the line at? What is the riders weight?
The last sentence can make a heck of a difference in how the bike performs. As is, with a 100 pound kid on it, vs some 300+ pound heifer riding it. NO insult meant to any heifers out there, but that bike may be a whole different animal at the strip if it isn't having to haul around an extra hundred pounds or so of dead weight.

My son and I road race cars, and shaving weight can mean the difference in first place or second (known as first looser) LOL!

Or if you want a mini bike reference, I built a Bird T-Bird, somewhat stock Predator. I weight 230, and with a 12 drive and 60 driven, it will launch hard, and fly. My son gets on it (140 pounds) and he can't keep the front wheel on the ground. Has to feather the throttle to get moving, and carefully add throttle once rolling, or he's doing wheelies.
 
Last edited:

Zaxphyr

New Member
#7
Haven't got a tach yet, but I only weigh 140 and it takes a lot of effort to keep the front down taking off from low speeds.
 
#8
So maybe it's geared too low? End up with too much torque, and loss of top end speed.
12 horse shouldn't need a very big driven gear.

With the "stock" one on mine I had an 80 tooth on it and it was down right scary torque wise, never even attempted to see how fast it would go. Swapped it out with a 60 tooth and it's not quite as bad launching and pretty darn quick..
 
#9
57mph @1/8 mile with a bike and rider at 240 total =11.60hp. With a cvt is going to be hard to keep the front end down. Get a tach to adjust gearing for optimum et at the track. If you post your combo then we can see if your on target for power to parts.
 
#10
Get a tach to adjust gearing for optimum et at the track. If you post your combo then we can see if your on target for power to parts.
That's exactly what I'm trying to do. I know the engine has the power, it's just the delivery I'm having issues with. I see these other bikes pulling 8 second passes with predator engines and I'm trying to get to that point. I was hoping for some advice so I don't spend tons of cash trying out different gears if I could help it.
 
Top