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Old 07-05-2019, 08:56 AM
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Default CT200U-EX | Torque Converter | Gearing Question

I have a CT200U-EX and have a "eBay China Special" torque converter on there. I have kept the rear 50T sprocket and purchased a 8T sprocket for the TC jackshaft. If my math is correct that is a 1:6.25 ratio with 19" original tires. It is running the Hemi 212 Predator with governor still in tact and right now has no problem getting to 40mph.

I used the china original belt on it (I know bad stuff) and it lasted all of two hours riding, it has a Comet belt on there now but I am concerned my gearing is too tall for me. This said I have plenty of weight to loose, as a 270lb rider I am way over what this bike is rated for but so far it is working like a champ.

I know the china belts are crap but with my weight and 19in wheels should I try and see if I can get a bigger rear sprocket? My biggest concern is to not make it a wheelie machine, and with the 8T/50T combo it is very manageable.

I just wanted the interwebs opinion on what they would do.

Thanks,
Daniel.
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Old 07-05-2019, 09:36 AM
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Yup, 6.25/1 ratio.
Top speed on the DIYGK calculator is 33 mph, so I don't know how you're getting 40!
Is that just a guesstimate, or is it GPS/speedometer verified?
I would get a bigger sprocket for sure. Probably a good place to start is a 60T, as they're very common.
That'd give you 7.5/1, and with 19" tires and a *cough* heavy rider, I think it should still remain manageable, especially with a stock engine.
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Old 07-05-2019, 12:14 PM
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Quote:
Originally Posted by frostyflammable View Post
that is a 1:6.25 ratio with 19" original tires. .. right now has no problem getting to 40mph.
Quote:
Originally Posted by JTSpeedDemon View Post
Yup, 6.25/1 ratio.
Top speed on the DIYGK calculator is 33 mph, so I don't know how you're getting 40!
funny.. at 3600 it's actually 36.2 mph (ten percent overdrive )
but chances are the CT200 has it'S governor set to 4k rpm
that would mean 40.some mph
(and governor somewhere in between would be somewhere in between those speeds of course )

belt wear sound excessive even for a chinesium belt IMHO..
let's see how well the Comet one does.

Ideal gear ratio for a total weight up to 420 lbs
would be ~6.7:1 (i.e. a 53 or 54 wheel sprocket [6.63:1 or 6.75:1 ratio])

I think you can get away with 6.5:1 [green lights for 405 lbs or less]
especially if your plan is to lower the moved masses

that means just two more teeth on the rear will do nicely.
(52 wheel sprocket with 8T TC sprocket)

your current ratio is sound for 375 lbs or less
and you wouldn't need to change anything at all.

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Old 07-07-2019, 07:45 PM
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Alright just to update here. I was going to just leave the gearing as is and see what happens with a Comet belt, however I had a 60T sprocket I bought for an old Baja Warrior that happens to fit. So today, since it was nice and cool in Texas lol (93 for the high) I decided to swap the sprocket from the 50T to the 60T. Oh man what a nice difference, I was worried about it becoming more of a wheelie machine but it is so manageable. I do believe that before with the 8T/50T I never got to the top RPM of the engine, right now it get to about 35mph really easily and then the governor kicks in. It feels so much nicer to ride, and honestly I do not miss any of the top speed, it is just as fast for me.

On a straightway it gets to about 35mph, slight downhill it went 37mph. I do not miss the 5 mph or whatever I lost on the top end since 35mph is plenty fast on the mini bike.

That is all, just wanted to update everyone.

--Daniel
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Old 09-12-2019, 05:47 PM
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Smart move on the 60-tooth, even a 72-tooth won't flip you over backwards as long as you scoot up on the seat. Everybody seems to forget that. That's why a 17" seat does more for a single rider than it does in being able to carry a passenger. Not street legal anyway, where would a passenger ride to? What worries me is that tiny 8-tooth drive sprocket. The more teeth, the more grabbing the chain. I run a 12/60 setup that's way too **** fast on the top end, going to a 12/50 with a #41 setup instead of #35. The 12-tooth makes me feel better about how all that power is being extracted from its birthplace, that's where the most torque is. That TC of yours, is it asymmetrical or standard V-belt? If a V-belt, then a cogbelt (notched-out belt for small pulley turns) will last a lot longer. If asymmetrical, sure you mounted it with the flat side to the flat side of the pulley?
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