FL250 Gearing Help Please

[MIKartDad]

See if that works …?

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This is one of the first drives after getting the throttle hooked up better

October 1, 2025

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[Denny]

If you go to a CVT it will be way more funner!!!!

 

[Hellion]

I would get rid of all that hokum on the drive train now and switch to a CVT with a 6:1 ratio. That would get you at or near 40 reliably.

He's right. The original FL250 had a CVT and a reduction gear case. Be interesting to mimic the OEM setup as close as possible because the FL250 does 45-50 mph...

 

[MIKartDad]

If you go to a CVT it will be way

He's right. The original FL250 had a CVT and a reduction gear case. Be interesting to mimic the OEM setup as close as possible because the FL250 does 45-50 mph...

Recommending a cvt to a gear ratio I have now ? I think in 10:1 now … with the 15t roller sprocket I have it’ll drop it to 7.5:1 I think , then I want to get 18” tires n ditch the 22’s

 

[Sparkwizard]

6:1 is way too steep for 21 inch tires. The belt would never shift up after engagement.
I would shoot for 9 or 10 to one between the TC and the axle.

 

[MIKartDad]

You have to understand .. the final “trans” gear is 9:1 … so the gears between the t/c n the trans need to be 1:1 or >1:1 to be 9:1 , … rn with the 18T/20T I’m 10:1 … so you’re saying stay there ?

 

[Sparkwizard]

That is what I would do.
I doubt you will find a TC with an 18 tooth sprocket, though.

 

[Denny]

6:1 is way too steep for 21 inch tires. The belt would never shift up after engagement.
I would shoot for 9 or 10 to one between the TC and the axle.

Wrong! Manco used 5.6-1 with 22” tires and many many others have used 6:1 with 22” tires with absolutely no ill effects! It’s what we recommend!

 

[MIKartDad]

Wrong! Manco used 5.6-1 with 22” tires and many many others have used 6:1 with 22” tires with absolutely no ill effects! It’s what we recommend!

Ty !! That’s what I’ve been seeing when I google it …

That is what I would do.
I doubt you will find a TC with an 18 tooth sprocket, though.

They sell 5/8” sprockets ! Found a 16T to go on the tc .. would be 8.43:1 , they also have a 24T which would bring it down to 5.62:1 …
Also plan to go to 18” tires in the future

 

[Sparkwizard]

I guess I've been doing something wrong. Let us know what you decide to do and how it works out, please?
@Denny , were you pointing to the Dingo? I would like to do some research...

 

[Denny]

Yes, the larger 8hp 385 Dingo. But most of the granddaddy builds on here also run 6:1 ratio with a 420 or larger engine and a 40 series CVT. See the CVT acts like an automatic transmission shifting from lower gears to higher ones as load and rpm change.

 

[Sparkwizard]

Assuming 3600 RPM crank speed
22 inch tire is 69 inch circumference
3600 /6 (gear reduction) =600 rpm axle.
600 x 69 is 41, 400 inches per minute.
41400/36 is 1150 yards per minute.
1760 yards per mile /1150 is 1.53 miles per minute
1.53x 60 minutes per hour come to 91.8 MPH at governed speed of 3600RPM.

Is that what Manco was selling?
Or is my math wrong?
Would you like to see the math with 22 inch tires @ 10:1?

 

[Sparkwizard]

I am very well aware of the functions of the CVT. It starts out about 3:1, multiply that by your 6:1 ratio and you have 18:1, and the 212 might have enough torque to gain enough speed to shift the belt all the way out to 1:1 going downhill with a tailwind on pavement. Otherwise, the engine will never even get to governed RPM and it will be a dog in sand or tall grass. With 10:1 gear BEHIND the the CVT, it will be able to adjust ratio tor terrain and RPM. Your 6:1 ration and that 91 MPH top speed will not be possible without ALOT more torque.

 

[Denny]

Your math must is off. 400 inches a minute is 33.333333 yards. Because at full throttle they cruise down the road at around 42 mph and can climb any hill. I’m no math whiz and I don’t care enough about it. All I know is 6:1 is a great all around ratio. I have seen it, built it and driven it. So have many others on here. Where is Bob when I need him? He is the theoretical physicist and math genius. He has proven the formula many times here.