Gear combo for fast 125 foot spurts.

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bugzaper

New Member
#1
#1
What is the best gear combination for quick 125 foot spurts.

Engine Crank:
Half Jack (from engine):
Half Jack (other side to rear wheel):
Rear Wheel:

Engine: Harbor Freight (clone) 5 hp stock
Rider: 225 lbs
Wheel: 12" with slick from the front wheel of a "John Deer" O-Turn Mower.

I'm (attempting) to build a "Drag Mini-Bike" but, we only go 125 feet.
 
minibikin'

minibikin'

Sho-nuff
#2
#2
If the engine is stock it will be governed to 3600rpm. That's the factor you need. Are you using an adjustable clutch? Determining clutch lock up and peak rpm/track length.
 
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bugzaper

New Member
#3
#3
minibikin' said:
If the engine is stock it will be governed to 3600rpm. That's the factor you need. Are you using an adjustable clutch? Determining clutch lock up and peak rpm/track length.
Click to expand...
I'm too new at this, what or how do I determine if my clutch is an adjustable clutch? I ordered what was called a "Max-Clutch" and can post a pic. if desired.
The engine (for now) is a stock Briggs 5 hp from around the 70s and can again post a pic..
 
minibikin'

minibikin'

Sho-nuff
#6
#6
So it's a Max Torque clutch? A stock 5hp Briggs flat head that is still governed? If so, 3600 will be you peak rpm for now. I believe the Burris gear ratio calculator requires tire diameter. I'm just guessing, but to hit 3600 in 125ft, you'd need around 7:1 with that tire. That's a guesstimate for now. That clutch should lock quickly out of the box.
Post some pics when you can. Sounds neat!
 
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bugzaper

New Member
#7
#7
minibikin' said:
So it's a Max Torque clutch? A stock 5hp Briggs flat head that is still governed? If so, 3600 will be you peak rpm for now. I believe the Burris gear ratio calculator requires tire diameter. I'm just guessing, but to hit 3600 in 125ft, you'd need around 7:1 with that tire. That's a guesstimate for now. That clutch should lock quickly out of the box.
Post some pics when you can. Sounds neat!
Click to expand...
"OK" here is the clutch and the engine I plan on using. I purchased the engine at few years ago at a garage sale for $20.00. I've started it a few times and it seems to run really good! The rear wheel sprocket is a 46 tooth with the wheel being 10" and the tire (I think...) around 13". Hope this helps.
 
David wulf

David wulf

#9
#9
With those tall tires i don't think a 7 to 1 will work unless you have really big power . I have a rupp with almost the same size wheels and a mild honda 160 and run a 8:33 to 1 gear and she starts well ,but if i were running 125' i would try 10 to 1 or 11 to 1 . I run a 11 to 1 in my super powell and she screams to 9k

Here's the rupp
 
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bugzaper

New Member
#10
#10
David wulf said:
With those tall tires i don't think a 7 to 1 will work unless you have really big power . I have a rupp with almost the same size wheels and a mild honda 160 and run a 8:33 to 1 gear and she starts well ,but if i were running 125' i would try 10 to 1 or 11 to 1 . I run a 11 to 1 in my super powell and she screams to 9k

Here's the rupp
Click to expand...
Very nice! I had a Rupp w..a..y back in the early 70s and rode the wheels off it!
When you speak of 10 to 1 or 11 to 1 what exactly are you talking about?
And, what tires are you using as I'd like to get a pair and get ride of the knobby type that is currently on it.
 
Briggster

Briggster

New Member
#11
#11
Let me know if you need any help, I'll be going to the rust revival as well. (Being that you are from MO, I'm assuming that's the 125 foot spurt you're referring to)

In my flathead days, I ran without the governor with a 11:65 with a 6" rim tire. I'm not sure the OD of the tire. I had difficulty keeping the front wheel on the ground and it would run out of rpm right at the end of the 125' track

 
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bugzaper

New Member
#12
#12
Briggster said:
Let me know if you need any help, I'll be going to the rust revival as well. (Being that you are from MO, I'm assuming that's the 125 foot spurt you're referring to)

In my flathead days, I ran without the governor with a 11:65 with a 6" rim tire. I'm not sure the OD of the tire. I had difficulty keeping the front wheel on the ground and it would run out of rpm right at the end of the 125' track

Click to expand...
"Yes" the "Rust Revival" car show is the one! What will you be driving I'll be in my "63" Nova Wagon (see pic.) and will keep an eye out for you! I can use all the help I can get....:thumbsup:!
 
Briggster

Briggster

New Member
#13
#13
I have a 28 A coupe, but I doubt ill drive it up there. Its a 5hr drive for me from cape. I'll definitely keep an eye out for you there. Dad will probably drive his 55 up thouhh
 
oldfatguy

oldfatguy

Active Member
#16
#16


I run around 10 to 1 on my Arco with a Tecumseh h60 which is very similar to your bike.
I'm using a standard clutch to a 20 tooth gear on the jack shaft to a 12 tooth on the sprocket side. Start there then if you want to change from there just use a bigger or smaller gear on the jack shaft side connected to the clutch.
 
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bugzaper

New Member
#19
#19
oldfatguy said:


I run around 10 to 1 on my Arco with a Tecumseh h60 which is very similar to your bike.
I'm using a standard clutch to a 20 tooth gear on the jack shaft to a 12 tooth on the sprocket side. Start there then if you want to change from there just use a bigger or smaller gear on the jack shaft side connected to the clutch.
Click to expand...
Thanks!
 
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