drag bike

[mini drag bike]

im going to be running my drag bike in the spring and was wondering what my gears should be in a 1/8 mile. right now i got a 8hp clone with 12 tooth clutch. what should my gears be out back. thank

 

[mteezey]

Are you going to use a jackshaft? What kind of rpm does your motor make? There's a ton of factors in figuring out what you actually want.

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[mini drag bike]

no jackshaft, max rpm is 4000

 

[bigrob]

Show us a picture of your bike , what size tire are you running

 

[mini drag bike]

im going to be running a 11/6-5

 

[LSCustoms]

im going to be running a 11/6-5

i used a speed calculator to help me figure out what i needed to start with for my goal... once that project is running, will see how it performs in the 1/8 and adjust from there, as far as to top out in the 1/8 or 1/4...

with your tire height being only roughly 11" (maybe im reading something wrong)... and your engine spinning to only 4000 rpm... with a 12t clutch sprocket, with a rear sprocket between 54-71 teeth.. you would top out at 22-29 mph (not fast at all, depending on your goal)...

the rear gear will help to determine how fast you top out at... but depending on what you goal is... a stock mini bike would be able to achieve that with no mods...

hopefully someone else will chime in in case i misread or calculated something here... you would need a taller rear tire and/or higher rev'd motor to go any faster :shrug:

this is the calculator i used and before the new engine swap and gear change on one of my projects, using gps, the calculator ended up being fairly accurate...
AGK - Top-Speed Calculator - Affordable Go Karts

 

[mini drag bike]

were i bought my engine from it shows max rpm is 4000. and on my other bike i got 12 tooth clutch and 71 tooth sprocket with a 10 inch tire, same exact engine and i clocked just a bit over 65

 

[LSCustoms]

were i bought my engine from it shows max rpm is 4000. and on my other bike i got 12 tooth clutch and 71 tooth sprocket with a 10 inch tire, same exact engine and i clocked just a bit over 65

sounds good.. not being argumentative with ya... just giving my experience as a response...

on my doodlebug, the first motor, which is now on my wifes kart, had the following:

predator 212cc, no governor (higher revving than 4000 rpm im sure of it :smile, billet rod, billet flywheel, isky black mamba cam and 26 lb springs, jet/etube/air filter/header, 12t front clutch, 70/1 rear sprocket (stock on db)... bike topped out at 45 mph (actually 44.9 mph)... was verified by gps and a new truck matching speed...

if you got 65 mph, you did very good...

my new setup has different tire combo, slightly more modded motor :anon.sml:, starting with a 54t rear and 13t manual clutch... and i hope to get 75+ out of it (sure i will, just dont know how fast in the 1/8)...

first motor was pretty healthy with the mods... limit was the stock sprockets as far as top mph...

in this vid topped out at 45 mph
https://www.youtube.com/watch?v=pAZ4nwr_Js8

made this vid to show how the muffler sounded vs the prev vid, but did not rev high at all, you can tell the diff in rpm between the two vids (this vid being closer to 4000 rpm i would guess)... i was no where near 65 mph

https://www.youtube.com/watch?v=c7vmyNasvTk

 

[mini drag bike]

thanks for the help