how do you determine the proper ratio for 1/8th mile drag bikes?

jprice

OldMiniBikes.com
#2
really depends on your motor..
good start would be 13/72 if your bike tops out before the 1/8 you can go down a tooth on the rear,or go up one on the front, every tooth you down in the back will drop the rpm 300 and every tooth you go up in the front will drop it 100 rpm thats what tom from arc said in one of his vids anyways , trial and error,
 
#3
Well you have that backwards. 1 tooth up in the front makes a lot more difference than 1 tooth down in the back 1 tooth in the front is like 3 teeth in the back
 

KB2ROCKET

Active Member
#4
its not a linear equation its all about what percent one tooth represents in the total circumference of the sprocket thats why adding or subtracting one tooth on a 10 tooth Drive sprocket has a large efect on the ratio and doing the same on a 60 tooth driven sprocket has a lesser effect
 
#5
Hey Rocket, Forget about all the gear calculations and that type of nonsense. Put a couple of gears on and run it through the 1/8th. If your motor is screaming and the rpm's top out half way down the track....you're geared too low. Add another tooth or two to the front. If you have to push with your feet for the first half of the run....you're geared too high. Drop a tooth or two from the front. Experiment until your rpm's peak about a hundred feet from the finish line. Then you're in the sweet spot. Ogy
 

KB2ROCKET

Active Member
#6
I dont really have a place to make practice runs around here im planning on building it once and running it next year at billet proof
.
hey does anyone know if they allow you to run a kart on regular test and tune night at lakewood? it might be worth one trip to figure it all out
 

pomfish

Well-Known Member
#8
I dont really have a place to make practice runs around here im planning on building it once and running it next year at billet proof
.
hey does anyone know if they allow you to run a kart on regular test and tune night at lakewood? it might be worth one trip to figure it all out
If you have no where to shake it down/practice, you are in trouble.

Look around, with this crap economy there has to be an strip mall out of business or a big box store.
Run behind the building till they tell you to leave.
Just saying, you don't want to show up at the show and wish you would have got it sorted out.
Practice makes perfect.
 

jprice

OldMiniBikes.com
#13
i played a lot with gearing,i would get it perfect,then change to a 4 degree advance timing and have to go up a tooth,put a bigger cam in and have to go down a tooth lol all part of the fun..
 
#14
All those "gear charts" don't take into equation the riders weight, aerodynamics, wind, traction, track surface..... they will get you in the ballpark, but trial and error are part of the fun. I had someone send me a pm saying my two clones were definetly not stock because of the speed and gearing. SURPRISE! They are and look what they did! The Double Whammy has a 12 in the front and a 38 in the rear. On one engine, it is a dog, start the second one and it's a whole 'nother ballgame.
It's not that great off the startline, but once it gets rollin' she tops out right before the line.
 

KB2ROCKET

Active Member
#15
All those "gear charts" don't take into equation the riders weight, aerodynamics, wind, traction, track surface..... they will get you in the ballpark, but trial and error are part of the fun. I had someone send me a pm saying my two clones were definetly not stock because of the speed and gearing. SURPRISE! They are and look what they did! The Double Whammy has a 12 in the front and a 38 in the rear. On one engine, it is a dog, start the second one and it's a whole 'nother ballgame.
It's not that great off the startline, but once it gets rollin' she tops out right before the line.
yes your bike's gearing is a great example of what Im shooting for . you just cant have everything when running a single fixed ratio so pick your gearing and where you want it to shine
.
when I ran my tractor trike I was the only guy using a torque converter I had to because of my big a$$ed heavy 23" tractor tires this helped a lot off the line but the the bike reached its top speed about mid track and I lost it in the lights ( this bike wasnt really intended for drag racing it was ment for tooling around the neighborhood . but the kart I am building will be ment for drag racing and nothing else :devil2:
 
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