Gear ratio help

[rollin devils]

Ok I am building a lowrider bike.it has 4 inch crank arms.I was looking for tooth count recommendation.I don't want to peddle like a crazy man.would like to have a fairly easy peddle and have speed.it has kickback brakes so that kinda limits the rear gear. I'm not to good with gear ratios so I figured I'd throw this up,and see what happens.
Here is a pic of the bike if that helps.

 

[KJV]

whats on the rear : 20-22 ?
try a 36-38 on front. :idea: :mrgreen:

 

[rollin devils]

The rear I have is 18. Could try another though.

 

[KJV]

try a 44-48 up front. :idea:

 

[Sinner4]

http://www.sheldonbrown.com/gears/
Id try 36 - 18 to start and see how it feels

 

[ozzmonaut]

4" cranks is going to make it harder to pedal to start with. Being as you have the 18t rear, 36t sounds like a good front sprocket. Your rear is likely the snap ring type, so if it is hard to pedal, you might just dig up a 19 or 20t for the rear. 36t is an easy size to find and available in a lot of lowrider styles, so changing the rear might be easier once you've already made your choice for the front.

 

[Anonymous]

Easy bike ratios...

#1-Small front,Big rear=easy pedal no top speed

#2Large front,Small rear=Hard pedal no low end speed but plenty of top end.

You can try a longer crank for torque with #2 but the pedals may scrape.

 

[Wildcat]

With 4" crank arms, you won't go fast unless you have the legs of Hercules. 36 teeth on the front sounds about right with an 18 rear, not fast but you'll be able to cruise around respectably. If you had longer crank arms, a 44 up front would work.

 

[LowpowerD]

I've been thinking alot about this lately and had almost written up a tutorial on gear ratios.
MagicRat hit the nail on the head:

Easy bike ratios...

#1-Small front,Big rear=easy pedal no top speed

#2Large front,Small rear=Hard pedal no low end speed but plenty of top end.

You can try a longer crank for torque with #2 but the pedals may scrape.

Here's some basic math to help you plan ahead on your build. We can express this simple gear ratio in one number; the front divided by the rear. The smaller the number the more low end power, The bigger the number more top speed.
Example #1, 36t/20t=1.8
Example#2, 46t/16t=2.875

The happy medium would be around 2 or 2.5.
I hope this helps.

 

[Anonymous]

Im running a 36 19 with 6 1/2'" cranks on my 20" "Grape Krate" (yeah it scrapes the rat trap pedals)

Its real good for wheelies but not much else for top end.

 

[rollin devils]

Thanks for the help guys.I'm thinking I'm gonna set it up and get a measurement to see if I can use longer crank arms. If not I'm going with 20 rear and 36 front.again thanks for the help.again thanks
For the help.

 

[frameteam2003]

Your most likely going to need the 4 inch arms for ground clearance---try and get a sprocket off a kid bike for the rear(snap ring) might find a 16.
and remember---as low as you are you can give yourself a push off to start---a lot easer to pedal once in motion.

 

[Anonymous]

My LBS got me a 3 1/2" crank for a LowRider that sits way too low.