I like to take my 77 Ironhead to motorcycle rodeos I would like to be more competitive in the drag race! My question is If you reduce the sprocket in the front and more theeth in the back dose that shorten your gear and if you get a taller gear would you be shooting yourself in the foot? We are racing under 100 yards in the dirt! I would like to pull a wheelie off the line and still have enough to make it to the end with out shifting! I do not care about top speed on this motorcycle

 

Example:
Front = 32T
Rear = 70T
Ratio = 70/32= 2.1875

Front = 30T
Rear = 72T
Ratio = 72/30= 2.400

The higher ratio will get you from point A to B quicker; that should answer your question. You will have to figure out a front/rear arrangement that works for your intended purpose. I don't think you are going to be pulling any wheelies in dirt.

 

I did some counting and measuring I have a 21 tooth in the front and 51 in the back within 83 inch tire circumference so if I put a 30 tooth in the front and 70 in the back will that make my tire spin twice as fast for twice as long ??

 

No, it won't.

 

There's got to be somebody on here that can tell me how I can get my back tire to spin faster and longer in first gear!!

 

Faster and longer in first gear are mutually exclusive; cannot be done. The lower the gearing is the higher the rpms are in any gear. How long you can go in first gear is a function of the maximum rpms your motor can spin without blowing up or hitting a rev limiter before you have to shift. I would be concentrating on second gear.

 

The figures djl gave you are for more recent bikes with belt drive, not your chain, although his underlying message is correct. There is no need to change both of your sprockets, as only changing one can probably achieve what you want. I suggest you concentrate on the front trans sprocket, trying first a 20T, then a 19T, etc, until you get to where you want to be.

Changing either sprocket, front or rear, may also require altering chain length. Fitting a smaller trans sprocket will involve shortening the chain, while increasing rear sprocket size will require a longer one, which is why the front is the best place to start!

 

Thank you everybody I am going to try a smaller sprocket in the front.