I have looked up the stock gear ratio sorta understand it. I would like to get more range out of my gears. I have read some things about going a tooth or two bigger on the gear up front. If you do that do you need to go smaller with the back? How much does it help by changing? More of a highway rider not stoplight to stoplight speed limit on interstate is 70 mph here and at 70-75 mph I'm close to 4000 rpm and would like to make the rpm number lower at that speed

 

Pri-Gear Ratios
883 = 57/34
1200 = 57/38

If I am not mistaken the 883 also has one less tooth on the drive pulley but I am not sure on that.

Your bike details would help others assist you better. Are you riding an 883 or a 1200? If you are riding an 883 you can make your gears longer by changing to the primary gears found on a 1200.

The 883 gearing will definitely give you a lot more acceleration but if you do much highway riding the higher rpms may seem too much. If on an 883, you can make it a 1200-1275 fairly easily and it will be a screamer with the 883 gearing.

 

Its a 1200 and yea I do a lot of highway riding

 

You can use this site to check your gearing and compare to different primary/final drive ratios.

http://www.gearingcommander.com/

On a 2007+ US sportster, one additional tooth on the front final drive pulley will drop the rpms at 70 mph about 100 rpms.