I have an 84 softail with a 4 speed, when im doing 65mph my rpms are about 3,400. What size sprocket can i put on the rear to lower the rpms. The stock sprocket is a 51 tooth in rear and a 23 tooth sprocket in the frount. I would have to go smaller on the back sprocket but how much smaller can i go?

 

Good thing about changing the gearing on a chain drive - much easier than a belt drive because you're not limited by few choices with belt length. You can even use half-links if you need to.

You can go up to 23 or 24 front, and down as far as 43 on the rear. Better to look thru the Shovelhead portions of catalogs when shopping. That'll give you more choices than the Evo sections since they're aimed more toward belt drives.

Here's a link to Baker transmission gearing page. You have to do some math though...

http://www.bakerdrivetrain.com/gearratios/index.htm

PS: they added a calculator at the bottom of the page, but you'll have to substitute your engine and clutch sprocket sizes since they only give example values for '85 up in the program - but it's pretty cool

 

TJ,
You got it covered man!!!