So what are my options. In my mustang I put 3.90 gears in the rear end and it now hauls ***. I want to do something similar to my dyna. Can I get a bigger rear sprocket or do I have to change the drive gear. It's an 08 dyna. With the 6th gear it rev really low at speed. I wouldn't mind if it revved higher. And will I need a new belt or can I just bring the rear tire in more to compensate. Thanks for any insight

 

Changing the front drive sprocket from a 32 tooth to 30 tooth will give you nearly a 10% lower ratio, and is the most cost effective since there is no need to replace the belt.

To get the same from a rear sprocket swap would require a 4 tooth change which usually means changing the belt. Since you have to open the primary to change the belt, you might as well just change the front.

Each tooth change on the rear requires about an 1/8" of adjustment, so a 4 tooth requires roughly a 1/2", which should be all you have, leaving no room for adjustment later.

 

There's lots of threads here on that mod. Just do a search for 30T.

 

I went with a 170/60/17 tire in the rear. It is a 3.15% drop circumference (and overall gear ratio) from the stock 160/70 tire. Going from a 32 tooth to a 30 tooth is about a 6.7% drop, for comparison. The new tire throws my speedo off a little (reads 72 when I am really going 70) but not enough to matter.

 

Great. Thanks guys. 30 tooth it is. I am also gonna install the woods 555s this winter and the a tuner. Auto tune seems to get great results. Thanks again guys.

 

Be sure to recalibrate the speedo. The tuner should have some way for you to do that.

 

Good info in this thread. I did the same with my 6 speed Corvette. Changed the 3:42's for 4:10's and it really makes a nice difference with little penalty in gas mileage since it is a 6 speed. Would love a 10% gear reduction in my FXDC. Have to price the 30 tooth sprocket and swap cost.

 

Yet another way is to change the front compensator sprocket. That makes a huge difference. I just bought a 2000 FXDX in August and the pre-owner changed the front compensator sprocket from the stock 25 tooth to a 23 tooth. Talk about a drag bike! 55MHP and turning 3100 RPM in 5th. No need to down shift from 45MPH up.

The drive chain also must be changed so this is a more expensive change.

In the end I changed the sprocket back to stock (he gave me the stock one also). Just to low for the freeway, but if you just wanted to ride twisties I would have left it that way. Only issue is shifting 1-3. It revs so quick you need to be real good at shifting fast.

 

Plus you lose the "compensator" in the sprocket which is not good for your crank. I would go with the pulley unless you have a darkhorse or similar crank.

 

Not sure why that is true. Why do you lose the compensator function with the 23 tooth?