Primary ratio change!

Discussion in 'Softail Models' started by Veep, Jun 16, 2008.

  1. Veep

    Veep Member

    28
    11
    0
    I ride a 2003 FXSTB Night Train and love it! It is carbureted with a stage one upgrade. My only complaint is that it seems to be geared too low. I have compared the final drive ratios of the 03 with an 08 and found that the later is geared higher (numerically lower) by about 8%. It was suggested to me that changing the primary ratio will adjust this without having to recalibrate the speedometer. Does anyone have any experience with this type of mod? Where can I get the parts/kit? Does anyone have any comments on this idea?
     
  2. Doc 1

    Doc 1 Member

    51
    18
    1
    Your stock final drive is 3.15:1 which is good for most builds, but with a .590 lift cam and higher we like to lower the gearing to a 3.37:1 which is the opposite to what you want to do. Are you sure your bike still has the 25 tooth compensator sprocket and the 36 tooth clutch shell?
     
  3. Veep

    Veep Member

    28
    11
    0
    As far as I know, the drive is a stock 36/25 setup. I have not visually checked, (pulled the cover) but I have no reason to beleive it isn't. I have noticed that on an 08 first gear is 9.312:1 where as on my 03 it is 10.110:1. I was hoping to simulate the 08 gearing so my topend RPM would be less (2.90:1 for fifth on mine versus 2.79 for sixth on an 08). I am constantly searching for that missing sixth gear. It still won't be a six speed, but it will be better. Most of my cruising is between 55-80mph (lots of open roads and interstates in Alabama).
     
  4. Doc 1

    Doc 1 Member

    51
    18
    1
    I don't believe you will be able to get the same primary gearing as the 07 and 08 bikes in your primary case, however installing a larger trany pully will get you the same results except the speedo will be off. A speedo calibrator can be bought for $125.00 to dial it back in....if you are getting a SERT in the future you might consider the new TTS Tuner because it has a VSS calibrator in it as one of it's upgraded features.