I have a cable driven speedo ( front wheel) on my Fatboy and it's way off. Faster I go the more it's off. After I get over 50 it's off by 10 mph. Doesn't make any noise or bounce around at all. Bikes gonna be down for a couple weeks so thought I'd try and figure this out. Any suggestions on what to start with?

 

What's changed recently? The speedo drive unit (there are 3 different ratios out there,) or its a new speedo? Different wheel set up? If none of the above I'd suggest that your speedo broke.

 

I've had the bike since May and nothings changed. Speedo has been off since I bought it just haven't tried fixing it till now. Bike has stock wheels and new stock size metzlers.

 

What year? And what size front tire?

 

Someone probably replaced the speedometer or speedometer drive with the wrong ratio before you got it.

 

I agree with them^ and I have done the exact same thing and had the same question that you have

 

Yup,my guesstimate.

 

Well guess I need to figure out what the correct one is for my bike/speedometer then. How would I do that?

 

Oh and to answer the other qustion it's a 96 Fatboy but has dual front disc breaks so the lowers have been changed, prolly wide glide. I'm actually looking at going to a 18 or 19" front wheel so I'm gonna take off the front to get a good measurement so I know for sure what will work.

 

I believe that yours runs the 2240:60 ratio drive unit.