My speedo is definitely out, so I did a test with a mate. Riding alongside his R6 I could see 28mph on his digital display, and had 40mph on my clock. This is a pain, mainly for riding through speed traps.

I thought it had been re-geared, but my sprockets are stamped 16 on the front and 44 on the rear, so just -1 on the rear. This is geared up isn't it i.e. higher top end, but only something like 3.5%.

The bike could be an import but from what I've read, it's just a matter of changing the overlay on the clock so that wouldn't account for it.

Could losing one tooth on the rear sprocket make so much difference on the speedo?

 

Tire/wheel size can also have an effect. Check your specs with gearingcommander.com by inputting your gearing and your tire sizes and see if it pans out.

 

Tyres are F 120/70 ZR 17 and R 180/55 ZR 17. These are standard I think. Chain is a 525, also standard

So only thing different is -1 on rear sprocket.

What else could it be - could a weak battery or faulty rectifier affect the speedo?

 

Hi again,
I answered on your other post not long ago.

Your Tyres are standard size as well as your chain, and a weak battery or faulty rectifier should not affect the speedo as far as I am aware.

you will need some expert advice on this
come on people!

 

Thanks - I thought it was best to start another post rather than carry on hijacking another

I am a bit stuck on this one, was pretty sure I'd find the sprockets were different but if they're standard then it's starting to get tricky.

Worth a look for a speedo healer but my guess is it won't be there! I will check though.

 

factory sprocket sizes are 16 front and 45 rear. its the one tooth down in the rear thats causing you speedo to be off. you can get a speedo healer and it'll fix it.

 

Black'n'Yellow has mentioned on another thread that 16/44 is actually correct for a UK FX, I think he is right too. However, US sites show 16/45.

Question is, where did my bike originally come from? It was registered in Northern Ireland in 2002, at 3yrs old. Before that it could have just been in the ROI, but it could have come from anywhere really.

Is there a site where I can punch in the frame number and find out exactly what the spec should be?

Even if it is supposed to be 16/45, could one tooth difference on the rear really send the speedo out by that much?

 

I would try to do your speed test again but with something more accurate than another bike.

Can you borrow a satnav unit for a while to test out the true speed vs the indicated speed ?

40 to 28 is only a ratio of 1.43 - that is not the typical mph to kmh ratio of 1.6.

Also - as well as your speed - you need to check if your odometer is reading correct - ie is one mile on the odometer also one mile by satnav ?

EDIT - the 16/45 gearing would only change the mph reading on the clocks by around 1.5 mph at 40mph compared to 16/44 ( the speedo would read 1.5 mph faster on 16/45 )

 

Cheers mate, I have a satnav so could give that a go.

I thought the same as you - gearing couldn't affect the speed that much.

The clock has MPH outside, and KPH inside, from what I've read even if a bike is imported it's simply a case of changing the card at the back of the speedo, no messy mods are required, so it's not likely to be a KPH problem either.

Odometer is a good question, I think it's got to be clocking up more miles than it's actually doing, but again will need to prove it against satnav.

 

Some updates:

- realised today that speedo says 10mph at standstill with engine running. FFS!
- odometer logs too many miles. 100 miles on trip counter today on a 60 mile ride
- margin of error is constant, doesn't increase with speed as I originally thought.

So it seems more electronic problem to me, definitely not gearing related. Speedo healer unlikely to work either because they gear the speedo up/down whereas my bike seems to need a fixed adjustment