Speedo healer?

Has anyone else done this?

I tested my new sat navs (zumo 220) speed readout against my Saab and discovered that the car's speedo is about 2.5 mph behind right round the dial beyond legal speeds. This seemed to stand as probably quite accurate as the older model sat nav I had indicated the exact same drift.

I then hooked it up to my bike to discover that from about 25 up, the bike drifts behind steadily from a couple of mph up to 40 to around 4 thereafter and about 5 from 80 on.
This conforms to what we've been told on various car shows on tv.

My question is therefore:

If I'm going for a torque gain by changing tooth numbers on my sprockets, what is the best ratio? Is it one down on the front, one up on the back?

And what would be the resulting speed error?

ie: if the bike travels slower becuase of the change then the actual speed would surely be closer to the current speedo error. Thus negating the need for speedo healer methinks.

Just thinking here, and waiting for somebody to call me a doofus or summat.
Help would be great

I cannot tell you what ratio gives you a more accurate speedo, but I know there is a combo of gearing that will get you close to accurate and have better acceleration.

Now... Your speedo is designed to have that error, so changing gearing might give you better speed readings, but you will be putting a higher number of miles on your odometer than you really drove. Could bring value down, and make scheduling maintentance more complicated.

Sent from my DROIDX using Tapatalk 2

17T/46T (stock is 16T/46T) makes your speedo accurate to within 1%, and will likely increase your economy too, at the expense of acceleration.

Cheers,
Rick

EDIT: BTW - the odometer reads LOWER than actual with a speedo healer or 17T sprocket change, as the bike is going further per rotation than the speedo is calibrated for. Correct speedo puts odometer roughly 6-7% low