Nc30 uk bike speedo is reading way slower than the bike is travelling, reads about 40 when I was riding next to it on another bike at 60.

Any ideas, jap gears on speedo?

Cheers

Is one in mph and the other kph.... 40 mph equals 60 kph?

gearing is the same.

you dont have a mph converter on it too right? ie blue box on speedo cable, they are only needed for km speedo.

"usual" ration in top gear is 10mph per 1000 revs...

What sprockets you running? Your drive nut thingy on the front sprocket might be knackered and running on friction rather than on the flats..so check that?

CMSMJ1 wrote:"usual" ration in top gear is 10mph per 1000 revs...

What sprockets you running? Your drive nut thingy on the front sprocket might be knackered and running on friction rather than on the flats..so check that?

These are also likely causes, two allen head bolts will get the speedo sensor off, check the nylon adapter isnt rounded off.

I thought the possiblity of a km/h convertor as 60mph with a speedo convertor would read 38ish (ive seen people fit the mph convetor with mph clocks before!) which seemed a little co-incidental for a worn nylon nut as that often causes erratic readings but it is good to mention them all just incase.

My bike was about 20kmh off at 100kmh (read 80~ or so). Turns out it had a CBR250RR speedo gearbox on the dash. They are both interchangable apparently.

Works fine now even with the +2 rear sprocket. I think its only about 2 or 3kmh off or there abouts.

Thanks all will check out.