speedi and tach ratio?

[Guest]

Okay so had this bike all summer steady worked on it. Didnt run when i got it and was in boxes. New intake boots some carb and electrical issues starts first compression stroke. Swapping gauges out. How do i determine the ratio for the tach and speedo so im spot on.

[Gorminrider]

Tach: count how many times the cable spins per rotation of the engine TDC->TDC. It's better to do it 10 times or so so you don't puzzle over fractions of a turn and put a kind of a "flag" on the cable end so you don't get confused by 1/2 turns...
But it will really only be as accurate as the manufacturer made the tachometer .The ol' dial type use a magnetic system and can get funky with age. A digital type tach might be your best bet per "spot on"

Speedo...same idea but you can get fancy by discovering how much distance your inflated tire travels per rotation (22/7 times diameter) per rotations of cable in a 1/10 of a km or mile and then comparing it to the speedometer's number of cable turns required to get the odometer to change 1/10 of a km or mile...At least, then you will know how accurate the odometer is. I think the odo is generally more accurate than the dial-hand because it's mechanically driven and should be used over a measured mile if you really want to know how fast you are really going.Or use a gps.
I think most speedos for Japanese type bikes are the same, but there will be variation in the cable drive at the front wheel.

[Gorminrider]

I think most speedos for Japanese type bikes are the same, but there will be variation in the cable drive at the front wheel.

but today after swapping a stock speedo out from a bike with a 19" wheel to a bike with an 18" wheel, I might have this backwards! The gauge reads too fast so I might have to do the math myself now! argh