An explanation of it all ( I think ).

First, the Honda's I've seen lately have all got the 'speed sensor' on the front sprocket. It assumes that you have stock sprockets and stock tires. It even has to assume your stock tires are average size (as your tire wears it has a smaller circumference).

Basically what happens is that it counts how many times a second the front sprocket goes around. Each turn around means that with stock sprockets the rear tire turns a CERTAIN ammount. Then because you know the circumference of the rear tire you know that means the bike has travelled a fixed distance (assuming no rear wheel spin or slide) in a certain time - aka speed.

Now - this assumes you know EXACTLY how big the tire is. If you are off by a few mm then the speedo is off by a PERCENT. Yes percent. If the bike thought the rear tire had a 1 meter circumference but in reality it was 1.05 meters ( off by less than the width of your hand) it would be ~4.8% error STOCK.

When you change sprockets you change how far the bike moves forward for every rotation of the front sprocket. This is important. The reason the sprockets make your bike accelerate harder is the SAME reason that the speedo is off. We've made the engine turn more times to travel the same distance... basic pullys here. It's easy to do the same work, but just takes a bit longer (more revs).

Anyhow.

Say you had a 16-45 stock speedo setup. The ratio would be 0.355555556. If we convert to -1,+2 then the new ratio is 0.319148936 OR 11.41% shorter.

TRANSLATION? If you want to do 60 mph with this setup, the speedo must read nearly 67 mph.

The big problem here is that you're running the odo up - instead of reading 6000 miles at the end of the season it reads 6700. The next problem is that you're always guessing what speed you're going. For me I've rounded my error to 10%... so if I want to go 60mph I say 60 + 10% of 60 (which conviently is a simple divide by 10)... 66. Your number is likely different but you can now easily work it out.

Now that I've said all this - the solution is a product like the speedo healer. It takes the sensors input, 'fixes' it using the same math I've used here, and sends the speedometer/odometer the CORRECT figures. I also think it has a handy flip switch to convert a miles bikes to kilometers for crossboarder trips.

Cheers,
woot.

 

? Thread has gone dead...

My cornflakes are salty

 

kinda died after everybody said the same thing

and as far as your cornflakes bein salty id deck the milkman for leavin the jailhouse juice

 

how many times can you say
speedo is off
get a speedohealer

i can learn how to type it in chinese if you like

 

Some people need to know why they need a speedohealer

I need one too... perhaps speedohealer will sponsor us to promote their product. They can even put a decal on my bike...

 

they do come with a decal
i didnt put it on

 

i bet u cant

 

just wonderin...if takin a tooth of the front will decrease your top speed, then will addin one increase it?

 

www.rogueracing.org has a gearing calculator
when you change the sprocket tooth count in the calculator it gives you the theoretical mph at a given rpm
when you add to the front the top speed increases on the calculator so it should be possible

it will take longer to get there though

 

thanks