Does anyone know for sure....

Where the gen 4 zx10s get their speedo reading from?
I had mine in the shop for a service this week and was going to go 1 tooth smaller in the front, but the service manager actually rang me and said that doing so would throw the speedo out. I told him that wasn't the case because it takes the reading from the front wheel.
He then rung me back an hour later and told me that he rung kawasaki and they told him it was taken from the front sprocket imput shaft.
So in the end, rather than telling him that he was full of shit, which i still think he is lol, just to leave it then.
Who was right??

I think your correct. I have read on other forums that I reads from the front and or rear wheel sensor. Besides I don't think there is a sensor on the counter shaft on the gen 4 anyway is there? I've gone -1 on my front and everything seems ok.

every other zx10r is from the front sprocket. Dont know why a Gen 4 would be different.

You may find that the front wheel sensor is for the traction and anti wheelie control.

My bet is the Mechanic is correct and you may owe him an apology

Hmmm
http://www.zx-10r.net/forum/showthread.php?t=103539

There isn't even a speedohealer listed on the healtech website for the gen 4s.

Hmmm
http://www.zx-10r.net/forum/showthread.php?t=103539

There isn't even a speedohealer listed on the healtech website for the gen 4s.

That's the forum I was referring to. There are a lot of other threads on there on the same topic all with the same answer.

It works off the rear tone wheel/ sensor (traction control) .

Oops mist that 10r net thing .