Speedometer reads 8 mph off constantly

[95katanarider]

Hello guys I'm riding a 95 suzuki katana 600... It reads 8 mph off all the time. I've read that manufactures make it this way so that we don't speed all the time is this true? I've cleaned my speedo cable and lubed it and still the same any ideas with what's going on or is there nothing I can do about it because of the manufacture?

[arsenic]

You can do something about it, but it's a giant pain in the ass. You'd have to take the speedometer apart, and it's not supposed to come apart. In other words, for 8 MPH on a Katana, I'd give that a big "fuck that".

[95katanarider]

Yeah I'm gonna say fuck it and go 8 over all the time

[arsenic]

works for me

[92xjunker]

What tires are you running? Incorrect tire size, any tire size change has an effect on the speedo reading. Such as using 70 series instead of 80 series. Like going from a 110/80/17 to a 120/70/17, they aren't quite the same diameter and worn out tires will be smaller and will screw with the speedo also but, yes the speedo is off.

[95katanarider]

I'm not running stock tire size I'm running the pirelli sport demon 110/70/17 on it which is a slightly lower sidewall heighth I believe so with that in mind could that be my problem?

[92xjunker]

Well stock is 110/80/17 so definitely is part of your problem. If you lower the profile you go wider on the width to keep the diameter as close as possible. You should of used a 120/70/17

[arsenic]

the speedometer is still gonna be off anyway. Just ride your motorcycle.

[92xjunker]

Yeah, I agree, just me being anal.... or being an anal...

[95katanarider]

Ok guys I have one more question for you. The faster I go will it be more off?

[michelm]

It is a mechanical speedometer, so yes.

[MotorBikeMike]

Slightly....not by much though. Its based on a percentage scale I believe. I had a BMW that did this. It was reading 10kms faster then what I was actually doing. I had thought everyone just started driving faster every day for some reason. Then I checked my GPS on my cell. That's when I knew the speedo was out. I'm OCD when it comes to stuff being off. I bought a NAV and used the speed off of that to tell how fast I was actually going.