Has any one experienced or noticed their speedometer being off?

I was riding with a friend and we had thought both our bike’s speedometers may be off. It seemed we where going slower than everyone else. It was more noticeable at higher speeds (55-65 MPH). He hooked up his GPS and found we where averaging 5-7 MPH slower than the bike’s speedometers.

I was wondering if this is normal for all bikes or maybe DS. My friends Bike is a Suzuki while mine is am 08 KLR.

yeah it is normal. I have an 08 also and its around 5 mph off (slow). I have read several other threads about the same issue. I just look at it like I am speeding down the road, but am really going the speed limit

4-5 would be pretty much the norm for most bikes (all makes and types).. My brand new Wing is off by 3 at most speeds, and my KLR is off 4-5, depending on what tire I have in the front. My old V Strom was almost 7mph off at speed.

Well that answers my question. I didn’t know if it was just mine, KLRs, or dual sports that are off.

Anyone know what the cause is? I had guessed maybe tires.

Lawyers..
The companies don't have a problem with you getting a ticket if you think you're going faster than you are, but if it were the other way around and you were getting tickets for 60 when you're being told that you're doing 55, there's grounds for a lawsuit.

According to my GPS, mine is 3 MPH off. 60 would actually be 57.

3 MPH is not bad. I didn’t have a GPS on mine but the friend I was with said his read 5-7 MPH (55 on the bike’s speedometer was really only 48-50ish on the GPS). That seems to far off! I’ll have to get my GPS out to verify exactly what mine is doing.

Ratio was 10% on every bike I've owned.

I'll have to confirm all of this with my GPS now as well. It's always been done with vehicles pacing me.

I'll post some numbers from 10 to 80.

I kept forgetting, but remembered to check it out tonight.

GPS verified - The speedo is slow at exactly 10% ratio through the entire speedometer. I made sure to keep the speedo dead on at each line. Why any other KLR would differ from this is unknown. Different tires should not affect this ratio much at all because they are all similar enough, even the knobbies. Changing a sprocket would affect RPM, but not the speedo. Changing the front rim size would probably be the only possible factor. Even so it would continue to be a ratio and not just 3 or 5mph off through the entire speedo.

Bike = GPS = 10% Difference
20 = 18 = 2
30 = 27 = 3
40 = 36 = 4
50 = 45 = 5
60 = 54 = 6
70 = 63 = 7
80 = 72 = 8

I think 10% is about right. That’s about what I’m seeing.

Why can’t this be more accurate? I hate being off 5 mph or more at 55 - 60 mph. I have enough to focus on without worrying and calculating the speed.