Speedo Question

[crazyaussie]

Alright, here's the deal. When I drive to work I go 75mph (both on my bike and in the car). When I drive the car I don't really get passed by other motorists (speed limit is 65 and 70 in some spots), but when I'm on my bike I get past by almost all the cars (even some semis). I suspected that my speedometer is misreading, so I performed a little test. I had my brother-in-law drive next to me in his car. The results are as follows:

While side by side, we signaled to increase to 40 mph. At 40 we stayed even with each other. After getting on the freeway he signaled to go 75. While we started out side-by-side he started to pull away and gradually built up his "lead." I had to go about 80-85 just to catch up.

Has anyone noticed their speedometer giving mis-reads? Is this a calibration issue? Can anyone explain this phenomenon to me? I read somewhere that the factory speedometer can be off by as much as 10%. Thanks for the help.

[mrock]

I hear "they" set the speedometer back, so you are not going as fast as you think...of course it may not be a conspiracy...what do others think?

[trinc]

the speed-o is hard to keep really accurate as your tire wears down. you can get a speedohealer or a yellow box which will get it pretty close.

if you change the gearing it will really throw the speedo off ( and the odometer ).

i like the speedohealer 'cause it has a button to report your top speed


tim

[katman05]

mrock said

I hear "they" set the speedometer back, so you are not going as fast as you think...of course it may not be a conspiracy...what do others think?

SHHHH.. they might be listening, seriously though, I've tried the same experiment and mine is off @ 10% or so.

[Black_peter]

I took m GPS on my last ride..
From 25-40 it was good, anything over 45 it was off.
I think (hard to look at two displays and the road ) that it was as far as 8 MPH over 60..
GPS recorded a max of 68 but I know the speedo was over 75 at one time..

[Anonymous]

I don't wear speedos...

[katana91]

yea i usually have to cruise at about 85-90 on the freeway to stay with the flow of 75-8 mph trafic and the copes dont look twice at me so i must not really be going that fast.
I know mines off once i get above 50mph b/c when my speedo shows 110mph im really only going like 95mph<<tested with a gps tracker and a friend who works for the police with the radar gun, speedo said 100 his gun only said 89

[katana bob]

I hear "they" set the speedometer back, so you are not going as fast as you think...of course it may not be a conspiracy...what do others think?

i heard the same thing.