Question about speedo variation

[VrUoLcCkAsN]

When I first came to this site I read many posts related to how the speedo is off for all of the Vulcans by anywhere from 6 to 10% and that I was actually going slower by that much than what my speedo read. I thought mine was off by about 9 to 10% due to an electronic speed/radar sign in one of the towns I pass through. The posted limit there is 35MPH and with my speedo at 40MPH it reads my speed as being 36MPH, a difference of 4MPH and almost exactly 10% off.

Well yesterday evening I was following my wife home and had previously asked her to go exactly 55 at a certain area so I could see what my speedo would read. With her at 55 my speedo read 59, a difference of 4MPH. I expected it to be reading at about 61 for the 10% to still be true.

It appears that I am just 4MPH off at any speed and not actually 10% as I had thought. Do any of you have a GPS and have compared your actual speed to the speedo with it at different speeds? Do you find that you are a % off or a specific amount?

[RichLockyer]

Cage speedometers are rarely dead-on.... and roadside radar signs are often quite inaccurate, particularly at picking up motorcycles.

The only accurate way to verify is with a GPS. A second way is to have a passenger count off mileposts using a stopwatch while you maintain a STEADY 60mph, but it's going to take 50-100 miles of that to get an accurate error indication... it's really only good for a ballpark.

Also, your odometer is running at about half the error of the speedo.


The error is a %, and it must be by virtue of the physics of how the unit works.

[A-J]

The speedo on my Ninja 250 was off by right about 10%,and so is the one in my truck. The speedo on my Ninja 650 is dead on compared to my GPS, buyt it reads it through the front sprocket (right?) and not at the wheel if that makes a difference.

[VrUoLcCkAsN]

Originally Posted by RichLockyer

The only accurate way to verify is with a GPS.

Thanks for the info Rich.

<Note to self: Get a GPS>

[mkelley]

Originally Posted by RichLockyer

The error is a %, and it must be by virtue of the physics of how the unit works.

Wouldn't a misaligned indicator needle give a fixed offset?

[flrbrddrggr]

Originally Posted by mkelley

Wouldn't a misaligned indicator needle give a fixed offset?

Yes. But the post is not about a misaligned indicator needle. It is about the inherent error in our (metric) speedo systems.

-Dwain

[VetteGuy]

The error lies in the digital to analog conversion in the speedo. My Corvette HUD speedo is dead accurate by GPS but the analog is off by about 3%. This conversion can yield a linear divergence (from actual speed) or it can have a non-linear divergence it just depends on the quality of the circuitry and the display unit (dial). The odometer is pure digital and will be linear and usually more accurate.

Thanks, Chris

[mkelley]

Originally Posted by flrbrddrggr

Yes. But the post is not about a misaligned indicator needle. It is about the inherent error in our (metric) speedo systems.

-Dwain

Well I got that, just pointing out that that there are sources of both relative and absolute errors!

[Sick Tom]

I got a 900 LT with the Scootworks front pulley and OEM tires,So not to many of us really know how fast we are going or what miles per gal we are getting, I thought I had it figured out at one point but gave up, it was to complicated!
Ain't that a Bit*h.

[RichLockyer]

Originally Posted by Sick Tom

I got a 900 LT with the Scootworks front pulley and OEM tires,So not to many of us really know how fast we are going or what miles per gal we are getting, I thought I had it figured out at one point but gave up, it was to complicated!
Ain't that a Bit*h.

Bingo.

Assuming that my speedo is off by 10%, and the odometer off 5%, then the 10% correction to the speedo ALSO slows the odometer by 10%, and puts it at 5% below actual.

So when I say that I'm getting 11-13k on a rear tire and getting 34mpg, I'm actually getting 11.5-13.6k on the tires and 36mpg actual, but compared to a bike with a stock speedo, they would be getting 12-16k on the tires and calculating 40mpg.
It also means that my odometer, which indicates that I have 34,500 miles on the bike, is off by 1,725 miles and I'm actually at around 36,225... a stock bike would be reading closer to 38k.

Also, larger tires and pulley changes have the same effect on the speedo and odo... so when you go to a larger tire, or change pulleys/sprockets, it will appear that you've lost MPG.

Every time I install new tires, I reset the Speedo-Healer to "passthrough" and run the bike up to 85-90 indicated and hold it there steady for a half mile or so and compare it to the GPS reading to get a solid correction factor, then reprogram the SH.

[powershotent]

I have a gps on my 2008 900LT. at speedo reading of 40mph doing 36 at 60 mph doing 54 at 70 mph doing 63..consistant 10% off(going slower than indicated). per kawasaki's guidlines up to 10%off is not covered under warranty.
If I want to run actual 75mph speedo has to be around 83mph..lots o' vibration then. Sorry guys..fed up with my cruiser..ditchin' it next year for a concours 14

[powershotent]

why pay big bucks for a bigger cruiser and have to get a better seat..lowers..exhaust..intake...risers...etc...etc ...etc... to make it comfortable. tired of wasting my money on something that will never be right.

[anarkust]

Originally Posted by powershotent

If I want to run actual 75mph speedo has to be around 83mph..lots o' vibration then. Sorry guys..fed up with my cruiser..ditchin' it next year for a concours 14

No vibrations on my 900 classic at 80+mph.

[powershotent]

Originally Posted by anarkust

No vibrations on my 900 classic at 80+mph.

Then i have a P.O.C. and i' am getting rid of it. Not one ore penny to try(and fail) to make it right..that is just in my case and in no way represents the opinions or real life experiences of other 900 riders

[vulcan_dude]

I have a gps, and my speedo is pretty accurately off by just over 6% at all speeds.