Spedo is 15 mph slow. WTF!

[MikeyZ]

Originally Posted by scottynoface

Stock is already off by 5-10% from the factory...

The way I read it was that it was fine before he got the chain and sprockets installed...

ah who cares? suck it up or get a DRD

[steves]

GPS is not an accurate representation of speed, although it's not common for a stock speedo to be off 10-15%.

Much of the GPS accuracy will reside in how good your receiver is.

GPS works by sampling, or taking readings over time. Most algorithims tend to calculate speed by measureing distance traveled in a straight line. most roads aren't perfectly straight. The other thing to take into account is movment along a Z axis. I don't know any GPS's that account for elevation when doing the speed calculation.

[cintidude04]

My zumo 660 does steve.

[MikeyZ]

Originally Posted by steves

GPS is not an accurate representation of speed, although it's not common for a stock speedo to be off 10-15%.

Much of the GPS accuracy will reside in how good your receiver is.

GPS works by sampling, or taking readings over time. Most algorithims tend to calculate speed by measureing distance traveled in a straight line. most roads aren't perfectly straight. The other thing to take into account is movment along a Z axis. I don't know any GPS's that account for elevation when doing the speed calculation.

I would assume one would test with a GPS by going straight down the highway and holding it at a steady number for a few seconds. It would get EXTREMELY close- close enough that nobody would ever notice.

[steves]

No it's not, and that's not the case.

I don't think I have data handy, but my Garmin allows me to download traveled route data and display it overlayed on a map. At higher speeds, your sample rate becomes smaller because it's more difficult to manage a lock on more than 2 birds.

So, what I've found is that in the overlaid map you'll see a "line" drawn between two points which represents the route, and the line does not follow the path of the road. GIS data for known entities such as highways is very good in almost all the commercially availibile mapping software.

Your interpretation of "good enough" may still be off by 5 or more percent, so it's not an accurate measure.

Originally Posted by cintidude04

My zumo 660 does steve.

It accounts for elevation change in the route details, but I highly doubt the speed calculation shown realtime does. I'd like to see that claim.

[MikeyZ]

Originally Posted by steves

No it's not, and that's not the case.

I don't think I have data handy, but my Garmin allows me to download traveled route data and display it overlayed on a map. At higher speeds, your sample rate becomes smaller because it's more difficult to manage a lock on more than 2 birds.

So, what I've found is that in the overlaid map you'll see a "line" drawn between two points which represents the route, and the line does not follow the path of the road. GIS data for known entities such as highways is very good in almost all the commercially availibile mapping software.

Your interpretation of "good enough" may still be off by 5 or more percent, so it's not an accurate measure.


It accounts for elevation change in the route details, but I highly doubt the speed calculation shown realtime does. I'd like to see that claim.

So you don't think if you went on x number of different highways and took your bikes speed versus the GPS speed, they would not be accurate?

Im talking on RT 95- Going 70 MPH (bike speed) for 20 or more seconds and looking at the GPS.

If GPS is not accurate, couldn't you say every way has its discrepancies?

[steves]

Radar is accurate because the hardware and sofware on the device is designed to account for the dopplar shift.

Every was DOES have it's own issues. I'm just arguing against using a generic GPS unit to "calibrate" your actual speed.

[astevens54]

Good post guys, I was just thinking about this very topic. So SpeedDRD or Speedhealer is the way to go if you want to correct speedo errors.

[il_ragazzo]

If you want to calculate your speed measure out a fraction of a mile. Hold a constant speed and use a stop watch to get how fast you traveled that fraction of a mile. Ergo your speed: distance over time.

Do this like 100 times, then take the average use that data to calibrate your speeding. It will be so accurate you wont care.

[christianguitarest]

fist, no there is not already a speed healer or another device equipped on the bike (darn, I like free stuff). Today I rode and tried real gps (not on my iphone) and found that Im only really 4mph off at 75. So I need to go 79ish to go 75. I think that my wife who I followed must have a led foot or misunderstood me when I said go 65 and maybe she went 75 in stead, the world will never no. But as far as I can tell Im off the factory 5%ish. Problem solved? On a side note I topped her out today, 147ish at redline angry engine mode, holy **** my pants batman!