Gearing vs Indicated Speed
Gearing vs Indicated Speed
This is for you gearing calculating Guru's. 2007 FLHTC
Out on the highway my sister in law came around me like her *** was on fire. When I asked her what her hurry was, she said I was only going about 63 mph. My indicated speed, on cruise, was 70. My wife says her sporty is showing 65 when my bike says 70.
On my way home I made some checks:
60 MPH, 5th gear, 2500 RPM
60 MPH, 6th gear, 2000 RPM
70 MPH, 5th gear, 3000 RPM
70 MPH, 6th gear, 2450 RPM
The only changes I've made to the driveline is a SE Compensator. The computer has never been plugged into, the bike is stone stock.
Is there something wrong with the calibration of my speedo?
Out on the highway my sister in law came around me like her *** was on fire. When I asked her what her hurry was, she said I was only going about 63 mph. My indicated speed, on cruise, was 70. My wife says her sporty is showing 65 when my bike says 70.
On my way home I made some checks:
60 MPH, 5th gear, 2500 RPM
60 MPH, 6th gear, 2000 RPM
70 MPH, 5th gear, 3000 RPM
70 MPH, 6th gear, 2450 RPM
The only changes I've made to the driveline is a SE Compensator. The computer has never been plugged into, the bike is stone stock.
Is there something wrong with the calibration of my speedo?
Grand HDF Member
Joined: Jan 2012
Posts: 4,459
Likes: 2,896
From: Oklahoma
Speedometer error is a common complaint. Since your machine is stock, chances are good you have a speedo near the max error and the Sporty in question may be near the minimum or even read a little slow. The speed signal is generated in the output side of the transmission, a certain number of pulses equals a certain speed. The ratio of engine rpm to transmission speed output is fixed by the primary ratio and since yours is stock, your error is in the speedo. What ever gear you have selected makes no difference to the output side of the transmission, the output rate of rotation generates the speed signal, not what gear you have selected. The owner can change the belt drive pulley, the wheel pulley, or both and alter the rear wheel speed vs the transmission rpm ratio. If the transmission now spins faster for a given speed than it did before the pulley change, the speedo will read too fast. Things used to be easier when the speedo was driven off the front wheel. The owner could change the drive any way he wanted but the speed would remain accurate, as long as the circumference of the front wheel remained unchanged.
Either do a GPS check of your speed indication or pay attention to any RADAR speed signs you may encounter to give you an approximation of your speedo accuracy. While the speed output of the transmission is digital, the speedo itself is still just a meter made with engineering and manufacturing tolerances which may cancel each other out or accumulate in one direction. It appears in your case, the tolerances accumulated to give a higher than actual speed indication.
There are variations in car speedometers also, but they don't seem to generate the same interest as shown by the Harley set.
Either do a GPS check of your speed indication or pay attention to any RADAR speed signs you may encounter to give you an approximation of your speedo accuracy. While the speed output of the transmission is digital, the speedo itself is still just a meter made with engineering and manufacturing tolerances which may cancel each other out or accumulate in one direction. It appears in your case, the tolerances accumulated to give a higher than actual speed indication.
There are variations in car speedometers also, but they don't seem to generate the same interest as shown by the Harley set.
Last edited by btsom; Dec 9, 2012 at 02:53 PM.
Outstanding HDF Member
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From: Western Illinois, land of bad roads, and corrupt politicians
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Road Master
Joined: Jan 2011
Posts: 855
Likes: 6
From: Riverside, Ca.
my 07 FLH reads 3 to 4 mph higher on the speedo compared to the police speed warning units they put on the street. It's been consistant that way from one city to the other. A little irritating but on the other hand gives you a little cushion
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Joe Kucinski
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
You can get as close as we can ever get using a gps, which will tell you your actual speed, so you can compare your speedo while riding. My understanding is that manufacturers are required to make speedos +zero, - 5% accurate. That means they will usually be slow. We have had several threads on this subject!
I reckon your wife is just winding you up! Sporty owners can be like that.....
I reckon your wife is just winding you up! Sporty owners can be like that.....
