Double post

 

Liability - there's a fair amount of variance - tire size, wear, inflation, HD and car companies want to stay clear of showing that you are going slower than you actually are.

Its similar to gas gauges - better to say you are empty when you are not, vs saying you have fuel, when you dont

 

If this is true, does anyone know why?


Mine seems to be 2-3 MPH too fast at 60. I guess if many others experience the same thing, my question is why?


It's too fast on my bike which is new. So once my tire wears more, it will spin more per equal distance, as it will have a smaller diameter. The more spins per distance should make the speedometer register even faster, thus making the MPH report even more fast. Am I understanding this right?

 

There are those that will say that a speedometer that is optimistic (reads higher than actual ground speed) will not effect the odometer. A few years back a few friends and I did some testing of various bikes that had optimistic speedos.

Each bike that was optimistic reported a mile travelled on the odometer short of a measured mile. They were all short the percentage the speedo was off. Testing was done at an Ohio vehicle testing facility and the measured miles were just that; measured.

Erorring on the side of caution is the excuse the factories give for such a variance but in truth it allows them by law to duck on as much as 10% of the vehicle warranty.

There are those that say the speedo, vehicle speed sensor and the odometer do not function interdependently. I call bullshit.

 

I've got a Dakota digital module that will correct the speed. New $75 shipped
The SIM-1 electric speed correction module will plug into newer speed sensor harnesses to correct the speedometer and odometer after a change in tire size, pulley size or transmission gearing. The unit plugs directly between the stock Harley transmission sensor and the original speedometer and is easily tucked away into the bike's wiring harness after adjustment is complete.

With factory Harley connectors, no cutting or splicing is required.
Two push button switches allow the original speedometer reading to be increased or decreased easily.
Ability to correct the speed to within 1 MPH or KPH from 50% t 284% o the original reading.
Sealed completely from water, dust, and dirt.

The new SIM-1 comes in a smaller size for easier mounting and allows more correction for calibrating more bikes.

Fits Harley Davidson models:

1995-2003 Sportster Models
1996-2006 Softail Models
1996-2005 Dyna Models
2006 and earlier Touring models with Factory Electronic Speedometer
2007+ Harley models require hardwiring into stock harness, speed correction can be made up to Harley's factory margin of error, typically 3-5% from correct mileage.

Part # SIM-1
Normal Retail: $114.95

**Please note that all photos are for REFERENCE ONLY, please read description for full details. Part numbers are as sold from manufacturer.

 

Is this something the dealer could fix?

 

There is no fix.
There is no speedometer that can recalibrate and be right all the time.

A new stock tire (0 miles) is 25" tall, when worn (13,000 miles) is 24.5" tall.

For reference just know that the difference equals about 3-3.5 mph error on your speedo. If it is half worn (6000 - 7000 miles), it is probably 1.5mph off.

Until there come out with a speedo that resets mileage at tire exchange, it is just going to be this way.

 

Among other benefits, my DJ Power Vision allowed me to address the fast speedo issue quickly. Brand new bike - speedo was off by > 5%. Adjusted the calibration via the PV software, along with some other tune tweaks, and then re-flashed the ECM. I'm still about 1% off, but for now it's close enough not to bother me too much.

 

The PV and TTS can calibrate the speedometer, but I was told by a Harley tech that SESPT, SEPST, and Digital Technician (dealer software) cannot. My speedo was 4% fast in stock form based on the MPH values given by my Zumo. The stock calibration value for my '07 was 2058 and 2150 put the speedo dead even with my Zumo. I don't know if these numbers coincide with those for newer bikes, but it's a reference. Notice that these two values are about 4% apart, so I think using that calculation as a reference will be a good starting point.