Speedo Accuracy
Seasoned HDF Member
Joined: Jul 2007
Posts: 6,336
Likes: 67
From: SW Minnesota
Here is the link to the Dakota Digital product to fix this issue.
http://www.dakotadigital.com/index.c...rod/prd238.htm
It plugs right into the harness on '06 and earlier models. According to a reply another poster received, it would work on newer ones but would have to be spiced in to the harness.
http://www.dakotadigital.com/index.c...rod/prd238.htm
It plugs right into the harness on '06 and earlier models. According to a reply another poster received, it would work on newer ones but would have to be spiced in to the harness.
Road Captain
Joined: Jun 2008
Posts: 578
Likes: 0
From: Florida Gulf Coast
Yep...mine is the same way. I pass one of those police speed box thingies that the po-po puts in the median of the road and I am always going slower than my speedo says. Probably has saved my butt from getting a ticket once or twice.
Thread Starter
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Extreme HDF Member
Joined: Oct 2008
Posts: 15,321
Likes: 29
From: Phoenix, Arizona
One of the responses was that the speedo is certified to be within 7% accuracy so if it reads 65 your actual speed could be anywhere from 60.5 to 69.5mph and still be within spec.
For most it looks like the speedo indicates 3-4mph higher than actual speed.
No need to spend $ to fix it, I'll just keep it in mind and adjust mentally.
For most it looks like the speedo indicates 3-4mph higher than actual speed.
No need to spend $ to fix it, I'll just keep it in mind and adjust mentally.
Stage III
Joined: Nov 2008
Posts: 3
Likes: 0
I've made a habit of measuring my (and my friends') vehicles with GPS. I haven't done my '07 Harley (haven't figured a good way to temp mount my GPS yet), but it feels slow. If it's 3mph slow, that's OK, but if it's 6mph slow, I will want to fix it.
I'm new to HD, but, a few years ago, I used to routinely read some of the more "rice-o-centric" mags, and they always measured speedo error when they reviewed. Bike speeds were typically slow by 2-3mph@30 and 3-6mph@60.
Tale of the tape (at 60mph - via Garmin 76sMap GPS unit):
'07 Ford F150 - Perfect
'03 Nissan Sentra - 2-3 mph slow
'05 Audi S4 - 2-3 mph slow
'98 Toyota 4Runner - 3 mph slow
'98 Toyota Corolla - 3 mph slow
'92 BMW K75 - 4 mph slow
'96 BMW K1100 - 10% slow (typical of model as delivered - has trim pot for adjustment)
I'm happy with 2-3mph slow. Saves me grief. I'm always having to be extra careful in my Ford.
I'm new to HD, but, a few years ago, I used to routinely read some of the more "rice-o-centric" mags, and they always measured speedo error when they reviewed. Bike speeds were typically slow by 2-3mph@30 and 3-6mph@60.
Tale of the tape (at 60mph - via Garmin 76sMap GPS unit):
'07 Ford F150 - Perfect
'03 Nissan Sentra - 2-3 mph slow
'05 Audi S4 - 2-3 mph slow
'98 Toyota 4Runner - 3 mph slow
'98 Toyota Corolla - 3 mph slow
'92 BMW K75 - 4 mph slow
'96 BMW K1100 - 10% slow (typical of model as delivered - has trim pot for adjustment)
I'm happy with 2-3mph slow. Saves me grief. I'm always having to be extra careful in my Ford.
Last edited by mainesails; Nov 9, 2008 at 07:16 PM. Reason: Forgot to add ..
Outstanding HDF Member
Joined: Jul 2007
Posts: 2,609
Likes: 1
From: Indy area
GPS is only very reliable when you're going in a straight line at steady speed. As was noted previously, it'll read low while in a curve, and even at that, the positional accuracy ain't that great anyway on consumer-grade gear.
There's no real need to get the Dakota whatever if you've got plans to tune your Delphi EFI anyway. The TTS tuner has a function for altering the speedo calibration internally to the ECU.
Unless you've done something to your wheels/tires/gearing, you should never indicate a speed slower than you're going. That's international standards type of stuff.
There is likely two separate indicator errors at work here. First is the offset from zero when not moving (mine shows a mile or so high). This will be a constant-at-all-speeds indicator error. The second one is relative to the indicated speed and will be a steady percentage. If it causes 3 mph less road speed indication at 60, it will be 1.5 mph less at 30, 4.5 mph less at 90, and 6 mph less at 100, etc.
All this stuff is such a non-issue; really.
When I want to check the calibration of my speedometer(s) I use a well-(mile-)marked stretch of road and my trusty HP-48 calculator. It operates at about 1.2 megaHertz and with it I can time the average speed since the last time I pushed the button I have the program assigned to. Lock it on cruise and record a few miles. Done deal. Using stock tires/pressures I average about 63/64 mph indicated to achieve 60 mph actual over all the vehicles I've owned over the past dozen years or so. I think two-lane state roads are best since I believe the mile markers are placed on tangents to the centerline of the entire roadway. If you're on a divided highway which predominantly curves one way or the other, your actual distance travelled will not match what's in the middle of the median (what's indicated on the signs).
There's no real need to get the Dakota whatever if you've got plans to tune your Delphi EFI anyway. The TTS tuner has a function for altering the speedo calibration internally to the ECU.
Unless you've done something to your wheels/tires/gearing, you should never indicate a speed slower than you're going. That's international standards type of stuff.
There is likely two separate indicator errors at work here. First is the offset from zero when not moving (mine shows a mile or so high). This will be a constant-at-all-speeds indicator error. The second one is relative to the indicated speed and will be a steady percentage. If it causes 3 mph less road speed indication at 60, it will be 1.5 mph less at 30, 4.5 mph less at 90, and 6 mph less at 100, etc.
All this stuff is such a non-issue; really.
When I want to check the calibration of my speedometer(s) I use a well-(mile-)marked stretch of road and my trusty HP-48 calculator. It operates at about 1.2 megaHertz and with it I can time the average speed since the last time I pushed the button I have the program assigned to. Lock it on cruise and record a few miles. Done deal. Using stock tires/pressures I average about 63/64 mph indicated to achieve 60 mph actual over all the vehicles I've owned over the past dozen years or so. I think two-lane state roads are best since I believe the mile markers are placed on tangents to the centerline of the entire roadway. If you're on a divided highway which predominantly curves one way or the other, your actual distance travelled will not match what's in the middle of the median (what's indicated on the signs).
Road Warrior
Joined: Sep 2006
Posts: 1,826
Likes: 87
From: Cookson, Ok
Met an OHP last week and glanced at my speedo. Showed 65MPH. Got several miles down the road and there he was behind me with his lights on. Wrote me a warning for 74. Guess I'll have to find someone with a GPS to make some adjustments.
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Road Master
Joined: Nov 2006
Posts: 1,227
Likes: 3
From: Central Illinois
All Harleys speedo's are certified. A certified speedometer for manufatures must be within -4 mph of actual speed. The exception is Road King and Cop speedo's. They are -2. Commercial GPS is I think within 5 feet now. Military is closer. That could lead to a small variance. I would say the GPS is probably closer to actual speed.
Last edited by Gutman; Nov 10, 2008 at 03:53 PM.