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post #1 of 24 Old May 7th, 2009, 9:13 am Thread Starter
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speedo vs. gps speed

greetings

new LT rider (00 LTC) (see avatar)

been riding dirt/enduro for a long time, and HD for the past 5 years... I'm happy I made the upgrade, this is one nice ride


anyway, I noticed that my speedo reads higher than the GPS speed. The GPS speed seems to better match traffic. Also, GPS in my car seems to be pretty close to that speedo.

other than measuring against a fixed distance (I haven't seen one of those roadside in a long time) what can I do to check it out, is there a 'calibration' that can be done?

roadside radar also favors the gps speed vs speedo.

'00 K1200 LTC
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post #2 of 24 Old May 7th, 2009, 9:17 am
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Re: speedo vs. gps speed

Most speedos, including the one on the LT, run a little fast by design for a variety of legal reasons. The LT speedo for your year range bike (99 - 04) are known to run 7-9% faster than actual speed. Your GPS will reflect the more accurate speed in most conditions.

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post #3 of 24 Old May 7th, 2009, 10:31 am
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Re: speedo vs. gps speed

There is a way to correct the speedo, and it's documented in the Hall of Wisdom (under Technical ^^ up there). It requires you take off most of your lady's garments though, so best done when the covers are off for other work. The fix involves adding a jumper on the speedo.

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post #4 of 24 Old May 7th, 2009, 10:31 am
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Re: speedo vs. gps speed

Yeah...BMW speedo's are notorious for reading under the actual speed. BTW, there's a fix fo it on this site...do a search. Also I believe GPS can only give you correct speed on a straight road since it reads distance (and thus speed) "as the crow flies." But most of the deviation you're seeing is in the speedo.

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post #5 of 24 Old May 7th, 2009, 11:11 am
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Re: speedo vs. gps speed

After I fixed mine, the two readings are within 1 MPH of each other. Your mileage computer uses a different input so it is unaffected by the speedometer error. It's nothing to worry about unless you just want it to be accurate like I did.


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post #6 of 24 Old May 7th, 2009, 11:44 am Thread Starter
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Re: speedo vs. gps speed

thanks for the info, I found the reference above


fwiw; my speedo reads about 9-10% above gps above 40 mph, a bit lower under it.

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post #7 of 24 Old May 7th, 2009, 11:53 am
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Re: speedo vs. gps speed

Your GPS is extremely accurate and should be your guide unless you undertake the speedo mod which, to me seems unnecessary. After riding for while with the GPS, you get used to making the speed adjustment as second nature when you glance at the speedo..
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post #8 of 24 Old May 7th, 2009, 11:58 am
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Re: speedo vs. gps speed

That pretty well covered the speedo...................welcome to the bright side ...
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post #9 of 24 Old May 7th, 2009, 12:11 pm
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Re: speedo vs. gps speed

It's ticket insurance.

My Suzuki was the same way, also confirmed by GPS. I'm just used to making the correction in my head above 40 mph and "riding" about 5 mph faster displayed on the speedo than the posted speed. For example if the limit is 65, I'll run at 70 or just above (on the speedo) so that I'm doing 65.

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post #10 of 24 Old May 8th, 2009, 9:23 am
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Re: speedo vs. gps speed

Hi , there is a quick way to check your speed . When you get up to speed , set your cruse control . Then put your computer to MPH , & at a steady speed , push the reset button . The computer will tell you your speed at that time . The computer uses the input from the odometer , So It is ... time X distance .... My mileage computer says around 55 , and the speedo says 60 . Hope this is of help .

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post #11 of 24 Old May 8th, 2009, 6:32 pm
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Re: speedo vs. gps speed

Quote:
Originally Posted by DavidTaylor
Most speedos, including the one on the LT, run a little fast by design for a variety of legal reasons. The LT speedo for your year range bike (99 - 04) are known to run 7-9% faster than actual speed. Your GPS will reflect the more accurate speed in most conditions.
I've read this often, but never seen any evidence that supports this. What legal reasons? If this is a legal issue, how does Harley get away with providing accurate speedometers?

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post #12 of 24 Old May 8th, 2009, 6:38 pm
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Re: speedo vs. gps speed

Quote:
Originally Posted by Reid
Yeah...BMW speedo's are notorious for reading under the actual speed. BTW, there's a fix fo it on this site...do a search. Also I believe GPS can only give you correct speed on a straight road since it reads distance (and thus speed) "as the crow flies." But most of the deviation you're seeing is in the speedo.
You will see no detectable error in most curves. Most GPS receivers update at least once per second and most new ones are several times per second. Even once/second is once every 88 feet at 60 MPH. In most turns that you can take at 60 MPH, the chord distance difference from the arc distance is pretty small.

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post #13 of 24 Old May 8th, 2009, 6:53 pm
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Re: speedo vs. gps speed

Yup, my speedo is 8% over stated. At 80 mph on the speedo I'm actually doing 73.7 mph according to the police officer and my "BC". Imagine my pleasant surprise.
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post #14 of 24 Old May 9th, 2009, 9:13 am
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Re: speedo vs. gps speed

My K12LT like my Suzuki did reads hight on the speedo but the odometer reads accuratlely.

It's not that Harley gets away with having accurate speedometers, it's just that they do it. From what I've heard on numerous forums of different manufacturers is that the error is intentional.

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post #15 of 24 Old May 9th, 2009, 5:23 pm
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Re: speedo vs. gps speed

As far as I know, the "optimistic" speedometer is a constant on European cars and bikes, all speedos somehow show and higher speed than the real one.

The point is the following: it's not allowed by law, that your speedo fails on the "pessimistic side" (i.e.: telling that you're going slower than your real speed) because that would let you travel faster than the speed limit, without you knowing that.
The law includes the mechanical/electronic tolerances, and must also count eventual variations inducted by a different tyre shape (and different tyre size, if allowed in the vehicle options). So, the "centre point" of the speedo setup is made higher than it should, so that it never happens that it goes lower.

The fix in the hall of wisdom is probably removing this higher setup and reverting to the zero centre point... at your own risk though.

Both my BMW car and the LT show 136 Kmh on the tachometer and on the cruise control (digital, for the car) when I'm actually travelling at 130Kmh (legal speed), so it's an error of about +5%

Trust your GPS, it's usually very accurate for the speed. We have roadside signs every 1km exactly and I used them once to check the GPS... it turned out to be 100% accurate.

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post #16 of 24 Old May 9th, 2009, 6:27 pm
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Re: speedo vs. gps speed

Quote:
Originally Posted by Voyager
I've read this often, but never seen any evidence that supports this. What legal reasons? If this is a legal issue, how does Harley get away with providing accurate speedometers?
There is no legal reason for them to report high, its the requirement that they *never* read low. The pre-2005 LTs were about 8% optimistic and the 2005 and later were about half that. The newer BMWs that I own are more in the neighborhood of 1-4% optimistic. I ride with two riders on Harleys - a Road King and an Ultra and both of their speedometers are more optimistic than my GS and about the same as my GT.

The only "legal" reason for making the speedometer optimistic is to avoid the penalty that exists if the speedometer reports any less than the actual speed.

My new VMax reports about 6-7% high.

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post #17 of 24 Old May 9th, 2009, 8:29 pm
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Re: speedo vs. gps speed

Quote:
Originally Posted by Randy
There is no legal reason for them to report high, its the requirement that they *never* read low. The pre-2005 LTs were about 8% optimistic and the 2005 and later were about half that. The newer BMWs that I own are more in the neighborhood of 1-4% optimistic. I ride with two riders on Harleys - a Road King and an Ultra and both of their speedometers are more optimistic than my GS and about the same as my GT.

The only "legal" reason for making the speedometer optimistic is to avoid the penalty that exists if the speedometer reports any less than the actual speed.

My new VMax reports about 6-7% high.
I've heard of such laws in Australia and Europe, but haven't seen that law in the US. Do you have a reference to it?

The interesting part is that my automobiles are almost always within 1-2 MPH of my GPS whereas every motorcycle I have ever owned is off by 8-10%. Is this law only applicable to motorcycles?

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post #18 of 24 Old May 9th, 2009, 9:10 pm
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Re: speedo vs. gps speed

Quote:
Originally Posted by Voyager
I've heard of such laws in Australia and Europe, but haven't seen that law in the US. Do you have a reference to it?

The interesting part is that my automobiles are almost always within 1-2 MPH of my GPS whereas every motorcycle I have ever owned is off by 8-10%. Is this law only applicable to motorcycles?
I'll see if I can find the reference, my recollection is that the standard is within a percentage (10%??) +2 mph over is OK but under is not. I have seen and heard this reported on a number of occasions, but I am not sure I have seen it on an "official" NHTSA or government site.

Likewise I was told that the EU standard is "the indicated speed must not be more than 110 percent of the true speed plus 4 km/h". Both the US and EU standards are applicable within a specific range of speeds.

Regulations notwithstanding, it is perfectly understandable what an attorney could do with an under reporting speedometer in the case of an accident. Conversely it would be more difficult to argue that an accident was the result of a vehicle going slower than its speedometer would indicate.

Years ago I had a link to the US standards, If I can find it I will post it.

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post #19 of 24 Old May 9th, 2009, 9:23 pm
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Re: speedo vs. gps speed

It's a German thing. My speedo agrees with the GPS up to 20 mph then the speedo takes off. By 30 on the GPS the bike is reading 33 and that that 3 mph bias exists all the way to 80 mph on the speedo. My Dodge Durango (under the development of Daimler-Benz) shows exactly the same bias in the same range. As indicated previously the issue is that in die Faderland it is Ok to read too high but a major problem to read too low...so programming a 3 mph bias into the speedo is a safe bet. I have a BMW 4 wheeler on order that I expect will do the same thing.

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post #20 of 24 Old May 10th, 2009, 5:01 am
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Re: speedo vs. gps speed

Quote:
Originally Posted by Duane_in_Florida
It's a German thing.
Surely not only German, as I've driven several European made cars (BMW, Fiat, Alfa, Opel, Renault, ...) and they all do the same.

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post #21 of 24 Old Sep 20th, 2009, 4:44 pm
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Re: speedo vs. gps speed

Has it been found that this fix corrects speedos in the 2009 era? K1300GT suspected of reading about 5mph low at 30mph. I have to find a GPS to test or try the OBC Cruise method.
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post #22 of 24 Old Sep 20th, 2009, 4:58 pm
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Re: speedo vs. gps speed

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Originally Posted by Duane_in_Florida
It's a German thing. .
My old Yamaha speedo also read high by about the same ratio, as does my friends Yamaha Road Scar.
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post #23 of 24 Old Sep 21st, 2009, 12:54 pm
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Re: speedo vs. gps speed

yup and it means your odo will be off as well. An BTW now you know how those guys get 50 mpg. haha
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post #24 of 24 Old Sep 22nd, 2009, 12:23 am
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Re: speedo vs. gps speed

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yup and it means your odo will be off as well. An BTW now you know how those guys get 50 mpg. haha
Nope.

The odo doesn't suffer of the problem.

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