[Rusted535]

Does anyone know why the cgt speedometer are so inaccurate?
Is it a quality issue or is something out of calibration.
I tested mine against GPS and it's 4-6mph slow.

[tooseevee]

Does anyone know why the cgt speedometer are so inaccurate?
Is it a quality issue or is something out of calibration.
I tested mine against GPS and it's 4-6mph slow.

     SO inaccurate? Are there ANY accurate cable-driven motorcycle speedometers? Before all this electronic interference we never paid any attention. Sometimes we compared with a buddy's car, but mostly not.

[Richard230]

My B5's speedometer varies from 2 to 6 mph fast.  It kind of depends upon what speed it is registering. It seems to become more accurate just as my bike runs out of breath.  When it indicates 80 the actual speed is 78 and when it reads 35 (as an example) the actual speed is somewhere around 30 mph.  I sure am happy that cops don't give out speeding tickets based upon Royal Enfield speedometers. 

[Adrian II]

The answer would be a genuine Smiths Chronometric speedometer, calibrated for the exact size of the tire on which your drive gearbox is located. The more recent digital Smiths instruments allow you to set up the calibration according to what you have fitted.

A.

[Rusted535]

 Ya I suppose your right. I never even checked all my old UJM bikes. Lol.
 Except once when I built up an old GS 850. The speedo stopped at 80mph so I ran it next to my buddy's sport bike. And I'm not sure his was correct either.
 I think it hurts my pride more than anything else. I was excited that I could pull the 535 up to near 80!! Only to realise it's only 69, by GPS.
 Oh well she's still a ton-o-fun to ride.
Thanks.

[Bilgemaster]

My old Norton daily driver of the '90s only had a speedo on there for show (i.e., state inspections). I once tried halfheartedly with a new drive and cable to get it to work, but its needle only just flew about merrily here and there, so I just pulled the cable and never again gave it a second thought. Given my sedate riding style it was never an issue.

As for my Bullet, given the oft-reported inaccuracy of their speedos on these Forums, I was fairly surprised to find mine pretty much spot on according to my GPS, at least with the original Avons. It must have been the only accurate speedo ever to leave Chennai. Now that it's wearing some far chunkier Dunlop K70s, I'm sure that's changed an mph or three, but I haven't bothered to check it against the GPS yet. Frankly, I only use it in concert with the engine sound to keep her thumping along in her happy places, where she runs sweetest and with the least commotion. For mine that presently seems to be at about 50, 54 and sometimes 59 mph when need be. As for avoiding costly interactions with law enforcement officers, with or without speedo, I'd say my chances of getting pulled over for speeding on my Enfield are about the same as my becoming Governor General of Samoa. But just in case, ladies and gentlemen, please stand for the Samoan National Anthem.

Gov. Bilgemaster, seen here in full official regalia,
receiving notification of additional dry cleaning
fees for both his and assistant  Skippy's (seen right)
outfits following what later became known in the
press as the "The Lu'au Cheezwiz Incident"

[kelsoo]

Checking with my GPS and those automatic speed display signs we have. Great fun by the way,  my speedo is consistently over reading from 3-4mph.   From 50 mph up it reads 4 mph over the actual speed.

[RedCGT]

My Ducati manual says the speedo reads 8% over the actual speed. I think it is due to government regulations. At 100 mph indicated it would be doing 92 mph actual. 50 indicated would be 46.

[Richard230]

I guess those "government regulations" don't apply to every motorcycle manufacturer.  My Yamaha FZ1, my Zero S and my Saturn station wagon all have speedometers that read within 1 mph of true speed.      Not so my two BMWs, Triumph, or my RE, though.

[Arizoni]

I think speedometers are designed to say your going faster than you actually are so your vehicle should never actually exceed the speed limit without your knowledge.

My RE's speedometer reads maybe 2-3 mph faster than the radar billboards around my area say I'm actually going.

[RedCGT]

I think it is a European thing. More accurately, a UN thing. Too much bureaucracy for me. There have been articles about accuracy in Car and Driver, etc.over the years. I think some manufacturers err on the extreme side of caution.

Here is a link to the regulation, with the specific text below:

https://globalautoregs.com/texts?rule_id=50

Regulation No. 39
UNIFORM PROVISIONS CONCERNING THE APPROVAL OF VEHICLES
WITH REGARD TO THE SPEEDOMETER EQUIPMENT
INCLUDING ITS INSTALLATION

5.3. The speed indicated shall not be less than the true speed of the vehicle. At the test
speeds specified in paragraph 5.2.5. above, there shall be the following relationship
between the speed displayed (V1 ) and the true speed (V2).

0 ≤ (V1 - V2) ≤ 0.1 V2 + 4 km/h

[Bilgemaster]

That's a hell of a find, RedCGT. My hat's off to you. That's some fine research.

I was browsing a little further through the various vehicle regs, particularly regarding motorcycle noise, and discovered that while the United Kingdom, by virtue of EU membership, agrees to abide by those regs, the USA is notably absent from the long list of countries that do, as is India. So, that's interesting.

[mattsz]

Regulation No. 39
UNIFORM PROVISIONS CONCERNING THE APPROVAL OF VEHICLES
WITH REGARD TO THE SPEEDOMETER EQUIPMENT
INCLUDING ITS INSTALLATION

5.3. The speed indicated shall not be less than the true speed of the vehicle.

If  it were the U.S. Coast Guard and U.S. Code of Federal Regulations we were dealing with, this statement would be crystal clear and leave no room for any other interpretation:  All our speedos that read low are in violation.

Opposite of what most of us understand, that the speedos are designed to read low so you won't unintentionally exceed the speed limit... 

[Richard230]

If  it were the U.S. Coast Guard and U.S. Code of Federal Regulations we were dealing with, this statement would be crystal clear and leave no room for any other interpretation:  All our speedos that read low are in violation.

Opposite of what most of us understand, that the speedos are designed to read low so you won't unintentionally exceed the speed limit... 

Who would do something like that?   

[mattsz]

Who would do something like that?   

Well, Arizoni said,

...so your vehicle should never actually exceed the speed limit without your knowledge.

But that's not exactly the same thing as "unintentionally exceeding the speed limit," so I'll just say: "Not me, nope, never!" and leave it at that...

[ace.cafe]

My CGT Speedo was right on the mark.

My 500 Bullets read at least 10mph faster than actual speed. And the needles wiggled around like mad.

[SSdriver]

My speedo said 90, and GPS said 88. So I'm surprised and happy.
Jimmy...

[Richard230]

My Bullet's speedometer reads between 3 and 5 mph fast, depending upon the speed.  Also the odometer measures more miles than I actually travel by about 3%.