Inaccurate speedos in Canada - Page 4 - Yamaha FJR Forum : Yamaha FJR Owners Forums
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post #31 of 43 (permalink) Old 08-13-2019, 08:10 AM
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Well, now that you made me think of that, the conversion factor is roughly 1.6, so a US bike with 3% error would be 4.8 in kms. (reading 104.8 kph at 100 actual)??

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post #32 of 43 (permalink) Old 08-13-2019, 08:58 AM
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Quite simply it is manufacturing tolerances, US national calibration standards (NIST) for instrumentation requires the instruments used for calibration have to be less than 1% error of full scale, normal use instrumentation can vary from 5-10% of full scale (what’s the max capable reading for a fjr speedo?) so a 1000psi pressure gauge could be up to 100psi off, it’s just manufacturing tolerances, now most are considerably more accurate than the allowable tolerances and our law makers want those inaccuracies set so you think you’re going faster than you really are. Digital instruments make it easier to do this.

When I called and asked Garmin about what kind of inaccuracy is in their speed readout of their gps all I got was the legal jumbo-jumbo non-answer. It has some error in it but they won’t admit to any. All instruments have inherent inaccuracy at some point, add in the metric conversion factoring and it becomes very easy to understand why our canadien cousins think their bikes are faster,,,,, particularly the candy cow pie one’s ������.

Anyway there is no absolute accuracy in any instruments, particularly a production instrument like a speedo, and when you realize that a calibration instrument has up to the 1% of full scale error in becomes easy to understand how they can be off.
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post #33 of 43 (permalink) Old 08-13-2019, 09:17 AM
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Steve, in the OEM auto biz for my career, when the car/minivan/whatever is spec'd out with certain axle ratios and tires, there was in the older days a selection of speedo drive gears (cable driven speedos, later electronic pulse type). These days, it is a number programmed into the ECU or transmission controller, chosen by the engineers. I'm sure there are tolerances, but reasonably small.

Most car speedos today are pretty much dead on....
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post #34 of 43 (permalink) Old 08-13-2019, 11:19 AM
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Originally Posted by N4HHE View Post
What “manufacturing tolerances”? How difficult is it to hold tire circumference to 1% across all 180/55-17 tires?
And when people put something other than the OEM tire on?

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And that is heart of the problem. You learn the speedometer is lying and no longer trust. Then especially when you get in a different vehicle with a different error but muscle memory has programmed correction based on the first vehicle.
Odd that even though I've know about speedo error for 30 years, that's never been a problem. My Gold Wings were always 10% off (more delta the faster you went). Meh. Teapot tempests.
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Last edited by bounce; 08-13-2019 at 11:23 AM.
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post #35 of 43 (permalink) Old 08-13-2019, 12:20 PM
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And when people put something other than the OEM tire on?
How many tires does Bridgestone (the OEM) make in 180/55-17? Several.

Honestly, tire manufacturers do a good job making all 180/55-17 very close the same size.

"Can't fix stupid" but that doesn't limit government from trying. The European regulation is just that: +10% -0%. Pre-emptive mandated error in anticipation of use of larger tires upon replacement.

Since when is honesty no longer the best policy?

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post #36 of 43 (permalink) Old 08-13-2019, 05:37 PM
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All I know is that if FJR was a cash dispensing ATM machine, there would be 0 (zero) manufacturers + 5 , +10% margins/tolerances and other BS excuses...so there is a way to make accurate devices, but it seems liability lawyers decided it's better to calibrate bikes with big errors...but (being so smart) why did they allow to sell bikes capable of 300kph,...where on earth will somebody ride this fast on regular roads? Maybe they think that at 300, the actual speed will ONLY be 276kph so that's ok.
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post #37 of 43 (permalink) Old 08-13-2019, 07:34 PM
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I wonder if this difference is caused by unit conversion from miles to km's (when switching in the settings)...
I doubt it. An 8% error is an 8% error. It will not matter it is kph or mph.
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post #38 of 43 (permalink) Old 08-13-2019, 09:14 PM
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Originally Posted by Damir View Post
All I know is that if FJR was a cash dispensing ATM machine, there would be 0 (zero) manufacturers + 5 , +10% margins/tolerances and other BS excuses...so there is a way to make accurate devices, but it seems liability lawyers decided it's better to calibrate bikes with big errors...but (being so smart) why did they allow to sell bikes capable of 300kph,...where on earth will somebody ride this fast on regular roads? Maybe they think that at 300, the actual speed will ONLY be 276kph so that's ok.
What do you think is manufactured so sloppy as to incur 5% or 10% speed error?

Bridgestone lists the 180/55-17 BT023 as having 24.7 diameter. The T31 is 24.8. That is 0.25 MPH at 60.

The 190/50-17 T31 is smaller at 24.6 not available in GT.

The 190/55-17 T31 GT is 25.3, but not-GT is 25.4

From 24.7 to 25.3 at 60 MPH is 1.5 MPH. Is 2.5% for a whole increase in tire size. 5% speed error is deliberate, not accidental.

Useful reference: https://www.bridgestonemotorcycletir...tabook2019.pdf
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post #39 of 43 (permalink) Old 08-13-2019, 09:18 PM
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My understanding is that all bikes are optimistic by an average of 9%. I have found this to be true on every bike I have owned. I don't know why this is, but I thought it was more well known than it appears to be by this thread. I just use 10% which makes the calculation easy, or if on a trip I go by the GPS. For whatever reason, odometers are far more accurate. Like someone else said 130 is about 119, which the OPP usually will tolerate on the 401.

I had a speedo healer on my Bandit 1250 because I went down a tooth on the front sprocket. It included the ability to change the speedometer to read in MPH. It also (probably not intended) would increase the odometer in miles rather than km's. If I had wanted to I could have left it on MPH and it would have been accumulating miles instead so I would have had only 62% of the actual mileage showing. It did not convert those miles to kms when I switched it back to kms. I did not do that and when I sold the bike it had 189000 kms showing. I did do a trip to Rhode Island with it showing MPH, so it maybe should have had another 500-1000 or so on it.
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post #40 of 43 (permalink) Old 08-13-2019, 09:35 PM
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My understanding is that all bikes are optimistic by an average of 9%. I have found this to be true on every bike I have owned. I don't know why this is, but I thought it was more well known than it appears to be by this thread.

That's what surprised me too. It seems that people are over-thinking it.


BTW: Bridgestone isn't the only tire mfgr. Wanna bet they aren't all that with each other on exact copies.

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