Speedo inaccuracy stats

[imdying]

Thought this might interest some, stolen from here (http://www.nzherald.co.nz/sideswipe/news/article.cfm?c_id=702&objectid=10623459).


Tony writes: "Autocar magazine use fancy equipment to test the speedo accuracy when they test cars. In the January 2010 issue they measured the actual speed when the speedo indicated 100. The actual speeds on 12 cars were 98, 97, 98, 97, 96, 97, 97, 91, 96, 97, 99, 93.5, 96 95 (the last two were motorbikes). This is always the case. Speedos always read too high. Maybe it's a legal requirement. Incidentally, speed cameras are not accurate. They have a margin of error of 2km/h (ask for a copy of the calibration certificate). When I got a speed camera ticket for doing 61km/h, I went to court to argue that my actual speed may have been 59km/h. They agreed and reduced my fine from $80 to $30. But I'll never do that again. I still had to plead guilty to the charge in front of a room full of people - somewhat humiliating. And they slapped me with $30 court costs."

[Blackbird]

Interesting! I recently checked the Striple against my GPS and at an indicated 100, the GPS was reading 95.

[crazyhorse]

In todays world, you would think they could get accuracy sorted :done:

[MSTRS]

It's not a case of that. It is (perhaps urban legend) that auto makers build in that inaccuracy, so that there is a margin of error for the driver/rider.

[p.dath]

It's not a case of that. It is (perhaps urban legend) that auto makers build in that inaccuracy, so that there is a margin of error for the driver/rider.

It's a European requirement that an error is built in (they also have a big formula specifying the error). At 100km/h the maximum permissible error is about 12%, so manufacturers usually make the error 6% to give them a little leeway.
The European law basically says that the vehicle is never allowed to be travelling at a speed faster than that reported.

Other countries, like Australia, report the average speed reported. So when a V8 Holden says your doing 100km/h, then you pretty much are.

[kwaka_crasher]

In todays world, you would think they could get accuracy sorted :done:

Yeah, once tyre wear becomes a thing of the past...

[steve_t]

Other countries, like Australia, report the average speed reported. So when a V8 Holden says your doing 100km/h, then you pretty much are.

Nope. V8 Holdens also have around an average actual speed of 96 when indicating 100 km/h, however, it can be altered if you get the car tuned. And of course it changes if you change the wheel dimensions

[slofox]

I have tried measuring distance (according to odo) over time at a constant indicated speed on the speedo, usually on the Southern Motorway - not that easy in practice, but for what it's worth, I found:-

SV650S 107 on clock = 100 in fact (ish)
Subaru Lancaster 104 on clock = 100 in fact (also ish)

Have not yet checked against a GPS doohicky.

[Leviticus]

Ford also have certain models that have an inaccuracy built in. The Ranger model built in Asia has a 10% deviation as required by their laws, so all models even exports have this as standard. For all you Ranger owners, this inaccuracy can be removed, but would mean the speedometer would need to be re-calibrated.

[YellowDog]

I understand that the manfacturers deliberately show the speed lower than the actual to reduce the chance of them being sued.

Changing your rim/profile size and the accuracy changes + or - again.

[imdying]

I have tried measuring distance (according to odo) over time at a constant indicated speed on the speedo, usually on the Southern Motorway - not that easy in practice, but for what it's worth, I found:-

SV650S 107 on clock = 100 in fact (ish)Here's something for you... your speedo is out, but your odometer won't be ;)

[slofox]

Here's something for you... your speedo is out, but your odometer won't be ;)

True. I have checked the odo out against the measured test sections on motorway - it is accurate to within a couple of metres over 5km...

[quickbuck]

Yeah, once tyre wear becomes a thing of the past...

That is right.
I know my CBR's speedo reads exact at 100km/hr when my front tyre is just at the point of failing a WOF.
Yup, got a friendly bikie cop to stand on the runway and point the Laser at us.

Well worth the effort.

Oh, and interesting that this is under electrical system.... Most bike speedos are mechanical.... Well, I guess that is slowly becoming a thing of the past too ;)

[Dadpole]

I have the old mechanical speedo and measured against GPS it is within 1%. Near enough dead accurate at 50 and 100km. The tyre is 1 size up from standard so I guess that evened up any original error.
I find with both my cages, they indicate 2 - 3 km above actual speed.

[Hitcher]

Having done quite a lot of riding with a GPS on my Shiver, I can report that the onboard speedo has a 6% error engineered into it, while the odometer's measurement is perfect.

[quickbuck]

Having done quite a lot of riding with a GPS on my Shiver, I can report that the onboard speedo has a 6% error engineered into it, while the odometer's measurement is perfect.

Reminds me of a 2 stroke 250 triple of 1984 vintage I used to own (Won't mention the name but becoming popular around these parts of late....)

Anyway, the Odo was perfect IAW the 5 km markers just south of the Blue Gum Motel just south of Hornby, a shame the speedo was 40% optimistic!
Nope, that isn't a typo!
Truly, it did 100 in first indicated, and went off the clock (180) in 3rd....
My mates used to take it out the back of town and think they were Eddie Lawson! No traffic to reference against, and in reality only doing 130k.

Were amazed, and used to say things like, I can't believe how fast it is going...., It is so smooth.
Of course they were used to XR200's and the ilk....

Oh, memories.

[F5 Dave]

Of course for pure-bread racing speedos the Italian Velga (sp) were the raciest. Back in the day a friend on her Guzzi V50 put her head flat on the tank & sped up, rather bemused I pull alongside sitting bolt upright with one hand on the bar on my GS550, -just to rub in a point as you see.

Anyway later she says all full of enthusiasm "Sometimes I just like to do the 'ton'"
"That's odd" sez I , "I was only doing 140"
What a bastard, clearly I wasn't trying to sleep with her & what I wasn't letting on was, that with my slightly over geared GS, that was pretty much my practical top speed sitting upright. But it did tell me not to trust instruments, especially not Italian ones.

[imdying]

True. I have checked the odo out against the measured test sections on motorway - it is accurate to within a couple of metres over 5km...
Having done quite a lot of riding with a GPS on my Shiver, I can report that the onboard speedo has a 6% error engineered into it, while the odometer's measurement is perfect.Yep, thus why you shouldn't fit a speedo healer to fix the speedo inaccuracy, only to correct for a gearing change, and even then you only want to correct it back to it's existing inaccuracy :rofl:

[imdying]

Oh, and interesting that this is under electrical system....Not at all, the description for this subforum reads:

battery, wiring loom, lights, ignition system, ECU, dash, charging system, starter motor & other electrical devices;)

[quickbuck]

Fair enough then....... Will blame electrics next time my speedo fails then ;)

Always electronic stuff more likely to fail than good quality mechanical stuff....
First rule of my job is: Always blame Avionics first....

[pete376403]

Old Brit bikes (ie 1950s, 1960s old) used Chronometric speedos (and in some cases rev counters) made by (IIRC) Smiths under licence from Jaeger. Very accurate indeed. The later Brit bikes used common old magnetic cup type speedos as standard, but when they were converted to MoT use, the speedos were replaced with the old chronometrics
http://velobanjogent.blogspot.com/2008/03/smiths-chronometric-speedometer-and_21.html

[hmmmnz]

my van at 100 was doing 91kmh (gps speed) now with 275/75/16's at 100km/h she's doing 99kmh :D
all my bikes read between 93 and 95 at an indicated 100, except the xz400 which at an indicated 100 she's actually doing 107kmh :O

[merv]

Interesting! I recently checked the Striple against my GPS and at an indicated 100, the GPS was reading 95.

Yep about right, the bike speedos (and car ones too) are typically fast compared to reality.

[AllanB]

So when my Hornet was reading 300 I was actually only doing 290?



Bummer ..........

[kwaka_crasher]

So when my Hornet was reading 300 I was actually only doing 290?

Bummer ..........Nah - dream kms are considerably shorter than real kms...