S60 speedo accuracy (UK)

  • Thread starter Thread starter Tim Riglar
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Tim Riglar

Took the trouble to try to calibrate the speedo in my S60 today (2.0 SE auto
with 17" wheels and correct 45 profile tyres) - no particular reason, just
out of interest. AIUI, UK legislation requires +0 -5% accuracy, but I'm
overreading by about 8.5% at 60, 70 and 80 (didn't check any others). I used
the 100m markers on the motorway, and set the cruise. The timings were
pretty repeatable. I suppose the markers could be inaccurate, but it doesn't
seem very likely. Interestingly I measured 16 posts to an indicated mile,
which would seem to indicate that the odometer is pretty accurate (and
confirms that they are at 100m, not 100yd intervals).

Has anyone else tried this? It's disappointing that the error is this large
and (strictly speaking) illegal.

Tim
 
Tim said:
Took the trouble to try to calibrate the speedo in my S60 today (2.0 SE auto
with 17" wheels and correct 45 profile tyres) - no particular reason, just
out of interest. AIUI, UK legislation requires +0 -5% accuracy, but I'm
overreading by about 8.5% at 60, 70 and 80 (didn't check any others). I used
the 100m markers on the motorway, and set the cruise. The timings were
pretty repeatable. I suppose the markers could be inaccurate, but it doesn't
seem very likely. Interestingly I measured 16 posts to an indicated mile,
which would seem to indicate that the odometer is pretty accurate (and
confirms that they are at 100m, not 100yd intervals).

Has anyone else tried this? It's disappointing that the error is this large
and (strictly speaking) illegal.
Click to expand...

I confess.

Yes, my name is Stewart, and I, too, am a marker post counter.

Not on a regular basis, you understand, but once, out curiosity, I
counted the posts over an indicated mile on my trip meter.

16. Exactly.

To confirm this, I counted them over 10 miles.

160. Exactly. My oddometer seems very accurate, too.

You are obviously much younger than me; I realised straight away that
they were at half furlong intervals. There are 8 furlongs (220 yards)
to a mile. An odd unit these days, but it equates to the length of a
cricket pitch, and one furlong by one furlong is ten acres.

So, half a furlong is 110 yards, which is slightly over 100 meters.

I would hazard a guess that your accuracy with the throttle, with
reading the meter while driving, and with the time taken for the meter
to respond may all contribute to the extra 3.5% error.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name
 
Stewart Hargrave wrote:

You are obviously much younger than me; I realised straight away that
they were at half furlong intervals. There are 8 furlongs (220 yards)
to a mile. An odd unit these days, but it equates to the length of a
cricket pitch, and one furlong by one furlong is ten acres.
Click to expand...

So, who noticed my (ahem) deliberate mistake?

A *chain* (22 yards) is the length of a cricket pitch - a chain is a
tenth of a furlong.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name
 
The furlong... the "chain" - I am so glad we are taught metric in Canada.

I wonder how many hectometers per unit decalitre my car is getting?
 
Come to Melbourne (or anywhere in Victoria for that matter)Australia. The
money hungry incompetents in Spring Street as well as the tunnel visioned
Police here allow you a 1-3% leniency on your speed. Pretty much every car -
including new ones are out by more than that. And they try to convince us it
is in our own interests.....

How did we get idiots like this?
 
out of interest. AIUI, UK legislation requires +0 -5% accuracy, but I'm

My understanding was that the speedo cannot under read (obviously) but
can over read by up to 10% at speeds above 10mph. Therefore, by that
your speedo is within tolerance.

David.
 
David Taylor said:
My understanding was that the speedo cannot under read (obviously) but
can over read by up to 10% at speeds above 10mph. Therefore, by that
your speedo is within tolerance.

David.
Click to expand...

I used to quote this 10% rule, too, then I'm sure I discovered it was 5%
(don't think I dreamt it, anything's possible). However, the Statutory
Instrument 1996 No. 3013 (The Motor Vehicles (Approval) Regulations 1996)
which I looked up this morning, actually states:

"For all true speeds of between 25 mph and 70 mph (or the maximum design
speed if lower), the difference between the indicated speed and the true
speed shall not exceed V/10 + 6.25 mph (where V = the true speed of the
vehicle in mph)"

which puts a different perspective on things, and seems to suggest that at
at true 60, the speedo could read 72.25mph, which is more like a 20%
allowance. Interesting that "10%" seems to be lodged in the mind of most
people.

Looks like my error is well within range, but still disappointing in a
modern car in my view.

Tim
 
(don't think I dreamt it, anything's possible). However, the Statutory
Instrument 1996 No. 3013 (The Motor Vehicles (Approval) Regulations 1996)
which I looked up this morning, actually states:
Click to expand...

I was looking for the right one but it wasn't turning up. Well done!
which puts a different perspective on things, and seems to suggest that at
at true 60, the speedo could read 72.25mph, which is more like a 20%
allowance. Interesting that "10%" seems to be lodged in the mind of most
people.
Click to expand...

Well, the point is to stop people speeding, driving at an indicated 70
and finding your doing much less isn't much of a problem. I have to say
that my Saab compares well between the speedo and a GPS, no more than a
couple of mph out by my reckoning (and ability to accurately read the
speedo).

David.
 
Tim said:
Took the trouble to try to calibrate the speedo in my S60 today (2.0 SE auto
with 17" wheels and correct 45 profile tyres) - no particular reason, just
out of interest. AIUI, UK legislation requires +0 -5% accuracy, but I'm
overreading by about 8.5% at 60, 70 and 80 (didn't check any others). I used
the 100m markers on the motorway, and set the cruise. The timings were
pretty repeatable. I suppose the markers could be inaccurate, but it doesn't
seem very likely. Interestingly I measured 16 posts to an indicated mile,
which would seem to indicate that the odometer is pretty accurate (and
confirms that they are at 100m, not 100yd intervals).

Has anyone else tried this? It's disappointing that the error is this large
and (strictly speaking) illegal.

Tim
Click to expand...

Not that this helps much, but a few years ago on a cruise in my '98 V70
to Montreal (500 km away) on the highway which has kilometer markers I
tested my accuracy. To get to a true 120 km/hr I had to set the speedo
to read 123. At this speed (cruise control) the average speed indicator
in the trip computer read exactly 120 after resetting. Also, over 200
km my odometer didn't even vary 0.1 km!

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Rob said:
The furlong... the "chain" - I am so glad we are taught metric in Canada.
Click to expand...


No, metric is a daft system.

25.4 mm to an inch
39.37 inches to a meter.

Madness.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name
 
Reminds me of a quote I can't quite remember fully, from the television
show: The Simpsons

"Bah!! Metric, thats the tool of the devil, my car gets 28 rods to the hogs
head, and that's the way I likes it!" - Abe Simpson
 
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