I don't know how useful this is in our GPS enabled times, but if anyone is geeky enough to want to callibrate their Cateye-type cycle computer, the place to do it is Turnhouse Road. There is an exact half-mile marked by two metal posts (& a stud in the road), both on the west side of the road. The first is opposite the little industrial estate by the Maybury end, the second is about 150 yards before the road bends left by the junction with the old car showroom. They can be a bit hidden by foliage at times, but the stud in the road is pretty obvious.
CityCyclingEdinburgh Forum » Resources
Callibrating your cycle computer
(30 posts)-
Posted 3 years ago #
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Posted 3 years ago #
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I think these were for calibrating motor car speedos, back in the day when speedos were inaccurate and Turnhouse Rd was the A9 to Perth...
The time taken to travel 1/2 mile at 30mph is exactly 60 seconds
Posted 3 years ago # -
Yes. That’s them. I was told, many years ago, that it was for the police to calibrate their speedos. Don’t know if they still do. They do look like they are kept visible with the addition of reflective bands, so maybe they are still in use.
Posted 3 years ago # -
@stiltskin - That's really useful to know.
Just been through a calibration exercise and know from discrepancy (c. 300 yards over 5 miles) between Strava and Computer (which is under-reading) that a bit of refinement is required!
Personally, I have my phone in my pocket running Strava and therefore find the computer useful for distance, speed etc. on the ride.
Posted 3 years ago # -
I've never been on Turnhouse Road. Ever. What else have I missed?
Posted 3 years ago # -
At the far end there is a house on the corner which has about 20 cctv cameras dotted about the garden. One evening, when coming down Lennymuir I could see in one of the rooms and there appeared to be a whole bank of TV screens on the wall. The owner appears to value his privacy.
You also get good views of aeroplanes.Posted 3 years ago # -
@stiltskin - also has signs of dubious legality advising risk of death etc in the event of trespass. Suspect he/she is an absolute rocket
Posted 3 years ago # -
I do love a household with a webcam on a stick. Sure sign of a balanced mind.
Posted 3 years ago # -
I wonder if the bollards will be retained as the building work progresses.
Now is the time to visit Turnhouse Road as it is about to be turned into just another residential thoroughfare.
Current delights include the remains of Meadowfield Farm and the back road to Edinburgh Gateway Station. And the wonderfully named strava segment: "Fly tipping across the universe".
Posted 3 years ago # -
Can I offer up an easier calibration location just for the fun of it?
It's been a long time since I did this, but I've checked the distance with different desk based tools on many occasions (and again carefully just now)....
Here to here I believe to be 1000.7 metres (plus or minus about 0.5m). That's the west wall of each bridge (Ashley Terrace and Yeoman Place), not the east wall of one and the west of the other.
That's accurate enough in my books to call it 1km given that there are going to be errors in any measurement anyway (e.g. front wheel travels a longer way than rear wheel), and I've not accounted for wobbles around the access control gates which presumably add a few centimetres here and there.
I like this stretch of towpath because it's relatively straight. GPS measurements should behave relatively well here too - there's a good view of the sky for most of it, and any errors that push the track sideways shouldn't add or subtract much distance.
Posted 3 years ago # -
Turnhouse road route to the BEA london shuttle when I were a lad
Posted 3 years ago # -
Porty Prom has a marked mile starting outside Tumbles and ending at Joppa. More usefully, it's there are several intermediate marks in metres up to 1800.
Posted 3 years ago # -
What do they use to calibrate the calibrations? And what random error of measurement is contained therein?
Posted 3 years ago # -
I personally never go anywhere without a vacuum and measuring how far light travels in 1/299792458th of a second within it to make sure I have an accurate distance.....
On a slightly less flippant tone I have visions of the bank of CCTV monitors at Turnhouse showing multiple CCE'ers out calibtrating their computers.....
Posted 3 years ago # -
@twinspark this is the accuracy i expect of CCE
The thing about the security house at Turnhouse is that you can see in his window. All those cameras and monitors but nae curtains?
Posted 3 years ago # -
Now is the time to visit Turnhouse Road as it is about to be turned into just another residential thoroughfare.
Oh really? This is one of my most frequently used roads since I moved to the Gyle, sorry to hear that, it’s one of the last hints of the patchwork of small holdings and villages you can see on the old maps of the area before the airport was built.
Posted 3 years ago # -
The cobbly breakwater thing leading from Newhaven Lighthouse to Lighthouse Park has distances marked every few hundred feet by plates on the ground.
Posted 3 years ago # -
I personally never go anywhere without a vacuum
Me too and this is why nature abhors me.
Posted 3 years ago # -
It used to be that one could see squads of cops there of a morning checking their speedos. As "speeders" are no longer apprehended by means of being followed for a certain distance I imagine they don't bother nowadays.
Whenever I acquired another vehicle I would go to Turnhouse Road (RIP) to check it. It's remarkable how much concentration it takes to hold a vehicle at exactly the same speed for half a mile, it certainly doesn't leave much over for looking at the road ahead, but there'd be two in a police car.
Posted 3 years ago # -
A loaded measurement of multiples of the tyre circumference should be enough precision for anyone. Think of it as analogous to Lenoir's repeating circle.
If your tyre is notionally 200cm in circumference and you can measure that to, say, a pretty crude ±0.5cm, the error is 0.25%. Over a 100km bike ride you might be out 250m on true distance. But if you measure over ten tyre revolutions with the same (im)precision, you divide the error by the same factor. And if you are careful to do the rollout on level ground with a straight path next to your surveyor's tape measure, with a well defined marker on the tyre, it's quite possible to increase the precision to ±0.2cm in 20m, or ±0.01%, which is ±10m over a 100km ride.
Edit: this is mainly because Turnhouse Road is too far away, and because the sensor signal to the Cateye Micro Wireless in the torpedo was frequently hijacked by the indicator flasher unit, strong wi-fi signals, weak wi-fi signals, and people talking too loudly, resulting in a cumulative odometer error of about 10%, and its wholesale replacement with a wired computer.
Posted 3 years ago # -
Arellcat's method™ sounds good, but you would need to factor in that the front wheel of a bike never follows a straight line (otherwise you would fall off!)
Posted 3 years ago # -
@neddie
Would you not be wheeling the bike so as to count the revolutions?
Also, centripetal forces cause the diameter of a wheel with a pneumatic tyre to increase with velocity.
Posted 3 years ago # -
You're overthinking it. You don't ride or steer the bike so much as simply bear weight on it, say sitting on the top tube, and paddling the bike along. If you do one revolution and measure approximately, you can then do ten and one need start checking the measure only once the end point is approached. Average the errors by doing more than one test.
I'm sure some enterprising individual somewhere has built a 20 metre long micrometer.
Posted 3 years ago # -
That would be a macrometer?
Posted 3 years ago # -
@iwrats - Sitting on the bike is better so the tyre is loaded as otherwise circumference varies between loaded and unloaded.
@arellcat - I normally do multiple revolutions however it was tipping down the day I did, so did in a hallway, which when I think about it also had carpet!
@arellcat - I too have a Micro Wireless. Phone with WiFi off can affect it and also a flashing cateye headlight. I have two cateye headlights and have computer mounted on left with fixed light also on left and flashing light on right. The body of the non-flashing light (either on or off, it doesn't matter) shields computer from the flashing one. I've also had the computer stop registering in heavy rain having gone through deep standing water - not a problem with the transmitter but the magnet getting deflected out of alignment....!
@iwrats - I don't think I would ever go fast enough to have centripetal forces come into play :-)
Posted 3 years ago # -
@twinspark
Excellent precision corrections.
Posted 3 years ago # -
I've never been on Turnhouse Road. Ever. What else have I missed?
Many of the Verges along the road have now been reduced to mud but there is a diamond in the rough.
This delightful stone has come out of the undergrowth:
According to streetview it was previously visible. However there is no mention of it on Canmore.
Of the w bollards which started this thread one is now also very visible. I hadn't planned to visit them so was looking in the wrong direction for the other one:
Not much else to report from the area jsut now other than mud.
Posted 3 years ago # -
Both bollards are there. Interestingly enough they dug them up & then replaced them. That implies to me they have some sort of official status.
Posted 3 years ago # -
Interesting. They aren't on canmore either.
Posted 3 years ago #
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