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Topic ClosedDarly moor speed?
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LeeW View Drop Down
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Points: 2382 		Direct Link To This Post Topic: Darly moor speed?
    Posted: 05 June 2006 at 11:32am
How did your avarage speed on your bike computer compare to the speed on the darly moor results page? I ask this since the speed on the results page is 1.1Mph faster than what I got on my bike computer so I am wondering if my computer needs re-calibrating.
Current fleet: Milan SL MK2 #027, Fujin SL II, Beany!
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Andrew S View Drop Down
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Points: 2433 		Direct Link To This Post Posted: 05 June 2006 at 11:53am
You will probably find that the length of almost all circuits as listed on our website is greater than as measured by your speedo, which accounts for the higher speeds. At least part of the reason is that the 'official' circuit length is measured down the centreline of the track, which is longer than any reasonable racing line. I've never been entirely convinced that this accounts for all of the difference, but have never actually measured the centre line and racing line on any circuit to see what the difference is.

For the record, I recorded avg 24.4mph vs 25.2 official - smaller than your difference. How do you calibrate your wheel diameter? I measure at least 10 rotations, using the tyres and pressures I use for racing, sitting on the bike. My neighbours can attest to the bizarre and obsessional measurement of the pavement outside my house.


Edited by Andrew S - 05 June 2006 at 12:01pm
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Rob View Drop Down
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Points: 1450 		Direct Link To This Post Posted: 05 June 2006 at 12:40pm
25.6mph on computer, 26.5mph 'official'. The difference is quite normal and consistent... In the past I've carefully recalibrated my computers to 'BHPC Speed' by fine tuning based on the %age differences over a few races but maybe that is being obsessive..... Measuring lower is an incentive to work harder! <grin>

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Rob View Drop Down
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Points: 1450 		Direct Link To This Post Posted: 05 June 2006 at 12:45pm
Originally posted by Andrew S Andrew S wrote:

I've never been entirely convinced that this accounts for all of the difference, but have never actually measured the centre line and racing line on any circuit to see what the difference is.


Ah, the old school book problem of raising a wire fence around the equator of the earth (yes, I know it is mostly water)... You put the first wire in and then decide you want a 2nd wire 0.5metre higher - how much more wire will you need for the 2nd wire than for the first?

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antony View Drop Down
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Points: 667 		Direct Link To This Post Posted: 05 June 2006 at 1:33pm

Would that not be dependant on how high (more accurately, how far from the centre of the earth) the first wire was?

Or were they looking for a formula for the answer rather than a specific number?

And, presumably, the book was wrongly assuming the earth to be a perfect sphere and also ignoring the minor imperfections of topography superimposed onto it.


Besides, I think you'll find the answer is:

No more. It'll stretch enough to cover the difference. And if not, just miss a bit out round the back somewhere where no-one will notice. Make sure you get paid in full, in advance. Don't forget to leave some slack to cover mid-ocean ridges and some tensioning devices for subduction zones.





PS. For all your fencing needs, see www.bodgitandscarper.com.

Ahem, sorry.


    

Edited by antony - 05 June 2006 at 1:34pm
Deja mu: The feeling you've heard this bull before
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LeeW View Drop Down
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Points: 2382 		Direct Link To This Post Posted: 05 June 2006 at 1:35pm
My magnet is on my right wheel. My speed would have most likley been a bit higher if my magnet was on the left wheel

Edited by LeeW - 05 June 2006 at 1:36pm
Current fleet: Milan SL MK2 #027, Fujin SL II, Beany!
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KevinJ View Drop Down
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Points: 1079 		Direct Link To This Post Posted: 05 June 2006 at 1:46pm

I can only see that making a difference of about 5 Metre distance per lap, so that would mean that it is only about 0.2% difference. 

Kevin Jenkins

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gNick View Drop Down
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Points: 1977 		Direct Link To This Post Posted: 05 June 2006 at 1:46pm

3.1415927(.....)m or PI metres

(circ=pi*D,and new circ=pi*(D+(2*0.5)= pi*D +pi*1; thus difference is pi*1)
 
So for a 10m wide track with all the curves in the same direction you will travel 31.416m further on the centre line than on the inside line. Most of us will not be travelling on the inside line all the way round so assuming the racing line is about half way between the inner line and the centre line we are doing about 15m less per lap than the specified distance. For Lee this makes a the projected average speed 25.032mph rather than 25.193 (based on 15 laps in 52min 9.89s).
Methinks speedo calibration might have a bit more to do with it!
gNick



"I'm afraid it's definite, Mrs Banker - your son has bicycles"
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KevinJ View Drop Down
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Points: 1079 		Direct Link To This Post Posted: 05 June 2006 at 2:06pm
Sorry gNick - was using the same formula (I am a mathematician!) but was just trying to account for the diffence between having the speedo magnet on the different wheel.
 
has it as 2.41 Km (we are only 2.35) so that woul make everyone even faster!!!
Kevin Jenkins

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legs_larry View Drop Down
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Points: 1554 		Direct Link To This Post Posted: 05 June 2006 at 2:13pm
Most of the circuit lengths were measured by the then-Editorial Cateye, so are at least definitively inaccurate...
====================

a bit ov a lyv wyr by slof standirds
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