Home Forum Bike Forum Velodrome – distance around blue line?

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• Velodrome – distance around blue line?
• robertgray05
Member

Hi all

Just wondering how much time you’d actually lose by riding a sub-optimal line around a velodrome… black line is 250m, so how long are the red and blue lines?

Specifically (although I doubt it makes much difference) I’m wondering about the Glasgow velodrome.

Cheers 🙂

Bob

iainc
Subscriber

Bob – I remember the coach talking about that at accreditation, can’t remember but think it was an extra 20m or similar

molgrips
Subscriber

They aren’t all the same length are they, velodromes?

theotherjonv
Subscriber

Not as much as you’d think.

Assume it’s a semi circle at each end and then two parallel straights.

The straights are the same irrespective of inner or outer line.

So you now have two semi circles = a circle. Circumference of a circle = pi x diam. Diam is the diam of inner circle, call it D, any other is D+d where d is the ‘extra’ diameter. So, the difference is

Pi x (D+d) – pi x D = pi x d.

So the line that’s half a metre wider (in radius, hence diam is 1m different) makes the track about 3 metres further. Significant when the race is won by cm or even mm, but not ‘vast’ in absolute terms.

 Just looked it up – the diff between black and red is 0.9m, hence difference is pi x 1.8 = 5.7m approx

iainc
Subscriber

so if the blue line is 2.5m out from the black line….

theotherjonv
Subscriber

5m diff diam, = 15m approx

crazy-legs
Subscriber

Varies depending on the track – although they’re all the same length (250m around the black line), the straights and bends can be different angles/lengths.

London for example has slightly shorter straights than Manchester.

Blue line is about 15m further per lap than the black line.

robertgray05
Member

So I couldn’t resist trying to calculate it… if I assume two semi circles either end of a 50m straight, the red line is pi metres longer than the 250m black, and the blue approx 5 pi (15.7m) longer. So ride the red and you’ll be 2 bike lengths behind the guy you tried to pass but couldn’t.

The geometry is more complex than that, for example the banking is steeper at the end of the turn than it is at the entry, but I don’t care that much.

EDIT: just refreshed and saw all the posts above 🙂

EDIT again: using 0.9m for the width of the sprinters lane, its 5.7m longer.

theotherjonv
Subscriber

It’s not dependant on the track. If the red line’s a determined distance outside the black, it doesn’t matter if the curves are tight with long straights, or if it’s a circular track.

By the same token, it doesn’t make a difference how long the track is. Approximate the m25 to a circle of 30 miles diam. Draw a black line, and then another red line 0.9m outside it. Distance round the black is pi x 30 miles, round the red is pi x (30 miles + 1.8m), cancel out pi x 30 miles and the difference is STILL pi x 1.8 = 5.7 metres

Do the maths.

crazy-legs
Subscriber

If you want it on time, assuming a race speed of 30mph (48kph or 13.5 metres per second) which is fairly standard in a scratch race, a rider on the blue line is going to be just under 1 sec a lap slower than a rider on the black.

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