Maths Genius Required - Impress Your Friends!!

[John the old'un]

Whilst I bow to your vastly superior experience I still feel you are not entirely correct.
In 2006 I set my (slow) pb on Q10/19 on 6th May at around 6.30 am. 27.35.
No training, just about seven or eight clubruns throughout the winter.
In 2007, with loads more training, including 2 months under a professional coach, my times on G10/42 were: 28.46, 28.26 and 27.59. None were early am starts, in fact two were on warm afternoons.

[richv]

John I am sure you are not the only person who has a pb on the Q10/19 which is faster than the G10/42. My point is not that it is slower than the G10/42 (which is most definitely not a quick course) but rather that it is overrated by people who trot out performances on the course from the 1980s as evidence of how quick a course it is when conditions were very different and traffic counts hadn't been invented. I'm sure it would be a quick course if we had 22 degree temperatures and heavy traffic (the most important constituent of any 'quick' course) but the events are now run at such a time that that is unlikely. It is probably the quickest course in Kent and Surrey but what I'm saying is that it is not that much quicker than other courses and certainly does not rate as a truly 'quick' course.

Marco I suspect the reason that faster riders appear not to be so affected by courses is a result of the cubic relationship between power and speed and the reciprocal relationship between speed and time for a given distance:

Travelling at 20 mph a 10 takes 30 minutes
Travelling at 25 mph a 10 takes 24 minutes
Travelling at 30 mph a 10 takes 20 minutes

Thus a fast rider who slows down by 5 mph loses only 2/3 of the time a middlemarker does.

However say for a standard rider on a fast course (the figures are roughly accurate but not intended to be absolutely precise):

travelling at 20 mph requires 275w
travelling at 25 mph requires 300w
travelling at 30 mph requires 350w

Thus if the course is such that an extra 25w is required to maintain speed (this will vary slightly with speed but not significantly):

A rider who would travel at 25mph on a fast course would drop to 20mph whereas a rider who would travel at 30 mph will drop to about 28-29mph.

The 'middlemarker' will then lose about 6 minutes but the fast rider will lose less than 2 minutes.

So the higher the power output the much less your time is affected by course variation. Similar arguments apply to weather conditions as well so faster riders just seem to be fast whathever the course or conditions.

[Sylv]

But why would a course be faster at 22 degrees than, say 10?

[quote]travelling at 30 mph requires 350w

[Andrew G]

Warm weather always helps as your muscles are nice and warm. Cold air is also denser than warm air so you should cut through the air better when it's warm.

Yeah, traffic helps nicely George. You can't draft, well I don't go quick enough to jump in behind a speeding car on a dual carriageway, but you can get a wash of air from cars. On just one TT I've had a coach come past me and it was like getting little shove from behind.

[richv]

It has very little to do with warm muscles - muscles should be warm whatever the weather if you're working hard enough and everything to do with air density.

The greatest slowing force on you when time trialling is drag. That's why riders will ride in inefficient positions in order to reduce drag - the pay back of reduced drag is worth the loss of power. The denser the air the greater the drag. At a fixed pressure the higher the temperature the less dense the air (Boyle's law). In summer this is partially offset by the high pressure systems that tend to be associated with settled weather - high pressure=denser air, but the warmer air is still less dense and undoubtedly improves speeds significantly.

The ideal weather for a really quick time is a low pressure system moving through in a period of warm weather when you get low pressure and warm air together thus very low density air. Problem is that low pressures tend to be associated with wind which is not good for quick times!

Traffic makes a huge difference even though you are not allowed to draft vehicles. Traffic passing will give a drag and as Andrew points out the bigger the vehicle the bigger the drag. At least one of the really 'fast' courses is rubbish for early morning events as the only reason it is fast is that it has nose to tail commuter traffic (with supermarket trucks mixed in) travelling at 50mph for the first half of the evening events. If you set off in that I reckon it's worth 30 to 45 seconds over a 10 mile course for the fast riders even compared with the later riders in the same event. Some events you need to check the ferry timetable to be sure when the 'quickest' conditions are or have a mate at Catterick who can tell you when the army are trekking up or down the A1.

George if you can't knock out a 19-minute ten in your first couple of rides I'd give up

[Andrew G]

[quote]It has very little to do with warm muscles - muscles should be warm whatever the weather if you're working hard enough

[quote="Andrew G"][quote]It has very little to do with warm muscles - muscles should be warm whatever the weather if you're working hard enough

[Sylv]

Ok thanks - George you better get yourself a barometer too then .

[Sylv]

So Rich, say you were doing 25mph at 8 degrees (like the temperature these days) - how much faster would you expect to go at 22 degrees - 0.25mph? (1%) - or more?

[richv]

Sylv

On the basis of a frontal area of 0.5m^2 and a drag coefficient of 0.5 (these factors will be determined by how good your position is, the larger the factors the more significant the effect of increasing density of air) and at a barometric pressure of 30.10 inches of mercury for a rider and bike weighing 95kgs on a dead flat course a change in temperature from 8 to 22 degrees celsius would increase their bike speed by approximately 0.3803 mph, i.e. over 1%.

In real numbers that means that they will gain about 23 seconds over a 10 mile TT if the temperature warms up with the pressure staying the same.

[mrP(Boonen)VT]

Without being all teccy, I was riding (or rather watching) the day that Sean broke the 20 minute barrier (in fact David Akam went a bit faster in the morning on the Portsmouth Road) and the event was run off just a few minutes before a violent thunderstorm, and the air had a stillness about it, yet warm.

I guess this ties in somehow with air pressure etc.

[richv]

Not pressure related but tyres have a lower rolling resistance on wet roads so you will go faster in a straight line if conditions remain the same but the road is wet. Downsides are going round corners can be a little slower and rain is rarely associated with still warm air (except on those exceptional summer evenings).

[Jon H]

Yes the summer thunderstorm evenings are the best due to the combination of warm temperature and low air pressure. The tricky bit is to time your ride so you're in the "calm before the storm" bit before the wind gets up and the rain comes down. The theory about more oxygen in the air is a myth.

[mrP(Boonen)VT]

or even falling off Rich