A Newtonian distraction

 For once I am going to write an unashamedly geeky post about cycling. Nothing about politics, life and death, films, music or the lockdown. For those of you struggling with big world events, or local issues, or family crises of any kind whatsoever, this post is the ultimate escapism. 

Back in March, for reasons I promised not to mention, I found myself with a bit more time on my hands. Time that of course I used productively to do more cycling. Now, as the dark approaches and the weather turns more inclement, that time is being whittled away and I have to take my opportunities whenever they present themselves.

Still, back to March. As I had all this time for riding, I decided I would ride when the weather was nice. A sunny Spring and the lengthening of the days, meant that was quite often. A further benefit of this fair-weather riding, coupled with the fact that I was riding on my own, and so I didn’t have to worry about spraying anyone with water and Somerset’s finest mud,  meant I could ride my Planet X bike all the time. The lighter bike. 

And the results, and bear in mind the only person any of us truly competes with is ourself, were very encouraging. After a tough year in 2019 with the whooping cough, and an early bout of that illness I can’t mention in March 2020, I saw both my VO2 and my FTP steadily, if not spectacularly, increase in line with the lengthening daylight.

Even when our life-affirming cycling trip to the south of France fell by the wayside, a quick pivot to the Land of his Fathers, allowed me to keep some kind of mountain-focussed goal in my head, to spur my motivation. This was particularly important as that available time started to shrink, for reasons I can’t mention.

Then, on the evening of 26 August, I found myself with a couple of hours to spare till sundown, so decided to head out on a loop of the airport, Bristol airport. Now, for Strava aficionados, I give you the Wrington-Redhill climb. One of my most climbed segments in the whole of the world, as I write I have done it 273 times since I joined Strava at the start of 2014 (an average of 39 times a year), but in 2020, Relatively hardly at all (only 15 times). The simple reason for this is because this climb is on one of my favourite commuting routes, and for reasons that I can’t mention, I’ve not been going into our Bristol office much since March. It was also a lovely evening.

It’s a very benign climb. The full route from the actual village of Wrington to the top of the hill at Row of Ashes, includes five steep sections (of 8-12% each), but this segment truncates that longer climb by chopping off the first and last two ramps. Consequently the segment has an average gradient of only 3.6% over the course of its 2.11 kilometres. Because most of my efforts are done whilst commuting to work I tend to bimble up it, enjoying the views and the sunrises, depending on the time of year.

When I was reviewing my Strava results after that ride on 26 August, to my astonishment I found it was my 3rd best ever climb of the segment, at a stunning 7 minutes and 9 seconds. Look, I know what you are thinking, and I know my place and ability. I’m competing against myself remember? Even if I wasn’t, despite there being 2,103 better performers on this hill than me, And my best was a few years ago, there are still 2,393 people who are either slower or can’t be arsed. Honestly, you Type A people, just relax. There are worse things going on, but I cant mention them.

Anyway, this “performance” was something of a surprise. It hadn’t been a commuting ride, but I hadn’t been making any specific effort to blast up the hill, so I put it down to a bit of good form (don’t you all?) and forgot about it.

Fast forward a few months to Wednesday of this week, and so much has changed. It’s cold, it’s dark, windy, and worst of all, it seems to be perpetually raining. And all that time I mentioned? Mostly gone, as I’m having to use my waking hours for things other than cycling. So a dry and still night Prompted me out the door in the direction of Bristol. I also had a small errand to deliver something to a colleague on the Wells Road. It now being November, and my Planet X being off the road for wheel repair, I was on the chug-a-long steel bike. Actually, it’s beautiful to ride, looks amazing and is equipped with just about everything you need for Winter riding. Which means that as well as being very comfortable, it is also very, very heavy. 

Needless to say my ride up Wrington-Redhill did not pull up any trees. At 8 minutes 40 seconds it was very firmly towards the fourth quartile of my own personal performances. Although it was a very lovely evening, with mist down in the valley, stars up above, and a nearly-full moon to illuminate proceedings. If I was allowed to mention it, I’d say it made me feel glad to be alive.

But the wheel I was using also has a Power meter in the rear hub, and I was equipped with a Heart rate monitor (and yes I do have a Heart) so enabling me to make some direct comparisons with that climb back in August. Brace yourself, it’s about to get geeky.

So why was my November ride nearly 20% slower than my August ride? What had caused such a dramatic decline in the speed of my climb? The obvious first choice would be that I was just bimbling as usual. Not putting in as much effort or worn out from a day at the coal face or ground down by the events out in the wider world. Well, actually no. Power output and average heart rate, at 211/163 for August and 212/164 this week were practically identical, if anything slightly more effort in November. There’s a possibility that the meter has been calibrated differently, but I’m pretty sure my heart hasn’t.

Students of physics, and specifically potential energy, will have seen one obvious answer. The energy require to move any mass uphill is a function of its mass, the amount of vertical ascent and the Gravitational constant (as I’m sure you knew). The latter two obviously haven’t changed in three months, although it does feel like the world is shifting on its axis sometimes. But obviously the mass has. Not the rider, no, despite what you might be thinking. I’m actually about the same as I was then. It’s the bike. Equipped with mudguards et al, as well as more and thicker clothing and lights galore, my Winter ensemble tops out at around 15kg, whilst the Planet X is a mere  8.7kg. So a proportion of those watts would have been used to carry lift that extra weight up the 85 metres of the climb, and the speed would have been sacrificed.  But how much of the fall in speed is used to do that? The equation to calculate the sacrifice is :

Energy = mass x height x gravitational constant [9.8 m/s] - for the truly geeky. 

It’s not a huge amount of energy though, 5248 Joules which equates to 1457 Watts being used to lift up the extra weight. Now, the figure from my power meter, of 212Watts, actually means I’m putting out 212 Watts per second on average. So in 8 minutes 40 seconds I am putting out 110,240 Watts in total over the whole climb. Which means that just 1.3% of my power output is used to carry the extra weight, which would make a difference of just 7 seconds.

The one caveat I’d put on these calculations is that it is 37 years since I did A level Physics, brighter minds and geekier cyclists may know better and I’m open to education.

If my Maths are right, what else would account for such a slower speed when the engine (me) was working at a similar level of output? We need to do a Sean Kelly and made the calculations. So what other factors are in play here? Well, for one, there is air density. As it’s a relatively shallow climb wind resistance plays more of a role in determining speed, and in the Autumn with a temperature of 7C the air would have been more dense than in the Summer when it was a relatively balmy 17C. 

Also consuming a few watts would have been my dynamo hub, not much I grant you, but those lumens have to be powered from somewhere, so the illuminating light of Exposure would have been paid for in speed.

And for those of you that know the local area and follow me on Strava, and are finding it hard to sleep in these troubled times, take a look at my angle of approach. Momentum is everything, unless you are Fleabag or Jeremy Corbyn. In August I was hitting the start of the segment at about 20 mph as I’d come from Congresbury, whereas this week I’d approached from the 10% ramp out of Wrington itself, so had no impetuous push from the landscape.

But the real big determining factor here, and I’d claim, without any evidence, (who would do such a thing as that?) that it’s the case for all PBs on Strava by middling cyclists where the gradient is less than 6% (that’s a pretty bold and specific claim isn’t it without a research-based study to back it up, but oh well, that’s modern life) Is the speed and direction of the wind.

August, tail wind - westerly- of 15.8 mph. It may not sound much, but if you are a cyclist, you will know it is. A full-on, right-behind-me tailwind. Whereas on the misty night of November, - northerly 2.2 mph - and with the side of the hill sheltering me, that’s as near to cycling in a vacuum as you are going to get.

So there you have it. Physics eh? Bloody hell. If anyone would like to work out all the parameters in detail, be my guest. I’ll even pretend to be interested. I’m just pleased to have taken you minds away from all the real-life shitshow at the moment. But, this shows the importance of critical mass, momentum, power, heart,  competitiveness, data, how to use your time, and having something behind you. Those and density, always important. Oh and being good at Maths too.

What’s that? I promised It would be about geekiness?  It is, isn’t it?