Wednesday, 15 June 2016

Theory and Practice - Part 1 - Aero

Theory and Practice (and feedback for theory that leads to the next practice, and so on).
In 2015, I rode in the local charity sportive, the 100km (62 mile) Tour de Vale.
I have entered again, and I am due to ride in about 10 days time.
Like a lot of folks, I am looking to get a bit better time this year, compared with last year.
Strava can be a useful measuring device for comparing performances, especially over out-and-back routes where the wind direction won't make a ride very fast one day, and very slow the next.
The Tour de Vale is basically a circular route heading out of town, then going in a big anti-clockwise (left-handed) loop until it eventually reaches the road it left town on, when it turns back into town for the finish.
The event has proper "official" times generated by a little microchip on the back of the entrant's number being picked up at the start/finish.
But the start/finish point spends much of the time being locked away, so it is hard to compare practice runs with the real event, because you can't actually do the bit at the start and the end, except on event days.
That's where Strava steps in.
A couple of segments have been set up.
One starts just outside the stadium gates, and is the closest you can usually get to the start. The other segment starts at the road junction where the road to the stadium meets the main road. The second segment saves having to cycle right down to the stadium gates, then back out again just to practice.
However, because I always approach the stadium from the side, I have to go very near to the gates anyway, so it is the first segemnt I will be looking at in this article.
So, here are my two times on that route:
1) last year's actual event time: 5hrs 20 mins 10 secs.
2) practice run last Sunday: 4hrs 40 mins 1 second.
For comparison, my "official" event time last year was 5 hrs 22 mins and some seconds. The "extra time" over the Strava segment is the bit from the stadium gates to the start/finish line!
So how did I knock 40 minutes off my time?
Well, a number of things changed:
1) I lost weight
2) I changed bikes
3) the weather was a few degrees cooler
4) I wore different clothes
5) I rode in a different position
6) I carried less stuff with me on the bike
7) My level of fitness may have been different.
For this first posting, I will mainly look at aero.
So let's look at all those things in turn:
1) Weight loss. Because I keep a weight diary, I can easily look up how heavy I was on the morning of my 2015 ride: I weighed in at 90.6 kg (199.3 lbs). Last Sunday I was 84.3 kg (185.5 lbs). So I weighed 6.3 kg (13.8 lbs) lighter.
2) Different bike. Last year I rode Mermaid, which weighed in at 18kg (39.6 lbs), while this year I rode Hoppy, which weighed in (stripped down as previously mentioned) 14.5 kg (31.9 kg). So that's another 3.5 kg (7.7 lbs) saved in weight.
But what about different gearing and tyres?
It just so happens that I moved various parts from Mermaid to Hoppy.
So in both cases I used the same Spa Cycles forged 175mm triple cranks, running the same 48,32,26 rings. The BB was the same Strongly aluminium unit. The rear gears were the same SRAM PG850 11-32 cassette. The front and rear wheels where the same, too, sporting the same tyres (no-name hubs laced to Mach 1 240 rims, bearing 37x622 Marathon Plus tyres).
So the main thing to look at here is the weight saving.
3) Weather was a bit cooler. Hard to quantify, really. I needed a bit less water this, but I brought some back, so I still ended up carrying a similar amount of water all round the route.
4) I wore different clothes. Last time, I wore a pair of black jeans, a check shirt and a hi-viz gilet. This time I wore heavyweight cycle trousers, a long-sleeve cycle jersey, and I taped over the three central vents on my helmet for some #GhettoAero
5) I rode in a different position. I fitted some aero "horns" to my handlebars. The actual 'bars themselves were the set I took of Mermaid, so they are the same. But this time I spent a lot of time in a more tucked-in riding position.
6) I carried less stuff. Last year I pretty much took the kitchen sink. Covered all eventualities, except, perhaps, a zombie apocalypse. This year, I stripped the kit right down, for more weight savings.
7) Different fitness levels? This one is hard for me to quantify -I was trying reasonably well until Easter, then it all fell apart. So I don't think I am much more trained that last year, when I was running more, and going on a lot of medium length rides.
Well that's a narrative account.
So how will I try an analyse things?
Specialized have done a series of wind tunnel videos that are useful, so let's start with this one:
This one looks at riding at 50 kph (a touch over 30 mph), and riding at 20 kph (about 12 1/2 mph). While fitter riders might get closer to the 50 kph mark, a little math shows that to get round 100km in 5 hours results in an average of 20 kph. So I ride more in the 20 to 30 kph range, dropping lower on hills.
And watch this one, too:
It explains why aero still matters for a slower rider like me ...
So Specialized have a variety of videos that relate to my riding.
Their favourite metric is "time saved over 40km" (25 miles).
Since I am looking at a 100km Strava segment, I will simply multiply Specialized's savings by 2 1/2.
Tighter fitting clothes for 2016. Still a bit loose in the bosy, but not as loose as last year's shirt.
I got my wife to tighten the wrists of my jersey a bit so they were a tighter fit.
(I have to order a bit big, because I have long arms!)
Next year, I'll see about taking some of the "slack" out of the body and sleeves of the jersey.
This video looks at wearing "baggies" over lycra.
My outfit last year was at least as "baggy" as the one shown, and while my lycra isn't "racer cut", it is reasonably form fitting.
In the video, they use the metric of time saved over 20km, and find it works out at 70 seconds. So scaling that up to my 100 km ride suggests that just changing my outfit saved me a massive 350 seconds.
THAT'S NEARLY SIX MINUTES SAVED, just by wearing different clothing.
WOW !!!
Reasonably close fitting trousers, and shoe covers, for 2016
This one looks at helmets.
40 seconds (over 40km) saved by moving from a Prevail to an Evade, and a further 20 seconds saved by wearing a TT helmet.
My "Ghetto Aero" helmet is unlikely to be as good as the purpose-designed Evade, but equally well, my unmodified helmet may not have been as good as a Prevail to begin with.
It stands to reason though, that taping over 60% of the vents in the front of a helmet will improve the aero, so I'll just guess at the 40 second figure, which, when multiplied up gives me 100 seconds for the 100 km event.
You can see the tape on my helmet above. Overheating might be a problem in some places, but it was nice and cool here for both the practice and the "real thing".
This video looks at aero and panniers.
Last year, I had no bottle cages, so I carried some water bottles in my front shopping basket, with extra water and a LOT of spare kit (that I never used!) in two rear panniers.
So, counting the front basket as a pannier (it is a 20 litre fabric-sided basket!), that makes three panniers for the 2015 time.
For 2016, I had 3 litre handlebar bag, a small 2 litre top-tube bag, and a half-empty pannier at the back. So call it one pannier.
So I ditched 2 panniers worth of drag.
Using what the chaps at Specialized reckon the loss for one pannier over 40 km is (about 120 seconds!), scaling up for 2 panniers over 100 km gives 600 seconds. TEN MINUTES!!!
While I am still talking about aero, what about my altered riding position?
This video looks at 4 positions - tops, hoods, drops, and tuck.
Last year I reckon I was using the equivalent of "tops". This year, I have the bars further forwards, and a touch lower, so I reckon my "standard" position is probably "hoods" now.
My other position is on my aero horns, with my forearms fairly flat. It is a good bit lower than my standard position. But it doesn't look anywhere near as good as the guy in the video. So I will call it as "drops". But I can't stay in my "low" position for the entire time - I can't drink down there, steering is harder, and the shifters and brakes are on the "standard" set up. Can't eat or drink down their either! But I was down there quite a bit.
So, as a pragmatic step, I'm going to assume that last year I was using the equivalent of "top", and this year I used "hoods" 50% of the time, and "drops" the other 50%.
Specialized reckon that (vs tops) hoods is worth 90s over 40k, and that drops is worth a further 65s over 40k. So scaling up to 100km gives 306 seconds.
How about the bike? Is it more aero?
Nope. Large diameter aluminum tubes this year, while last year was slightly smaller diameter steel tubes. The riding position I have set up is lower, but I have already looked at that under the aerodynamic analysis.
As I mentioned above, I am using wheels, tyres, and gears taken from my previous bike, so that are the same.
Summary of savings from aero:
1) Weight loss: hard to quantify - small.
2) New bike: hard to quantify - likely small
3) Weather: hard to quantify - small
4) Clothes: 350s (clothes) + 100s (helmet)
5) Riding position: 306s
6) Water and equipment: 600s (panniers+basket)
7) Fitness: hard to quantify
Total aero gains (over 100km) is therefore:
350s + 100s + 306s + 600s
Which equals 1356 seconds.
22 minutes 36 seconds.
That goes a good way towards explaining the drop in my time of 40 minutes!
I am surprised that the biggest element came out as the basket and panniers. I will be try to do without that remaining rear pannier for the actual event, and perhaps save another 100s (I will still have the small bar bag and/or top tube bag in the airflow!) or so by doing so. Or I will strap it to the top of the rack and save about 45 seconds (according to the Specialized video I linked to above).
Next time I will look at weight!

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