Author Topic: The effect posture has on speed on a nomad  (Read 1470 times)

ourclarioncall

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The effect posture has on speed on a nomad
« on: April 21, 2021, 04:04:27 PM »
Wondering what difference the difference in posture would make in regard to speed/mileage

Probably impossible to answer, but say on a Nomad , what kind of difference could I expect in riding in the most efficient (sporty?) position to the least efficient (comfort?) position

Say over 100 miles, is my sporty position going to get me there in a significantly faster time ?

martinf

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Re: The effect posture has on speed on a nomad
« Reply #1 on: April 21, 2021, 05:29:02 PM »
Yes. About 20 years ago when I had a 44 km round trip as a commute I did an experiment to compare the effects of "roadster" bars (relatively upright position) with drop bars (relatively sporty position) on a Moulton bicycle, while keeping gearing and tyres the same.

Averaged over several trips to try and reduce the inevitable bias due to weather, differences in physical condition/motivation, etc., the speed with drops was 25 km/h, with "roadster" bars 22.5 km/h, so about an 11% increase.

More recently, about 10 years ago I did a test ride with my Brompton folder, riding predominantly in the low position on P-bars (very aerodynamic but very uncomfortable).

Around my usual moderately hilly training circuit of about 50 kms I managed an average speed of 25.89 km/h, despite the lower efficiency of the folder due to bar and frame flex, slightly less efficient 5-speed hub gearing and inferior tyres. This speed was slightly better than my average of 25.19 km/h for 26 circuits on my lightweight derailleur bike with drop bars and a relatively sporty position.

The ride with a very low position was a one-off (too uncomfortable to repeat), so not statistically significant.

The big difference was that I could just about sustain the very low position on the Brompton for less than 2 hours, whereas I could go all day in the less extreme but more comfortable position on the derailleur lightweight.

Another bit of anecdotal evidence in favour of comfort was a couple of rides I did from where I live in south Brittany to the coast in north Brittany. The distance is about 130 km give or take 10 kms.

The first time I used my derailleur lightweight, and my speed for the trip was about 24 km/h.

The second time I used an old 16" wheel Moulton, with 5-speed hub gears and drop bars, with this I took longer and my speed for the main trip was about 22.5 km/h.

But the Moulton has an effective front and rear suspension system, so at the end of the ride I felt much fresher and was able to do another little circuit of about 20 km.

Relatively wide tyres run at relatively low pressures have a similar effect to suspension, which influenced my choice when I came to buy a Thorn touring bike.

So for best efficiency when cycling my priorities are :

1 - Aerodynamics, so a reasonably sporty position with drop bars or flat bars and bar ends. But NOT at the expense of comfort.
2 - Efficient tyres. I like them fat but light, with supple side walls and not much tread. There are tables on the Internet comparing the efficiency of different models of tyre. As for position, this is a compromise, the fastest possible tyres have no puncture protection so are actually slower when the time spent on changing tubes or patching them is factored in.
3 - Weight. As I am fairly heavy myself I don't bother about having the lightest possible bike or components. But if cycling somewhere hilly it makes good sense to carry the smallest reasonable amount of luggage. Having lots of pannier bags is also not very aerodynamic, so will affect speed even on flat terrain.

Other stuff, like the type of gearing, is less important for me. Hub gears are supposed to be less efficient than derailleurs, but in back to back tests comparing Shimano Nexus 8 Premium and derailleur I didn't notice all that much difference. Rohloff is supposed to be more efficient than the Shimano hub gears and has the range needed for mountain touring.

Anyway, factoring in the extra time spent maintaining derailleurs makes hub gears faster overall for me for commuting and other utility rides. Once I got over the price hurdle for the Rohloff, the same principle applies for my idea of long-distance touring.

It would be different if I was into road racing. 





JohnR

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Re: The effect posture has on speed on a nomad
« Reply #2 on: April 21, 2021, 09:34:49 PM »
Wind drag is, I think, proportional to the square of the effective wind speed (bicycle speed +  any headwind or - any tailwind). I don't normally go fast enough (a good average speed is 12 mph) to worry about the wind drag but if I'm cruising downhill or fighting with a headwind then I'll get into a more sporty position.

PH

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Re: The effect posture has on speed on a nomad
« Reply #3 on: April 21, 2021, 10:02:19 PM »
As JohnR says the faster you go the more it makes a difference, you could play around with the calculator here
http://bikecalculator.com/

Pootling along on an un-aerodynamic bike with luggage strapped all over it, the difference is going to be minimal
Pushing a bit harder at Audax pace and it maybe adds as much as 10% though 5% is probably more realistic
If you're a lean mean racing machine, riding solo, then it makes a huge difference, Time Trialists value aerodynamics over weight, for good reason.
For most of us, it's a bit academic, we're most efficient when we're comfortable, you wouldn't have to lose much comfort to negate any aerodynamic gains.
There are some easy wins of course, really basic stuff like not having flapping clothing.

steve216c

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Re: The effect posture has on speed on a nomad
« Reply #4 on: April 22, 2021, 09:28:19 AM »
It is fairly easy to experience the difference posture has on your bike speed without making any big mechanical changes. I have a couple of long downhills on my home commute (obviously uphills in the other direction) which are perfect for the experiment. You'll need a bike computer or need to time between start and a finish point if you don't have one.

Start at the top of your favourite hill and roll without pedalling sitting in the most upright position you can. Keep an eye on your bike computer for the maximum speed reached on the roll down the hill. If you don't have a bike computer have a point around the bottom of the hill and time how long it took rolling from top to that point.

Now repeat, but this time start rolling but with your over body as low down as you can get it to reduce wind resistance. Compare your top speed or the time it took to reach your chosen point.

You should see that the 2nd attempt would have achieved a faster descent despite gravity being the same force powering your bike. What will have slowed you was the wind resistance. Replace gravity with your own muscle power and it stands to reason that the same amount of effort with less wind resistance would achieve similar results. So posture plays a key part of how fast you can ride.

But it is not all about speed. The ultimate riding position depends on your comfort requirements and factors concerning why you are riding as well as the kinds of rides you are making. Although my own bike has quick release options for adjusting saddle and handle bar positions, I generally leave them in the position I feel most comfortable with most of the time rather than constantly tinker for optimal settings for top speed on every single ride. Arriving feeling invigorated because the ride was enjoyable is always a better feeling than arriving in record time but feeling worse for wear. Finding that compromise that suits you and your riding style is the key. If you aren't enjoying your rides, you simply won't use your bike so much- which defeats the object of purchasing a decent thoroughbred if it doesn't get out of the bike shed on a regular basis.

For me, I prefer a sporty lower but still upright position. My bike came with butterfly style bars, and although this allowed me to ride in a dropped position and cheat the wind, I found that flat bars (+ bar ends) suited me better for 95% of my daily use- which I retrofitted after around 1000 miles of ownership. I like to take in my surroundings and have good visibility, and dropped bar position meant for me that this was compromised. Dealing with traffic, avoiding potholes or taking in the flora and fauna as I cut through the forest short cut (Wild boars anyone?) would not be so easy for me with dropped bars.

A comfortable compromise on  posture when riding will allow you to ride longer even if not as fast as in a racing position, but allowing you to cheat some of the wind to get a reasonable speed. Even if commuting with your bike- a slightly slower comfortable posture may add less than minutes to a 10 mile ride- which in the grand scheme of things is a small price to pay if the experience is more pleasurable than a sporty posture that is not so comfortable.




If only my bike shed were bigger on the inside...

JohnR

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Re: The effect posture has on speed on a nomad
« Reply #5 on: April 22, 2021, 09:47:06 PM »
As JohnR says the faster you go the more it makes a difference, you could play around with the calculator here
http://bikecalculator.com/
Thanks for that link which I hadn't previously come across. The numbers it produces are quite credible and it clearly shows the effect of a headwind or tail wind (put in a negative number). However, it's a fit cyclist who can maintain their speed into a significant headwind. I instinctively tend to slow down in order to reduce the effort.

Danneaux

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Re: The effect posture has on speed on a nomad
« Reply #6 on: April 23, 2021, 12:23:08 AM »
Headwinds are a major reason why I prefer drop handlebars (and for the wide variety of hand positions). Riding on the drops, "knees inside elbows" make a considerable difference, even on a touring bike with panniers as I found riding along the North Sea in the Netherlands on a day with Beaufort 7 winds gusting to Beaufort 8.

First composite photo below shows my preferred all-'round riding position with back at a 45 angle with elbows slightly bent and hands on brake hoods. The second photo shows how I battle stiff headwinds. Third photo shows the  variety of hand positions I use with drops.

Best,

Dan.
« Last Edit: April 23, 2021, 06:50:39 AM by Danneaux »