# Aero Spokes vs Weight... resolve the debate !

northernneil
Posts:

**1,549**
My mate has not long ago got his first 'decent' road bike, a Boardman Carbon Pro jobby. However on his old bike the first upgrade he bought were some decent wheels.

I suggested he change the standard mavic rims that came with the Boardman for the decent wheels he had made that have the aero spokes. Anyway when he weighed them he found his decent wheels with the aero spokes were 150GM heavier than his decent wheels. Now my argument is that aero spokes will reduce his drag and save far more in energy in the course of a ride than he will notice in 150GM on the bike.

He disagrees.

Who is more likey to be right ?

(hes a big rugby type lad by the way)

I suggested he change the standard mavic rims that came with the Boardman for the decent wheels he had made that have the aero spokes. Anyway when he weighed them he found his decent wheels with the aero spokes were 150GM heavier than his decent wheels. Now my argument is that aero spokes will reduce his drag and save far more in energy in the course of a ride than he will notice in 150GM on the bike.

He disagrees.

Who is more likey to be right ?

(hes a big rugby type lad by the way)

0

## Posts

10,862Fat faux-aero alloy spokes are generally less aero than both CX-Rays and round spokes and tend to be heavier too.

Aero+smooth running bearings+stiff will beat a small increase in weight any day.

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13,279Carbon 456

456 lefty

Pompino

White Inbred

1,246I'd love to see any data on that? :shock:

10,862What's so unbelievable about that?

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1,246I'm sure, years ago that I had seen some data that said there was 'no' difference between them, I was wondering if you'd seen something else?

From a theoretical pov how would such a small shape make a measurable difference, I can see it happening with a tri spoke or xentis but not for normal spoke?

10,862Afterall the aero benefit you gain from a CX-Ray is quickly lost, and you are aerodynamically worse off, if the spoke twists.

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3,20488785Unless he is a pro climber, 150g in weight will be barely noticed by an amateur. I Run two bikes one a Spez Allez Elite which weighs around 9-10kgs and a Edge carbon which weighs 6.7kg, on training runs there is barely a time difference. Although my Edge climbs a wee tad faster.

Stevie.

727Therefore I wohuld have to say that IMHO yes - the aero wheels DO make a difference (not so sure on just the aero spokes though)!

http://coastalcommando.wordpress.com/5,987I have never noticed any benefit of aero profiles / spokes except slightly on my TT bike, where going to cosmic carbones is probably worth 10-15s on a 25 so long as you are above 25mph. Body weight (and therefore aero profile) and bike position are so much more influential on speed.

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4,1615,987But if drag increases as a square function of speed, then surely the faster you ride the much greater power required to maintain that speed, so small aero savings must have a bigger effect on actual watts (as opposed to % reduction). Otherwise, my aero wheels would have as noticeable a benefit at 1-2mph as they do at 26-27 etc?

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4,161You need to go away and think it through.

It is just a myth that aerodynamic improvements are only of benefit to really fast riders or only kick in above 25mph or other some such speed.

4,161two riders, one can do a 10-mile TT in 20-min, the other in 24-min.

Now reduce their aero drag by 5%. For the same power, all else equal:

The 20-min rider saves 20 seconds (2-sec / mile).

The 24-min rider saves 24 seconds (2.4 sec / mile).

1,246Alex you've just done a classic maths teacher thing there. Possed the problem told the pupil to go away and think about it but instead told him the answer yourself.

You should change profession.

13,279Carbon 456

456 lefty

Pompino

White Inbred

5,987OK, so what is the maths?

The wiki site is a bit vague:

http://en.wikipedia.org/wiki/Bicycle_performance

Given this simplified equation, however, one can calculate some values of interest. For example, assuming no wind, one gets the following results for kilocalories required and power delivered to the pedals (watts):

175 W for a 90 kg bike + rider to go 9 m/s (20 mph or 32 km/h) on the flats (76% of effort to overcome aerodynamic drag), or 2.6 m/s (5.8 mph or 9.4 km/h) on a 7% grade (21% of effort to overcome aerodynamic drag).

300 W for a 90 kg bike + rider at 11 m/s (25 mph or 40 km/h) on the flats (83% of effort to overcome aerodynamic drag) or 4.3 m/s (9.5 mph or 15 km/h) on a 7% grade (42% of effort to overcome aerodynamic drag).

165 W for a 65 kg bike + rider to go 9 m/s (20 mph or 32 km/h) on the flats (82% of effort to overcome aerodynamic drag), or 3.3 m/s (7.4 mph or 12 km/h) on a 7% grade (37% of effort to overcome aerodynamic drag).

285 W for a 65 kg bike + rider at 11 m/s (25 mph or 40 km/h) on the flats (87% of effort to overcome aerodynamic drag) or 5.3 m/s (12 mph or 19 km/h) on a 7% grade (61% of effort to overcome aerodynamic drag).

Surely there is a danger of mixing up proportional aero savings (5%0 as opposed to fixed reduction in x sectional area?

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4,1615,987Not quite "go away and think it through"

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4,161Besides - the main reason slower riders attain greater time savings from a given aerodynamic improvement is not because the % improvement in speed is better or worse than that attained by a faster rider (it's about the same) but simply because they are on course for longer, so they attain a greater absolute time saving.

It's this later point that you needed to latch onto - you were chasing the wrong line.

That maths looks worse than it is, and some of those factors can be simplified/removed for steady state efforts.

I did take the time and solved the equation for speed from power + assumptions in an excel model. This is what has enabled me to do performance predictions, and develop models for pacing strategies and analysis.

BTW - the paper it comes from tested the equation thoroughly versus actual power meter data and it was found to be an excellent predictor of actual performance (and it still is and has stood the test of time). There are variations on a theme that Martin has developed, some with additional factors for velodrome riding to account for the impact of the banking.

5,987Yes, took me a while to realise this! :oops:

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