Aero Spokes vs Weight... resolve the debate !

northernneil

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)

redddraggon

Proper Aero spokes, ie Sapim CX-Ray will be faster than standard round spokes, but they are also lighter than the standard round spokes.

Fat 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.

ride_whenever

Drag isn't really relevant, but if the aero ones are properly handbuilt jobbies with 32 3x spokes i'd run those purely because they'll be tougher.

chrisw12

redddraggon wrote:

Proper Aero spokes, ie Sapim CX-Ray will be faster than standard round spokes, but they are also lighter than the standard round spokes.

Fat 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.

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

redddraggon

chrisw12 wrote:

redddraggon wrote:

Proper Aero spokes, ie Sapim CX-Ray will be faster than standard round spokes, but they are also lighter than the standard round spokes.

Fat 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.

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

What's so unbelievable about that?

chrisw12

That there's a wind tunnel that has the sensitivity to pick up the differences.

I'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?

redddraggon

Well the difference is minute , but it is there. I can't provide any peer reviewed papers for a definitive proof. Most papers out there seem to concern themselves with rim depth and shape.

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

rake

didnt know boardman came with mavic rims?

White Line

rake wrote:

didnt know boardman came with mavic rims?

+1. Thought it was Ritchey.

Stevie2wheels

150g? I doubt he would notice the weight difference when riding to be honest.

Unless 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.

Chrissz

I've just switched from Fulcrum Racing Zeros to Mavic Cosmic Carbone SLRs - running exactly the same set-up (tyres, inner tubes etc.) the Mavics are heavier (by around 150g) and DEFINITELY faster on the downhill parts of rides I do regularly - by around 3 - 5mph with no noticeable penalty on the up-hill bits!

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

SteveR_100Milers

If he is a big rugby player type of bloke, then he is hardly in te category of princess and the pea. I doubt he'd notice 500g difference let alone 150g. The most important factor will be stiffness - if you are ig and heavy (as I am) then stiff wheels are far more responsive than super light weight ones, aero spokes or not.

I 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.

Alex_Simmons/RST

SteveR_100Milers wrote:

I 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.

One does not have to be above 25mph to benefit from an aero improvement, that's just another cycling myth. Indeed the same aero improvement will result in a greater time saving for a slower rider.

SteveR_100Milers

Alex_Simmons/RST wrote:

SteveR_100Milers wrote:

I 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.

One does not have to be above 25mph to benefit from an aero improvement, that's just another cycling myth. Indeed the same aero improvement will result in a greater time saving for a slower rider.

But 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?

Alex_Simmons/RST

SteveR_100Milers wrote:

Alex_Simmons/RST wrote:

SteveR_100Milers wrote:

I 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.

One does not have to be above 25mph to benefit from an aero improvement, that's just another cycling myth. Indeed the same aero improvement will result in a greater time saving for a slower rider.

But 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?

For a given aerodynamic improvement, the time on a given course is reduced by a greater amount for the slower rider.

You 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.

Alex_Simmons/RST

e.g.
two 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).

chrisw12

Alex 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.

ride_whenever

the internet is much like maths, it's more fun to give people the answers and then watch their heads implode trying to figure out how you got there...

SteveR_100Milers

Alex_Simmons/RST wrote:

e.g.
two 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).

OK, 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?

Alex_Simmons/RST

SteveR_100Milers wrote:

OK, so what is the maths?

SteveR_100Milers

Alex_Simmons/RST wrote:

SteveR_100Milers wrote:

OK, so what is the maths?

Not quite "go away and think it through"

Alex_Simmons/RST

SteveR_100Milers wrote:

Not quite "go away and think it through"

I didn't set a time line.

Besides - 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.

SteveR_100Milers

Alex_Simmons/RST wrote:

SteveR_100Milers wrote:

Not quite "go away and think it through"

I didn't set a time line.

Besides - 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.

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