Quality high spoke count carbon disc rims.

[Samuel D]

The % gains from better aeroz are bigger at higher speeds

Technically true, but if you do the sums (or compare Hoods versus Drops positions on Bike Calculator for a couple of power outputs), you’ll find this effect to be small: on the order of a tenth of one per cent for reasonable power differences. That is, the percentage improvement of any aero gain barely changes across normal power outputs. Or in still other words, weak riders benefit nearly as much as strong riders from aero gains (except to the – probably large! – extent that weak riders care less about speed).

As you say, slow riders actually benefit more in absolute time gains, but that’s not a sensible comparison metric. It’s a bit like saying a marathon runner beating the record by 5 seconds is a more outstanding athlete than a 100 m sprinter beating the record by 1 second.

Fertile ground for marketing departments, of course. If you take a company like Specialized, it’s clear that they have marketing people who understand maths. They often play with the public’s weak understanding of maths in their performance claims.

[mrcharly-YHT]

Samuel, have you ridden any of these events?

[Samuel D]

Certainly not. Should that bar me from discussing the technical performance of wheels?

[mrcharly-YHT]

No - but you are telling people who have ridden these wheels and ridden in these events that their personal experiences are wrong.

Such long events involve exposure to varied conditions, varied wind speeds and angles. That is difficult to calculate and analyse.

I would listen to practical experience over theoretical analysis.

[Karla]

How much? I don't know, and haven't tried to work it out properly, but I'd guesstimate of the order of a couple of hours over the course of a long race.  Likely to be much more worthwhile on a flatter, windy event like IndyPac or TABR, than a hillier one with a prevailing tailwind like TCR.  Aero wheels won't power the bike for you: will make nowhere near as much difference as optimising body position, pedalling slightly harder, taking fewer / shorter breaks or even getting rid of a dynamo, but still worth having, and will make more difference than shaving grammes off luggage weight.

Not so fast!

According to Wattshop (who should know), upgrading box section rims to deep carbons will save 20-25W at 40 kph.  Halving the speed will divide the power gains by 8, assuming (as I am) that you're still in the same region of aero operation - so the saving from aero wheels will probably actually be pretty much the same as from running a 3W dynamo, turned on. That's a bigger saving than running a dynamo turned off, obviously.

[Karla]

No - but you are telling people who have ridden these wheels and ridden in these events that their personal experiences are wrong.

Such long events involve exposure to varied conditions, varied wind speeds and angles. That is difficult to calculate and analyse.

I would listen to practical experience over theoretical analysis.

Much as I hate to agree with Samuel D, Zigzag's claim that a rear disc could take him from 52 to 60 kph is pretty suspect: you need to apply about 1.5 times the power to bridge that gap, so that advantage isn't going to come solely from changing a rear wheel.

[Samuel D]

No - but you are telling people who have ridden these wheels and ridden in these events that their personal experiences are wrong.

Sometimes they are wrong, just as my conclusions from my experiences are sometimes wrong. Humans have a vivid imagination. Knowledge is useful to know when our imagination is getting the better of us.

But experience is valuable and I respect it.

According to Wattshop (who should know), upgrading box section rims to deep carbons will save 20-25W at 40 kph.

I’m not convinced they should know. First, they’re in the business of selling gear, to which end it is customary to exaggerate the importance of gear. Second, their latest blog entry (the only thing I’ve read by them), while interesting, includes this mistake:

“10% lower air density means 10% less aero drag or 2.15% (10^1/3) faster.”

That’s incorrectly defining the problem, which seems to be endemic in performance cycling. The correct answer is about 3.5% faster.

[Frank9755]

The % gains from better aeroz are bigger at higher speeds

Technically true, but if you do the sums (or compare Hoods versus Drops positions on Bike Calculator for a couple of power outputs), you’ll find this effect to be small: on the order of a tenth of one per cent for reasonable power differences. That is, the percentage improvement of any aero gain barely changes across normal power outputs. Or in still other words, weak riders benefit nearly as much as strong riders from aero gains (except to the – probably large! – extent that weak riders care less about speed).

As you say, slow riders actually benefit more in absolute time gains, but that’s not a sensible comparison metric. It’s a bit like saying a marathon runner beating the record by 5 seconds is a more outstanding athlete than a 100 m sprinter beating the record by 1 second.

Fertile ground for marketing departments, of course. If you take a company like Specialized, it’s clear that they have marketing people who understand maths. They often play with the public’s weak understanding of maths in their performance claims.

That's not correct. In a competitive cycling, such as time trialling or ultra-racing, weak(er) riders do care an awful lot about speed.  Some spend large amounts of time and money to obtain small gains. 
Your sprinter analogy is not right: a better one would be to say a marathon runner coming in 1st place would have x seconds benefit while a runner in 1000th place might have 2x seconds benefit.

Bottom line is that it would be worth the OP getting some more aero wheels for his next TCR.  But better route-planning would make a far bigger difference!

[Frank9755]

Much as I hate to agree with Samuel D, Zigzag's claim that a rear disc could take him from 52 to 60 kph is pretty suspect: you need to apply about 1.5 times the power to bridge that gap, so that advantage isn't going to come solely from changing a rear wheel.

Yes - that kind of difference will mainly be due to wind conditions and leg strength being different on the different days.

The way you test this kind of thing if you don't have a wind tunnel is to do a roll-down on a hill with no traffic on a day with no wind.  You roll down the hill with set-up A and see how far you get before you stop, then repeat with set-up B.  Ideally you do each at least three times and take the average.  The differences you are looking for are usually small (or else you wouldn't need to do the test)

[Frank9755]

Halving the speed will divide the power gains by 8

Only if you halve the headwind too!

[zigzag]

Much as I hate to agree with Samuel D, Zigzag's claim that a rear disc could take him from 52 to 60 kph is pretty suspect: you need to apply about 1.5 times the power to bridge that gap, so that advantage isn't going to come solely from changing a rear wheel.

Yes - that kind of difference will mainly be due to wind conditions and leg strength being different on the different days.

The way you test this kind of thing if you don't have a wind tunnel is to do a roll-down on a hill with no traffic on a day with no wind.  You roll down the hill with set-up A and see how far you get before you stop, then repeat with set-up B.  Ideally you do each at least three times and take the average.  The differences you are looking for are usually small (or else you wouldn't need to do the test)

there is this training loop that i regularly ride (have ridden 70+ times) and on one short but enjoyable stretch i always push hard to check what speed i can achieve. with the box section wheels it's always between 50-55kph, depending on wind direction; with the front 55mm and rear disc i managed to hit 60kph three times iirc. it's nowhere near scientific, but also not a one off massive tailwind situation.

[Frank9755]

Psychology also plays a part: when a rider believes he has a fast setup and is pushing for high speed can often find a little bit more than when he knows he has a slower setup and, even the best effort won't lead to a pb.

[grams]

According to Wattshop (who should know), upgrading box section rims to deep carbons will save 20-25W at 40 kph.

The citation on there goes to a page by FLO cycling that doesn't include any measurements in Watts, and following the links to the rest of their website is a rabbit hole of incredibly dodgy maths. The nearest I can find to a trustworthy number is "156 g" of drag savings in a 30 mph wind tunnel test, which is a weighted averaged across various yaws. This can also be expressed as 1.51 Newtons, which is 20.25 Watts.

According to another chart there a rider on the drops has a total aero drag at 30 mph of 35.241 N, which is 471 Watts! So you only save 20 watts if you were already putting out 471 watts +mechanical resistance.

Aero drag power is proportional to the cube of velocity, so scaling these down to 40 km/h it's 11.6W saving and at 20 km/h it's 1.4W.

(also, they're comparing to Open Pros, which are the boxiest of box section rims. Comparing to typical semi-aero alloy rims found on most bikes the savings would be even less)

[Karla]

1) 40 kph is 25 mph not 30 mph.
2) A saving from the wheels will be (almost) independent of rider position, which has a huge effect on aero. 
3) You could be doing 0 W going downhill at 40 kph and the aerodynamic properties of the wheels would still be exactly the same. 

For all these reasons, saying "You only save X power if you're already putting out Y power" is rubbish. 

FYI, Wattshop is Dan Bigham, whose career has included being an aerodynamicist in F1, working with olympic athletes at British Athletics and working in the Drag2Zero wind tunnel.  He currently runs an aero testing service similar to what Xavier Disley's setup at Aerocoach.  Oh, and he's won national titles on both track and road.  Flo are a reputable brand of wheels who have been around for several years and should know their CFD onions pretty well by now.

[grams]

1) 40 kph is 25 mph not 30 mph.

That's exactly my point! The Wattshop's citation for its "20-25 watt" number at 40 km/h is web page that features no numbers in watts, and only includes wind tunnel tests done at 30 mph. I've attempted to work out how a watt number might be derived from the numbers there and come up with a very different number.

2) A saving from the wheels will be (almost) independent of rider position, which has a huge effect on aero.

3) You could be doing 0 W going downhill at 40 kph and the aerodynamic properties of the wheels would still be exactly the same. 

For all these reasons, saying "You only save X power if you're already putting out Y power" is rubbish.

That's a fair point but what proportion of any given ride might that apply to? And any ride that has a lot of downhill will also have a lot of uphill, where you don't benefit much from aero gains.

FYI, Wattshop is Dan Bigham, whose career has included being an aerodynamicist in F1, working with olympic athletes at British Athletics and working in the Drag2Zero wind tunnel.  He currently runs an aero testing service similar to what Xavier Disley's setup at Aerocoach.  Oh, and he's won national titles on both track and road.  Flo are a reputable brand of wheels who have been around for several years and should know their CFD onions pretty well by now.

None of that means the numbers (and especially the way they've chosen to present them) on their respective websites aren't garbage.

[Samuel D]

The citation on there goes to a page by FLO cycling that doesn't include any measurements in Watts, and following the links to the rest of their website is a rabbit hole of incredibly dodgy maths.

Let’s not forget that FLO Cycling is the company that used to promote the fairy tale that we usually ride around in high-yaw conditions. I complained about this a while ago. Now FLO has redesigned the wheels and put this statement on their website:

“After analyzing our data, we learned that a cyclist experiences much shallower angles than we originally thought. We now know a cyclist spends 80% of their time riding between 0 and 10 degrees of yaw. This discovery led us to design the new FLO wheels to be fast at low yaw angles.”

Oops!

History shows they make up this stuff as they go along.

FYI, Wattshop is Dan Bigham, whose career has included being an aerodynamicist in F1, working with olympic athletes at British Athletics and working in the Drag2Zero wind tunnel.

Then the maths howler I mentioned here is all the more surprising.

Trust but verify. Snake oil abounds. In the absence of snake oil, incompetence often stands in.

[morbihan]

The % gains from better aeroz are bigger at higher speeds

Technically true, but if you do the sums (or compare Hoods versus Drops positions on Bike Calculator for a couple of power outputs), you’ll find this effect to be small: on the order of a tenth of one per cent for reasonable power differences. That is, the percentage improvement of any aero gain barely changes across normal power outputs. Or in still other words, weak riders benefit nearly as much as strong riders from aero gains (except to the – probably large! – extent that weak riders care less about speed).

As you say, slow riders actually benefit more in absolute time gains, but that’s not a sensible comparison metric. It’s a bit like saying a marathon runner beating the record by 5 seconds is a more outstanding athlete than a 100 m sprinter beating the record by 1 second.

Fertile ground for marketing departments, of course. If you take a company like Specialized, it’s clear that they have marketing people who understand maths. They often play with the public’s weak understanding of maths in their performance claims.

That's not correct. In a competitive cycling, such as time trialling or ultra-racing, weak(er) riders do care an awful lot about speed.  Some spend large amounts of time and money to obtain small gains. 
Your sprinter analogy is not right: a better one would be to say a marathon runner coming in 1st place would have x seconds benefit while a runner in 1000th place might have 2x seconds benefit.

Bottom line is that it would be worth the OP getting some more aero wheels for his next TCR.  But better route-planning would make a far bigger difference!

That last point you made gave me and my wife a good chuckle at this end Frank. Maybe a set of MTB endurance wheels would be better suited to this rider .
The reality is on these ultra races that have no set route is that  pretty well everyone will find them selves on some  rough/mixed surface at some stage, even if its not to the extent that I experienced it on TCR. Hence the emphasis on a bomb proof aero wheel that can deal with some rough stuff as well as the heavier bike set up.

On the (few) days I kept to the tarmac my average speed hovered around 25kph average, and with hours on the aero bars ( for example coming down the Trento valley from Brenner, or day one east of Geraardsbergen) I'm sure the aero wheels would pay pretty big dividends.
Likewise, grinding up the likes of Monte Grappa would have been less of a nut buster.

As you say though, job one is to get to the end on a sensible route.

[Frank9755]

Let’s not forget that FLO Cycling is the company that used to promote the fairy tale that we usually ride around in high-yaw conditions. I complained about this a while ago. Now FLO has redesigned the wheels and put this statement on their website:

“After analyzing our data, we learned that a cyclist experiences much shallower angles than we originally thought. We now know a cyclist spends 80% of their time riding between 0 and 10 degrees of yaw. This discovery led us to design the new FLO wheels to be fast at low yaw angles.”

Oops!

The other comment you linked to was very interesting!

[Samuel D]

It certainly interested me. Anyone who wants the Catalyst Cycling white paper, Mathematical Model of Yaw Angle Distributions for Bicycle Wheels, may email me for it (the company, a startup, seems to have disappeared along with their hosting of the paper). If someone feels like hosting it for a while, even better. As said in the other thread, it ends like this:

“The main conclusion that can be drawn then is that wheels should be designed for much lower yaw angles than those that are currently being used. This means using narrower tires and narrower rims, as well as less bulbous rim shapes.”

[Pedal Castro]

It certainly interested me. Anyone who wants the Catalyst Cycling white paper, Mathematical Model of Yaw Angle Distributions for Bicycle Wheels, may email me for it (the company, a startup, seems to have disappeared along with their hosting of the paper). If someone feels like hosting it for a while, even better. As said in the other thread, it ends like this:

“The main conclusion that can be drawn then is that wheels should be designed for much lower yaw angles than those that are currently being used. This means using narrower tires and narrower rims, as well as less bulbous rim shapes.”

I'll happily host it linked via one of my blog posts.

[Samuel D]

Cool. Think I could email it to you? Contact me by PM or email if so.

[zigzag]

yaw angle rarely exceeds 10deg, most often it is 4-5deg as explained in this video

toroid shaped wheels handle better (i.e. are easier to steer) in crosswinds as the airflow doesn't have a sharp edge to cling onto.

[DuncanM]

While their previous statements seem fairly dumb, the science section on their website seems relatively sensible. It seems like an eminently logical process to measure the conditions in which the wheels are used, recreate them in a model, test a variety of designs in that model, and iterate.
http://flocycling.blogspot.co.uk/2016/03/flo-cycling-wheel-design-series-step-4.html
The CFD images have parts that I think are a bit odd, but the tech that they have been using is pretty solid, so I can't shoot any holes in it...

[morbihan]

I switched out my regular dynamo Bel head rims from the endurance bike last week for a set of mavic Krysirium carbon disc. They are not deep profile and no dynamo so comparatively light. Same tires . paris/roubaix 32mm.
I've ridden them on a set rolling loop of a about 55km several times, and in comparison to the Bel Hed wheels they feel MUCH faster. (holding 32kph average)  Momentum is not lost up hills so quickly and I suspect the ride is more comfortable. I was pretty shocked at the contrast actually.
The spoke count is 24. Enough? I'm not sure. Would adding a big son dynamo to a similar wheel build negate all the benefits? Also not sure.
Will definitely be ditching weight off the bike for the next long distance/bike packing race and I keep an eye out for some racier wheels that still retain enough strength for peace of mind.

[Frank9755]

Nice wheels make riding much more pleasant.
Answer depends on how heavy you are. 24 is fine (depending on rim, spokes and build) if you are <70kg, maybe not if 90kg (+ much luggage)