Aero versus weight

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j18ter
Posts: 3
Joined: Sat Apr 29, 2023 4:07 pm

by j18ter

There is a lot of hype about aero wheels with deep rims. Some vendors of carbon wheels go so far as to claim that aero wheels win versus lighter non-aero wheels in most cases except steep climbs.
I find the supporting evidence often biased towards pros who can ride at as significant speed even uphill.
Do aero wheels make any significant difference for someone who doesn't get much beyond 30 km/h on level ground?
Currently looking for aluminium wheels for a traditional quality steel road bike. Should I go with light-weight 2.1 cm deep rims, or are 3.1 cm slightly deeper rims worth the extra weight?

Thanks,

Joachim

by Weenie


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Singular
Posts: 537
Joined: Mon Jul 27, 2020 8:59 am

by Singular

For that kind of riding and speed - choose whatever you think looks best and will make you happier. Don't sweat the weight/aero tradeoff and performance.

For me, for that use case, I'd go with shallow wheels both from a looks and feel perspective.

Hexsense
Posts: 3270
Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

A really light wheel can "feel" snappy to accelerate.
But since you are on steel bike and looking for alloy wheel anyway. It wouldn't be so light and snappy in the first place.
In that case, I'd take wheels that carry the speed better and that's the more aero one.
Also, depth isn't the only indicator of aero design. Width too. Ice-cream cone shape made of wide tire on narrow rim isn't aero.
Try to get wheel that is as wide as the tire. If you are looking to use 25mm tires, find alloy wheel that is 26.5mm wide externally.
If you use 28mm tires, find one that is wider than 28.5mm.

TobinHatesYou
Posts: 12456
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

ESPECIALLY on flat ground, aero matters more for the slower rider than a faster rider. Your time saved in absolute terms, not relative terms, will be greater.

So look at your ride profiles…are you spending a good amount of time on >5% climbs? Do you even care about speed? What are your goals?

IMO if you aren’t trying to win hilly road races, go with 50mm deep wheels.

kervelo
Posts: 866
Joined: Wed Jan 21, 2009 6:58 am
Location: Finland

by kervelo

The bikerumor had an article about these things recently:
https://bikerumor.com/aerodynamics-vs-w ... -cyclists/

MasterBean
Posts: 72
Joined: Thu Apr 30, 2020 11:18 pm

by MasterBean

Hed Belgium Plus rim. Lots of spokes. Dt Swiss 350 hub. Whatever tyre size you like.

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HBike
Posts: 190
Joined: Sun Aug 14, 2022 8:22 pm

by HBike

kervelo wrote:
Thu May 11, 2023 6:08 am
The bikerumor had an article about these things recently:
https://bikerumor.com/aerodynamics-vs-w ... -cyclists/
Nice. And as it shows again, differences are not huge esp. when people talk about wheels, where you pay 2000$ more for a 50 to 100 g reduction and a bit better aero saving you 10-30s over an hour, unless you do racing at a high level (my opinion).
For me, servicability, price/performance (and looks, too) etc. are far more important, as I ride alone and don't race. Saving 10-25s over 1h of riding at constant W/kg performance is not important _for me_.
Sure, it is nice to have, if budget allows it, or if you understand and value the physics of it (my profession), or race e.g. professionally.

So in the end, although I can afford it, I sill would stick with a Giant SLR 1 50 instead of a Cadex 50 Ultra, for example, to me a much more resonable choice which saves me 1500 Euros to be spend for other nice things.

j18ter
Posts: 3
Joined: Sat Apr 29, 2023 4:07 pm

by j18ter

This is all good information, thanks everybody.
There is one additional factor that could be significant, but hasn't been mentioned in any comment, and was not discussed in the referenced article either. Although the article thankfully explains differences between pro and amateur riders, it only discusses the steady state, i.e., riding at constant speed, essentially a race-like ride without stop and go. About half of my commute is on inner city streets with frequent stop and go at intersections. The other half has longer uninterrupted stretches, but still the occasional traffic light requires stops. How does the frequent need for acceleration from a standstill affect the equation? In the inner city portion, when I've reached full speed it is almost time again to slow down.
It was mentioned that a lighter wheel will feel snappier, but is it only a matter of feel? Doesn't the lighter wheel objectively accelerate faster and hence have a bigger impact on average speed for my use case than the steady state case would imply?
I can certainly notice a difference when I switch from my significantly heavier winter bike to the lighter road bike, but admittedly there are many other things different between these bikes than the weight of the wheels.
In the end, the snappier feel is not unimportant psychologically. Regarding the suggestion to get 50mm deep rims, that's out of the question for me. These would look out of place on this steel bike. That would also imply carbon, which I want to avoid. This means the aero difference wouldn't be huge. For me it's just between a mildly aero 31mm rim versus lowest possible weight with 21mm rims.

Nickldn
Posts: 1866
Joined: Mon Mar 25, 2019 12:35 am

by Nickldn

If your question is: would replacing my steel bike and shallow aluminium wheels with a light carbon bike and 50mm deep carbon wheels make your commute faster and more fun than the answer is yes!

Even with traffic lights, junctions and other road users to contend with, all things being equal, the carbon bike with deep wheels will be faster and more fun. But probably not by much.

Marketing talks about time savings at a constant rate of power and long distance because it's a somewhat objective measure of efficiency, which allows comparisons between products (maybe). Yet as you point out it is also deeply unsatisfactory for anyone riding on real roads. But the same kinds of savings apply: a lighter bike will accelerate better, an aero bike will reach a slightly higher speed for a given amount of effort and hold that speed a bit longer. These savings add up even when commuting, but of course they are not easy to quantity if a press release.
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j18ter
Posts: 3
Joined: Sat Apr 29, 2023 4:07 pm

by j18ter

If your question is: would replacing my steel bike and shallow aluminium wheels with a light carbon bike and 50mm deep carbon wheels make your commute faster and more fun than the answer is yes!
No disagreement about the conclusion, but that's not my question. I'm not in the market for an expensive new bike. I'm looking to replace a wheel, or possibly both wheels, that has a nearly worn break track.

The question is whether slightly deeper aluminium rims are worth the extra 200 g weight. As has been said, the difference is bound to be small, but I still need to decide between them.

Nickldn
Posts: 1866
Joined: Mon Mar 25, 2019 12:35 am

by Nickldn

j18ter wrote:
Sat May 13, 2023 7:12 pm
If your question is: would replacing my steel bike and shallow aluminium wheels with a light carbon bike and 50mm deep carbon wheels make your commute faster and more fun than the answer is yes!
No disagreement about the conclusion, but that's not my question. I'm not in the market for an expensive new bike. I'm looking to replace a wheel, or possibly both wheels, that has a nearly worn break track.

The question is whether slightly deeper aluminium rims are worth the extra 200 g weight. As has been said, the difference is bound to be small, but I still need to decide between them.
I guess the point of my post is that if you make a significant change then you are likely to notice a wothwhile difference. Otherwise not so much.

Trying slightly different wheels is likely to be much of a muchness, don't expect to be overwhelmed....
Giant Propel Advanced SL Red Etap 11s Easton EC90 wheels CeramicSpeed BB Zipp SL70 bars 6.5kg

Vitus ZX1 CRS Campy Chorus 12s Bora WTO 45 disk brake wheels Zipp SL70 bars 7.5kg

SL8 build with Craft CS5060 Wheels in progress

Hexsense
Posts: 3270
Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

Hed Jet 6 plus has alloy brake track and it's also pretty deep.
But it's only 25mm wide. So it perform best with 23mm tires. Still pretty good with 25mm tires but not wider.

If not Hed Jet 6 plus, then I'd look for alloy wheel that is 28mm wide externally, regardless of the depth.

Alumen
Posts: 165
Joined: Tue Aug 18, 2015 1:47 pm

by Alumen

I'd go for the 31mm wheel. Weight is highly overrated by people on wheels and tires, rotating mass bla = forum myth. Probably I will now get the whole forum over me, but if you know the physics formula for kinetic mass, then you understand that weight only plays a role at lower speeds. Basically when climbing on really steep slow climbs.

The 31mm wheel will be stiffer than a 21mm wheel, that also something that counts.

Otherwise, if you want to have good aerodynamics, I think the consensus is that 50mm is the minimum. Aerodynamics start to play a significant role with speeds over 20km/h, so with an ambient speed of 30km/h on ground level...

Personally, I'd pick a more heavy aerodynamic and stiffer wheel over a lightweight non aerodynamic wheel every day. Comfort levels I will figure with my tire pressure.
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sevencyclist
Posts: 92
Joined: Thu Mar 25, 2021 6:36 am

by sevencyclist

Given you have worn brake tracks, I would assume this bike sees quite a bit of braking. In cases of frequent brake use, lighter wheels would be favored by me rather than aero. The aero benefits and the power needed to build up the inertia gets washed when braking slows or stops the momentum.

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spartacus
Posts: 1049
Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

IME a nice 30mm alloy wheel feels a little faster than a standard shallow wheel.

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