Newbie - Why aren't Aero section rims good for climbing?

Wesselwookie wrote:

edster99 wrote:

Strava tells a story of an average speed difference of about 2.6kph between winter bike (blue ribble / 11kg / 36 spoke low profile rims) and summer bike (carbon Ridley /8.2kg / variety inc deep section carbons). Right now, that is a comparison of almost exactly 3000km on each so quite a good comparison. So - something is making a difference, and its not just the legs!

That may be true but unless you are using both bikes in exactly the same conditions it may simply be you travel slower in the winter than the summer.
My winter average is 1 to 2 mph slower.

Colder air is denser...

700c wrote:

The idea that anyone would neglect their own training or technique and rely on expensive equipment 'to make them go faster' is also pretty patronising in this debate, to be honest.

Really? Many, many people are buying bike kit (often prefixed with the word "carbon" or "lightweight") simply because they can. For lots of cyclists training is not a priority, while having the 'right' gear most certainly is.

If you're happy with your wheels that's great. I really don't have a problem with it, and you don't need to justify yourself. I am merely trying to explain that the marketing guff and the real world can be some distance apart. Wind tunnel data is certainly not irrelevant, it's how people test aero performance.

Simon E wrote:

Another point: when comparing wheelsets you don't know where the weight has been saved. If it's from the hub it is of very little value in helping you go uphill; but if it's off the rim then it is likely weaker, with a thinner brake track. You may end up having to replace them much sooner than you might expect.

Keith Bontrager's now famous aphorism applies: Strong, light, cheap. Pick two.

disagree going uphill it's just about all up weight.
saving weight on the rim is only beneficial for accelerating, I dont normally find myself acelerating uphill.
each 'micro acceleration' will be accompanied by an equivalent micro deceleration between thr downstrokes. No net benefit when climbing from lower rotational mass. There may even be a benefit from angular momentum storing energy like a flywheel. (heavier rims but identical overall bike weight) but this would be tiny for the sorts of weights we are talking about.

Simon E wrote:

Firstly, let's dispel a couple of myths: lightweight wheels will not make much difference to your climbing and aero wheels will not noticeably improve your speed on the flat.

A lighter wheelset may feel a bit nicer but it won't have much effect on the time it takes. If you're on the heavy side then the percentage of all-up weight saved (which is what really matters) is miniscule.

As for aero wheels, even at 25mph you're looking at going 1-1.5% faster compared to a traditional 32-spoke box section wheel. A semi-aero rim (25-30mm) with ~20 spokes that is common now is likely to gain you at least half of that. American Classic 430, Bracciano or any number of others would do the job but after reading more wheel discussions than I care to count I'd get a handbuilt set with something like H Plus Son Archetype or Velocity A23s.

Unless your wheels are worn and need replacing I'd spend the money on a week riding somewhere nice. Riding your bike lots will do more for your fitness and enjoyment than all the bling in the world ever could.

I basically agree with this and I'm glad someone has explained more about this type of wheel! However I have a couple of cavets with your excellent reply.

First, there is an argument that if you do not have good souplesse (smooth regular pedalling style) then wheels do have micro accelerations all the time. Pedalling style is likely to be worse at high power input, such as when ascending. This effect is plain to see when using an inappropriate gear on a slope as the bike lurches forward with each downward stroke.

This means the the lower rotational weight, especially on climbs is helpful. For beginners this is more likely to be the case. So it's possible that light wheels could actually give someone with a poor pedalling style a small but measurable advantage on climbs.

Secondly, the 1%-1.5% figure for aerodynamics only applies for time trialists moving at 25mph+ who have presumably already adopted an aerodynamic position. For general riding any effect is unlikely to be noticeable at all

vorsprung wrote:

the lower rotational weight, especially on climbs is helpful. For beginners this is more likely to be the case. So it's possible that light wheels could actually give someone with a poor pedalling style a small but measurable advantage on climbs.

Measurable? I doubt it. We're talking about tiny micro-accelerations within each pedal stroke. An improvement in pedalling technique (and choice of gears, if possible) will be far more beneficial. Lighter, fast rolling tyres and lightweight inner tubes would be a better bet.

vorsprung wrote:

Secondly, the 1%-1.5% figure for aerodynamics only applies for time trialists moving at 25mph+ who have presumably already adopted an aerodynamic position. For general riding any effect is unlikely to be noticeable at all

The numbers are from wind tunnel tests of just the wheel and tyre. The aero effects still exist at lower speeds since physics doesn't change from 15mph to 25mph. But I agree, it's meaningless for general riding.

700c wrote:

It's basically personal opinion. This has been covered many times before and there are a couple of usual suspects here who always come out against aero/ lightweight wheels - or perhaps the idea of someone else spending what they consider to be a lot of money on equipment.

It's not my opinion, the numbers are consistent across a wide number of sources. We all like shiny kit but just because brand X says their wheels are fast/light/whatever doesn't mean you just buy it and automagically go faster.

Simon E wrote:

The numbers are from wind tunnel tests of just the wheel and tyre. The aero effects still exist at lower speeds since physics doesn't change from 15mph to 25mph. But I agree, it's meaningless for general riding.

It's strange how the 'you have to be going fast to benefit' thing is so often repeated when it's not the case, as you can see with a play on here:

http://www.cyclingpowerlab.com/componentaerodynamics.aspx

vorsprung][quote=Simon E wrote:

... then wheels do have micro accelerations all the time.

How does wheel "micro accelerations" affect the overall speed of climbing?  The amount of energy to increase the rotational speed of a wheel is negligible, my 3 year old daughter can accelerate a wheel significantly with her one finger,  you should hold a couple of different wheels and give it a try yourself and see if you can feel the difference in energy required to accelerate different weight wheels.

PaulBox wrote:

I've been told that aero section rims will improve average speeds on the flat by between one and two miles per hour, is that bull?

Yes!

PaulBox wrote:

I've been told that aero section rims will improve average speeds on the flat by between one and two miles per hour, is that bull?

If you want aero wheels because they are shiny and everyone wants them, get it. But for the majority of normal people riding around they offer very little to no increase in performance. If you have money to throw around you are better off getting some lighter wheels. OR you have enough money to get wheels that are both light and aero.

SammyG wrote:

Your not going to feel 500g on a climb, or notice aero wheels. The only time you do notice aero wheels making a difference is when you have a side wind and your getting blasted of the road, especially annoying on a decent.

I'd disagree re not noticing 500g, I've just switched to 300g lighter wheels and they certainly feel faster up hills to me. My hill times seem to confirm they are too.

I find it particularly noticeable when spinning them up to speed again after a steep section on a hill.