On the benefits of lightweight wheels

ggoysens

Hi all,

As some may have seen in a previous post, I'm on the search for a new set of road bike wheels. Having read a lot of reviews and buyer's guides etc, I would like to discuss the benefits of a wheel being light as opposed to losing weight on some other part of the bike.

I suppose it is already well known that the main benefit from losing weight at the wheels is that it helps in acceleration as the wheels are rotating mass. But... Already a couple of times I also read something like this (quote from https://www.active.com/cycling/articles ... difference) :

"Climbing wheels are built extra light because when the grade becomes steep, the bicycle slows and then accelerates slightly between each pedal stroke. The extra energy that this pulsing motion eats up can be considerable, so reducing the mass of the wheels—especially the rims and tires—can save a lot more energy than removing considerably more mass from the bicycle or rider."

I simply don't think this is true... Imagine your riding at a constant speed uphill and the way you apply torque to the pedals is like: Torque = T, Torque = 0, Torque = T, Torque = 0 and so on at the rithm of your cadence. T is just some value. Now, let's call the gravity induced counter torque G. So, every time you put power on the pedals the net torque is T-G, every time the torque is 0 on the pedals, the net torque is -G. So, call the equivalent inertia of your bike and wheels J. During power output, you accelerate (T-G) /J, during dead spot you decelerate by - G/J. We now know that, as we are riding at constant speed, the amount of time accelerating compensates for the amount of time decelerating, or t_acc * (T-G) /J = t_dec*(G) /J. This can then be rewritten as t_acc * (T-G) = t_dec*(G). So, inertia again does not matter at constant speeds. only the total weight, through G, matters for steady state climbing.

Are there errors in this line of reasoning?
Thanks!

lesfirth

Just buy some nice wheels, ride the bike ,smell the flowers and give your brain rest.

ggoysens

lesfirth wrote:

Just buy some nice wheels, ride the bike ,smell the flowers and give your brain rest.

probably the best advice anyone has ever given to me. But yeah... This is who I am I suppose, just couldn't let it go. Both for myself and just to try to correct this piece of misinformation (if that is what it is).

But I shouldn't be so consumed by it, you are 100% right

akh

If your speed is constant, and the wheels aren't slipping, then their rotational speed is also constant and so it makes bugger all difference compared to saving the same amount of weight anywhere else on the bike. People trying to sell you stuff will blow anything they can think of way out of proportion to try and sell you something "better".

If you aren't trying to break a work record or win a grand tour, you're devoting way to much brain power to something that will make less difference than how much rest you got last night because you went the pub with you friends. If you're not going to the pub with your friends because you're worried about it's affect on your cycling performance, speak to your team manager about your contract.

ianbar

don't get me wrong, i love the technical and since side of cycling....but, i couldn't even be bothered to read all of that! same as when buying a bike, if it gets you excited buy it, ride it, love it

ggoysens

AKH wrote:

If your speed is constant, and the wheels aren't slipping, then their rotational speed is also constant

Thanks for the reply. To be sure, I meant that the average speed is constant, as I'm talking about acceleration and deceleration as well, the immediate speed of course varies.

And yeah, you are also right, about the brain power spending thing.

crescent

I have a similar approach to buying things, I enjoy the research and comparing specs etc, often to the point of over-thinking it, so I get where you are coming from. What I would say is this though, you will probably buy a set of wheels and, for whatever reason, you will want to upgrade them or replace them in the months/years to come, so don't approach it like it is the last set of wheels you will ever buy and try to find something that ticks every single box. I currently have three bikes and four sets of wheels, amassed over a period of 12 years or so. I don't race, so none of the wheels are what I would consider 'high end'. Over the years I have upgraded various stock wheels from Shimano, Alex and Fulcrum 7. I currently have a set of Fulcrum Quattros (budget aero wheel - excellent, but not especially light), a set of Campagnolo Scirocco 35s (basically rebadged Quattros I think - again, excellent but not especially light), a pair of Mavic Aksium Elites which came with my new BMC (don't have enough miles yet but seem decent enough) and a set of Cero AR24s which are quite light and make a noticeable difference to my bike when I ride it. I quite enjoy swapping things around and finding what works well for me or just moving something down the pecking order onto my winter bike for instance if I buy something new. This tinkering is part of the appeal of cycling as a hobby for me. I'm not sure of your ability on the bike, or your aspirations, but why not use your budget to buy two sets of decent wheels instead of one set of 'do it all' wheels, if such a thing exists. This will give you options and allow you to find what works for you. For what it's worth, I noticed differences in my average speeds when I swapped my Fulcrum 7s for Quattros and also a noticeable improvement on some local climbs when I fitted the Cero AR24s - my abilities on a bike are pretty modest but I felt the benefits were very much worth the expenditure. Enjoy whatever you choose

ggoysens

Crescent wrote:

I have a similar approach to buying things, I enjoy the research and comparing specs etc, often to the point of over-thinking it, so I get where you are coming from. What I would say is this though, you will probably buy a set of wheels and, for whatever reason, you will want to upgrade them or replace them in the months/years to come, so don't approach it like it is the last set of wheels you will ever buy and try to find something that ticks every single box.

Thanks for this advice. I kind of start to feel life stupid (if that's a thing) by all your advice . Don't get me wrong, I'm grateful for it.

To maybe shed some light on where I'm coming from. I'll be joining the tour transalp next summer. Only riding for a little less than 2 years now, I felt it was time to change my stock wheels (both for performance and because they start to get worn out). I'm on a rather tight budget, amongst others because I have spent already a lot of money on cycling the last few years, the merits of being quite new to the sport and going from no cycling to a lot of it in a short time I guess. So.. I'm really trying to optimize my purchase for that tight budget with the transalp in mind. That's why I felt like I didn't want to attribute more importance to wheel weight than necessary based on this, what I think, wrong information. And I also don't want anybody else to. But yeah, I am probably taking my optimization a little too far.

cougie

If you Google you'll find an account of a rider being made to carry a kilo of water up the Alpe d'huez.

He carries it in his bottles and then in his inner tubes. And then without and keeping a constant power. It didn't make as much difference as I expected it to.

First.Aspect

That analysis is correct. The sales pitch is that you speed is fluctuating slightly, though, so the rotational inertia adds up in the end. In reality, it doesn't though, because it works both ways and your bearings are pretty damn efficient. There was even a guy about 15 years ago who did the hour record on steel rimed wheels I think, so that the rotational inertia would carry through flat spots in his pedal stroke.

Light wheels do feel nice though. Probably because they are expensive, tend to look nice and have been bought against any sort of financially sound judgement.

There are much better ways to save weight on a bike; seatposts, bars, stem, tyres and tubes are the first place I'd look. Particularly on stock bikes these tend to be fairly low end. Also cables and housing, believe it or not.

If you are going to be in the Alps and have low end brakes, you could do worse than upgrade the calipers.

cycleclinic

The benefit of lighter wheels is as follws if you drop 500g you could carry 500g less water and have the same effect give or take a second or two on an alpine climb. inertia effects are minimal because a bicycle wheel does not rotate fast enough.

andyh01

I thought aerodynamics are more important than weight anyway?
As always comprises have to be made, weight, aerodynamics, stiffness costs, and you can only get any three out the four.
Same with ceramic bearings, the effective gains are minimised when grease is applied.

cycleclinic

it worse than that for ceramic bearings. unless they are campagnolo cult the races gets galled and wear more quickly meaning after a few hundred miles they bearing has more drag than a half decent steel bearing.

Aero light and stiff are all possible if you spend enough. I have a 26mm wide 45mm deep tubeless clincher set that weighs 1280g (bare) and the spoke count is 20F/24R. They dont cost too much either given what they are.

crescent

ggoysens wrote:

Thanks for this advice. I kind of start to feel life stupid (if that's a thing) by all your advice . Don't get me wrong, I'm grateful for it.

No worries, not trying to sound like a life coach by any means but I am one of life's procrastinators when faced with a purchasing decision. I usually narrow it down to two choices, pick one, then wonder what the other one would have been like :roll: .

simon_e

cougie wrote:

If you Google you'll find an account of a rider being made to carry a kilo of water up the Alpe d'huez.

He carries it in his bottles and then in his inner tubes. And then without and keeping a constant power. It didn't make as much difference as I expected it to.

IIRC a weight reduction of 1kg will save 2 seconds per 100m of vertical ascent. It doesn't really make much difference where the weight is. Yes, aerodynamics can save more time than weight until about 5% but even beyond that point the time saved from less weight is small. More at https://www.cyclist.co.uk/in-depth/1467 ... eight-rims

I think this is the original article:
http://www.training4cyclists.com/how-mu ... lpe-dhuez/

lemonenema

My personal experience with very light shallow rimmed wheels are that they accelerate quicker and feel easier on steep climbs but are not as fast on flats or descents as a deeper rimmed heavier wheel. Theyre just different, unless youre racing I wouldnt pay much notice to it.

step83

Seems to make sod all difference, I'm as slow up hill on my heavier summer rims as my winter light ones.

On the flat yes heavy ones take more oopmh to get up to speed but once your up too speed the hold it better on the flat (plus wooshy noises you only buy deep rims for wooshy noises)