cooker

So would that mean that making the upper part of the bike lighter would save more rider energy than making the wheels lighter, because the bike would be easier to rock? Or would more weight up top be better as it would somewhat resist side-to-side swaying?

gregf83 

It takes very little effort to move your bike back and forth, likely under a watt.

WhyFi

I don't think that it's terribly hard to feel a 200-300g difference in rim/tire weight when it comes to moving the bike side-to-side. When changing out a tire, hold a bare-rimmed wheel by the skewer, spin it and try tilting from one side to the other. Try it again after adding the tube/tire - it's a noticeable difference, even at the ~2 revolutions per second while in-hand, but even more pronounced at higher speeds.

I don't think that this translates to any significant difference in forward speed, but handling feel? Yeah, noticeable.

redfooj

your contact point to the bike is at a position with 50cm+ of leverage.....

WhyFi

Sure, that'll diminish the effect, but it's still noticeable.

hsuehhwa

There are a lot to consider/trade off:
1. climbing faster vs descending (brake) safer? The best climbing wheels are usually not the safest descending wheels, particularly when avg grade ~10%
2. your weight? (cross winds, spoke count...)
3. your riding style... (do you bake overly when you descend?..)
.....

bikebreak

Yes.


Also, I don't keep my bottles on my rims.

howheels

Math is hard, so here's a spreadsheet for everyone repeating the claim that wheel weight has such a drastic effect for climbing: https://docs.google.com/spreadsheets...-Uk/edit#gid=0

tl;dr: a 1KG lighter wheelset will save you ~28 seconds over a 10 minute climb. Which is the same effect as losing 1KG of body fat. Rotational weight makes zero difference. The good news is you can lose a lot more weight from your backside than you can off your wheels for even bigger gains.

Doge

The "reverse pendulum effect".
Don't know. I think it washes out. My son has me add weight on the BB for handling (because he has to make weight), while I kinda like heavy seats and it gives me a tandem feel I like.
Most the racers when having to add - add low. Even the Di2 battery has moved fro seat-post to low in the seat tube.

Doge

It is the wheels that move with the bike.
The wheels contact the pavement in a SIN wave. The front having the higher amplitude and heavier a lower amplitude. And on something like a smooth track, this does not matter much.
But on the road a pot hole hit jars the bike off course and the rider spends energy to recover. If the pot hole is to be dodged that is another change in momentum. It is easier (less work and less power) with lighter wheels.

Doge

Then the math is wrong or incomplete. I haven't looked yet, but I'm looking for the course correction calculations. the kind you might not need on a track, but do on the road. So the wind gusts (change), the road surface, the bumps hit, pot holes dodged. Are those in there? I'll look now.

Edit Add:
No they are not. So it might hold for track (and I doubt it). Not for out of the saddle real world.

wphamilton

Lower down has the weight moving less distance (left and right), with less speed. Thus requiring less force to move and having less momentum change.

Regarding the rotational inertia of heavier wheels and energy expended, I'm going to say that for straight forward motion it makes no difference to energy - power expended - except to the extent that you use brakes. Uphill and downhill, it's the same as non-rotating weight. Catching up to get in someone's draft quicker is where it could cost you.

How it impacts the serpentine motion that we all use to keep the bike balanced is a different question. I see two physical aspects of it, and two physiological aspects. Physically, there is the energy needed to make these small control maneuvers, and the actual path taken by the bike which is longer than a straight-line path. Physiologically, I think that the frequency of the needed control inputs and the force needed for each will have impact beyond the energy needed.

I propose, as a hypothesis, that the energy and force needed for control inputs are both insignificant, leaving the frequency/amplitude of control and the path taken as having more fundamental impacts. I'll posit further that heavier wheels, which oppose control changes more, will tend to produce wider arcs during the balance corrections. More particularly with lighter riders. I propose that, in practice, the wider arcs also trace a greater path distance than a series of much shallower ones. If true, the greater path taken will certainly require more energy to traverse than a straighter path, given the same bike velocity. So I think if there is anything to lighter wheel's rotational inertia requiring less energy of the rider, it's probably due largely to this path length effect. This is just a hypothesis, needing actual testing to know either way.

gregf83 

I just look ahead and avoid the potholes

howheels

You can calculate the effect yourself. How much does a pothole slow you down? 0.5 KM/h? How much time will you save accelerating from 29.5 KM/h to 30 KM/h with 1KG less rotational weight? I suspect the difference is not nearly as large as you are making it out to be.

Not to mention, the flywheel effect of a heavier rim will result in less deceleration as a result of a pothole.

bonz50

snork

Doge

In a TT you are constantly 10-20X a min making adjustments using your core. Different wheels in different environments affect the heart rate. The maths are too hard to get a good picture, but wheels can mean a few beat here or there in HR. To those that do things where winner vs 2nd (who got 2nd to Kittle by .0003 sec?) can be measured in fractions of a second look at this stuff.

howheels

I'm glad that we can now agree what the benefit a set of wheels can make

Doge

I think we are agreeing everything matters for a human performance sport.

I spent some time testing between an 80mm profile thinner wheel and 50mm profile wider wheel and found 2-3 beat in HR correlated to the wheel choice. In the testing the power was set and held to the watt. It was just one set had a higher HR. I concluded that one set was harder to control and required more core muscles to do so. And while I didn't have a portable VO2 machine, I expect energy was higher too.

I have no idea how I could have calculated it, but in several test runs I saw the pattern. All the physics helps to understand why, but actual tests are needs for things so hard to calculate.

Retoocs

Do you put down the same amount of power going downhill vs going uphill? If you aren't going flat out downhill, what difference does it make?

JohnJ80

If your wheels really are 2000g or more (rim, spokes, hubs), then those are monster heavy wheels. Almost anything you go to is going to be a major improvement. So while we can get down into the fine points of performance, this is still a pretty gross adjustment if you make the wheel change.

It's pretty easy to get to around 1500g even with alloy rims - I built a set of tubular HED Belgium wheels, DT Swiss 240 hubs and bladed aero spokes that came in around 1450g or so (28/32 spokes). The same setup with clincher rims are going to be a bit more but both are going to save you about a pound (or more) in rotating weight on your bike. That's an awful lot and you're going to notice that big time. It will be a lot easier to accelerate while climbing for sure and I doubt you'll notice much of a difference downhill but they will handle better than the heavy wheels you have now.

J.

PepeM

When you start considering the energy required to avoid a pothole into your equipment purchases, that's when you know you've gone too far.

Maelochs

Serious cyclists go ahead and fill the potholes before riding ....

Samuel D

Something is wrong with that maths. Saving a kilogram has nowhere near that effect. Climbing speed on steep gradients is straightforward: power divided by all-up weight. So saving a kilogram on an all-up weight of 80 kg improves speed by barely 1% (fewer than 8 seconds over 10 minutes). Where rolling resistance and aerodynamic drag have a significant effect – i.e. on shallower gradients – the improvement is even less.

The other factors discussed in this thread are lost in the noise.

Kittel was mentioned. His current bicycle weighs over 8 kg. So even though he win races by the slimmest of margins, and his livelihood depends on it, he doesn’t obsess about bicycle weight. That’s how unimportant it is.

It’s unseemly for avocational riders to care about a few hundred grams here or there. It just doesn’t matter.

wphamilton

10 mile climb, rather than 10 minute climb, he'd be about right with 28 seconds. If it was a tough climb. He probably just wrote it down wrong.

Extra pounds, slow-rolling wheels, dirty drive train, bad position and flapping clothes, it all adds up even for avocational riders. It's no more unseemly than other competitive behavior of cyclists, like trying to drop each other on group rides or racing to light poles. I'd say, exactly as unseemly as that.

Psimet2001 

Funny thing about this is that HED was indeed testing heavier wheels for descending around this timeframe. While the article linked is an April fools joke they did in fact run some tests. In the tour that year they had Floyd swap bikes at the top of a mountain for a descent and then swap bikes at the bottom.

Guesses on whether they were heavier wheels for descending on swapping on and off of a bike with a motor - meh.