I hate those lizard people. My sister married one, and he turns every family gathering into some kind of mind control experiment. On the upside, he can get a table at any restaurant in town on short notice.

On the topic of rotating mass: where does the energy to overcome gyroscopic inertia encountered when rocking the bike side to side come from? Surely that energy would have not been available to move the bike forward?

Jonathan: I need your help. Where can I buy a $1,500 disc brake frame with endurance geometry (i.e., stack:reach > 1.5) that I can build a 7 kg bike with?

Real question.

I last built a bike in 2017. The 800-gram frame cost $800. The 105 (5800) group set cost I think $400. Wheels were about $500 (about 1500 grams.) Riding weight, with pedals, pump, tools and tubes, tail lights, no computer, was (I think) 16.25 or so. Really nice, light bike. Oh ... it has rim brakes.

The cost of each component has doubled, last I checked. And the disc version of the frame (which I wanted, but it was not available any more) would have weighed more, as would the brake components.

Please send the build list for your $1500 15-lb disc bike. I have the cash. I don't need the bike, but .... wow, i would like it.

Factor disc aero wunderbike:

Factor's new Ostro VAM blurs boundaries with aero and lightweight design | GCN (globalcyclingnetwork.com)

And here is what Factor sponsored rider thinks about discs on road racing bikes:

Chris Froome unhappy to be on disc brakes | Cyclingnews

Chris Froome once again derides disc brakes on road bikes | Cyclingnews

Quite unusual for a sponsored rider to even peep about gear. You ride on whatever you are given, and personally accept blame for any (any!) problems experienced on the road.

Froome may have kissed and made up, but two years ago he was one of the few riders with the experience and prestige to be able to critique anything about his gear. Now, given his age and recent record, he'll be happy to ride what he's given. So now he'll be happy on discs. Or a skateboard if that is the team issue.

Thank you !


The static analysis presented elsewhere here assumes the rider and bike combo is like a sold block of wood getting pushed up an incline. In the real world, on the hard climbs, the rider is humping on the pedals with the bike swaying back and forth underneath. A lot of that energy ends up on the pedals, but some ends up absorbed by the riders legs and arms. And then there is the constant surges and accelerations that require immediate responses, and even on the climbs, frequent braking to avoid pile-ups. As if a single rider isn't enough of a complex system, then add 100 other riders to the mix, some of which are trying to help you, but most trying to lose you or make you go slower. This is so complex that basic physics isn't enough.


And what the UCI-sponsored teams use on the mountain stages may not be an indication of best gear solution. For example, everyone wants to be on tubulars for the combo of lower rotating weight and safety. But the team may not have tubular options, and have to accept something sub-optimal for their sponsors, such as tubeless clinchers. The sponsors pay money not just to win races, but to showcase gear that will be bought by dentists with platinum cards. Nowadays, you cannot sell tubulars.


Or you put most of the team on heavier aero bikes/wheels, because they are disposable and will certainly be shed off the peloton on the first giant climb. But the team leaders: they will be on the lightest possible bikes and wheels.

So what? If you don't want to ride a disc brake bike, don't ride one. Lots and LOTS and LOTS of riders with the knowledge and experience to make informed decisions about their own preferences have chosen disc brakes, and recognize the advantages.

Froome changed his opinion in 2023, citing rubbing and alignment issues with his first disc brake experiences, and acknowledged that the issues had been resolved.

This really is tedious. While the whole energy system is quite complicated, the contributions of mass and rotational inertia are quite simple. That's why it's not too hard to accurately estimate real world climbing times etc with a reasonable power model.

Or maybe they won't.

Bingo!

So should we consider all this in terms of quantum physics or perhaps string theory?

So it seems you think sponsors want their teams to lose. If I was a sponsor I'd want my team to win and I'd give them the fastest stuff possible.
But it would seem that the sponsors are indeed doing that. If you look at the fastest rubber at bicyclerollingresistance you'll notice that the fastest tubular on there isn't even in the top 10. Tubulars can't beat tubeless any more.


So just out of curiosity, do you watch professional cycling? Because it seems you don't.

If you grab the axle of a wheel, and tip it side to side, that takes energy. If you spin that wheel, and tip it side to side while it's spinning, that takes much more energy. If you tip a lighter spinning wheel, that takes less energy than a heavier spinning wheel. Energy that is used for something other than moving the bike and rider forward doesn't help you go faster, cf: tire pressure.

Despite your claims, no one is treating this as a static problem. Either you don't read what other poster write, or your comprehension is poor.

It is basic physics.

I hadn't compared TL vs. Tubular in a while. This was surprising...

Vittoria Corsa Speed 23mm tubular @ 132psi = 8.9W (narrow and hard is the fastest!!)
Vittoria Speed G+ 2.0 25mm tubeless @ 80psi = 8.3W

I intentionally compared tires from the same manufacturer. The Veloflex Record TLR 25 is faster than the Vittoria.

That pesky scientific data ruins everything! :notamused:

This might explain why I didn't like the feeling of sprinting on lightweight wheels - easier to destabilize the foundation.

ftfy

Well the bike with heavier wheels will just rock a bit less from side to side with the same effort. It might even be seen as a positive trait. A few hundred grams of wheel mass isn’t going to make much difference to this anyway, especially not at climbing speeds.

Good point.

My understanding of physics is pretty elementary, but the discussion about gyro effect and weight makes sense with what I was feeling on different wheels.

Lol. It takes more energy to move rotating mass side-to-side than it takes to move non-rotating mass. That energy comes from somewhere, and it's not going into moving the bike and rider forward.

Provide quantities. Everyone "knew" that rotating mass was more important or impactful than static mass .... until the actual math proved that differences were minuscule.

Everyone "knew" that lighter was better ... until actual experimentation and calculation proved that except for very long steep climbs, aero saved more energy.

If you think that side-to-side leaning is seriously impacting speed, do the testing, analyze the results, show the math, and people can see what's up.

Otherwise we are all just talking, and none of it means anything.

I am very different than many posters here. I can actually admit that there have been times when I said, "Well, it is just that way. It makes sense.. Think about ti and you will see." only to later be shown the actual experimental results, at which time I was (eventually) able to say, "Okay, I was wrong about that."

I feel okay about this because even Albert Einstein, did it ... he rejected quantum mechanics at first ("God does not play dice with the universe") but later he had to admit that even though the premises seemed ridiculous, the math worked out.

So ... my takeaway is that it is alright to learn.

I wish that opinion were more widely shared.

I am not a physicist, I'm offering plausible physics- based frameworks that could validate what are at present subjective observations. In the case of rotating mass, I have not seen calculations that take into account gyroscopic inertia, but it makes sense that it would matter more than non-rotating mass.

But you are not going to actually put more effort into rocking your bike are you? You will put the same force into rocking the bike, but it will just rock slightly less.

I understand why there might be a significant gap between your perspective and that of a substantial proportion of forum members, the cycling community, and current industry trends. Your typical description of cycling experiences, characterized by intense bordering on violent efforts like "humping up a hill," attacks within the pack, and being shelled out the back as you struggle home solo with tears streaming down your face, appears extreme. It's worth noting that a vast majority of sporting cyclists, including professionals in the Pro Tour, do not typically engage in such intense riding styles, except for rare occasions mid-race. Riding to many is about being smooth and efficient even thoughtful at times.

How far the bike rocks has more to do with range of motion and skeletal measurement ratios than with how much "work" it takes to rock the bike that far. It's obviously simpler to model a non-rocking bike, but I think that's an oversimplification.