Rotating Weight Doesn't Matter (GCN Content)

[oldpotatoe]

Originally Posted by charliedid View Post
If wheels that spin up fast make me feel faster will I go faster?

I'm inclined to say yes.

Except most times they spin up faster' cuz they are stiffer, not lighter.

"Energy it takes to accelerate a bike and rider depends on the mass of the bike and rider"...180 pound rider and 20 pound bike or 185 pound rider and 15 pound bike...

[reuben]

Originally Posted by Mark McM

You missed the point (perhaps on purpose). The exercise was to show that lighter bikes won't always accelerate faster. If the difference in air resistance was omitted, then you get back to simplistic question of whether lighter bikes perform better, all else being equal, which we all agree was true

No, I got the point. You claimed that the heavier system accelerated faster, but it was only because you changed the resistance. The key phrase is "all else being equal".

Originally Posted by Mark McM

Because air resistance increases non-linearly with speed, doing the true calculation would require non-linear differential equations.

Agree that it's nonlinear, but diffeqs aren't needed. You'll reach terminal velocity.

[madsciencenow]

Originally Posted by ergott

Then you can just tell the rider they are lighter and not bother upgrading the equipment.

"Hey this wheelset has a special internal carbon matrix layup schedule that drops 200g in each rim"

I’m as susceptible to this as the next guy and would swear up and down that I can perceive this difference or that but I bet if there was a way to blind the wheels, frame, etc., I’d be hard pressed to know a 200g difference all other things being equal. The average piss is about 12 ounces or 340 g and I don’t ‘feel’ this after stopping for a bio break by the side of the road (i.e. I don’t feel lighter weight but I do feel relief from the pressure).

I’ve ridden a ton of different wheels and there seems to be major differences in how they feel and I’d go so far as to say they even feel different based on weight but there is just no good way for me to objectively say it’s the weight that’s providing this result or perception. I like to believe it is but to circle back to my opening line, I’m susceptible...


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[redir]

I love how this argument still comes up once in a while

If you compare two wheel sets, one set is a climbers wheel set with carbon rims versus the other wheel set that for the sake of arguing to the extremes to prove a point are made with rims of granite then no one will argue that rotational mass doesn't matter.

It will be much harder to spin up the granite wheels then the carbon one's. Of course once they are spun up they will retain that energy but you could get blown off the back at the start line while trying to spin up.

But when you are talking about normal bicycle wheels even comparing carbon Zipps to Aluminum Shamal's or something like that, the difference between the weight is just not enough to matter.

[cmg]

the GCN vid didn't differentiate where the weight was located on the wheel, whether the weight was located at the rim or the hub. This is an old argument, try riding a wheelset with "gatorskin" tires and puncture resistance tubes and then ride the same wheelset with Vittoria Diamante Pro Light tires (180g or less) and latex tubes. Which would you prefer? Yes, aero matters and you'll probably be only 15% slower but why carry any extra weight if you don't have to? It doesn't take into account on the rider providing the torque, how much energy is expended to spin the wheels overall. It only looks at the final result in terms of time and speed. Flawed, incomplete.............

[Black Dog]

Originally Posted by redir

I love how this argument still comes up once in a while

If you compare two wheel sets, one set is a climbers wheel set with carbon rims versus the other wheel set that for the sake of arguing to the extremes to prove a point are made with rims of granite then no one will argue that rotational mass doesn't matter.

It will be much harder to spin up the granite wheels then the carbon one's. Of course once they are spun up they will retain that energy but you could get blown off the back at the start line while trying to spin up.

But when you are talking about normal bicycle wheels even comparing carbon Zipps to Aluminum Shamal's or something like that, the difference between the weight is just not enough to matter.

This is what physics and all the data tells us. I will give anyone my bikes if they can discern the difference between two wheels that are other wise identical except for a few hundred grams added to the rims of one set in a blind test. Or move the mass from the rims to the frame and repeat the same experiment. When people say that this wheel or that (within the realm of wheels that we would consider for performance oriented road bikes) spins up faster they are simply misperceiving and exhibiting a conformation bias driven placebo effect. The mass differences as a percentage of total rider/bike mass is so small and the delta-v and duration of the acceleration are also so small as to be well below the physiological perception threshold for humans. There are more than enough studies to confirm this. Our perceptions and anecdotes are not necessarily reality. We are very fallible and terrible and perceiving our surroundings in an accurate way.

[BRad704]

Originally Posted by bicycletricycle

if you think about it, nothing matters.

I've been doing a lot of thinking lately... and I've come to the same conclusion.

[eddief]

still hard to take in. i think i really don't want to believe it.

not talking about getting to the finish line faster, talking about in the moments enjoying the ride experience.

carbon, 1295 grams, $1729
https://us.huntbikewheels.com/collec...33272407293997

alloy, 1579 grams, $439
https://us.huntbikewheels.com/collec...-28deep-22wide

[weisan]

Originally Posted by Black Dog

I will give anyone my bikes if they can discern the difference between two wheels that are other wise identical except for a few hundred grams added to the rims of one set in a blind test.

Where I can sign up for the challenge?

I have a 50/50 chance of getting it right...for a couple of new bikes added to my stable, i will take my chances.

[Tony]

On a dyno I lost 3 horse power by switching from a 160 to a 180 rear tire?

[Mark McM]

Originally Posted by ergott

Feel? They will feel noticeably different. I've compared a difference in rim weight of about a pound on the same bike.

Once difference in feel is most notable in how the bike turns in due to the gyroscopic effect. After riding the given wheels the difference tends to disappear in the noise of so much other stimuli experience while riding. There are so many other things to concentrate on during the ride.

The other is very steep climbs where you're barely getting over the pedals. You can feel the lighter wheels accelerate a bit faster, but you also notice they carry less speed over the weaker portions of your pedal stroke.

As mentioned in the video, the difference can be measured but it's not something that yields a significant difference. There's no realistic reason to deal in absolutes here.

Like ergott says, being able to sense that there is some difference is not the same as a change in performance. Here's an example of this that I experienced:

I once decided to do a completely unsupported century ride. I would carry all the food, water, clothing layers, etc. with me. In order to carry more water, I installed a double cage water bottle holder to my saddle rails, which placed an extra 2 the water bottles directly behind the saddle. I tried an experiment in which I rode with 2 full water bottles, located either in the standard frame cages (lower to the ground), or in the behind the saddle cages (higher from the ground). In seated riding, including seated accelerations, I couldn't feel any difference between the bottles on the frame or behind the saddle. And that shouldn't be surprising, since the total mass and inertia were the same. But when standing and rocking the bike, I could immediately notice the difference in weight distribution. So much that I had to modify my riding technique when the weight was higher up, needing to rock the bike less when the weight was higher. In both cases, the system weight was identical, and there weren't even changes in rotating inertia or gyroscopic effects. Although I could easily sense there was a change, it made no difference acceleration.

When the weight distribution change is in the wheels, it introduces changes in gyroscopic effects, which can magnify the effects that the rider feels. But the gyroscopic effect of the wheels does not change their acceleration. So even though a rider can easily sense changes in the bike due to even small differences in wheel weight, it doesn't mean the bike's performance has any significant difference.

[vincenz]

Originally Posted by Mark McM

Like ergott says, being able to sense that there is some difference is not the same as a change in performance. Here's an example of this that I experienced:

I once decided to do a completely unsupported century ride. I would carry all the food, water, clothing layers, etc. with me. In order to carry more water, I installed a double cage water bottle holder to my saddle rails, which placed an extra 2 the water bottles directly behind the saddle. I tried an experiment in which I rode with 2 full water bottles, located either in the standard frame cages (lower to the ground), or in the behind the saddle cages (higher from the ground). In seated riding, including seated accelerations, I couldn't feel any difference between the bottles on the frame or behind the saddle. And that shouldn't be surprising, since the total mass and inertia were the same. But when standing and rocking the bike, I could immediately notice the difference in weight distribution. So much that I had to modify my riding technique when the weight was higher up, needing to rock the bike less when the weight was higher. In both cases, the system weight was identical, and there weren't even changes in rotating inertia or gyroscopic effects. Although I could easily sense there was a change, it made no difference acceleration.

When the weight distribution change is in the wheels, it introduces changes in gyroscopic effects, which can magnify the effects that the rider feels. But the gyroscopic effect of the wheels does not change their acceleration. So even though a rider can easily sense changes in the bike due to even small differences in wheel weight, it doesn't mean the bike's performance has any significant difference.

That's why I don't ride with saddle packs because it makes the bike handle like a pig when out of the saddle. Also why I won't ride with heavy wheels. If my performance bike feels like a truck, I'm doing it wrong. Doesn't matter how fast or not you're going. In that case, yes it matters. Also, since the title was so absolute, it must be also be said that 1 second difference as measured in the video also matters. This difference will be even greater when there is more braking scenarios required and no draft advantage. For being in the F1 industry, he should know 1 second is a lot.

[Mark McM]

Originally Posted by reuben

No, I got the point. You claimed that the heavier system accelerated faster, but it was only because you changed the resistance. The key phrase is "all else being equal".

On a practical level, that is frequently the choice - lighter, but less aerodynamic wheels, or heavier but more aerodynamic wheels. In a real world competition between commonly available wheels, the heavier aero wheels win every time.

But if you insist on keeping all else equal and only chaning wheel weight, the argument still breaks down to splitting hairs. Yes, lighter wheels will acceleration a little bit faster, but the difference is so slight that it is insignficant compared to other factors. If you wanted to get into the realm of the ridiculous you can say that riders should wear insect repellent, because if a fly were to land on them it would slow them down.

Originally Posted by reuben

Agree that it's nonlinear, but diffeqs aren't needed. You'll reach terminal velocity.

No, you really do need differential equations, and in example given neither rider reached terminal velocity. But if they did, the one with the lower aero drag would reach a higher terminal velocity (and get their quicker).

[Black Dog]

Originally Posted by weisan

Where I can sign up for the challenge?

I have a 50/50 chance of getting it right...for a couple of new bikes added to my stable, i will take my chances.

Lets save you the trip (you are in Texas after all ) and just get a zoom call going and flip a coin.

[Black Dog]

Originally Posted by Mark McM

On a practical level, that is frequently the choice - lighter, but less aerodynamic wheels, or heavier but more aerodynamic wheels. In a real world competition between commonly available wheels, the heavier aero wheels win every time.

But if you insist on keeping all else equal and only chaning wheel weight, the argument still breaks down to splitting hairs. Yes, lighter wheels will acceleration a little bit faster, but the difference is so slight that it is insignficant compared to other factors. If you wanted to get into the realm of the ridiculous you can say that riders should wear insect repellent, because if a fly were to land on them it would slow them down.

No, you really do need differential equations, and in example given neither rider reached terminal velocity. But if they did, the one with the lower aero drag would reach a higher terminal velocity (and get their quicker).

How heavy is the insect repellant?