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PostPosted: Wed Mar 05, 2014 12:24 am 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 300
Location: Phoenix, AZ
I take your point, but calculating where the pool balls will go is really, really easy. What's hard is applying the cue to the ball exactly the way you mean to. Again, I know what you mean.

Regarding steady-state riding, you can believe what you want; that's the nature of beliefs. We agree that a heavy wheel would slightly smooth already infinitesimal variations in speed. But I don't see a mechanism for this tiny degree of smoothing to somehow result in faster riding. What losses are being avoided with a heavy wheel?

Cheers,

Jason


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Posted: Wed Mar 05, 2014 12:24 am 


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PostPosted: Wed Mar 05, 2014 1:21 am 
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Joined: Tue May 03, 2005 2:20 am
Posts: 5783
Location: Belgium
Hi,

Quote:
One poster suggested that heavy wheels "help to sustain a steady cadence." The masses he suggests are much to small compared to that of the bike/rider system to have any effect. But even if they weren't, why would a very slightly more steady cadence be an advantage?


When pulled out of context it doesn't make much sense. However energy is stored where mass is.
Remember E=MC squared?
I gave specific examples where this would be an advantage and wasn't generalising. So let's stick to that or drop it entirely.

Ciao, ;)

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PostPosted: Wed Mar 05, 2014 1:41 am 
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Location: Phoenix, AZ
fdegrove wrote:

When pulled out of context it doesn't make much sense. However energy is stored where mass is.
Remember E=MC squared?
I gave specific examples where this would be an advantage and wasn't generalising. So let's stick to that or drop it entirely.


Yes; we were talking about flat time trials and velodromes. That's still the context, as far as I can tell. Why did you think otherwise?

I imagine the equation you were thinking of is E=1/2mv^2.* But yes, a heavier bike in motion at a given speed stores more energy. That's why it's slower to accelerate up to the steady state speed. But I still haven't heard an account of how storing that energy somehow increases speed on the flat road/velodrome in question.

Cheers,

Jason

*If you're pedaling fast enough that relativistic effects come into play, wheel mass is probably the least of your concerns. The mass of both you and your bike increase dramatically as you approach the speed of light, so a few hundred grams in your wheels and tires is neither here nor there. Besides, that Lorentz-Fitzgerald contraction is a bitch.

Edit: moved relativity digression to footnote.


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PostPosted: Wed Mar 05, 2014 1:59 am 
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Joined: Tue Apr 18, 2006 3:03 am
Posts: 1868
Location: Islip, NY
Zoro wrote:
ergott wrote:
On 40+mph long descents I would favor aerodynamics over weight every time.

When pedaling isn't an option, do this.

Image

If you were doing that for 10+ min, how significant do you think the freewheel drag would be? (all else being equal)


Less bearing/freewheel drag is better in every case. I'd rather have a hub optimized for the least amount of loaded bearing drag which is why I mention the Alchemy and Dura Ace hubs. With sealed removed and grease replaced with oil they will both fly, more importantly spin freely under load. I don't think either hub has significantly large pawl drag when freewheeling.

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PostPosted: Wed Mar 05, 2014 2:15 am 
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Joined: Thu Mar 08, 2012 3:20 pm
Posts: 103
I have used a lot of the major hubs out there and the best coasting one was american classic - they use a cam actuated engagement system that is very low drag, there is only one little spring dragging when coasting. Narrow flanges could be more aero too?

In general the hubs with more pawls (also how much spring tension is on each pawl) will have more drag - that's what I noticed at least.

Why isn't he using a disc though?


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PostPosted: Wed Mar 05, 2014 2:35 am 
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Joined: Tue May 03, 2005 2:20 am
Posts: 5783
Location: Belgium
Hi,

Quote:
But yes, a heavier bike in motion at a given speed stores more energy. That's why it's slower to accelerate up to the steady state speed. But I still haven't heard an account of how storing that energy somehow increases speed on the flat road/velodrome in question.


The bike is still the same overall weight. The difference is that mass has been moved from non-rotational areas to rotational areas hence increasing overall mass in rotation thusly rotational increasing inertia.
IOW, it will take more energy to bring the bike up to a given speed but OTOH it will take an equal amount of energy to slow it down as well.
I don't think it has been stated that it would make you faster, it would make it easier to maintain a steady speed on flats and on track (which amounts more or less to the same kind of exercise except perhaps for the sprints).
At the end of the day it's the overall mass in movement that prevails, inertia of the wheel has only a minor impact in the grand scheme of things.
I'd also forward that it may not be to every riders liking. Some like to push constantly, others may enjoy the more even flow of the bike ride being able to just maintain a steady speed at just a minor input.
This allows some to recover from earlier efforts and so on.

Since TS stated his young son prefers to coast downhill I figured he may give this a try. Nothing more, nothing less. No need to analyse everything to pieces: math is one thing people is quite another, right? 8)

Ciao, ;)

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PostPosted: Wed Mar 05, 2014 6:03 am 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 219
fdegrove wrote:
The bike is still the same overall weight. The difference is that mass has been moved from non-rotational areas to rotational areas hence increasing overall mass in rotation thusly rotational increasing inertia.
IOW, it will take more energy to bring the bike up to a given speed but OTOH it will take an equal amount of energy to slow it down as well.
...

This is no different than any other mass on the bike. It takes more energy to bring the mass up to speed and it takes energy to slow it down.

So why not have more mass on bikes too to go faster?

Also - there is always side to side movement, and changing of direction. The less mass there is to deal with - the less energy.


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PostPosted: Wed Mar 05, 2014 6:12 am 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 219
youngs_modulus wrote:
I take your point, but calculating where the pool balls will go is really, really easy. What's hard is applying the cue to the ball exactly the way you mean to. Again, I know what you mean....
Jason, the cue ball going where you want is part of the equation. Just like pointing your bicycle. Does your easy calculation take into account the exit angles of the ball not equaling the entry angles based on ball velocity and rubber durometer - which varies even on a given table? Anyway, glad you know what I mean.


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