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I have been running a set of dual dutys on m495s set up ghetto tubless. They did geat, wide foot print and stayed true. I got a promotion at work and wanted a set of real tubless wheels. I had a set custom built locally by Buzz: archs, xl14s, m775s. The set is 711 grams lighter. When I put them on my bike and picked it up I couldn't feel the 1.5lb difference. I went for a ride today not expecting anyting (since I couldn't feel the weight difference) but riding up the first hill I didn't have to shift to granny. Same thing at the next hill I was able to easily climb it in the middle ring. Not only does it climb better but it's easier to loft the front wheel and seems like it turns quicker too. I know people talk about rotational weight on here, but I never thought it would make that big of a difference. I am honestly blown away, they have completely changed the way the bike handles.
 

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Always Learning
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UnderPar said:
Not only does it climb better but it's easier to loft the front wheel and seems like it turns quicker too. I know people talk about rotational weight on here, but I never thought it would make that big of a difference. I am honestly blown away, they have completely changed the way the bike handles.
Shhhhhhh....don't tell anybody.;)

BB
 

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1.5 lb is actually 3lb

I was told a while ago that due the rotational mass of the wheels as they spin increasing, the 1.5lb weight is closer to 3lb when the wheels are moving.

Makes sense but I'd like to know if that's actually correct - anyone?
 

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It takes energy to spin a wheel that is lifted off the ground. The heavier it is the more it takes to get it going. Once at a constant speed it will spin a long time and only slow down for things like bearing & wind resistance. Good wheels are also normaly stiffer so they will transfer more power to the ground.
 

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the mountian is within
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Hey J.!
Glad you like them! Where did you ride? I guess out of town-you didnt go in the ice here!
Let me check the tension again next week-i imagine they are still perfect-thanks fro letting me take my time on this build! I still cant sit on my truing stool for more than 10min at a time! Just dont fall on your butt!
 
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party_wagon said:
Once at a constant speed it will spin a long time and only slow down for things like bearing & wind resistance.
...and changes of direction. That's how gyroscopic stability works.
 

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party_wagon said:
Good wheels are also normaly stiffer so they will transfer more power to the ground.
Untrue. Even if you replaced your spokes with springs (they actually are springs), there would be no energy loss.
 
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fallzboater said:
Untrue. Even if you replaced your spokes with springs (they actually are springs), there would be no energy loss.
Yes...if one wheel transmits more power to the ground than another, then that would mean one wheel is absorbing power that's not getting to the ground. It sounds good but it's ridiculous.
 

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HeezaGeeza said:
I was told a while ago that due the rotational mass of the wheels as they spin increasing, the 1.5lb weight is closer to 3lb when the wheels are moving.
This fairytale will never die.

A physicist in german http://www.mtb-news.de/forum made an exactly calculation of rotating masses with a weight difference of 250 g at every wheel. The result was, that you need for example to get from 0 km/h to 25 km/h in 4 s, you have to create only 4-5 Watts more power!

Of course on a XC race this will sum to a few minutes at an 3 hour race, but this doesnt lift a freetime bike up the hills like an e-bike. If you think youl feel this, its just a placebo effect - sorry...
 

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DerBergschreck said:
This fairytale will never die.

A physicist in german http://www.mtb-news.de/forum made an exactly calculation of rotating masses with a weight difference of 250 g at every wheel. The result was, that you need for example to get from 0 km/h to 25 km/h in 4 s, you have to create only 4-5 Watts more power!

Of course on a XC race this will sum to a few minutes at an 3 hour race, but this doesnt lift a freetime bike up the hills like an e-bike. If you think youl feel this, its just a placebo effect - sorry...
point taken...but seeing that MTB is 50% physical and 50% mental...light wheels do have a noticeable feel...which make the "I think I can" much more of a reality test or no tests....
 
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DerBergschreck said:
This fairytale will never die.

A physicist in german http://www.mtb-news.de/forum made an exactly calculation of rotating masses with a weight difference of 250 g at every wheel. The result was, that you need for example to get from 0 km/h to 25 km/h in 4 s, you have to create only 4-5 Watts more power!

Of course on a XC race this will sum to a few minutes at an 3 hour race, but this doesnt lift a freetime bike up the hills like an e-bike. If you think youl feel this, its just a placebo effect - sorry...
Not having german language skills and not being provided a direct link, I could not find any "exactly calculation" under the conditions you described. I did find, however, following text referred to a number of times. This is translated from German by Google:

So on this issue is just an interesting Articles from the bike.
I can post a couple of times values.
It is measured in joules of energy, its necessary to accelerate the wheel (tire height) from 0 to 25 km / h..
1. Hügi S240 + XR 4.1 D (1456 g) -> 61 Joules
2. Hügi FR + Mavic D3.1 (2270 g) -> 88 Joules
Then they do not have one and tested the same wheel with 2 different tires.
Twister Impeller with SS -> 101.8 joules
Impeller with Vertical Pro -> 134.4 joules

I think the results speak for themselves!
These are not calculated numbers but observed ones and only represent one wheel. 134.4 joules in 4 seconds takes 33.6 watts per wheel to spin up, and the difference between that and the same wheel with another tire is 16.3 watts per two wheels. Weight added at the hub is noticably different than in the rim or tire, so saying that 250g added results in 4-5 watts is meaningless. That is demonstrated in the first comparison where added weight did not produce added kinetic energy linearly. The proportion of weight in the hubs changed.

The difference in feel between two tires with 250g of weight difference is noticable. Ignoring the watt calculation, there's another issue of importance: the extra energy expenditure is not just a one time thing but occurs continuously since wheels are constantly accelerated on an MTB. A heavier wheel takes more effort to steer and that's because you're fighting rotational inertia. People like to think that this energy is simply stored in the wheel but it is often more accurately considered a parasitic loss. Even if this loss is only 5 watts, over the course of your ride what power output do you think you average?

Your argument, or the one of some "physicist" you claim to be quoting, is a common one but is naive. It holds somewhat more validity with roadies who ride in much straighter lines but is still an incomplete view. If you're going to call it a fairytale and a placebo effect, I'd hope you could back it up.

Curiously, one of the standard claims of 29er superiority is greater rollability due to higher angular momentum. Are we to accept this as the gospel if its perception is nothing but placebo effect? Frankly, I think that claim is garbage but it's clear that many perceive it.
 
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