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Re: Softride/Beam bike Rolling Resistance [Tom A.] [ In reply to ]
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Tom A. wrote:
Jiowa wrote:
So how much energy is lost by a bike moving vertical due to bumps in the road? Let's say like going over train tracks.

And would the dampening caused by a beam when going over the train tracks make a difference in the loss in energy? I'm guessing it does. What say you?



I say you should be bunny hopping those train tracks anyway ;-)

How about a double track?




Running is a gift.
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Re: Softride/Beam bike Rolling Resistance [Jiowa] [ In reply to ]
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Jiowa wrote:
Tom A. wrote:
Jiowa wrote:
So how much energy is lost by a bike moving vertical due to bumps in the road? Let's say like going over train tracks.

And would the dampening caused by a beam when going over the train tracks make a difference in the loss in energy? I'm guessing it does. What say you?



I say you should be bunny hopping those train tracks anyway ;-)


How about a double track?

Get going REALLY fast and "table top" the doubles! :-)

http://bikeblather.blogspot.com/
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Re: Softride/Beam bike Rolling Resistance [tdstegner] [ In reply to ]
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tdstegner wrote:
I'm thinking that the difference in energy lost has to do with the direction of the forces acting on the wheel. With a supple tire, a bump causes the tire to deform, with force vectors going up and back. On the "back" side of the bump the tire returns to it's original shape causing forces down and forward - returning most of the energy to the bike's forward movement. With a stiff tire, the force encountered with a bump is directed through the wheel directly to the bike moving all of it (bike and rider) almost straight up. This causes the bike to move up vertically. When it comes down. there is very little force in a forward direction, it's all vertical in a downward direction... I'm also thinking that a beam doesn't store much energy in a horizontal direction. When a beam absorbs energy from forward motion, it's changed to vertical and forward energy is lost. Thoughts?
Is this just restating what you have already said?

Yeah...that's mostly it. In short, the more "suspension" you can have performed by the tire, the better (from a "resistance to forward" motion standpoint)

http://bikeblather.blogspot.com/
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Re: Softride/Beam bike Rolling Resistance [Tom A.] [ In reply to ]
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Tom A. wrote:
Yeah...that's mostly it. In short, the more "suspension" you can have performed by the tire, the better (from a "resistance to forward" motion standpoint)

To me that means the heavier the rider the lower the rolling resistance?

What am I getting wrong?




Running is a gift.
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Re: Softride/Beam bike Rolling Resistance [Jiowa] [ In reply to ]
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Jiowa wrote:
Tom A. wrote:
Yeah...that's mostly it. In short, the more "suspension" you can have performed by the tire, the better (from a "resistance to forward" motion standpoint)


To me that means the heavier the rider the lower the rolling resistance?

What am I getting wrong?

No. A heavier rider has a larger average contact patch for a given pressure...hence the "moment arm" of the force difference between the leading and trailing portions is longer. Therefore, the Crr is higher.

Like I told Dev, read through the "Tires and Wheels..." article in the Tech section, and then go on to the "What's in a Tire?" and "What's in a Tube?" articles too...

http://bikeblather.blogspot.com/
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Re: Softride/Beam bike Rolling Resistance [Tom A.] [ In reply to ]
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I did read through it.

Larger contact patch... got any other sources of info I could read?




Running is a gift.
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Re: Softride/Beam bike Rolling Resistance [Jiowa] [ In reply to ]
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Jiowa wrote:
I did read through it.

Larger contact patch... got any other sources of info I could read?

http://www.amazon.com/...Wilson/dp/0262731541

...plus, a WAY oldie, but a WAY goodie :-)

http://books.google.com/...html?id=7aI7AAAAMAAJ

http://bikeblather.blogspot.com/
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Re: Softride/Beam bike Rolling Resistance [Damon] [ In reply to ]
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Damon wrote:
This is only true if loss due to tyre deformation is linear, which it isn't. You lose more energy from one deep deformation than from two shallow ones.
Why? The tyre carcass deforms more on large impacts, and a tyre loses energy each time it stretches and returns to a position (it's not a perfect spring, it has hysteresis). The most efficient system varies the deformation of the tyre as little as possible.
So suspension is better for rolling resistance.

Not true, radial deformation of tires doesn't exhibit hysteresis but it has viscous damping.

Tom A. wrote:
If you truly believe what you wrote above, then you have a complete misunderstanding of the sources of rolling resistance in a bicycle tire and how the pneumatic tire construction acts as the most "efficient" suspension you can get.

In short, you WANT the tire to take up the deflection because it can actually RETURN the energy (most of it...minus tire internal losses) back to the road surface in the trailing half of the contact patch. Use a tire with low internal losses, and "Voila!", you have low rolling resistance on ALL surfaces. Remember, it's the "torque arm" caused by the difference in energy absorbed in the leading half of the contact patch and the energy returned in the trailing half of the contact patch that is the source of rolling resistance.

In contrast, any energy that makes it "past" the tires (e.g. if they are too stiff) cannot be returned to the road surface as the tire does. It needs to be dissipated somewhere...either in the rider, or in a damper of some sort (i.e. read "beam"). That energy needs to be supplied by YOU to keep going forward. Sure, you may have actually reduced the rolling resistance of the tire by stiffening it up, but the total "resistance to forward" motion is overall higher.


Tom, I think you are mixing two concepts here: the effects of tire carcass stiffness in rolling resistance and the effects of reduced normal load in rolling resistance. Everything you have said here it's true but you have to take into account that Crr isn't constant for zero slip conditions. As you know, Crr depends of the pressure for a given load or, alternatively, it depends of the sinkage depth, the bigger the sinkage depth, the bigger the Crr.

A more compliant rear end can reduce the effective load in the contact between the tire and the ground and reduce the average Crr during the fluctuations of the sinkage depth. So we have to consider two aspects, the losses caused by the viscous damping and the variations of Crr of the tire and the losses caused by rear end's deformation. As you can imagine, there isn't an easy answer

http://cds-0.blogspot.com
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