Spoke Tension Meter, Hows This Work?

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NATURAL ANKLING
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Re: Spoke Tension Meter, Hows This Work?

Postby NATURAL ANKLING » 8 Jan 2019, 1:06am

Hi,
I am still struggling with my lower tension (ear) in my 32 than my 36 front wheel :?
Brucey reckons the other way round.
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 8 Jan 2019, 8:53am

ideally the tension ought to be a touch higher (if the rim permits it) in a 32 spoke wheel than a 36 spoke wheel. However you/they won't necessarily have built it this way and in addition even if the tensions are identical, the spokes will be a touch longer in an otherwise identical 32 spoke wheel, so when plucked won't make the exact same tone as shorter spokes at the same tension.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Airsporter1st
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Re: Spoke Tension Meter, Hows This Work?

Postby Airsporter1st » 8 Jan 2019, 7:51pm

Airsporter1st wrote:Post deleted. Unnecessarily condescending response below.


I now understand that I took what was intended to be a humorous response by Brucie the wrong way. I apologise unreservedly.

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NATURAL ANKLING
Posts: 10593
Joined: 24 Oct 2012, 10:43pm
Location: English Riviera

Re: Spoke Tension Meter, Hows This Work?

Postby NATURAL ANKLING » 8 Jan 2019, 8:06pm

Hi,
Brucey wrote:ideally the tension ought to be a touch higher (if the rim permits it) in a 32 spoke wheel than a 36 spoke wheel. However you/they won't necessarily have built it this way and in addition even if the tensions are identical, the spokes will be a touch longer in an otherwise identical 32 spoke wheel, so when plucked won't make the exact same tone as shorter spokes at the same tension.

cheers

Ah yes, 295 vs 290 :P
Ta,
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 8 Jan 2019, 8:48pm

Airsporter1st wrote:
Airsporter1st wrote:Post deleted. Unnecessarily condescending response below.


I now understand that I took what was intended to be a humorous response by Brucie the wrong way. I apologise unreservedly.


not my intention to cause any offence and if any was taken I apologise; perhaps I should have chosen my words better.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

MikeDee
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Re: Spoke Tension Meter, Hows This Work?

Postby MikeDee » 8 Jan 2019, 9:22pm

Brucey wrote:
Somewhat counterintuitively the cyclic fatigue loadings in the rim can increase in a slack build; the reason is that not only do the spoke tensions vary as you might expect, but the rim sees additional bending because it is no longer so well supported by the spokes. The two stresses can add to one another in certain places. However I don't think this happens too much unless there are at least some spokes that are going completely slack in a wheel. IIRC someone has done some FEA work which suggest that between lateral and torque loadings when climbing, it is the 'pushing' NDS spokes which are most likely to go slack first. Sprinting out of the saddle on a climb is potentially even more violent than the condition modelled, I think, so it may be that there is even more slack running going on that the model suggests.

cheers


Interesting you say this, because Brandt in his book says that tension changes from torque loads from pedaling and braking are insignificant. "These tension changes are small and few compared to those caused by just the radial load of the rider's weight on a smooth road."

Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 8 Jan 2019, 10:04pm

in most normal use I'd agree with Brandt. But strong riders can push out about 1.5kW when sprinting uphill out of the saddle which is a whole different situation; total bicycle torture. And some riders dish this out nearly every time they ride. IIRC the forces under these conditions are considerably in excess of any that Brandt considered. For example a strong rider might be pushing with a peak force of about 300lbs on one pedal, when the bike is about 20 degrees off vertical.

Its been a while since I read his book but IIRC he considered wheel torque when pedalling fairly normally, using large flange hubs and the only brake torque he considered was that on a rear coaster brake, which is limited to a fairly low value by weight transfer; any high torque unloads the rear wheel and then the wheel locks.

It is pretty much a double-whammy with (say) a disc brake front wheel; you can have a vertical force component that is the entire weight of the bike plus rider (or momentarily more than this if the bike is accelerating into a stoppie), a horizontal component that is equal to the vertical component, and a force resisting all this at the brake caliper that is about five times higher than that. It is easy to see that the spoke tensions are going to be all over the place under these conditions.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~