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if wheels stand on the spokes below... how come the nipple doesnt thread into the rim? the spoke would just fall through into the tube?
some bizarre ideas here..
bikewhisperer - Memberjesus.. you lot are hilarious.
spokes have a LOT of strength in compression, provided they are pre-tensioned.
utter tripe - a pretensioned spoke is in tension. Compress it and you remove some of the tension. It remains in tension. However it is supporting no weight at all - it is in tension. the weight is sported by the top spokes
A spoke has no strength in compression at all - it just bends.
if wheels stand on the spokes below... how come the nipple doesnt thread into the rim? the spoke would just fall through into the tube?
It's because it's PRE-TENSIONED. If the spoke tension was too low then the greater force of the compression that the bike hit would be more than the tension in the spoke, so the compressive force would out-do the available strength. Then the rim would be the only bit opposing the compressive force, and if it was too great it would bend.
EDIT.. thanks TJ
dont shout pre-tensioned at me!
regardless of if its in tension or not, the spoke is not supporting weight. i.e the hub is not standing on the spoke, it is hanging off the one above...
bikewhisperer - MemberIt's because it's PRE-TENSIONED. If the spoke tension was too low then the greater force of the compression that the bike hit would be more than the tension in the spoke, so the compressive force would out-do the available strength. Then the rim would be the only bit opposing the compressive force, and if it was too great it would bend
Therefore the bottom spokes are NOT IN COMPRESSION 🙄
Ah, forget it. You are welcome to continue being wrong.
ok big boy. slow clap for you being so damn right about a pre tensioned structure suddenly being able to support load, despite not being constrained at the bottom end.
bikewisperer - you are talking utter tripe - a spoke has no strength in compression at all. None. It just bends.
In a spoked wheel all the weight is hanging from the upper spokes - the bottom ones carry no load at all. None. Not 1 g of the weight.
At rest with no weight loaded all the spokes are in tension. When a load is applied the upper spokes gain more tension, the lower ones loose tension - thus the load is hanging from the top spokes.
where you are getting confused is the entire wheel has strength in compression. Put a load on the rim from the top of the rim the wheel wiill try to go eggshaped - but the spokes front and rear will resist this as the tension in them increases while the tension in the to and bottom ones decrease.
it basic mechanics. A spoke has no strength in compression whatsoever
bikewhisperer; show us some numbers.
TJ... If you put tension on a spoke then it has compressive strength to resist that amount of tension. Above that point it will bend. I've got no prolems with that bit.
The net force on a bike wheel is compressive on the bottom spokes.
Yep BW up to you to prove this.
I think I can see your point but for me it is meaningless. If one were to cut a bottom spoke in the wheel, it would ping apart in 2 AS IT IS STILL IN TENSION. The fact that it is in less tension than the other spokes does not make it "in compression".
thats just not right buddy. thats not how it works. if anything, the pre tension reduces its resistance to compression...
Plus, unless you've built radially spoked wheels (and they'd have to be perfectly radial which will never happen), the spokes can never be in compression because even if they couldn't bend, they'd simply rotate in the spoke hole in the hub.
Cynic-al.. Can you imagine a spoke being compressed enough to equal its tension? It's the resultant overall force I'm talking about, not the force on individual spokes. Even so, when you even out the forces, wheels do stand on their lower spokes. All the other forces cancel out.
Can you imagine a spoke being compressed enough to equal its tension
That's what happens on loose wheels (or tight ones that have been loaded very heavily!) and what happens? The spokes bend and rotate in the spoke holes. They don't support load in compression.
That's what happens on loose wheels (or tight ones that have been loaded very heavily!) and what happens? The spokes bend and rotate in the spoke holes. They don't support load in compression.
rotation is not a problem. if they were built well then that wouldn't happen. If they were built with prolock or spoke freeze then also not a problem, unless they were not relieved. If they were not relieved enough when they were built then they might have this problem.
No, not rotation of the spoke in the nipple 🙄 Rotation of the spoke in the hub.
bikewhisperer - MemberTJ... If you put tension on a spoke then it has compressive strength to resist that amount of tension. Above that point it will bend. I've got no prolems with that bit.
The net force on a bike wheel is compressive on the bottom spokes.
Nope - no spoke is ever in compression until it becomes lose and then it will bend
bikewhisperer - Member
Cynic-al.. Can you imagine a spoke being compressed enough to equal its tension? It's the resultant overall force I'm talking about, not the force on individual spokes. Even so, when you even out the forces, wheels do stand on their lower spokes. All the other forces cancel out.
I can see this, I just can't see its relevance when discussing spoke tension in wheel builds.
The spoke will bed in at the hub. If the wheel is built well then this won't be a problem.
I can see this, I just can't see its relevance when discussing spoke tension in wheel builds.
well that's not my problem.
The spoke will bed in at the hub. If the wheel is built well then this won't be a problem.
Seriously? You really don't understand wheels.
bikewhisperer - MemberI can see this, I just can't see its relevance when discussing spoke tension in wheel builds.
well that's not my problem.
Whoop de ****ing doo for you, you've still not justified it 🙄
Bikewisperer - maybe this will explain it to you
http://hea-www.harvard.edu/~fine/opinions/bikewheel.html
You are I am afraid totally confused about how a wheel works. Have a read and a think
No spoke is ever in compression. No spoke can hold a load in compression. The load hangs from the top spokes
Edit -It is possible to build a wheel with string that has no ability to hold any sort of load in compression
well what do you want me to do? Teach you a physics a-level?
And Clubber.. yes spokes do cause deformation of hub flanges. I wasn't suggesting otherwise. Stress relieving while building will resolve this.
In mathematical terms it is possible to describe the bottom spokes as being in compression. The have less tension than they had before, so if you count the starting (pre-tensioned) state as the zero state, you have put them "in compression". The reason they can support this compression is that the spoke has been pre-tensioned.
Thanks tj
Bikewhisperer, stop trying to re-invent the wheel
bikewhisperer - Member
well what do you want me to do? Teach you a physics a-level?
Already got that thanks, my point is that yours is just irrelevant to the discussion, seems most others are with me.
bikewisperer - nice selective quoting.
Answer me this. Bike stationary, rider on the seat. The spoke that is vertical from the bottom of the wheel to the hub. Is this in tension or compression?
Edit - higher physics here
[img] 
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Was that you cycling to work earlier?
If you get an elastic band and stretch it (call this point A) then release half of that stretch (point B), it's still in tension though from point A to point B you have 'compressed it' in the sense that it has shortened. It has still at no point been in compression. Same for the spokes.
EDIT - A grade Physics A level and Masters in Mech Eng since we're now quoting qualifications 😉
Oh, and a BSC - Bronze Swimming Certificate
Already got that thanks, my point is that yours is just irrelevant to the discussion, seems most others are with me.
yep. me too. So lets go with the "my gang's bigger than your gang" logic and say you won. hubs hang from the upper spokes and tension has nothing to do with compressive strength.
Correct at last. You cannot have something in compression and tension at the same times. Tension is nothing to do with compressive strength. As I said earlier you are confusing what happens to the component and to the entire built up wheel.
You cannot have something in compression and tension at the same times.
cough
bending
cough cough
so if you count the starting (pre-tensioned) state as the zero state, you have put them "in compression"
Not the same as actual compression, just means that the tension is lessened.
And yes TJ.. They ARE in tension. The relief of tension is compression. Therefore the relief of tension has EVERYTHING to do with compressive strength.
If you look at it from an outside point of view, then who cares how tight the spokes are, it's all to do with how strong the wheels are in compression.
TandemJeremy
Edit -It is possible to build a wheel with string that has no ability to hold any sort of load in compression
Remember the tioga disc drive wheel anyone? Carbon fibre (or kevlar "string") no spokes as such, and it was under tension!
jesus.. you lot are hilarious.spokes have a LOT of strength in compression, provided they are pre-tensioned.
bikewhisperer, on the contrary, You are hilarious and slightly confused I fear.
Answer me this. Bike stationary, rider on the seat. The spoke that is vertical from the bottom of the wheel to the hub. Is this in tension or compression?
Have you no answer for this simple question? compression my arse
Sorry, late post, I see you have aswered this with nonsence! A relife in tension is not compresion, it is simply less tension.
Right - so the spoke is in tension - so how can it be holding a compressive load if it is in tension? simple - it cannot. It does not have any compressive strength if it is in tension
Please - go and have a read up with an open mind - you have got yourself very confused
relief of tension is not compression. it is just less tension.
the rubber ban analogy is correct... with the exception that you are not compressing it to reduce the length only reducing the tension.
the spoke is in tension, when loaded the tension is reduced. it is not in compression. if it were it would poke out of the nipple end hole and shred your inner tube as it is unconstrained at that end.
If a static system is in a pre-tensioned state then any compressive force acting upon it can be considered as a compressive force upon it's components. In the case of a wheel the compression would be relieved as a reduction of tension in the lower spokes and as an increase in compression around the rim and transferred to the hub as an increase in tension in the upper spokes. The other forces cancel out and leave just a compression in the lower spokes.
I give up. You're all welcome to think what you might, but it's entirely down to the spoke tension. We're all arguing over the fact of agreement that tension is equivalent to a reduction in compression. Fine. Please make a special effort to include atmospheric pressure when you check the gauge to inflate your tyres the next time.
Under no load, every spoke is under tension and the system is under equillibrium.
Under say a vertical load applied at say the hub, then there will be an increase in tension in the upper spokes and a REDUCTION in tension in the lower spokes, but at no time will any spokes be under pure compressive loads only, if they were they would bend.
You cannot say that because there is a reduction in tension that the spoke is suddenly being compressed, it is not!
wow - 3 pages discussing how a wheel works ......
You cannot say that because there is a reduction in tension that the spoke is suddenly being compressed, it is not!
OK then.. So how come the lower spokes get shorter? I've said all along that the resultant force is compressive on the lower spokes. Under the equilibrium state they are in tension.
Just because something becomes shorter does not mean it is in compression. It's the elastic band analogy again.
It think you're getting confused by language. "compressing" means to shorten. Compressing something that is in tension does not make cause that something to be "in compression" unless it fully relieves the tension.
That's why tight wheels ate stronger - because the usually never lose tension when loaded. If they do ( become "in compression" ) then the spokes bend and the rim is likely to bend as it's unsupported.