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Great Egret
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Built it from a bare frame up myself.
somebodyelse
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Britten had another variant of the same idea. Back to bicycles, there's the Moulton variant using rubber in shear for spring and damping where you might expect there to be bearings.Brit inventor NormanHossack came up with this suspension design:
BMW kinda stole the design and near-perfected it for the K1200S and called it the "DuoLever".
It separates the suspension from the steering.
DuoLever introduces different riding style because you can actually brake while turning w/o the bike jacking straight-up and off line.
Even counter-steering becomes added novelty to hooking into a turn; as you can push the rear to do a weird opposite lock steer... while you are doing the same in the front but the other opposite lockand that is when you realize that 160 horsies, around a turn, is hairy, fun and not useless!
GeorgeBynum
Active Member
My son, 203 cm (6'8") rides a pseudo mountain bike, the Trek Marlin 6 in XXL. Trek says it is optimum for 6'5" to 6'8". Other than customs, these are the best he's found for folks his size. I believe they make some road/touring bikes in that size as well.
Whet gets me is the wheels on large bikes. The old (early 1970s) Nishiki Competition in (I think) 25.5" had 36 spokes laced cross 4. I would EXPECT a bike for a person in the 300 lb range would use 40 spokes laced cross 4. Are materials that much better today that the 32 spoke wheels laced cross 2 or 3 can handle big guys?
Even tandems, which used to "always" be 40 spokes, are 32 in many cases.
Great Egret
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One thing that comes to mind is that we are able to make double walled rims that are stronger then single. And maybe wheels are less overbuild as they use to do...
OP
JaccoW
Senior Member
- Thread Starter
- #286
The short answer is, yes.
We have learned a lot about what forces act on the rims and modern spokes are much stronger than 40+ year old spokes. The main reason why touring bikes had 40H wheels is because spokes were much, much weaker. That's where the British 32H front and 40H rear came from. Metallurgy has come a long way since then.
I still prefer 36H wheel on a touring bike but I have to admit my 32H wheels held up flawlessly over the summer when I did ride a lot of really rough terrain with a combined rider + cargo weight of 125kg (275lbs) excluding the bike itself.
It's also nearly impossible to find 40H rims and hubs nowadays. Especially silver rim brake models.
HorizonsEdge
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Helicopter
Major Contributor
I smash the shit out of 32h rear wheels in short order, but have never broken a front wheel. My 36h rears hold up OK, but I have busted a couple of them too. 6'4" and 300+.
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Curious, what are the wheel/use deteails other than spoke count? I've found my 32 spoke straight gauge were useful for my fat butt at one point, but have gone with even triple butted spokes with less problems....and these days my wheels are more in the 24/28 area on my mountain bikes but I'm a svelte 220 ( LOL ).
One of my old friends in the bicycle science community was Jobst Brandt (RIP), a mechanical engineer at Hewlett-Packard and machine designer. He was the first to document a proper structural analysis of a bicycle wheel, using finite-elements numerical analysis.
He found that rims deflect in normal bending as they pass across the contact patch. As a result, the spoke within the zone of that deflection loses tension. It must therefore be tight enough so that it imparts compressive strength as it loses tension (meaning: tensile stress is never fully relieved). Thus, wheels stand on the bottom spokes. This violates the long-held myth that wheels hang from the spokes at the top.
Biasing a transistor is a useful analogy. We apply enough voltage to keep the transistor in its operating envelope, and we apply enough tension in a spoke to always keep it in tension. It imparts compressive strength only when “biased” by tension; otherwise it would simply buckle.
So, two things determine the strength of a wheel: the bending strength of the rim and the allowable operating tension on the spokes. The allowable spoke tension is constrained by the tangential compressive strength of the rim, and by the strength of the spoke and its attachment points.
So, a thought experiment: an extremely weak, light rim with, say, a hundred spokes. The weak (read: light) rim with too many spokes may not allow the spokes to be tensioned as highly as their own strength might allow—doing so might collapse the wheel—and they are left looser. But there are more spokes near the contact patch to stand on. The biased tension is lower but so is the compressive loading on any one spoke—maybe a wash overall. Adding spokes does not gain the benefit one might expect if the wheel is properly tensioned.
But a strong rim has both greater bending strength and also allows higher spoke tension. This can make a stronger wheel than a lighter rim with more spokes.
Thus, the big change has been heavier, stronger rims. Many are deep to provide a blade shape for reducing aerodynamic drag, which makes them much stronger in bending. And if the cross-section is greater (and it is), it will provide more tangential compressive strength allowing tighter (more heavily biased) spokes.
We used to race on very light box-section rims with no bead, using tires that are sewn together to contain the inner tube and then glued to the rim. Now, we use beaded tires, and the rim has more material to provide the bead. Even without the blade shape, modern rims are heavier and stronger.
Spokes are not much stronger than they used to be. I was using DT stainless steel spokes 50 years ago, and they still sell them. But stronger rims permit heavier gauges and higher tensions. My race wheels in the mid-70’s were 36h, three-cross, 15-17-15 butted Trois Etoiles spokes with brass nipples (which are still much better than aluminum nipples) on Dura Ace hubs. I still have them. Current wheels are 32h, two-cross, 14-15-14 butted DT stainless spokes in Campy Chorus hubs. But the rims on the new wheels are heavier and have twice the section depth.
The key is that spokes must be tight. We did not used to tighten them enough, and many still don’t. They really should be tightened to a high percentage of yield strength—75-80%. The highest stress on a spoke is when the wheel is unloaded, because the bias tension should be higher than compressive stresses, which can only reduce tension in the spoke.
An impact makes a wheel collapse either by buckling the rim or by momentarily unloading enough spokes so that the rim can no longer impart compressive strength and it becomes unstable. When spokes break, it’s because of fatigue, and fatigue cracks are more likely if spokes are not over-tensioned briefly when the wheels are built to force any residual internal stresses to yield. Those internal residual stresses provide roots for fatigue cracks. Good builders always squeeze pairs of spokes together—hard—to perform this function.
We used to think that increasing the number of crosses made a wheel more comfortable, but that’s mostly myth. Increasing the crosses does permit slightly greater spoke tension, however, which makes the slightly wheel stronger.
Rick “fewer spokes are more aerodynamic, too” Denney
He found that rims deflect in normal bending as they pass across the contact patch. As a result, the spoke within the zone of that deflection loses tension. It must therefore be tight enough so that it imparts compressive strength as it loses tension (meaning: tensile stress is never fully relieved). Thus, wheels stand on the bottom spokes. This violates the long-held myth that wheels hang from the spokes at the top.
Biasing a transistor is a useful analogy. We apply enough voltage to keep the transistor in its operating envelope, and we apply enough tension in a spoke to always keep it in tension. It imparts compressive strength only when “biased” by tension; otherwise it would simply buckle.
So, two things determine the strength of a wheel: the bending strength of the rim and the allowable operating tension on the spokes. The allowable spoke tension is constrained by the tangential compressive strength of the rim, and by the strength of the spoke and its attachment points.
So, a thought experiment: an extremely weak, light rim with, say, a hundred spokes. The weak (read: light) rim with too many spokes may not allow the spokes to be tensioned as highly as their own strength might allow—doing so might collapse the wheel—and they are left looser. But there are more spokes near the contact patch to stand on. The biased tension is lower but so is the compressive loading on any one spoke—maybe a wash overall. Adding spokes does not gain the benefit one might expect if the wheel is properly tensioned.
But a strong rim has both greater bending strength and also allows higher spoke tension. This can make a stronger wheel than a lighter rim with more spokes.
Thus, the big change has been heavier, stronger rims. Many are deep to provide a blade shape for reducing aerodynamic drag, which makes them much stronger in bending. And if the cross-section is greater (and it is), it will provide more tangential compressive strength allowing tighter (more heavily biased) spokes.
We used to race on very light box-section rims with no bead, using tires that are sewn together to contain the inner tube and then glued to the rim. Now, we use beaded tires, and the rim has more material to provide the bead. Even without the blade shape, modern rims are heavier and stronger.
Spokes are not much stronger than they used to be. I was using DT stainless steel spokes 50 years ago, and they still sell them. But stronger rims permit heavier gauges and higher tensions. My race wheels in the mid-70’s were 36h, three-cross, 15-17-15 butted Trois Etoiles spokes with brass nipples (which are still much better than aluminum nipples) on Dura Ace hubs. I still have them. Current wheels are 32h, two-cross, 14-15-14 butted DT stainless spokes in Campy Chorus hubs. But the rims on the new wheels are heavier and have twice the section depth.
The key is that spokes must be tight. We did not used to tighten them enough, and many still don’t. They really should be tightened to a high percentage of yield strength—75-80%. The highest stress on a spoke is when the wheel is unloaded, because the bias tension should be higher than compressive stresses, which can only reduce tension in the spoke.
An impact makes a wheel collapse either by buckling the rim or by momentarily unloading enough spokes so that the rim can no longer impart compressive strength and it becomes unstable. When spokes break, it’s because of fatigue, and fatigue cracks are more likely if spokes are not over-tensioned briefly when the wheels are built to force any residual internal stresses to yield. Those internal residual stresses provide roots for fatigue cracks. Good builders always squeeze pairs of spokes together—hard—to perform this function.
We used to think that increasing the number of crosses made a wheel more comfortable, but that’s mostly myth. Increasing the crosses does permit slightly greater spoke tension, however, which makes the slightly wheel stronger.
Rick “fewer spokes are more aerodynamic, too” Denney
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Newman
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If the tensile stress is never fully relieved, then the axle (and the rider and the bike) must be hanging from the spokes above the axle (or more technically, spokes that connect to the rim higher than where they connect to the hub). And the "long-held myth" is true.
New-"mythbuster buster"-man
somebodyelse
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This sort of terminological argument comes up whenever anyone tries explaining prestressed structures. Which part of the structure sees a change in conditions when load is applied?
Sorry, but that is wrong. It works on the assumption that the rim is perfectly stiff such that it would transmit contact-patch stress around to the spokes at the top. The rim is not perfectly stiff, and it does not transmit stress around the rim as the bike rolls along. Instead, it deflects at the contact patch, reducing tension on the spokes there, with no change to the tension in the spokes elsewhere in the wheel. Deflection means that the material changes shape, and if it is elastic, stores energy rather than transmitting it (or absorbs it and turns it into heat if it is plastic--the tire does that but hopefully not the rim).
Rick "https://www.amazon.com/Bicycle-Wheel-3rd-Jobst-Brandt/dp/0960723668" Denney
Yes, that is the correct question. Brandt's finite-elements analysis predicted and measurements confirmed that stress and strain only change at the contact patch.
Rick "strain is to deflection as stress is to load" Denney
Newman
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Sorry right back at you, because you are wrong.
Several more-recent FEAs build on Brandt and say they don't contradict him. This one shows spoke tension changing in every spoke.
And even if only the bottom few changed, my statement would still be 100% correct. "If the tensile stress is never fully relieved, then the axle (and the rider and the bike) must be hanging from the spokes above the axle (or more technically, spokes that connect to the rim higher than where they connect to the hub)."
New-"mythbuster busting is a fool's errand, so I'm just the man for the job"-man
I hope you misquoted Brandt, because that statement (my bold) is wrong too.
Several more-recent FEAs build on Brandt and say they don't contradict him. This one shows spoke tension changing in every spoke.
And even if only the bottom few changed, my statement would still be 100% correct. "If the tensile stress is never fully relieved, then the axle (and the rider and the bike) must be hanging from the spokes above the axle (or more technically, spokes that connect to the rim higher than where they connect to the hub)."
New-"mythbuster busting is a fool's errand, so I'm just the man for the job"-man
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All you guys need to do is take a bike with properly tensioned spokes. Have someone sit on it, and start snipping spokes from either the top or bottom. You'll find out soon enough. Destructive testing is the funnest kind.
somebodyelse
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Another analysis sensibly starts with a section titled Semantics.
