what are good training wheels

[Johan Bornman]

Ooops don't get into the titanium is not an appropriate material for bike frames here on the wheel issue' date=' you'll just divert the topic. How much is that unobtainium per g?[/quote']

 

The last I checked it was about double the price of ceramic bearing material. However, the benefits are vast: stiffer, lighter, stronger. Unfortunately, there's a world-wide scarcity of the stuff, it being the primary ingredient in Russian missile nose cone technology.

 

Couldn't resist that last word. It's important to always use the "T" word when talking bike.

 

JB

 

Oh yes, and people have urged me to  show my softer side. Here's a smiley:  

Johan Bornman2007-09-07 01:34:32

[Ox_Wagon]

I was enjoying the thread up to the point where it was stated that wheels ?stand? on it spokes.  I was shocked to read the same thing in the Bicycling a few years ago.  <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

The reality is that the hub hangs from the top spokes in a similar way as a suspension bridge.

The mechanical interface between the spokes and rim does not allow any compression force to be transferred.  Some high end hubs like Mavic and Campy also does not allow compression force to be transferred between the hub and the spokes.  That is why spokes like spinery?s PBO work.

http://www.spinergy.com/Bicycle/tech_specialFeature_PBO.html

[Johan Bornman]

I was enjoying the thread up to the point where it was stated that wheels ?stand? on it spokes.  I was shocked to read the same thing in the Bicycling a few years ago.  <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

The reality is that the hub hangs from the top spokes in a similar way as a suspension bridge.

The mechanical interface between the spokes and rim does not allow any compression force to be transferred.  Some high end hubs like Mavic and Campy also does not allow compression force to be transferred between the hub and the spokes.  That is why spokes like spinery?s PBO work.

http://www.spinergy.com/Bicycle/tech_specialFeature_PBO.html

 

Your reality and the world out there seems to differ.

 

No-one said there is a compressive force transmitted as you described. The compressive force is applied to the bottom spokes but they only go into reducing the tension in the spoke. If the spoke has a 150kg tension and a 80kg man sits on the bike, the compressive force (that is absorbed by the overall tension that is much larger) will look something like this:

 

1) Assume the rim is quite stiff and four spokes are therefore in the load affected zone at the bottom of the wheel. If the rim was not so stiff, fewer spokes would be affected, but lets stick to four for now.

 

2) The man's weight distribution is equal front and back.

 

Therefore a force of 40 kg (the other 40 goes to the other wheel) is placed on the four load affected spokes, each taking up 10 kg.

 

But remember, they already have 150 kgs of tension in there, so now they only have 150-40-110 kgs of tension in there.

 

That looks like a lot of margin, but hitting a pothole puts about 4 times the normal load on a bicycle. If the spokes are not tight enough, the compressive force could easily overshoot, the spoke temporarily go slack, the nipples unscrew and the wheel goes out of true.

 

If the compressive force is very high, such as a 100kg man doing a very high jump onto concrete, then the compressive force will overshoot the tension and the wheels will collapse at the bottom.

 

Therefore I say wheels "Stand" on their bottom spokes. I have no better word for "stand", so try and envisage what happens. You'll see that no compressive force is therefore distributed between the spoke and rim and spoke and hub, because the spokes remain in tension.

 

It is quite easy to prove. Pluck a bottom and top spoke on your bike and memorise the tone. Now load the bike with your mother in law and pluck again. You'll see that the bottom spokes now produce a lower tone and the top ones a slightly higher one. I say slightly because although they produce a higher tone, it is not in the same relation as the bottom spoke's reduction in pitch. This is because the overall shape of the wheel changes when the rim is slightly flattened at the bottom, which makes the hoop larger and hence ever so slightly increases the overall tension of the spokes. This does not mean that the wheel hangs from the top spoke though.

 

Wheelbuilders see this phenomenum quite often but few have managed to interpret the data they get from the wheel. For instance, when a wheel has a slight hop at the 6-O-clock position, you tighten the spokes at the 6-O-clock position, not at the 12-O-clock position.

 

This perfectly demonstrates the phenomenum.  A pre-stressed structure works counter-intuitively and it is difficult to get your head around it.

 

I haven't ever examined a Spinergy up close, they're too ugly to approach without sunglasses. But I think you're talking about those four-spoked monstrosities. I have no idea whether those blades are in tension or not.

 

I hope this brings back your enjoyment to this thread.

 

JB

 

 

 

 

[Johan Bornman]

From the Spinnergy website: "The PBO fiber strands are encased in a chemical resistant, water / UV proof composite offered in a variety of colors. The outcome is a flexible spoke with incredible strength that will absorb impact more efficiently while staying in true. Our patented PBO spokes are lighter than traditional steel spokes which results in less rotational weight and a faster responding wheel ? giving you the ultimate edge. All this delivers a wheel that is lighter, stronger, faster and superior in every way."

Mostly nonsense, about 99% nonsense I reckon. They forgot to mention these thick "spokes" of their that have about 400% more wind resistance than traditional steel spokes.  They also forgot to mention the cost of these cords and the crappy fasterning system - a huge bulge at the rim.

 

However, they did manage to include the obligatory ligther, stronger faster claim. Pity they don't put any figures forth for their silly rotational weight argument.

 

They claim to deliver three times the strength of stainless steel but omit tha that the thing is six times thicker and plain silly.

 

And wow, these things are water and UV resistant. How's that for a benefit over stainless steel?

 

 

Strong enough is strong enough.

Johan Bornman2007-09-07 07:15:38

[Guest Michelle]

Johan: Did your saddle start out white?

[Johan Bornman]

I was enjoying the thread up to the point where it was stated that wheels ?stand? on it spokes.  I was shocked to read the same thing in the Bicycling a few years ago.  Cut cut cut.....<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

OK, I had a look at those Spinergy non-spokes of yours. They're just spokes. They work by tensioning the wheel and the fact that they're floppy is neither here nor there. In tension, a wheel is a prestressed structure and it acts counter-intuitively.

 

What shocks me is that you read this is a bike magazine....four years ago one of the magazines took me on when I postulated that behaviour and of course, having more ink than me, won the argument. The editor also chose to have the last say.

 

May I suggest you read Structures by JE Gordon (available from Exclusive Crooks) and thereafter The Bicycle Wheel by Jobst Brandt. The latter is available from Amazon and I have a few copies I use for my wheelbuilding courses. I'll sell you one, but don't expect to pay the cover price of $24, they cost me $13 each to import and then I pay VAT at the PO as well.

 

Also, do some research on lintels. Just walk to a building site and see how a concrete slab that normally breaks like a biscuit, can support weight in tension.

 

JB

 

 

 

 

 

[Johan Bornman]

Johan: Did your saddle start out white?

 

 

As a matter of fact, yes. I then at some stage used some shoe dye and made it black. This failed miserably because the black paint stuff kept on sticking to my shorts and eventually came off. I then dyed it yellow, which didn't work because the underlying black and white just overpowered the yellow. Now its a kinda smeary, pukey yellow-white.

 

JB

[Gumpole]

Johan whats the point of the concrete analogy?

The concrete slab, lintol, beam etc doesn't break because of the bottom steel which is in tension.. the concrete itself (at the top half of the slab) is in compression.

[Johan Bornman]

Johan whats the point of the concrete analogy?

The concrete slab' date=' lintol, beam etc doesn't break because of the bottom steel which is in tension.. the concrete itself (at the top half of the slab) is in compression.

[/quote']

 

The point I'm trying to make is that a prs-stressed structure does not act as one expect it to act. In the case of the lintel, we have a piece of concrete that can take tension. You're right that the top half is in compression and the bottom half in tension, but I didn't want to confuse the issue with the bit in compression.

 

However, it doesn't break for the reasons you give, namely that there is steel in there. It could have been PBO fibres (or whatever Spinergy calls their string) for that matter. What is important is that they are in tension.

 

A lintel is a concrete slab poured over a set of wires which are pulled tight  - very tight. The concrete is poured over it and allowed to dry. The wires are then cut off from their tension levers and the slab is a so-called pre-stressed slab or in this case, lintel. These wires inside are under tension in the concrete and compress (pre-sress as the industry calls it) the concrete at a force of X. This allows the lintel to accept a tensile for not exceeding X before it breaks.

 

If those wires were not tensioned before the concrete was poured, the lintel would break like a biscuit under tension.

 

JB

 

 

 

 

[Ox_Wagon]

So you say it works according to the following principal

Sorry no amount of pulling on something will make it possible to push on it.  It is like saying that if you stand on a piece of rope and now pull on it hard enough it will magically support your weight.  <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[E1A104]

Good afternoon. Pardon my ignorance, but I thought that titanium can and has been used to manufacture bicycle frames?

[Johan Bornman]

So you say it works according to the following principal

 

Sorry no amount of pulling on something will make it possible to push on it.  It is like saying that if you stand on a piece of rope and now pull on it hard enough it will magically support your weight.  <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

OK, I can't help you anymore. You'll have to get it yourself.

 

JB

[Johan Bornman]

Good afternoon. Pardon my ignorance' date=' but I thought that titanium can and has been used to manufacture bicycle frames?[/quote']

 

 

No problem, all questions are valid questions. I never claimed that it hadn't been used for bike frames, I said it is not an appropriate material for bike frames. There's always someone that will do the inappropriate. Look around you and you'll see plenty of 4X4s and cars with top speeds of 240 kph in the traffic.

 

JB

[jeremyd]

you're stepping on hallowed ground....careful.

[Icycling]

Jihan Bornman - you mentioned about the lack of aerodynamics of the Spinergy spoke - Is this not just perfect for training then?

 

 

 

From the racing side - how important are aero wheels. Most of the time you in the slip stream of the riders ahead of you anyway not to metion the terbulance all spoked wheels create - and then the terbulance betwean the frame!

 

 

 

Surprisingly Mavic also now have re-looked at a fat round spoke for their new R-Sys wheels. These wheels are above the well knowen Ksyrium range.

[Johan Bornman]

Jihan Bornman - you mentioned about the lack of aerodynamics of the Spinergy spoke - Is this not just perfect for training then?

From the racing side - how important are aero wheels. Most of the time you in the slip stream of the riders ahead of you anyway not to metion the terbulance all spoked wheels create - and then the terbulance betwean the frame!

Surprisingly Mavic also now have re-looked at a fat round spoke for their new R-Sys wheels. These wheels are above the well knowen Ksyrium range.

 

Piter Wheeler - introducing gratuitous air drag is just silly. Whilst I'll argue that exposed nipples are not an issue and that cross spokes are not an issue and that reduced spokes are not an issue, the act of purposely increasing the diameter of your spokes for the hell of it, is nonsensical. Making them more expensive and proprietary is a crime.d

 

Mavic will do anything to draw attention, including aluminium spokes, cut-out rims, one yellow spoke and unpronounceable wheel names.

 

Mavic's latest spoke trick is stupid.

 

JB