Bike journo doesn't do physics shocker

onewheelgood – Member
Jobst Brandt will be along in a minute and then this thread will never end.

Well here’s one I prepared earlier:

Jobst Brandt – bicycle science guru
the elasticity of spokes arises from the material properties of steel and is not affected by more or less tension (p.71, The Bicycle Wheel, 3rd Edition, Jobst Brandt)

so does the hub hang from the top of the rim or stand on the spokes below, he asked, innocently?

😆

What a rubbish thread. 😐

I can spice it up with some pictures of buildings if you like. Just let me know, innit.

Insufficient spoke tension

Full supsension bridge! 😮

its a building that looks like a wheel

Good call there, RS…. 8)

My insomnia isn’t in bad I’m about to read the article just yet, but I can’t see how aracer is correct on any meaningful definition of wheel stiffness…which does not include this:

The normal measure of stiffness of wheels is when the spokes haven’t gone slack – try re-reading that article I linked, and you’ll see there are significant differences in stiffness between different wheels without spokes going slack.

I’ve seen Jobst come out with meaningless analogies/theories for no purpose I can see other than to make himself look clever.

OK I read Sheldon’s article…interesting….

But can you offer an explanation incorporating your superposition of forces line?

Please don’t say “”look it up yourself” as we’ll then know TJ has nicked your log in 😛

http://en.wikipedia.org/wiki/Superposition_principle

😀

Internet nerd being a tough guy nerd on the Internet shocker.

Spokes are elastic. Them more you stretch an elastic thing, the more it resists stretching. No?

As simple as I can manage: spokes are made of steel which is a normal elastic solid which obeys Hooke’s law – ie stress is directly proportional to strain in the elastic region. Because the stress/strain curve is a straight line in the elastic region, if you increase the tension by a fixed amount x, it will stretch by a fixed amount y which will be the same no matter how much tension there already is in the spoke. Put the spoke in a wheel and put a force on the rim – this force results in an increase in tension in the spoke. From the above, the amount the spoke stretches due to this increase in tension is the same no matter how much tension the spoke is already under.

Taken in the context of the mag quote, the caveat wasn’t needed – it should have been quite clear what I meant to anybody paying attention and not deliberately taking my comment out of context.

A fair few shared the confusion [ because it does need a caveat ]but yes its my/our fault you did no stay it properly because we did not pay attention 🙄
It was incomplete {Wrong as stated] and tension does matter because if you dont have any you have a wobbly wheel
Obvious;y you are too proud self righteous to accept , fine
Hardly a huge issue to just accept that and move on.
It was not clear hence why a number countered it.

So Junky, you didn’t pay proper attention to what the thread was about, and because you weren’t alone that means you’re right? 🙄

Or do you actually think Matt was writing about the difference between a wheel with some tension in the spokes and no tension in the spokes?

I think if you’d started with that you may have gained more support….

Like winding more pre load onto a coil spring in suspension. Changes the sag point on suspension but not the force required deflect the fork a certain amount.

But as physics howlers go i’d go with forgiveable.

Wheel builders/experts

is it true that stiff wheels, wheels built with stiffer components tend to use higher spoke tension. I’m thinking a wheel designed for say freeride would be built with strong and stiff components and use higher spoke tension to avoid slack spokes

I fell off the other day. The spokes in one of my outrigger wheels were slack!

So Junky, you didn’t pay proper attention to what the thread was about, and because you weren’t alone that means you’re right?

Well the evidence appears to be my view as you confused everyone then altered the statement with a caveat. I suppose we are all worng and you are right though eh 🙄

I cant be arsed you wont change and accept a fairly minor point that you could and should have worded it better.
I have no idea why you wont just go ok fair enough its hardly a big deal

Well the evidence appears to be my view as you confused everyone then altered the statement with a caveat.

Ah – so you are still relying on the fact you weren’t alone in your lack of comprehension, and you’re thinking that my explanation for those who weren’t paying attention is an admission of guilt? By my count, “everyone” is about 4 people 🙄

Let’s try a couple of questions:
Do you think Matt was writing about the difference between a wheel with some tension in the spokes and no tension in the spokes?
Do you think my comment that spoke tension doesn’t affect wheel stiffness was a completely isolated statement unconnected to the original quote, and not in answer to “Why not simply explain his ‘mistake'”?

I won’t be offended if you can’t be arsed to reply – even if you’ve currently not been arsed enough to reply twice. Hardly a big deal to accept you’re wrong, is it?

Like winding more pre load onto a coil spring in suspension. Changes the sag point on suspension but not the force required deflect the fork a certain amount.

Good analogy and a very similar issue – another one people don’t understand.

The quote in the OP does make sense if considered with thisisnotaspoon post:-

The point is a tighter wheel takes more load to reach this point. So the “very tight” set of wheels won’t deflect during a hard corner, landing a jump or hittig a rock where the “tight” wheels MIGHT deform IF the force is grat enough to slacken off a proportion of the spokes.

The greater the spoke tension, the harder the wheel can be ridden before spoke tension slackens off and the wheel deflects.

Except that’s not what people mean by wheel stiffness. Any well built wheel (even one without “incredible spoke tension”) will take a very big load to slacken the spokes – one most normal riders won’t ever have. After all, as I mentioned above, it’s a very small step from there to a bent wheel. Cornering certainly won’t do it and given typical MTB tyre pressures you’d be bottoming out the tyre (and denting the rim) before you managed it landing a jump or hitting a rock.

He’s behind you!

Oh no he isn’t….

Now I remember why I haven’t been around on this forum for the past 2 year…….but it has cured my insomnia 😉

Oh. My. God.

aracer… I can’t be arsed to read the physics on this right now, but I am intrigued to know what is happening when I felt my bike to be rather ‘weird’ at the back end. This was cured by tightened up the spokes in that wheel, none of which were loose, but there was uneven spoke tension.

Is it because it was uneven?

This was cured by tightened up the spokes in that wheel, none of which were loose, but there was uneven spoke tension.

Uneven tension – a sign of a not well built wheel. Chances are that whilst the spokes weren’t actually loose, their tension was also very low meaning they were going slack in use.

Except that’s not what people mean by wheel stiffness.

(I’m quoting your initial response, before you had time to think about it and edit it some more.

The journo was writing for a bike mag, not a paper for Physical Review. If the journo was trying to say he could ride the bike harder before he felt the wheels deflect, I would let him off with that.

The Sheldon Brown article was interesting, I’d never really thought about this before. It would have been interesting if he had repeated the experiment but with a different load. That might have showed the wheel suddenly deflecting at, say, points 8 & 9 rather than 9 & 10. If it had, then that would have blown your arguments out of the water.

Aracer, as a member of the Institute of Physics and co-owner of the mag I have to agree with your technical point on the relationship (or lack of) between spoke tension and stiffness and as such it will be discussed at the office next week.. However, you’ve communicated it so badly and smugly that your point has been somewhat lost in your insufferable attitude. Despite accepting your point of physics your ‘Bike journo doesn’t do physics shocker’ thread title has won you few fans.

What I’m wondering is, just what is it that makes the wheel feel so stiff to an experienced bike rider like Matt who would be familiar with riding similar rims, spokes, hubs, etc.?

Mark, Matt. I accept my thread title is rude and insulting, and for that I apologise – sorry Matt. I should have thought a bit longer before posting.

However if my “insufferable attitude” is defending my point against those determined to misinterpret it, or not understanding the science, then I’m not apologising for that. As somebody with a scientific background, you surely have to agree Mark that there is far too much incorrect junk science written in cycling magazines (STW is far, far less guilty of this than many others I’ve read, which is maybe why this one jumped out at me), hence the irritation at the repetition of myths like this.

Once again my apologies to Matt – wasn’t really meaning to have a dig at him, even if it seemed like that. I actually really liked the review apart from that point – not at all surprised if the wheels felt very stiff, but that’s likely to be down to the stiffness of the rim.

+1 aracer

the issue here is multiple numpties under tension when their strawman arguments are outed, and getting hard when they back each other’s flawed beliefs. And then there’s Elfboy polishing his rim just to be noticed as per usual

Pete Poddy once twisted my nipples, and we both went a bit stiffer. Is that what we’re taking about?

DrP

It might well be, Pij; it might well be….

Sort of except aracer will start having a hissy fit with you for not also pointing out that once you had achieved sufficent stiffness with Peter Poddy, no amount of further nipple-twisting would have changed that.

😆

That’s where Pete resorts to 5 inches in the rear… (any less and it’s too rough apparently-I never understood that, but he assures me)

DrP…

(I must grow up!)

Aaaaaaaaaaaahhhh!!!!!!!!

Aaaaaaaaaaaaaaaaaagh!!!!!!!!

I can’t stand it any longer!!!!

Pump away hard enough on his little valve and there’s a explosion of white sticky stuff too.