BS of the week

On the TdF commentary just now, in response to a question about using helium in tyres:

"they do use helium in tyres for downhill mountain biking because it compresses more evenly"

Look another one

cynic-al – Member
Oh well I guess you are white, middle class and identify with gangsta rappers?

i'm guessing you are indeed sir… a..

Ha, that is amazing. Helium compressing more evenly… Did they also say it can help you jump further.

helium compressing more evenly: any pure gas will have more predictable compression and expansion properties than a mixture such as air. Helium would be a poor choice because is is a small molecule and escapes well. Nitrogen is pretty well accepted in formula 1 tyres.
so maybe not total bullsh1t, more like lazy reporting

I'd be very interested in the science behind that theory, do you have a reference?

any pure gas will have more predictable compression and expansion properties than a mixture such as air

*sniggers*

bassspine – Member

helium compressing more evenly: any pure gas will have more predictable compression and expansion properties than a mixture such as air

Can I make this my BS of the week please..

Sorry Basspine you will have to wait until this week;'s edition of the thread.

I'll have to remember that one for my next crash.
"It's not my fault, the air in my tyres compressed unevenly"

We're talking about linearity rather than predictability, aren't we?

I love the way this thread has become self perpetuating.

This thread should be on the wiki page for stw forum.

It's so dope, it's gnarly. Right I'm off to bust a move to meet my homies and rail some rad, sick pipes. laters.

What tyres for filling with helium for predictable compression and expansion? It's getting to the point where I don't even bother going out on my bike any more due to the unpredictability of it all. 🙁

so – why do FI cars use nitrogen? There is some sort of advantage in doing so I believe

helium would make your bike weigh less ( but mass the almost the same )

TJ google is your friend

We've done nitrogen and helium in tyres before, haven't we ?
Nitrogen was touted for truck tyres a while ago because of the reduced change in pressure with temperature.
It never caught on. For vehicles that have already got air brakes and air suspension, On Board Tyre Inflation linked to the vehicle's ECU is a much better idea, constantly adjusting tyre pressures to suit vehicle speed and load.

This thread perfectly encapsulates everything that I hate about STW. Good job!

This thread perfectly encapsulates everything that I hate about STW. Good job!

+1000000000

I'm gonna make it a weekly feature.

Along with a "pwned of the week" – I anticipate Surf Mat will feature heavily.

Any thread with SPOILER in the title.

That's because they are threads about sporting events or films on which the ending of the subject matter may be discussed. The warning is there so that anyone interested in the subject but as yet not aware of the outcome or ending doesn't accidentally click on it and have that ending or outcome spoiled.

Seems fair to me.

Cross bikes have slacker seat angles, which means less power on the pedals…

That's not bs! Definitely easier to get the power down when you're sat more forward. Well known f-a-c-t.

helium would make your bike weigh less ( but mass the almost the same )

😯
is it gravity that changes, then TJ

anything davidtayford writes , pure bs

I was about to accuse scaredypants of a Physics fail, then I started typing and I remembered thermodynamics.. but I was always rubbish at it..

PV = nRT

So if P and V are the same (same pressure in your tyres, same R and temperature, then n must be the same too right? Or almost the same.. because they'd both be similar to an ideal gas…

But n moles of helium would have less mass than n moles of air, by fair bit since a mole of helium is only 4g and a mole of air would be what.. 15g ish? So the density of gas in your tyres would indeed be much lower hence reducing the weight (due to buoyancy) and the mass would be significantly less, around a quarter.

So maybe scaredypants was a physics fail. Or maybe it's me.. 🙂

Here's another one:

Definitely easier to get the power down when you're sat more forward. Well known f-a-c-t.

How come road riders don't use triathlon style steep seat tubes if it's that much of an advantage?

So maybe scaredypants was a physics fail

clearly – if you can see why (under same gravity) mass is almost the same but weight is less, you're a better phyicist than me

A helium balloon has no weight but it still has mass.

Err, no.

A helium balloon has mass and weight (whilst its within a gravitational field). But it has bouyancy in Earth's denser atmosphere causing it to rise.

I thought weight was what you measured on a set of scales?

a balloon full of helium has no weight surely – even tho it has mass.

Rest it on a set of scales the scales read zero.

I was just thinking that,positive bouyancy rather than no weight,Helium weighs 0.1785 grams per liter, so a ballon full of helium can't have no weight.

"Rest it on a set of scales the scales read zero."

yup, but if you have scales accurate enough and weigh a liter bottle of air, you will get the weight of the bottle plus the weight of the air shown on the scales.

If you then measure exactly the same bottle with a liter of helium in it, the helium will weigh less than the air, so you'll get a different reading.

it has a mass of 0.1785 grammes per litre.

Does it have any weight? or is it only when in orbit it has no weight?

Wiki

Weight, by definition, is a measure of the force which must be applied to support an object (i.e. hold it at rest) in a gravitational field. The Earth’s gravitational field causes items near the Earth to have weight.

But the helium balloon does not require any force to support it in a gravitational field. Does it have weigt? or only mass?

I have convincingly confused myself now

TandemJeremy – Member

"But the helium balloon does not require any force to support it in a gravitational field"

It does require a force to support it, which is provided by its buoyancy. Just because nothing's visibly holding it up doesn't mean nothing's holding it up. If you put it in a vacuum jar and put it on a scale, what would the scale show? (well, the baloon would burst)

I thought weight was what you measured on a set of scales?

Interesting theory. So the QE2 would weigh nothing…..until it sunk, and gravity pulled it to the bottom of the ocean ?

I guess if you put the scales and the helium balloon into a vacuum, then it would register a reading no?

In a world of Hydrogen, Helium is the fat bastard.

My head hurts.

I guess if you put the scales and the helium balloon into a vacuum, then it would register a reading no?

yes it would

ernie_lynch – Member
Interesting theory. So the QE2 would weigh nothing…..until it sunk, and gravity pulled it to the bottom of the ocean ?

Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

My head really hurts now

Ernie's example is way better than mine 🙁 But at least I got there before Deadlydarcy!

Basically, forget about scales. The only time that'll ever cause you a problem is if you're baking a cake that has lighter than air ingredients (in which case just turn the scales upside down)