Bike Weight Illusion

[rich65]

Why is there an apparent difference in the weight of a bike when lifted from 2 different handling positions?

If you lift it up with both hands on the top tube there is a distinct illusory sensation of the bike feeling lighter than if you pick it up by the seat and the stem

Can somebody explain why this is?

 

[Racing roadkill]

It's not the weight that's causing this. It's that the work you're doing to lift the bike from different positions is varying ( work = force X distance ) so if you're lifting the bike's 'heavy bits' from directly at the location of the heavy bits, it will feel like less of an effort than if you lift it from any distance away from the 'heavy bits'. A bit like if you try to lift a heavy box, with your arms against your body, it feels like the box weighs less than if you lift it at arms length.

 

[lutonloony]

It's not the weight that's causing this. It's that the work you're doing to lift the bike from different positions is varying ( work = force X distance ) so if you're lifting the bike's 'heavy bits' from directly at the location of the heavy bits, it will feel like less of an effort than if you lift it from any distance away from the 'heavy bits'. A bit like if you try to lift a heavy box, with your arms against your body, it feels like the box weighs less than if you lift it at arms length.

Surely it is just the position of your arms, nothing to do with lifting the heavy bits

 

[midlife]

It's an illusion as you are doing the same amount of work as long as the bike moves exactly the same each time

Shaun

 

[deptfordmarmoset]

Jeez, don't you guys know the first thing about bicycle feng shui?

 

[KneesUp]

And, ahem, in an attempt to address the actual question as to why there *seems to be a difference* I would imagine it's to do with the leverage in your arms and (more likely) the rotation of your wrists. Bend your elbow at 90 degrees. Place your other hand on your bicep and rotate the wrist of the bent arm. You'll feel a muscle move under your bicep. I don't know what it's called. I expect if you life a bike with your hands on the seat tube and head tube you use that one more than if you have your hands flat under the top tube - and furthermore I suspect that in most of us it's not as strong. Or something.

 

[Racing roadkill]

It's an illusion as you are doing the same amount of work as long as the bike moves exactly the same each time

Shaun

Well you've just re- written the laws of physics. You should write a book or something.

 

[midlife]

Well you've just re- written the laws of physics. You should write a book or something.

Iirc from my a level physics work = force times distance

If you apply the same force for the same distance it doesn't matter if you apply the force to the top tube or somewhere else on the frame. Are you thinking about centre of mass?

Shaun

PS I haven't written a book but I have written a chapter in a book, does that count?

 

[Racing roadkill]

Iirc from my a level physics work = force times distance

If you apply the same force for the same distance it doesn't matter if you apply the force to the top tube or somewhere else on the frame. Are you thinking about centre of mass?

Shaun

PS I haven't written a book but I have written a chapter in a book, does that count?

You're right in the sense that if you're lifting the same weight over the same distance the amount of work is the same, no matter where you lift it from, the OP was talking about the illusion of a difference, depending on where you lift it from, this is due to the fact that you are at a different relative distance from the bike's center of gravity, if you try to lift the bike's rear wheel from right over the heaviest bit, then lift it from ( say the bars). It's going to give the illusion that the bike is heavier, when lifted from the bars.

 

[midlife]

You're right in the sense that if you're lifting the same weight over the same distance the amount of work is the same, no matter where you lift it from, the OP was talking about the illusion of a difference, depending on where you lift it from, this is due to the fact that you are at a different relative distance from the bike's center of gravity, if you try to lift the bike's rear wheel from right over the heaviest bit, then lift it from ( say the bars). It's going to give the illusion that the bike is heavier, when lifted from the bars.

Yep, I think we agree on the classical Newtonian mechanics

The centre of gravity thing you mention is interesting in that I came across a shed load of frames in the 70's and early 80's. BITD we were all used to picking up a bog standard 531 frame and grabbing it by the top tube by the seat cluster. I guess the centre of gravity was towards the rear as the "heavy" rear triangle made it that way.

As Columbus etc tubing appeared the rear end lightened and frames felt different to pick up. Total weights according the manufacturer's in the very early 70's were about the same so it was a balance thing. My Avatar is a 70's Bob Jackson frame and given the shape of the rear end it's likely a mix of 531 main tubes / forks with some Columbus in the rear as it was lighter. Doesn't feel like a 531 frame to lift up.

Cheers

Shaun

 

[Profpointy]

Iirc from my a level physics work = force times distance

If you apply the same force for the same distance it doesn't matter if you apply the force to the top tube or somewhere else on the frame. Are you thinking about centre of mass?

Shaun

PS I haven't written a book but I have written a chapter in a book, does that count?

you're missing out a key point. If your arms hang straight down you're pulling against the weight of of the bike. If your arms are at an angle holding either end of the bike the they are pulling against the weight of the bike AND against each other. You do tire merely holding a static load so you expend more "work" even though force x distance(zero) would mislead you into thinking otherwise and no work is indeed done not lifting. I half recall the term "conservative forces" may be in there somewhere

 

[midlife]

you're missing out a key point. If your arms hang straight down you're pulling against the weight of of the bike. If your arms are at an angle holding either end of the bike the they are pulling against the weight of the bike AND against each other. You do tire merely holding a static load so you expend more "work" even though force x distance(zero) would mislead you into thinking otherwise and no work is indeed done not lifting. I half recall the term "conservative forces" may be in there somewhere

Does an Albatross do any work holding it's wings out?

Shaun

 

[Profpointy]

Does an Albatross do any work holding it's wings out?

Shaun

depends how he's designed. If i were designing an Albatross I'd have gone for the no-work option

However for people holding a weight I contend it's tiring to merely hold in position thus you are working / using energy just to stand still - even if it's not "doing work" on the weight since it hasn't moved. You have thus turned (chemical) energy into heat, without gaining any "potential energy" by actualll lifting

 

[jefmcg]

Why is there an apparent difference in the weight of a bike when lifted from 2 different handling positions?

If you lift it up with both hands on the top tube there is a distinct illusory sensation of the bike feeling lighter than if you pick it up by the seat and the stem

Can somebody explain why this is?

It feels the same in either position to me.

Does everyone else experience this illusion?

 

[Southside Mike]

It feels the same in either position to me.

Does everyone else experience this illusion?

Yes, but that's because you are the only real person in the world and all the rest of us are constructs of the alien experiment you are in