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Q: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub..... ( Answered 5 out of 5 stars,   5 Comments )
Question  
Subject: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.....
Category: Science > Physics
Asked by: johnfrommelbourne-ga
List Price: $5.00
Posted: 01 Nov 2006 05:47 PST
Expires: 01 Dec 2006 05:47 PST
Question ID: 779090
.... so at this point I am lifting wheel directly straight up above ground
surface(i.e 90 degrees) about 6 or 7 inches. I understand that at this
stage I am lifting a true weight of 17 kilograms( app.38pounds).
However obviously when I then have to hold and manouvre same weight
onto axle hub, with  slightly outstretched arms exactly parallel with road
surface this time, the effective weight or pressure required  to hold
wheel steady but directly in line with hub shafts increases
significantly. The procedure is tricky and requires strong hands but
just what is the exertion/pressure required ( or
effective weight for lifter) compared to simple task of lifting a 17
kilo wheel straight up off the ground 90 degrees.

 I imagine the same principle applies when you see acrobats on the
hoops; i.e  simply holding themselves off the ground( 90 degree
lift)with arms pointing directly up is clearly very different to same
height above ground where they have to go into crucifix position (
parellel arm position ).

Request for Question Clarification by sublime1-ga on 01 Nov 2006 12:11 PST
Hi John...

Myoarin did a good job of explaining the essential principles,
which have to do with vectors and the fulcrum. The fulcrum is
the pivotal point around which a lever turns. In this case, 
your bones act as the solid levers, and the fulcrum points
are the joints. So if you have a weight held directly over
your head with locked arms, the levers (your arm bones) bear
little tension, and the weight is pushing down on your 
shoulder muscles. If you begin to lower your arms in front
of you, with your arms held straight, the bones take up 
more tension, and the effective weight transferred to the
shoulders increases, peaking when your arms are parallel to
the ground. The further the weight is from your shoulders
(or the longer your arms), the greater the effective force
is on the shoulder (and back) muscles. If you were to bend
forward at this point, it would put unbearable pressure on
your lower back muscles.

The basic formula for levers and fulcrums is F1 x D1 = F2 x D2,
as seen in the illustration at the top right of this Wiki page:
http://en.wikipedia.org/wiki/Lever

I don't know the formulae to figure out the effective weight in
a precise manner, and it would be somewhat foolish to attempt to
do so, given that, when lifting the tire, your arms are "slightly
outstretched", so the amount of effective weight borne by each set
of muscles would vary with the length of your forearms, the angle
of your arm from shoulder to elbow, and more.

However, there is a general statement made on this page from
Steven Publishing which addresses safe lifting, which echoes
the estimate I have heard before:

"Encourage all workers to bend at the knee, not at the back.
 Have them keep the product close to their bodies. A load held
 at arm's length from the body puts 10 times as much stress on
 the back."
http://www.stevenspublishing.com/Stevens/OHSPub.nsf/frame?open&redirect=http://www.stevenspublishing.com/Stevens/OHSpub.nsf/d3d5b4f938b22b6e8625670c006dbc58/77e609a2071d50fe86256e0b007173d1?OpenDocument


Obviously, if your forearms are parallel to the road, but your
arms from the shoulder to the elbows are at, say, a 75 degree
angle to the road, the effective weight will be less than 10
times the actual weight, but you can get some idea of what it
might amount to. The closer you can keep the weight to your 
body, the better.


By the way, I've found a way to mitigate the weight when doing
this maneuver, which is to place my elbows on my knees as I lift
the tire. This provides a good deal of leverage, and takes the
strain off the back muscles to a great degree. This effectively
places another fulcrum closer to the weight, and shortens the
distance from the weight to the first fulcrum, thus reducing
the effective weight and force.


Let me know if this satisfies your interests...

sublime1-ga

Clarification of Question by johnfrommelbourne-ga on 02 Nov 2006 06:41 PST
Hello Sublime,I remember you from way back but did not know you were
still around. I have read much of what you gave me directly and  from
the links as well.  I can see  the mathematics/geometry to work out an
actual answer in figures is  fairly elusive unless one goes to a lot
of trouble or solicits assistanc from an expert in the science so dont
really expect you to do much more; unless you think there is another 
solid avenue you could explore that would not take much time.
Otherwise please take the fee and thanks very much for your time.

 JohnFrom Melbourne  P.S I may try and seek out somone closer to home
here that counts themeselves as an expert in this field as I would
realy like to know

Request for Question Clarification by sublime1-ga on 02 Nov 2006 11:28 PST
JFM...

I'm happy to wait for awhile before posting a finalizing answer,
as I'd much prefer that you receive what you feel is a 5-star
answer.

As for solid avenues, a tailored search which should bring the
information to the fore if it exists is:

"replacing a tire" weight lifting
://www.google.com/search?q=%22replacing+a+tire%22+weight+lifting

And it produces only 52 unique results, none of which are
helpful, while "replacing a tyre" produced only 4 results.

sublime1-ga

Clarification of Question by johnfrommelbourne-ga on 07 Nov 2006 05:52 PST
Sublime,

  Again thanks for having a real red-hot go but given the price I
posted I dont think you need do a lot more; especially considering the
fact that it really appears as if there is nothing on the net that
directly and very specifically relates to  the bodily mechanics
involved.

  Just between you and I, as I dont think anyone is "listening in" at
this late stage so long after qusetion being posted I really wanted
some sort of answer for a particular purpose as follows-:

 I am working on something at the moment where I aim to show that some
people, a typical female for instance, will never be able to always
and reliably change a tyre (if she finds herself stuck in the  middle
of nowhere for example), no matter how much she is schooled in the
subject purely due to physical/biological limitations. In other words
she could be taught to be an expert in the theory but always fail the
practical if put to the test, simply because at an average of 39
pounds deadweight it is already heavy and a reasonably heavy  lift but
when required to be held quite steady parallel to the ground(as an
absolute neccessity to be able to fit wheel to hub) the effective
increase in weight is just too much for the average female.
 If I can establish that point as sound in theory then I can move on
to something that allows me to capitalise on that for another related
purpose.

 John From Melbourne
Answer  
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.
Answered By: sublime1-ga on 07 Nov 2006 13:30 PST
Rated:5 out of 5 stars
 
JFM...

Okay, given the price and the lack of an audience, I'll post
my answer here.

------------------------------------------------------------

Myoarin did a good job of explaining the essential principles,
which have to do with vectors and the fulcrum. The fulcrum is
the pivotal point around which a lever turns. In this case, 
your bones act as the solid levers, and the fulcrum points
are the joints. So if you have a weight held directly over
your head with locked arms, the levers (your arm bones) bear
little tension, and the weight is pushing down on your 
shoulder muscles. If you begin to lower your arms in front
of you, with your arms held straight, the bones take up 
more tension, and the effective weight transferred to the
shoulders increases, peaking when your arms are parallel to
the ground. The further the weight is from your shoulders
(or the longer your arms), the greater the effective force
is on the shoulder (and back) muscles. If you were to bend
forward at this point, it would put unbearable pressure on
your lower back muscles.

The basic formula for levers and fulcrums is F1 x D1 = F2 x D2,
as seen in the illustration at the top right of this Wiki page:
http://en.wikipedia.org/wiki/Lever

I don't know the formulae to figure out the effective weight in
a precise manner, and it would be somewhat foolish to attempt to
do so, given that, when lifting the tire, your arms are "slightly
outstretched", so the amount of effective weight borne by each set
of muscles would vary with the length of your forearms, the angle
of your arm from shoulder to elbow, and more.

However, there is a general statement made on this page from
Steven Publishing which addresses safe lifting, which echoes
the estimate I have heard before:

"Encourage all workers to bend at the knee, not at the back.
 Have them keep the product close to their bodies. A load held
 at arm's length from the body puts 10 times as much stress on
 the back."
http://www.stevenspublishing.com/Stevens/OHSPub.nsf/frame?open&redirect=http://www.stevenspublishing.com/Stevens/OHSpub.nsf/d3d5b4f938b22b6e8625670c006dbc58/77e609a2071d50fe86256e0b007173d1?OpenDocument


Obviously, if your forearms are parallel to the road, but your
arms from the shoulder to the elbows are at, say, a 75 degree
angle to the road, the effective weight will be less than 10
times the actual weight, but you can get some idea of what it
might amount to. The closer you can keep the weight to your 
body, the better.


By the way, I've found a way to mitigate the weight when doing
this maneuver, which is to place my elbows on my knees as I lift
the tire. This provides a good deal of leverage, and takes the
strain off the back muscles to a great degree. This effectively
places another fulcrum closer to the weight, and shortens the
distance from the weight to the first fulcrum, thus reducing
the effective weight and force.

------------------------------------------------------------

As for using these principles of physics to assert that the
"weaker sex" will consequently be unable to reliably change
a tire, I'm afraid it would be presumptuous to assert anything
other than that it would make it highly unlikely that most
women would ever attempt to change a tire by holding the 
wheel straight out from their bodies.

Children reach a weight ~40 pounds between the ages of 3 and
6 years old, and mommies are lifting them all the time at the
younger ages. They may be in better shape than you think!

Additionally, I recently watched a segment on the Rachel Ray
show where a female guest demonstrated how a woman should
change a tire. Included in the recommended kit were some
bricks. Two were to be used to place in front of and behind
the tire that was not being changed. The third one was used
to roll the spare tire up to the level of the lug bolts and
maneuver the wheel onto them. Add to that the possibility of
using the jack to raise or lower the car to assist in the 
process of aligning the wheel with the bolts, using the brick
as an aid. What they lack in muscle can be supplemented with
brains.

Finally, most true spare tires these days are not full-size
tires (at least not in the US). They're half-size jobbies
that are smaller in diameter and also narrower in width.
They are specifically designed to get you to a gas station
and allow repair of the real tire, and you are cautioned
not to exceed 50mph when using them, as they aren't made
to take that kind of stress for long. Here's an image:
http://www.cheapfragrance.net/ebay/spare_tire.jpg

These specially-designed spares weigh more like 25 pounds,
and don't pose anywhere near the challenge of a regular
car tire.

So, unless mom's driving the family Hummer (in which case
she probably has AAA club priveleges), I'd be reluctant to
draw the inevitably controversial conclusion that, with 
training, a woman would have a much harder time changing a
tire than a man.

If you have any thoughts or questions, feel free to post a
Request for Clarification...

sublime1-ga


Searches done, via Google:

"replacing a tire" weight lifting
://www.google.com/search?q=%22replacing+a+tire%22+weight+lifting

"physics of lifting"
://www.google.com/search?q=%22physics+of+lifting%22

"proper lifting" "effective weight"
://www.google.com/search?q=%22proper+lifting%22+%22effective+weight

"proper lifting" "effective weight" -training -management
://www.google.com/search?q=%22proper+lifting%22+%22effective+weight%22+-training+-management
johnfrommelbourne-ga rated this answer:5 out of 5 stars and gave an additional tip of: $2.00
Sublime, You have done very well indeed. Especialy thanks for last
bits of info you provided, which was especially useful. Would have
loved to have seen TV piece on how best a woman can change a tyre with
limited physical input. There is a sound reason for all this and I may
hit you particualrly with some related questions later on if you dont
mind.

 Thanks again Sublime,

 JohnFRomMelbourne

Comments  
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.
From: myoarin-ga on 01 Nov 2006 06:20 PST
 
G'day,

It has to do with fulcrums and vectors and where the muscles are that
are used to carry the weight.  Your example of an acrobat on the rings
is easier than that of you with your tyre.  When he just hangs, with
his arms vertical, his shoulder and body muscles can be fairly
relaxed.  With his arms horizontal, he needs more muscles than most of
us have, since they are attached very close to the fulcrum of his
should joints, while his hands bearing his weight are many times that
distance from the fulcrum, thus requiring him to exert about that many
times as much force with his muscles to keep his arms horizontal.

I hope that helps a bit.  I probably didn't use the correct expressions.
Where is Redhoss-ga?
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.....
From: probonopublico-ga on 01 Nov 2006 06:22 PST
 
This varies dependent upon the gravitational force.

What part of the Universe are you calling from?

Why is it that everybody assumes that we are all Earthlings?
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.
From: myoarin-ga on 02 Nov 2006 04:42 PST
 
Hey Bryan,
The questioner is John from Melbourne, Victoria, Australia, southern
hemisphere, earth.  He is no doubt, changing his winter tyres for
summer slicks.  ;-)

Myo
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.....
From: probonopublico-ga on 09 Nov 2006 23:45 PST
 
Could this, I ask myself, be the latest product from that famous
Antipodean inventor who markets fabulous new gizmos under the trade
name of 'Maid in Melbourne'?

I wouldn't be surprised!

John, Could I please have the European rights?

Many thanks!

Bryan
Subject: Re: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub.
From: sublime1-ga on 10 Nov 2006 00:04 PST
 
John...

Thanks very much for the 5 stars and the tip. I'll be happy to
keep my eyes peeled for future related questions. Mention my 
nickname in the subject line if you like, and if I'm not up
to it, I'll pass it on to my colleagues.

sublime1-ga

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