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Q: I'm changing a tyre on typical family car; I lift wheel ready to fit to hub..... ( Answered ,   5 Comments )
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 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```
 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:
 ```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: 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```

 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```