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Tire balance
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<h2 id="static-balance">Static balance</h2> <p>Static balance requires the wheel center of mass to be located on its axis of rotation, usually at the center of the axle on which it is mounted. This has some similarities to radial run-out, but involves where the center of mass is located, unlike <a href="/facts/Radial_run-out/r8QUuxea">radial run-out</a> which involves the variance in the distance to the outer surface from the axis of rotation. Static balance can be measured by a static balancing machine where the tire is placed on a vertical, non-rotating spindle. If the center of mass of the tire is not located on this vertical axis, then gravity will cause the axis to deflect. The amount of <a href="/facts/Deflection_(engineering)/xroy2lX2">deflection</a> indicates the magnitude of the unbalance, and the orientation of the deflection indicates the angular location of the unbalance. In tire manufacturing factories, static balancers use <a href="/facts/Sensor/RN8SXbjs">sensors</a> mounted to the spindle assembly. In tire retail shops, static balancers are usually non-rotating bubble balancers, where the magnitude and angle of the unbalance is indicated by the center bubble in an oil-filled glass sighting gauge. While some very small shops that lack specialized machines still do this process, they have been largely replaced in larger shops with machines. </p> <h2 id="dynamic-balance">Dynamic balance</h2> <p>Dynamic balance requires that a principal axis of the tire's moment of inertia be aligned with the axis about which the tire rotates, usually the axle on which it is mounted. This is similar to <a href="/facts/Axial_run-out/r8QUuxea">axial run-out</a>, but again, dynamic balance involves where the center of mass is, while axial runout involves the distance of the outer surface from the axis of rotation. In the tire factory, the tire and wheel are mounted on a balancing machine test wheel, the assembly is rotated at 100 <a href="/facts/R/min/fdNmLToF">r/min</a> (about 5–7 m/s (18–25 km/h; 11–16 mph) with recent high sensitivity sensors) or higher, 300 r/min (about 25–27 m/s (90–97 km/h; 56–60 mph) with typical low sensitivity sensors), and forces of unbalance are measured by sensors.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> These forces are resolved into static and couple values for the inner and outer planes of the wheel, and compared to the unbalance tolerance (the maximum allowable manufacturing limits). If the tire is not checked, it has the potential to cause vibration in the suspension of the vehicle on which it is mounted. In tire retail shops, tire/wheel assemblies are checked on a spin-balancer, which determines the amount and angle of unbalance. Balance weights are then fitted to the outer and inner flanges of the wheel.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>Although dynamic balance is theoretically better than static balance, because both dynamic and static imbalances can be measured and corrected, its effectiveness is disputed because of the flexible nature of the rubber. A tire in a free spinning machine may not experience the same centrifugal distortion, heat distortion, nor weight and camber that it would on a vehicle. Dynamic balancing may therefore create new unintended imbalances.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>Dynamic balancing has traditionally required removing the wheel from the vehicle, but sensors installed in modern cars, such as for <a href="/facts/Anti-lock_braking_system/SmXvJn6G">anti-lock brakes</a>, could enable estimating the imbalance while driving.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="vehicle-vibration">Vehicle vibration</h2> <p>Vibration in automobiles may occur for many reasons, such as wheel unbalance, imperfect tire or wheel shape, brake pulsation, and worn or loose driveline, suspension, or steering components. Unbalance can result from collision-induced wheel deformations, uneven tire wear, or a shift of the tire on the rim. In some cases, losing a counterweight or bumping the curb hard can lead to wheel unbalance. Foreign material, such as road tar, stones, ice, or snow, that is stuck in a tire's tread or otherwise adhered to the tire or wheel may also cause a temporary unbalance and subsequent vibration. Uneven weight distribution in the wheel and tire assembly can result from manufacturing inaccuracies, uneven tread wear, damage over time, or improper tire mounting.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h2 id="environmental-consequences">Environmental consequences</h2> <p>As balancing weights are attached to the exterior of the wheel, they may break or fall off while driving. Traditionally, these weights have been made of <a href="/facts/Lead/EYljasJN">lead</a>; it is estimated that up to 230 tonnes (500,000 lb) of lead, having fallen off car wheels, ended up in the environment.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> According to the <a href="/facts/United_States_Environmental_Protection_Agency/ghI985SI">United States Environmental Protection Agency</a>, these total more than 20,000 <a href="/facts/Tonne/gMymLmWv">tonnes</a> of lead worldwide every year,<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> and therefore the use of less-toxic materials is encouraged.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> In <a href="/facts/Europe/DTAtrKfh">Europe</a>, lead weights have been banned since 2005; in the <a href="/facts/United_States/P0sCdLe5">United States</a>, they have been banned by various states but have not been restricted at the federal level. Alternatives include weights made of zinc-lead or <a href="/facts/Leaded_copper/chU9TQqx">leaded copper</a>, or weights that are altogether lead-free.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Speed_wobble/7FKUjFeU">Speed wobble</a></li> <li><a href="/facts/Rotordynamics/kzXd96r1">Rotordynamics</a></li> <li><a href="/facts/Run-out/r8QUuxea">Run-out</a>, an inaccuracy of rotating mechanical systems</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Balancing tires". Continental Tires. Retrieved 2024-11-11. <a href="https://www.continental-tires.com/products/b2c/tire-knowledge/balancing-tires/" target="_blank">https://www.continental-tires.com/products/b2c/tire-knowledge/balancing-tires/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Baruh, Haim (2014). Applied Dynamics. Hoboken: CRC Press. p. 586. ISBN 978-1-4822-5079-4. OCLC 908079666. <a href="978-1-4822-5079-4" target="_blank">978-1-4822-5079-4</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Car Care Guide: 14. Tires". Popular Mechanics: 200. May 1976. <a href="https://books.google.com/books?id=ReIDAAAAMBAJ&q=dynamic+tire+imbalance&pg=PA200" target="_blank">https://books.google.com/books?id=ReIDAAAAMBAJ&q=dynamic+tire+imbalance&pg=PA200</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Jianbo Lu, Dimitar Filev and Len Johnson (2011). "Real-time Tire Imbalance Detection Using ABS Wheel Speed Sensors". SAE Int. J. Mater. Manuf. 4 (1): 1036–1047. doi:10.4271/2011-01-0981. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Kingston Heritage (February 19, 2016). "What to do if your car gets the shakes after a snow storm". Metroland Media Group Ltd. Archived from the original on 2019-12-14. Retrieved 2018-10-05. You may end up with ice and snow packed in your wheels. This solid clump of ice causes a steering-wheel shake because the added mass rotating with the wheel throws off the wheel balance. <a href="https://web.archive.org/web/20191214061323/https://www.therecord.com/news-story/6325956-what-to-do-if-your-car-gets-the-shakes-after-a-snow-storm/" target="_blank">https://web.archive.org/web/20191214061323/https://www.therecord.com/news-story/6325956-what-to-do-if-your-car-gets-the-shakes-after-a-snow-storm/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"How long does an alignment take". 18 April 2021. Saturday, 17 July 2021 <a href="https://curateview.com/how-long-does-an-alignment-take/" target="_blank">https://curateview.com/how-long-does-an-alignment-take/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Reifen auswuchten: Was es kostet, wie oft und wann es gemacht werden sollte" (in German). Retrieved 2024-11-11. <a href="https://www.autodoc.de/info/reifen-auswuchten-was-kostet-es-und-wie-oft-sollte-es-gemacht-werden" target="_blank">https://www.autodoc.de/info/reifen-auswuchten-was-kostet-es-und-wie-oft-sollte-es-gemacht-werden</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Schnubel, Mark (2014). Today's Technician: Automotive Suspension & Steering Classroom Manual and Shop Manual. Cengage Learning. p. 607. ISBN 9781305178410. <a href="9781305178410" target="_blank">9781305178410</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>National Lead Free Wheel Weight Initiative (NLFWWI). epa.gov. Retrieved on 2012-06-26. (dead link 21 January 2023) <a href="http://www.epa.gov/wastes/hazard/wastemin/nlfwwi.htm" target="_blank">http://www.epa.gov/wastes/hazard/wastemin/nlfwwi.htm</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"Postal Services pledges to remove 8,000 pounds of lead". American Recycler. January 2009. p. B2. Retrieved 3 May 2016. <a href="https://books.google.com/books?id=1bpxyxP1YSoC&q=tire+weights+lead&pg=PA30" target="_blank">https://books.google.com/books?id=1bpxyxP1YSoC&q=tire+weights+lead&pg=PA30</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Gilles, Tim (2012). Automotive Service: Inspection, Maintenance, Repair. Cengage Learning. p. 1167. ISBN 9781133420682. <a href="9781133420682" target="_blank">9781133420682</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> </ol>