輻條

輻條是从車輪中心的轮毂（即与轴相连的地方）辐射出来的杆、条等，它把轮毂和圆形的轮圈连接起来。 辐条轮的出现使车辆更加轻便。辐条最早出现在公元前2000年的安德罗诺沃文化中。不久之后，高加索地区的游牧民族就使用了装有辐条轮的马战车，持续将近三个世纪。他们随后开始迁移，深入希腊半岛，与当地的地中海民族汇合，在米诺斯文明消亡之后建立了古典希腊（后被斯巴达吞并）。凯尔特人则在公元前几百年就在战车车轮外加上了铁圈。这种辐条轮一直沿用至1870年代，这时钢丝轮和橡胶轮胎问世了。 辐条的材质可以是木头、金属、合成纤维等，这取决于辐条是受拉还是受压。 木质辐条轮最早用于马车和马拉的货车。早期的机动车用的通常是装在炮架上的木质辐条轮。 简易的木质轮轮毂受压时，轮圈靠近地面的地方会略有凹陷，最低的一根木质辐条因受压而变短，而其他的辐条则没有明显变化。 木质辐条常沿半径方向安装，同时呈向外的碟形，以避免车辆摇晃。通过增加碟形的程度还能抵消辐条因受潮而产生的膨胀。 自行车的车轮不是笨重的木质辐条轮，而是钢丝轮（英语：wire wheels）。这种车轮更加轻便，它的辐条是拉紧但可调节的金属丝。轮椅、摩托车、汽车也用这种车轮。 有些车轮的辐条可以一根根取下，若有弯曲或折断便能更换。自行车和轮椅车轮的辐条就是这样。质量高的自行车所配的常规车轮用的是不锈钢辐条，而比较便宜的自行车用的是镀锌或镀铬的辐条。高质量的辐条可承受225千克力，不过实际使用时负载只有它的几分之一以避免疲劳损坏。因为自行车和轮椅的辐条只会处于拉伸状态，其材质也可以是柔韧性强的材料（如合成纤维）。 当编得很好的钢丝辐条轮承受径向负载（如车手坐在自行车上）时，车轮与地面接触处附近会略有凹陷，其余部分则基本保持圆形。 所有辐条的张力都没有显著增加，轮毂正下方的辐条张力还有所降低。 对如何描述这种情形存在争议。 有人认为轮毂“站”在正下方那根张力减小的辐条上， 还有人认为轮毂“挂”在正上方那根张力较大的辐条上。 虽然钢丝轮的辐条又细又柔韧，但沿半径方向却是刚性的，所以辐条的悬挂随动与高压自行车轮胎相比都不值一提。 Herlihy, David. Bicycle: the History. Yale University Press. 2004: 141 [2009-09-29]. ISBN 0-300-10418-9. （原始内容存档于2016-01-06）.  Hansen Wheel and Wagon Shop. 2006 [2006-08-22]. （原始内容存档于2006-08-14）.  PBO Spoke Technology. 2006 [2011-10-21]. （原始内容存档于2011-10-30）.  Forester, John. Held Up By Downward Pull. American Wheelmen. August 1980.  Whitt, Frank R.; David G. Wilson. Bicycling Science Second. Massachusetts Institute of Technology. 1982: 106–138. ISBN 0-262-23111-5.  Ian Smith. Bicycle Wheel Analysis. [2008-12-31]. （原始内容存档于2021-04-18）. I conclude that it is perfectly reasonable to say that the hub stands on the lower spokes, and that it does not hang from the upper spokes.  C.J. Burgoyne and R. Dilmaghanian. Bicycle Wheel as Prestressed Structure (PDF). Journal of Engineering Mechanics. March 1993, 119 (3): 439–455 [2015-08-21]. ISSN 0733-9399. doi:10.1061/(asce)0733-9399(1993)119:3(439). （原始内容 (pdf)存档于2020-11-12）. Only the spokes in contact with the ground, or near the ground, show significant strains.  Brandt, Jobst. The Bicycle Wheel. Avocet. 1981: 12–20. ISBN 0-9607236-2-5.  Wilson, David Gordon; Jim Papadopoulos. Bicycling Science Third. Massachusetts Institute of Technology. 2004: 389–390. ISBN 0-262-73154-1.  Tom Fine. Hubs hang from the rim!. September 1998 [2010-03-16]. （原始内容存档于2021-05-06）. I still say, without any doubt, that the hub hangs from the upper spokes.  Henri P. Gavin. Bicycle Wheel Spoke Patterns and Spoke Fatigue (PDF). ASCE Journal of Engineering Mechanics. August 1996, 122 (8): 736–742 [2015-08-21]. doi:10.1061/(ASCE)0733-9399(1996)122:8(736). （原始内容 (pdf)存档于2012-09-07）.  Kraig Willett. Hang or Stand?. BikeTech Review. 5 September 2004 [2010-03-16]. （原始内容存档于2010-03-11）. A little known semantic debate ... has been raging on the usenet newsgroups for quite some time. The point of contention in this debate is whether or not a loaded bicycle wheel "stands" on the bottom spokes or "hangs" from the top ones?  Samuel K. Clark, V. E. Gough. Mechanics of Pneumatic Tires. U.S. Department of Transportation. 1981: 241. The system of load transmission is analogous to that of a cycle wheel where the hub hangs by the steel wire spokes from the top of the rim, which is loaded at the bottom.  John Swanson. Performance of the Bicycle Wheel, A Method for Analysis (PDF). BikePhysics.com. 2006 [2012-06-25]. （原始内容 (PDF)存档于2012-09-15）. Radial Stiffness: There's almost -no- vertical compliance in your wheel and people who insist that they can feel the vertical stiffness or “harshness” of a wheel are mistaken. The radial stiffness of a bicycle wheel is ~ 3-4000 N/mm. This equals a deflection of 0.1 mm under a 40 kg load. Sorry princess, but that gets obscured by the amount of deflection in the tires, fork, saddle, handlebar tape, frame, and even your gloves.  Henri P. Gavin. Bicycle Wheel Spoke Patterns and Spoke Fatigue (PDF). ASCE Journal of Engineering Mechanics. 1996 [2012-06-25]. （原始内容 (PDF)存档于2012-09-07）. radial wheel stiffness (N/mm): 2500-5000  Ian. Spoke Patterns. astounding.org.uk. 2002 [2012-06-25]. （原始内容存档于2021-04-14）. A radially spoked wheel is about 4.6% stiffer than a tangentially spoked one. Alternatively, if you apply 1000N (about 100kg, 220lb) to each of the wheels, the tangential (four-cross) spoked one deflects 0.0075mm (0.0003 inch) more than the radial spoked. Since the tyre is likely to deflect several millimetres at least (if 3mm, that's 400 times more deflection) I conclude the spoking is unlikely to make a discernible difference to the vertical stiffness of the wheel.  Jobst Brandt. Sheldon Brown's Bicycle Glossary: Radial spoking. Sheldon Brown (bicycle mechanic). 1981 [2012-06-25]. （原始内容存档于2007-12-18）. There is no change in radial elasticity between a radial and crossed spoke wheel with the same components, other than the length of the spokes. A 290 mm spoke is 3% stiffer than a 300 mm spoke of the same type. Since spokes stretch elastically about 0.1mm on a hard bump (not ordinary road ripples), the elastic difference between the radial and cross-three wheel is 3% x 0.1mm = 0.003 mm. Copier paper is 0.075 mm thick, and if you can feel that when you ride over it on a glassy smooth concrete surface, please let me know. You have greater sensitivity than the lady in "the princess and the pea" fable.