你的身體在自行車上的位置直接影響到你的騎行。它影響蹬踏力量的傳導效率，也影響到你的騎乘舒適程度。一個讓你感覺更舒服的位置會使你擁有更多能量蹬踏。那麼，你應該如何決定身體所處的位置呢？
問 你自己吧，“你打算用自行車來幹什麼？”，你騎行的目的是什麼呢？一名場地自行車手根本就不會考慮他是否輕鬆舒適，在比賽中（整個過程也許不到一分鐘）， 他也許僅僅只需要坐上5—10秒鐘。而一位橫穿美洲大陸的長途旅行者也許每天要花上5—12個小時呆在他的坐墊上。比起選手的高速度，他大概更關心的是能 否騎得舒服並享受沿途的風光。
這篇文章僅涉及到傳統的公路和山地自行車。我對斜躺式的自行車一無所知，當然對它的尺寸選擇也就無能為力了。
你 的身體有3個部位和自行車直接接觸，手，臀部，腳。這3個部位在車上的相對位置就決定了你在車上的舒適程度以及騎行的效率。有幾個數值決定了這些位置的所 在：曲柄的長度、五通中心到坐墊的距離、坐墊的角度、坐墊表面的材料、坐墊和車把之間的距離、坐墊和車把到地面的高度。車把的寬度、以及公路車把的下垂的 角度。我會逐條的討論這些。
曲柄的長度
曲柄的 長度決定了你蹬踏所產生的圓周直徑。直徑越大，你的膝蓋和大腿的肌肉就要加大伸縮幅度才能蹬動曲柄。在整個運動的過程中，你的大腿肌肉的承受力並不相等。 這一點很好證明：下蹲，並使你的膝蓋完全彎曲，然後站直。這時，你就會花費比只下蹲15釐米然後再站直所消耗的更多的精力，在完全下蹲的情況下，肌肉所用 的力量也並不相同。所以，當你不得不面對僅有兩種選擇的情況：
1、曲柄的長度使你的膝蓋在整個圓周運動的過程中都處於彎曲的狀況；
2、合適的曲柄長度：使你的膝蓋屈伸幅度在20度角左右。你最好還是選擇較短的曲柄，它會使你的肌肉在整個運動的過程中更有效率，而且不會使你的膝蓋做大幅度的屈伸而導致無用功。
那 麼，究竟多長的曲柄才比較合適呢？這個問題提的好，我希望我能對此有很好的答案，可惜我沒有。不過有一點非常明顯：一名身高170釐米的車手肯定不會想到 去使用和身高180的車手所用的一樣長的曲柄，除非他們的腿長恰好一般長（這種情況是非常罕見的）。一些已有的研究表明了腿長和曲柄長度的最佳百分比，但 我懷疑是否真的有一個最佳的百分比來適合所有人。好幾年前，一位作者在一份權威性的雜誌上宣稱，經過與許多不同的車手的大量實驗，在赤腳的情況下，從股骨 的頂端到地面距離的18.5%就是所需的曲柄長度。你可以很容易的發現股骨頂端的位置，它大概處於你的盆骨下端12.5~15釐米。當你抬起膝蓋的時候， 它就向後運動。讀了這篇文章之後，我迅速的把我那符合工業標準的170MM長的曲柄換成了175MM長的。我的蹬踏的力度和耐力馬上得到了改善。於是，當 我向我的顧客推薦曲柄的時候，我開始使用這條規律。一直以來我都沒有受到任何的投訴。當然，這並不意味著我的顧客不喜歡使用其他長度的曲柄，而且我也必須 承認我從來沒有花費足夠的時間使用長度超過175MM的曲柄並由此判斷我是否喜歡他們。
對股骨頂端的測量忽視了腿部本身的差異。從小腿長度到大腿長度的局部差異將會影響到最佳的曲柄長度。和大腿短、小腿長的車手相比，一位大腿長、小腿較短的車手應該使用較長的曲柄來使膝蓋的伸縮幅度相同。
如 果有兩位身體條件相似的車手，其中一名喜歡採用較快的頻率騎行，那麼他很可能會比較鍾愛較短的曲柄。兩位骨骼完全相同的車手很可能經過實驗後會發現：僅僅 因為肌肉條件的不同，他們需要使用不同長度的曲柄，才能使他們自身的水平發揮得淋漓盡致。通過試用不同的曲柄來找到適合自己的最佳長度，這個過程既耗時又 費錢。我相信這是每個人判斷正確的曲柄長度的唯一方法，當然先得假設這個長度的曲柄確實存在。把各種長度的曲柄，裝上各種各樣腳踏進行測試，這看起來確實 很不錯。但我知道這事從來沒有人幹過，我自己也做不來。當然，也確實有很多不同類型的車手說道曲柄長度的差異並沒有給他們帶來什麼不同的感覺。自己琢磨 吧！在沒有更好的測量系統之前，我還是堅持使用18.5%的理論來引導我的顧客。它至少沒有出過岔子。
坐墊的高度
曲 柄長度確定了，（不論用什麼方法），坐墊就應當調整到合適你的高度。對於任何一個車手來說，都不該僅僅根據腿的長度就對坐墊的高度下結論。有的車手可能會 自然的使用前腳掌進行蹬踏，而其他人則讓自己的腳掌處於更為平坦的位置。對於初學者來說，坐上你的坐墊，騰出一隻腳，自然下垂，擺正你的臀部（不要偏向任 何一邊），把坐墊調到足夠的高度，使得你的另一隻腳的腳跟能夠在你的腿伸直的情況下剛好夠到踏板。這時候踏板的位置也應當處於座杆和五通延長線的最低點。 對大多數人來說，這個坐墊高度會使你的膝蓋在踏板的軸上做圓周運動並到達最低點的時候有少許的彎曲，同時防止你的臀部隨著曲柄的轉動而左右搖晃。這樣，適 合你的坐墊高度就基本確定下來了。你可以通過其他部件的尺寸選擇程式後在對其進行細微的調整。對坐墊高度的後期調整不會對其他部件的調整造成什麼影響。
坐墊的角度
為 了能和車子熔為一體，你需要一個能坐在上面的坐墊。這話聽起來毫無意義。可令人遺憾的是，大多數出售的自行車上面坐墊似乎都是由那些從來沒有騎過車的外行 人來裝配的。為了緩解使用這些刑具所帶來的痛苦，人們經常會把坐墊的前部調低，使坐在坐墊上成為一件不可能的事情。你會向前滑，這時你就得通過向車把施力 來使自己的身體固定在坐墊上。找到一個你自己能夠坐在上面的坐墊，使你的骨盆能夠呆在一個平坦的表面上。此時，大多數的坐墊前部都會比他的後部要高一些。 因為女性的骨盆更寬一些，所以女式坐墊也會比男式坐墊更寬一些。現在許多女式坐墊中央都有一個孔或者是塑膠的凹槽，其主要作用是平坐在坐墊上時分散對恥骨 的壓力。坐墊越平坦，你就越容易找到坐墊和車把之間的最佳位置。
坐墊的前後位置的調整
現 在讓我們來到我認為是自行車尺寸選擇中最重要的部分：坐墊的前後調整。一旦你弄清楚了這點，其他的就很簡單了。這個位置比其他的位置更多的決定了你打算如 何使用你的車輛。我們來看一輛典型的車子，它的坐墊的位置一般都處於曲柄中間或五通的後部，在從曲柄到坐墊之間有一根車架的直管（坐管），坐管有一定的角 度。這個角度部分決定了坐墊相對於曲柄和腳踏的前後位置，而這個位置又決定了你的身體在車上的平衡程度，而平衡程度又決定了你的舒適程度和蹬踏效率。
站 直然後側對著鏡子，仔細觀察你自己。當站直的時候，你的頭、手、足和臀部幾乎是在同一條直線上的。然後彎下腰，注意到僅僅只是你的頭部超過了你的腳，但你 的身體後部的位置卻處在你的腳後。如果不這樣，那你就會向前跌到。在你彎腰的時候，你的臀部向後移動以保持身體的平衡。
有兩個理由需要你的身體前 傾：力量的輸出和空氣動力學。如果你挺直身體，那你的肌肉就不能很好的運動，不能使你有效的把車子停住。一個挺直的身軀也不符合空氣動力學原理。在平坦路 面騎車的時候，風阻是你受到的主要阻力。如果你的身體越容易穿過空氣，那麼你所花的能量就越小。當你的身體越接近水平線的時候，身體的正面迎風面積就越 小，你也就不需要消耗太多的能量來保持速度了。
很明顯，在連續幾小時的越野騎行過程中，最符合空氣動力學的位置並不是讓人愉快的位置。因此我們需 要綜合考慮。當你的身體越接近水平的位置，你的坐墊就應該越向後調以保持身體的平衡。這和你彎腰時身體後部向後移動的餓情況一樣。相比較之下，賽車手們會 比旅行者們更傾向于使用接近水平的姿勢騎行，並且喜歡把車把往前調使他們在爬坡和衝刺時的站立騎行更為有效。
如果一輛自行車的坐墊位置處於曲柄的 正上方假設沒有手臂支撐你的體重，你就不能使自己的身體前傾。因為在一般的自行車上，坐墊的位置是處於曲柄延長線的正上方。試著做下面這個實驗，你需要你 的朋友幫忙扶車，或者把車固定在訓練臺上。坐在車上手扶車把，並使曲柄臂處於水平位置。如果你使用的是一個公路的彎把，那麼請握住手柄彎曲部位底部，嘗試 鬆開手把而不移動你的身體。如果你感到身體的肌肉繃緊了，那就意味著你的手臂承擔了你的體重。
對於初學者，我建議他們把坐墊的位置調節到鬆開車把 並保持原來的姿勢時身體的肌肉也不會感到緊張的位置。當你提起車把的時候，你不會喜歡自己似乎要向前跌出去的感覺。是否鬆開車把對你的背部肌肉沒有什麼影 響，因為你知道你不是用你的手臂來支撐自己的上身。反之，你的雙肩和手臂就會在長途的旅行中感到疲勞。但這一切僅僅只是一個開始，記得自行車尺寸的選擇是 不斷綜合考慮的結果。
那麼，什麼因素應當綜合考慮呢？力量，當你坐在車上時，它就限制了你能舒適的握住車把的距離。當坐墊為了保持平衡向後調整 時，車把的位置也應當相應向後調整。但是為了能在離開坐墊騎行時能將足夠的力量傳遞給腳踏，將車把到曲柄前端的距離作出相應的調整會有所幫助。尤其是當你 站立式爬坡騎行的時候，最好的位置是應當和車把之間有一個較長的距離。你也可以這樣判斷，在站立式爬坡騎行的過程中，你的雙手盡可能的前伸來握住刹車手把 的頂部。然後在爬同一座山的時候，你的手盡可能的握住車把的後部。你會發現，當你的手向前伸得越多的時候，你就能爬的越快。因此你就得在舒適騎乘的位置和 盡可能的將車把前伸之間找到一個折中點，並且在你站立騎行時候找到一個車把前伸的位置。僅僅是車把位置前後2.5~5釐米的調整都會在爬坡時讓你感到巨大 的差別。同樣的，坐墊位置的 2.5~5釐米的調整帶給你或許是一個50英里長的愉快的旅行，或者是一個僵硬的脖子和酸痛的肩膀。
當你把坐墊從原來的位置向前調整的時候，你的手臂就承擔了更多的體重。但你也可以把車把前伸來獲得更多的力量。場地自行車的坐管角度幾乎是垂直於地面的。這樣的坐墊位置會比旅行者們要求的要向前很多。但我還是要再次強調，一個場地自行車手只會花幾秒鐘時間呆在他的坐墊上。
假如你不能通過前後調整坐墊來獲得你想要的位置，你也用不著失望。各種不同類型的坐墊都會提供滑軌位置比較靠前的版本。或多或少有點補償。也有許多坐杆，他們的坐杆夾會和坐杆本身的中心線有一定的角度。（這也是一種補償吧）
那 麼，到底你想在你的車上得到什麼樣的收穫呢？你強調的是速度和加速性能嗎？或者更多的考慮的是騎乘的舒適性和欣賞沿途的風景？你對這些問題的答案決定了你 應該如何調整你的坐墊，而不是某個電腦程式或者是某人那充斥了各種圖表的系統。即使你最好的朋友擁有和你完全一樣的身體結構，他如何選擇車輛的尺寸和你也 毫無關係。只有你自己清楚騎車的目的，也只有你自己明白如何將一切進行綜合考慮來達到你騎車的目的。
你可能同時擁有一輛短途高速的車子和一台長途 的旅行車。因為需要不同的零件使他們能勝任自身的任務，他們的尺寸大小會有所不同。騎手沒有改變，你還是你自己，但你的目的改變了。一台輕快的短途車子會 比一台旅行車擁有更低、更為靠前的車把位置，當然它的坐墊位置也應當相應的向前調整。
關於膝蓋處於踏板軸上方的問題。
大 多數的測量系統詳細的描述了一種情況：當踏板軸和曲柄正好連成一線時（通常是踏板在前而曲柄處於水平的位置），你的膝蓋的正好處於踏板軸的正上方，這種描 述毫無意義。想像一下，有兩名幾乎一模一樣的車手，其中一名車手的大腿骨比另一名長3釐米，這就意味著他的小腿比另一名短3釐米。這兩位車手的其他身體條 件幾乎完全一樣，包括身體的全長，軀幹的長度，臂長和體重。如果把坐墊的位置調整到正好處於踏板軸的正上方，那位大腿骨比較短的騎手就必須把他的坐墊調整 到比另一名車手要靠前不到3釐米的位置。當他的大腿骨和踏板都處於水平位置的時候，精確的資料是3釐米，而實際是沒有這種情況的。
但是隨著坐墊的前移大腿骨較短的那位車手就不得不讓他的手臂分擔更多的體重僅僅只是出於那種主觀的讓膝蓋處於踏板軸正上方的理論。那理論毫無意義，重要的是你如何合理的把體重進行分配，而這取決於坐墊相對於曲柄的前後位置。
車把的位置
接 下來我們看看車把的位置應該如何處理。和坐墊一樣，它也取決於你如何使用你的自行車，車把的位置越靠前，你在站立騎行和加速的時候就會獲得更多的力量，並 且你的身體也就越符合空氣動力學，高速騎行的穩定性也會更佳。車把越低，你就越能在快速加速的情況下更好的制動。當車把和你身體之間的距離越短（或越 高），你就能夠挺直上身並獲得良好的視野。
我喜歡使用一個可調節的把立，它能夠讓我的顧客幾天中在不同的位置花上足夠的時間來下結論。但我們從哪 里開始呢？對於使用公路彎把的車手來說，如果你把手放在車把下垂部位。（這個位置應當讓你很容易的觸到刹車把），然後彎曲你的肘部使你的前臂達到水平狀 態，在這種情況下，如果你的肘部和前臂的角度形成一個直角，那就是一個好的開端。從這裏開始，試著把你的車把前後調整大約1釐米的距離，找到對你來說是最 合適的位置。大多數人會對肘部處於直角的位置感到很舒服，但這不一定適合你。當然，這不是一個讓你長時間騎乘的位置，除非你恰巧處於一個長途的公路下坡路 段。
賽車手們通常會把車把高度降低到比坐墊要矮5~8釐米，而旅行者們則把它們調低到同一高度。山地車手們的車把高度通常會比坐墊高度低5釐米，關鍵是要花足夠的時間找到適合自己的位置。如果要把一台旅行車的車把降低到比坐墊低10釐米，你會接受嗎？
我推薦在感覺舒適的情況下，使車把和你之間的距離盡可能的長，高度盡可能的低（舒適性的車子也同樣適用）。
車把的寬度（公路車和山地車）以及公路車把的下垂角度
有 一些品牌的公路車把，他們的設計理念在於從頂部算起的下垂幅度，除非你是一名場地自行車手，你都不會需要一個深度下垂的車把。大多數的車把著重於寬度，很 多人在他們車把上的雙手之間的距離與肩同寬的情況下會感到最舒服，這樣他們的手臂在夠得著車把的情況下會大致保持平行。當你選擇不同長度的把立時，試著使 用各種不同寬度的車把，從和你的肩寬一樣的開始。最後你會明白哪個對你來說最為合適。
對坐墊高度的精確調整
當 你對車輛各部分的調整感到習慣之後，回頭再檢查一下坐墊的高度。你應該在踏板達到最低點的時候也不會完全繃直你的膝蓋，並且也不用在踏板上晃動你的前腳 掌。如果上述情況之一產生了，那你的坐墊高度就太高了。在踏板轉動的過程中，繃直你的膝蓋會限制你流暢的蹬踏的速度，並由於腿長的限制，導致你想把坐墊的 後部調整到不那麼有效的位置。通過限制腿的伸長幅度，你能夠更流暢的蹬踏，並獲得更高的頻率。這對你的肌肉和關節都有好處。假如坐墊過低，你的腿部肌肉會 感到這點。
常備的車架尺寸的測量
剛才我們所講到的這些對你到本地的一家車行測量的尺寸有什麼聯繫呢？不同長度的坐管和把立可以構成各種尺寸的組合。這就意味著你可以使用不同尺寸的車架並仍舊配合的很好。
當其他的部件搭配均衡後，一個長的上管會使你的自行車的軸距更長，穩定性更好，並且能更好的吸收震動，當然它也需要一個更短的把立。由於下管（連接五通和頭管的管子）也會隨之變長，因此車架在加速的時候會變軟並產生一些形變，這是長上管車架性能上的一個缺陷。
即使使用同一個把立，在車架上較長的坐管也會抬高你的車把，並給水壺和氣筒留下更多的空間。這也可能使你不能把車把降低到你想要高度。而且更長的坐管也會使車架的上管抬高，並縮短了你橫跨車架時襠部和上管之間的距離。因此，你必須對此慎重考慮。
後續：
注意到在這裏我們沒有提到任何關於身體測量方面的事情。我也沒有要求你用懸垂法來測量你的膝蓋到地面的距離，或者是要求你前後調整你的車把來使你不能在正面直接看到前軸。
或 者是拿你的前臂長度和坐墊前部到車把之間的距離做比較，等等。我的這套方法和大多數人在自行車店擁的那套方法有很大的區別。FIT KITS和其他在市場上使用的系統是建立在對許多不同的車手和他們的車輛進行大量測量的基礎上的，它們可以保證在一定的程度上的，你選擇的結果會比較適合 你。
但是讓我們來看看關於兩個車手的例子吧：車手A，和車手B。車手A的上身肌肉很少，但他的腿部肌肉很強壯。車手B的體形和車手A的很相象，可 是由於一直在 PALPH‘S GYM進行戶外工作，使他看起來向個健美運動員。對這兩位車手來說，坐墊的前後位置會有一些輕微的差異。為了獲得同樣的平衡，車手B上身發達的肌肉需要他 把坐墊的位置輕微的想後調整。但這並不意味著車手B 就必須要把坐墊後調。他可能還會喜歡比較靠前的位置。只有他自己知道他想要什麼。
以 我自己為例，我在20世紀70年代開始長途旅行。反復實驗多次之後，我得到了一個為我而做的測量系統。（根據這個系統），我可以騎一個世紀而不會疲勞。我 也有一輛精確的依照競速車輛設計的自行車。我沒有長高，也沒有變矮，我的胳膊也沒有變長或縮短，但是我的脖子和背在20001年的時候比他們在1975 的時候要僵硬的多。當我爬山的時候，較低的車把位置還是很好的。但是在60英里的平地路途上我的脖子就不會象以前那樣舒服了。年紀變大了，我需要一個比較 高的車把。
測量我的身體不會不會指出我需要把車把調高。我過去常常在握住公路車把的下部的時候感到很舒服，如果我現在這樣做，那我就幾乎看不到前面的路了。
在場地車和長途旅行車之間找一個折中點是我們大多數人想要的。但我們首先得知道自己的追求是什麼。記住，當你選擇車輛的時候，只有一位專家能幫你。只有你自己知道你在車上的感受。只有你知道應該如何對你自己的騎行進行綜合考慮。你就是那位專家。
順 便說幾句，由於我的粗心大意，我經常受到某些人的電子郵件。他們告訴我他們讀了我的文章，很喜歡，但有一個問題。然後他們告訴我自己的腿有多長，胳膊有多 長，軀幹又有多長，隨之告訴我某家自行車行想要向他們出售一輛特定的車子，想要我告訴他們這台車子是否適合他們。我的第一反映就是擔心我是否把文章寫清楚 了，或者是他們讀了它但是不理解，或者是他們根本就沒有讀。我有時會回過頭複讀我的文章，確定我把觀點表達的很清楚了。可究竟為什麼那些人不清楚，我就不 得而知了。
於是我得再強調一遍，我不知道那台車子是否適合你。即使我知道車子和你的身體的每一個細節，我也不能告訴你它是否適合你。所以別在寫信問我這些我不可能回答的問題。請再讀一遍文章。
如 果你需要那些關於你的自行車的權威數字，那麼就去那些有KIT FIT或者其他類似的系統的車行吧。給他們錢，找他們說的做。有些人就得照章辦事，但是我不想告訴你要做什麼。我寧願提供你們需要的知識，然後你們自己去 尋找。有了這些知識，我想你們自己會比那些要你們付錢的專家幹得更好。
順便說兩句，我是一個自行車商人，不是醫生。如果你的膝蓋或者脖子或者手腕或者背因為根據我的文章所提供的資訊組裝的自行車而受傷，那麼我想你可以控告我，但是別指望我呢能對你的傷勢作出診斷。去看醫生吧，然後在控告我。
請不要誤解我。如果我寫了什麼你不能理解的東西，或者你認為我遺漏了某些關於車輛尺寸選擇的觀點，請讓我知道。為了回答讀者的問題，這篇文章已經被下載了很多次了。那麼，就請繼續來信吧。
以下為英文原文
by Peter Jon White
Copyright 1989, 1998, 2001
Overview
Bicycle fitting is a subject most people find quite mysterious. Fitting systems with charts and graphs, computer software, measuring devices and "rules of thumb" make for a lot of confusion. But I believe it's really quite simple. Bicycle fit involves compromises. Compromises between comfort and performance, quick acceleration and handling stability, top speed and "taking in the scenery".
Your body's position on the bike affects how you ride. It affects how much power you can efficiently deliver to the pedals. It affects how comfortable you are on the bike. A position that is more comfortable may not allow you to put as much energy into moving the bike forward as a less comfortable position might. How do you decide where to position your body on the bike?
Ask yourself, "What do I want to do with my bike?", "Why am I riding?". A track sprinter is not the least bit concerned with how comfortable he is sitting on the bike. During the race, (which may last for less than a minute), he may only be seated for 5 or 10 seconds. A long distance tourist traveling coast to coast across the USA might spend 5 to 12 hours a day in the saddle, day after day. He is probably far more concerned with being comfortable and enjoying the scenery than with going as fast as he can.
This article relates only to traditional road and mountain bicycles. I know next to nothing about recumbent bicycles and have absolutely no advice to offer regarding recumbent fitting.
Let's get started
Your body contacts the bicycle in three areas; your hands, your seat, and your feet. The relative positions of feet, seat and hands determine your comfort and efficiency on the bike. There are several variables that determine these positions; crank length, distance from crank center or bottom bracket to saddle, saddle angle, seat tube angle and saddle offset, distance from saddle to handlebar, relative height of saddle and handlebar, handlebar width, and handlebar drop on road style handlebars. I'll discuss each of these variables.
Crank Length
Crank length determines the diameter of the circle that the pedals move in. The larger that circle is, the more flexion of your knee and thigh muscles will be needed to turn the cranks. Your thigh muscles cannot exert the same force throughout their range of motion. This is very easy to demonstrate. If you squat down so that your knees are fully bent and lift yourself up, say, five inches, it takes a good deal more effort than it would to squat down just five inches from standing straight and then lift yourself back up. At the full squat position, your muscles can't put out the same power as when your knees are just bent enough to drop you down five inches. So if you had to choose between a crank length that had your knees bending through their entire range of motion and a length that only required, say, 20 degrees of flexion at the knee, you would choose the shorter crank. That crank would have your muscles working through a more efficient range of motion. You would avoid having to flex your knees enough to bring you into an inefficient range of motion.
So how long should the cranks be? Well, that's a good question. I wish I had a good answer but I don't. It should be obvious that a 5' 2" rider would not want to use the same length crank arms as a 6' 7" rider unless they somehow managed to have the same leg length (highly unlikely). Some research has been done to determine the optimum percentage of leg length to crank length. I doubt that there is an optimum percentage that would apply to all people. One writer in a major magazine article quite a few years ago claimed that after considerable testing with many different riders, 18.5% of the distance from the top of the femur to the floor in bare feet should be the crank length. You can find the top of the femur pretty easily. It's 5" to 6" below your hip bone, and moves rearward when you raise your knee. After reading this I promptly changed from the industry standard 170mm cranks for road bikes to 175mm cranks. There was an immediate improvement in power and endurance. I began using this formula when recommending cranks to my customers. So far, I haven't gotten any complaints. But of course that doesn't mean my customers wouldn't be as happy or happier with some other length. And I must admit that I have never tried still longer cranks than 175mm for enough time to tell if I would be even happier with them.
The top of the femur measurement ignores differences in legs themselves. Differences in the proportion of calf length to thigh length should affect the optimum crank length. A rider with longer thighs and shorter calves would use a longer crank to get the same flexion at the knee as a rider with short thigh and long calf. Of two riders with the same body proportions, one might prefer to pedal at a faster cadence. That might favor a shorter crank length. And perhaps even two riders with identical skeletal proportions would find after testing that they required different crank lengths to achieve maximum performance due simply to differences in their muscles.
Trying different cranks to find the optimum length would be time consuming and expensive, but I believe it is the only way to determine the correct length for any individual, assuming there is a correct length. It would be nice to have a crank with many pedal threads at various lengths to test. But I know of no such thing being made and I lack the ability to make one! Of course, some riders with multiple bikes report being just as happy on one crank length as another. Go figure! So, for lack of a better system, I'm staying with the 18.5% guide for my customers until something better comes along. It hasn't failed yet.
In the United States, it has been difficult and expensive to obtain cranks shorter than 165mm or longer than 175mm. But a French company, Specialites TA has been making high quality cranks in lengths of 150mm through 185mm for many years. In order to offer my customers better fitting bicycles, I've decided to sell these cranks. See my web page; http://www.PeterWhiteCycles.com/Zephyr.asp for details.
Saddle Height
Once the crank length is determined, (by whatever means), the saddle should be set at a nominal height. There is no objectively determined ideal saddle height for any rider based on leg length alone. Some riders naturally pedal toes down, while others have the foot in a more level position. For starters, sit on the saddle with one leg hanging free and your hips square, (not tilting to either side). Set the saddle high enough so that your other heel can just touch the pedal with your leg straight, and with the pedal at the bottom of the stroke, in line with the seat tube. For most people this results in a saddle height that leaves some bend in the knee at the bottom of the pedal stroke, when you're pedaling with the balls of your feet over the axle of the pedals. It also should prevent you from having to rock your hips through each crank rotation. This gets you close enough to your optimum saddle height that you can go through the rest of the fitting process and fine tune saddle height later. Any later saddle height adjustments shouldn't be enough to throw off the other adjustments.
Saddle Angle
In order to fit a bicycle, you need a saddle you can sit ON. That may seem too obvious to even mention. But sadly, most bikes seem to be sold with saddles designed by people who have never ridden a bicycle. In order to ease the pain of using these implements of torture, people often angle the saddle with the nose down. This makes it impossible to sit ON the saddle. You tend to slide forward. You end up pushing against the handlebar just to keep yourself on the saddle. Get yourself a saddle you can sit on so that your pelvis is resting on a level surface. For most saddles that would put the nose of the saddle a bit higher than the rear. Women's saddles should be wider than men's since a woman's pelvis is wider. Many women's saddles now have a cutout or low density foam section in the center to take pressure off the pubic bone while allowing a level saddle position. The closer you can get to a level platform, the easier it will be to find the best fore-aft position of saddle and handlebar.
The Fore-Aft Saddle Position
Now we get to what I think is the most important part of fitting a bicycle, the fore-aft position of the saddle. Once you get this right, everything else is easy. This position is determined more by how you intend to use your bike than by anything else. If you look at a typical bike, the saddle is behind the crank center, or bottom bracket. There's a frame tube (the seat tube) running from the cranks to the saddle, and it's at an angle. That angle partly determines the fore-aft position of the saddle relative to the cranks and pedals. That fore-aft position determines how your body is balanced on the bicycle. Your balance determines how comfortable you are, and how efficiently you can pedal the bike.
Stand up straight in front of a mirror and turn to the side. Look at yourself in the mirror. When standing straight your head, hands, seat and feet are all fairly close to being in line with each other. Now bend over at the waist. Notice that not only has your head moved to a position ahead of your feet, but your rear end has moved behind your feet. If this were not the case, you would fall forward. Your seat moves back when you bend at the waist to keep you in balance.
Your torso needs to be leaning forward for two reasons; power output and aerodynamics. With an upright torso, you can't use the gluteus muscles to good effect. Also, you can't effectively pull up on the handlebar from an upright position. An upright torso is also very poor aerodynamically. When cycling on level ground, the majority of your effort goes against wind resistance. The easier it is for your body to move through the air, the less work you'll have to do. With your torso closer to horizontal, you present less frontal surface to the air and don't have to work as hard to maintain a given speed.
Obviously, the most aerodynamically efficient position may not be the most pleasant position to be in for several hours on a cross country tour. So there's a tradeoff. As you move to a more horizontal position, the saddle needs to be positioned further to the rear to maintain your body's balance, just as your rear end moves to the rear as you bend over while standing. It so happens that racers are more inclined to use a horizontal torso position than tourers, and racers are more concerned with having the handlebars further forward to make climbing and sprinting out of the saddle more effective.
If a bicycle had the saddle directly over the cranks, you wouldn't be able to lean your body forward without supporting the weight of your torso with your arms. Because the saddle on a typical bicycle is behind the cranks, your seat is positioned behind your feet and your body can be in balance. Try this test. You'll need a friend to hold the bike up, or set it on a wind trainer. Sit on your bike with your hands on the handlebars and the crank arms horizontal. If you have a drop bar, hold the bar out on the brake hoods. Try taking your hands off the bar without moving your torso. If it's a strain to hold your torso in that same position, that's an indication of the work your arms are doing to hold you up.
For starters, I like to put the saddle in the forward most position that allows the rider to lift his hands off of the handlebar and maintain the torso position without strain. You should not feel like you're about to fall forward when you lift off the handlebar. If it makes no difference to your back muscles whether you have your hands on the bars or not, you know that you aren't using your arms to support your upper body. If you are, your arms and shoulders will surely get tired on a long ride. But this is a starting position. Remember that bicycle fit is a series of compromises.
So what's being compromised? Power. There's a limit to how far you can comfortably reach to the handlebar while seated. If the saddle is well back for balance, the handlebars will need to be back as well. But to get power to the pedals while out of the saddle, it helps to have the handlebars well forward of the cranks. Particularly when climbing out of the saddle, the best position tends to be had with a long forward reach to the bars. You can tell this is so by climbing a hill out of the saddle with your hands as far forward on the brake lever tops as you can hold them, then climbing the same hill with your hands as far to the rear as you can on the bars. Chances are you can climb faster with your hands further forward. So you need to find the best compromise between a comfortable seated position and reach to the handlebar, and a forward handlebar position for those times when you need to stand. Only an inch or two in handlebar placement fore-aft can make a big difference while climbing. That same inch or two in saddle position can mean the difference between a comfortable 50 mile ride and a stiff neck and sore shoulders!
As you move the saddle forward from that balanced position, you'll have more and more weight supported by your arms, but you'll be able to position the handlebars further forward for more power. The track sprinter has the frame built with a rather steep seat tube angle, which positions the saddle further forward from where the tourer would want it. But again, the track sprinter spends very little time in the saddle.
If you can't move your saddle forward enough or backward enough for the fit you want, don't despair. Different saddles position the rails further ahead than others, giving more or less saddle offset. Seatposts are available with the clamps in different positions relative to the centerline of the post.
So, how do YOU want to balance on YOUR bike? Do you want to emphasize speed and acceleration? Do you care mostly about comfort and enjoying the scenery? The answers to these questions determine how you position the saddle, not some computer program or someone's system of charts and graphs. How your best friend fits his bike should have no bearing on what you do even if he has exactly the same body proportions as you. YOU know why you ride a bike. Only YOU know what compromises you are willing to make in order to achieve your purposes on a bicycle.
You may have a bicycle for short fast rides, and another for long tours. Just as the two bikes will have different components so as to be well suited for their purposes, so might the fit be different. The rider hasn't changed. You are still you. But your purpose has changed. The light, fast bike for short rides will likely have a more forward and lower handlebar position than the tourer. And so the saddle may well be further forward too.
What about knee over the pedal axle?
Most fitting "systems" specify that some part of your knee be directly over the pedal axle at some alignment of the crank, usually with the pedal forward and the crank horizontal. This is pure nonsense. Imagine two riders, almost identical, but one rider's knees are 1 inch lower than the other's. In other words, the thigh bones of one rider are 1 inch longer than the other, and his lower legs are 1 inch shorter. Everything else about these two riders is identical, including overall height, torso length, arm length and weight. If you position the saddle such that the knee is directly over the pedal axle, the rider with the shorter thighs must have his saddle a little under 1 inch further forward of the other rider. It would be exactly 1 inch if his thigh was horizontal at that pedal position, which it isn't likely to be.
But with the saddle positioned forward, the rider with shorter thighs now has more weight that must be supported by his arms, all because of this arbitrary rule about having your knee over the pedal axle. This makes no sense. What matters is your weight distribution fore and aft, and that's determined by the fore-aft position of the saddle relative to the cranks.
Handlebar Position
Next, where does the handlebar go? Just like the saddle, it all depends on what it is you're doing on a bike in the first place. The further forward the bar, the more power you will have standing and accelerating, the better the aerodynamics and high speed control. The lower the bar, the more you can pull up under hard acceleration and the better the aerodynamics. With the bar closer to you and/or higher, you can sit more upright and take in the view.
I like to use an adjustable stem that my customers can use for a few days to try different positions for a long enough time to be meaningful. But what about a starting point? For riders with drop bars, if you place your hands down in the drops at the forward most position, (the point that allows you to easily reach the brake levers), then bend your elbows enough that your forearms are horizontal, your elbow would be at a ninety degree angle for a good starting point. From there, try moving the bar in one half inch increments forward and back to find the best reach for you. Most people are quite comfortable just with the ninety degree elbow position. But that doesn't mean it's right for you. And of course this isn't a position you'd want to spend much time riding in, except on the occasional banzai descent down a mountain pass!
Racers generally end up with the handlebar height two to three inches below the saddle height, tourers will often like to have the bar at the same height as the saddle. Mountain bikers usually position the bar a couple of inches below the saddle. The important thing is to take enough time to find the best position for you. If that means setting up a touring bike with the handlebar four inches below the saddle height, so be it. I recommend the longest reach and lowest position you feel comfortable in, (with emphasis on comfortable).
Handlebar width (road & ATB) and drop for road style bars
A few brands of drop style bars come with a choice of how much lower the drop section of the bar is from the top. Unless you are a track sprinter or a criterium racer, you don't need the very deep drop bars. Most bars come in a selection of widths. Most people seem happiest with their hands positioned on the bar at about the same distance apart as the width of their shoulders, so that your arms are roughly parallel when reaching to the bar. When determining stem dimensions, try the different bar widths available, starting with one that's the same as your shoulder's width. Then see which works best for you.
Fine tune saddle height
As you get familiar with the way your bike feels with these changes, go back to the beginning and check your saddle height again. You should be able to pedal through the bottom of the stroke without completely straightening your knees, and without rocking your hips on the saddle. If either is the case, your saddle is too high. Straightening your knee during the pedal's rotation limits how fast you can smoothly rotate the pedals, and causes you to want to use a higher gear than that which would be most efficient. By limiting the extension of your legs you smooth out your pedaling and make higher RPMs possible. That's better for your muscles and joints. If the saddle is too low you'll feel it in your quadriceps or thigh muscles.
Stock frame sizing
So what does all this mean when it comes to pick a frame size down at your local bike shop? Stems and seat posts come in lots of different configurations. That means you can choose from several different frame sizes and still get the same good fit.
All other things being equal, a longer top tube will give you a bike with a longer wheelbase, less twitchy handing, better shock absorption, and require a shorter reach stem. Since the down tube, (which connects the bottom bracket with the head tube) will be longer, it can twist a bit more making the frame somewhat less stiff while accelerating, so there is a performance penalty.
A longer seat tube will allow for a higher handlebar position with the same stem and give more room for pumps and water bottles. It can also prevent you from getting as low a handlebar position as you may want. Most importantly though, the longer seat tube raises the top tube and decreases stand-over clearance, something you should give careful consideration to.
Methodology
Notice that in most of this there is no mention of measuring body parts. And nowhere do I have you dropping plumb lines from knees, positioning handlebars so they block views of front hubs, comparing the length of your forearm to the distance between the front of your saddle to your handlebar, etc. My methodology is quite different from what most people are doing in bike shops. The Fit Kit and other marketed fitting systems are based on the measurements of lots of different riders and their bikes. It assumes that the averages of those measurements are somehow going to result in a good fit for you.
But take the case of two riders; Rider A, and Rider B. Rider A has very little upper body muscle but very strong legs. Rider B is identical to Rider A but has been working out at Ralph's Gym and looks like a body builder. The fore aft position of the saddle will be slightly different for the two riders. The extra upper body mass of Rider B will require a slightly further back saddle position to give the same balance. But that doesn't necessarily mean that Rider B should have his saddle further back. He may prefer the more forward position. Only he knows what his preference is.
Take me for example. I started riding long distances in the mid 1970s. After much trial and error, I arrived at a bike fit that worked for me. I could ride a century without much fatigue. I still have a bike that's set up exactly like the racing style bike I rode back then. I haven't gotten any taller, or shorter. My arms haven't grown or shrunk. But my neck and back are a lot stiffer in 2001 than they were in 1975. The low handlebar position is still great while I'm climbing a hill, but on the flat after 60 miles my neck isn't as comfortable as it once was. A higher handlebar is called for now that I'm older.
Measuring my body wouldn't tell me that the handlebar needs to be higher. But I used to be comfortable in the drops, (the lower part of a road handlebar). Now, I can't see the road ahead of me if I'm in the drops.
Somewhere between the fit of the track racer's bike and the long distance tourer's bike is where most of us want to be. But each of us has to find that point for ourselves. Remember, there is only one expert when it comes to fitting your bike. Only you know how you feel on your bike. Only you know what compromises you are willing to make while riding. You're the expert!
By the way, for reasons that escape me, I frequently get email from folks who tell me that they read my fitting article, loved it, and have a question. They then tell me how long their arms, legs and torso are, proceed to inform me that some bike shop wants to sell them a particular bike, and want to know if I think the bike would fit them well. My reaction is to wonder whether I wrote the article clearly, or if they read it but didn't understand it, or if they just hadn't read it. I sometimes go back and reread my own article, assuring myself that yes indeed I did make my ideas clear, and for whatever reason the person just didn't get it. Oh well...
So I'll take this opportunity to rephrase myself. I don't know if a particular bike will be a good fit for you. Even if I knew every dimension of the bike, and every dimension of you, I couldn't tell you if it's a good fit or not. So please don't write asking me to tell you something that I can't possibly know. Reread the article.
If you need an authority figure to tell you how your bike should fit, then by all means go to some shop that offers the Fit Kit or some such thing, pay them whatever they charge, and do as they say. Some folks need to be told what to do. But I don't want to tell you what to do. I'd rather give you the knowledge you need to fit yourself. Because with that knowledge, I believe you can do a much better job of it than some expert charging you money.
And, by the way, I'm a bike mechanic, not a doctor. So if your knee or back or neck or wrist hurts, and you've set your bike up using the information in this article, well, I suppose you could sue me, but please don't expect me to diagnose your ailment. See a doctor. Then sue me. ;-)
By the Way
This article is for your information only. It's not intended as the jumping off point for a conversation with me about bicycle fit. I'd like to discuss it with everyone who reads it, but unfortunately if I did that I'd have no time to build wheels, which is how I make my living. I don't do bicycle fittings any longer. Nor do I have the time to respond to or even read all of the mail I get regarding this article. So, when you write to me and I don't reply, don't feel as though I've singled you out. I no longer reply to any email on this topic. No time. Sorry.
http://www.PeterWhiteCycles.com
This article is Copyright 1989, 1998, 2001, 2002, Peter Jon White. Revised September 8, 2002
