What does the length of your forearm and the price of fish have to do with stem length?
Mon, February 18, 2019 
This method of determining handlebar stem length has been around forever. My cycling experience dates back over 67 years and it was practiced then, and many years prior. Actually it is not a bad guide and works for most people.
Of course in an age of computerized bike fitting, this may seem to be bordering on an old wife’s tale, but believe it or not, back in the day before computers people figured shit out using only the power of their mind, and the wisdom of old wives.
Place your elbow against the nose of your saddle and if your fingertips do not fit behind the handle bars as shown above, then your stem is probably too short. If the bars are more than 2cm. away from the finger tips your stem maybe too long.
When I was racing I used a stem that placed my fingertips one centimeter from the bars. Now as a mild concession to my aging body I’m using a stem a centimeter shorter. If you are wondering as I did for many years what the length of a person’s forearm has to do with stem length? I will explain.
When I am determining frame size I take into account three body measurements.
1. Inside leg length (Often referred to as inseam.) measured crotch to floor without shoes.
2. Overall height.
3. Shoe size. (Length of foot.)
I do not require body length because I have overall height minus inseam. I do not require arm length because this is relevant to leg length and foot length combined.
Human bodies although all different do generally follow certain rules of nature. We have the same basic design and structure as most other animals on this planet except we walk on our hind legs while most others walk on all four. So it follows a person with long legs will also have long arms; short legs, short arms.
Four legged animals generally walk on their toes (and finger tips) whereas we stand and walk on our heels. So some people have a long body, but short legs and it is not unusual for a person with this build to have longer feet, and also longer arms. The long arms are not out of proportion if you consider the leg length is a combination of inseam plus the length of foot.
When pedaling a bicycle the toe is pointing downward at the bottom of the pedal stroke so the foot becomes an extension of the leg, which is why it has to be taken into consideration when determining frame size. The person with short legs, long feet needs a larger frame than their inseam alone would suggest. The larger frame with its proportionally longer top tube will also accommodate this rider’s longer body and arms
The length of the forearm is proportionate in length to the length of the foot. Take one of your shoes and hold it against your forearm and you will see it is the same length as the distance from your elbow to your wrist. In other words the big bones in your forearm are the same length as your foot.
So assuming you are on the right size frame and your seat is set at the correct height, then chances are if you have very long feet then you will have a short inseam and a long body.
Because you have long feet you also have a long forearm and if you do this little elbow against the saddle trick it will show you need a long handlebar stem which will be right for your long body and arms.
A person with very long legs for their height will also have long arms but will have a short body and small feet relative to their height. Small feet mean short forearm and a shorter stem which will be right for their short body. Because this rider has long legs his saddle will be set high making a greater distance from the seat to the bars. This will accommodate his long arms.
There is another method for determining stem length which states: “A rider seated with their hands on the drops of the bars, will have the front hub obscured from view by the handlebars.” This works in the same way, longer body calls for a longer stem and vice-versa.
The only thing is that this method could be affected by the head angle of the frame and the length of fork rake. I prefer the length of forearm method because it is simpler. It works for most people but there is a small percentage that it will not. I always say if you are comfortable and happy with your current position, don’t change it. Go by the old “If it ain’t broke, don’t fix it” adage.
And what does all this have to do with the price of fish? Nothing at all, but it got your attention.
This is a rewrite of a post from the very early days of the Bike Blog. At the time it was shot down by a reader as “Utter Rubbish.” I repost it today for the reasons I did the first time. Not to get people to rush out and buy new handlebar stems, but rather to explain that before the days of high tech bike fitting, people managed to get by. I hope also I have explained why this method did have some merit, and the reasons why.
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Reader Comments (12)
I've always needed a 58cm top tube along with a 13 or 14cm stem. I'm still pretty flexible, so my bars are 11cm ahead of my fingertips. (I have a very long torso)
That kind of reminds me of tyre pressure. We had no tyre gauges in the 1950s so we pumped our Dunlop #3s tubs for TT till they pinged. You would flip your finger on the tyre and it pinged it was hard enough. Also we would tell the flex of a frame by pushing on the crank arm wit the pedal in the lowest position and push it in, to see how much it flexed. High tech HUH!!! BUT It was surprising how much flex there was on some frames.
You made me check my bikes again, they're all OK, thanks!
This post brings me the question of why using this for adjusting (replacing) the stem and not just adjusting the saddle.
I mean (theoretically, not claiming anything):
1. Set the saddle so that the leg is fully extended when placing the heel on the pedals.
2. Set the fore/aft of the saddle so that the arme placed like you mention just touches the handlebar.
3. Go to step 1 until no further iteration is required.
I know this can break KOPS but it is other "myth" so I am wondering what pseudo-scientific reasons make my silly proposal wrong...
Thank you, Dave! :-) Interesting method ;-)
Comments follow-up from a different e-mail address...
Seems to me there's no absolute. I've spent the winter doing indoor rowing and one of the nice and completely unexpected benefits is that my back got much more flexible. Now I have my handlebars set 2 cm lower and my stem went from 12cm to 14cm (on a 59cm frame), and my back is significantly flatter than previously. As Dave infers, the forearm test is a starting point.
On the fore-aft of saddle, I use Steve Hogg's "just balanced" approach, and then set the stem from there.
Pedro Martinez-Julia …….I actually did this when I first started riding 35 years ago. It didn't take me long to realize that method gave me a virtual 72 or 71 seat tube angle and just messed up my bike handling...Get your bike set up correctly and get the proper stem.
@BillK... What I try to discuss is theoretical. I have never fitted me in such way but I am wondering "why not?".
At the end of the day, the famous KOPS is relative. The key is the shape of the "levers" and their attachment points. Therefore, what matters is the relation in the position of the feet (pedals), hip (saddle), and hands (handlebar).
Using a theoretical rigid model and fixing such points, you can attach the feet of the model to the pedals, adjust the handlebar and stem to make them meet the hands of the model, and finally adjust the saddle to make it meet the hips of the model. In this way, the only variation would be that, if the handlebar point is too forward, the model would have a more aero position but there would be more weight in the arms. If the handlebar point is too backward, the model would have a less aero position and less weight in the arms.
Finally, I insist that if all elements of the bicycle can be fit within some margin, beginning from the stem and using the arm to adjust the saddle would give the same or even a better fit than doing the opposite.
As I am saying "would" I am, again, wondering "why not?". Is it just to sell new stems to customers with wrongly set saddles?
I was interested in this method and tried it, but all my bikes would seem to have much too long top tubes/stems using the forearm method that Dave describes. These are bikes I've used for thousands of miles that seem to have fit me well over the years. I have extraordinarily long arms for my height, but now I'm wondering if that length is all in my upper arm rather than my forearm. Interesting post nonetheless.
Just checked my bikes. I'm 180cm tall with 86cm inseam riding 56cm frames and my fingertips just reach the front side of the steerer. To make this work I'd need a really small frame.
This cant be right for all people (tall people) I can barely touch the stem the way the handlebars are touched in the photo.