As you can imagine it is not possible to change the top tube length of a bike unless you are choosing a new bike, where you can shop for a bike that will give you the ideal length to work with. All adjustments are made by altering the height and length of the head stem and it is ideal to keep your stem within 25mm of 110mm for handling (freeride, trials and downhill excluded)
Bar height
Systems such as the FitKit make recommendations for how to adjust the saddle, width and drop of handlebars, shoe cleat adjustment, etc. There is one vitally important adjustment that is ignored by most of these systems, for good reason–the handlebar height. These systems cannot specify handlebar height because this is not determined so much by the dimensions of the cyclist’s body, but by the cyclist’s conditioning, flexibility and type of cycling activity.
Low handlebars puts your body in a very leaned-over position riding position. What supports the upper body in this leaning forward position?
Picture a recreational rider who rides 50 kilometers a year to the shops and back compared to performance rider chasing the peleton (bunch of riders).The recreational rider coasts in a very upright position. If positioned with low handlebars, the weight of the upper body will bear heavily on the wrists and hands, causing soreness and discomfort to the shoulders and neck as well. Whereas the performance rider’s upper body is being held up by the pedaling force of the legs. Not only is little weight resting on the handlebars, the sprinter is actually pulling up on the bars to resist the downward pressure of the legs. Their upper body is perfectly comfortable with a very low relative handlebar position. Therefore the ideal handlebar to seat height relation ship depends on the intensity and flexibility of the rider however, for performance riding it is advisable to work within a 2cm – 6cm drop from the seat to the handlebar.
The old school measures are a little different to today although are still very useful, believe better than some of the smart guys with "the latest ideas". These old rules have been tried and proven. The old way says you should sit well behind the cranks on a comfortable saddle although how far back you sit is up to you (as is everything else), but you should be back far enough so that your weight is being supported by your butt, not your hands. Compared to the position most riders have, this one has the seat a little farther back and the bars much higher, and it works well for most people.
Handlebars can be too high. If you climb a lot of hills off the saddle and holding the brake hoods, you need to be able to completely relax and nearly straighten out your arms as the bike rocks side to side. When you rock the bike to the left, it allows your left arm to extend and relax; same thing on the right. But if the bars are too high your arms won’t extend and relax, and your biceps will get tired from being flexed all the time.
Downhill bikes often have higher handlebars, only because they need to keep weight back in case you hit an obstacle that will throw you forward or to neutralize your position on the bike on steep terrain
There are two stem systems available, A-Head (the thread-less system) which is by design far superior, however if you wish to raise or lower your position beyond the spacers provided, you will need to change the stem. The older Quill system where the stem expands inside the fork steerer does have a vertical adjustment but be careful not to raise the stem above the max height mark and for Quill or Cone stems (threaded not ahead) watch using expanders inside a treaded portion of the streerer.
Stem Length
Next, determine the correct "reach" to the bar, or horizontal fit. Proper reach gives you easier breathing, better neck and lower back comfort, and better weight distribution for comfort and handling.
That "ideal position" varies here more than anywhere else for cyclists, depending on riding style, flexibility, body proportions, and frame geometry, among other biomechanical variations, plus your upper body position will evolve with more hours in the saddle. That is, you may find that you develop a lower, longer position as your fitness and flexibility improve. As Davis Phinney notes, though it may be difficult to achieve a truly flat back, we cyclists should all strive to be “longer” across the top of the bike.
Unfortunately, there is no formula for sizing the top tube and stem that works as well as the inseam method. Although the end result can be checked by any of the following;
- A well-known formula is to convert torso and arm length measurements to total reach (length of top tube + stem). For example, for a road bike sport/racing position:
(Torso Length + Arm Length) / 2 + 40mm = ( Top Tube + Stem)
Learn how to measure Torso here
Learn how to measure Arm length here
- The Eyeballing the Hub Method a: While riding with the hands on the hoods (road bike), the handlebar obscures your view of a portion of the front of the hub.
- The Eyeballing the Hub Method b: glancing down at the front hub while riding in the drops; your view of the the front hub axel should be obstructed by the handlebar.
Although this measure may also be affected by the reach and drop of the handlebar. Nitto #185, Cinelli #64 and #66 have, for instance, drops of, resp., 140mm, 145mm and 156mm and reaches of, resp., 87mm, 80mm and 87 mm. The requirements on stem length for a given position "on the hoods" or "in the drops" between a Cinelli #64, #66, Nitto #185, Modolo Q-Even, ITM Italia Pro or a 3TTT Merckx can vary by as much as ½ to 1 cm! [ed: So much for the folklore of "eyeballing the hub" even with average morphology]. Deep drops (e.g. the Cinelli #66) are, in general, for larger cyclists and, in particular, those with relatively longer upper-arms and/or shorter torso. In general, the stem should be no lower than the above (Handlebar under Seat) value.
- The Le Mond method; LeMond recommends that your elbows, bent at 110° with your hands in the drops, should be within an inch or two of your knees at the top of your stroke.
- The Knee Touch Method: With the hands in the drops and the elbow at a 45o angle, the knees should nearly brush (or overlap) the elbows at the top of the stoke.
- The Nose Plumb Method: With the hands in the drops, the stem is selected so that a plumb bob dropped from the nose would fall around 20 to 30 mm. behind the handlebars
- The Cubit Method: This method seems to be the most popular in Europe. With the elbow against the tip of the saddle one selects a stem so that the finger-tips extend (at least) to the middle of the extension.
- For performance riding it is suggested that you aim for the optimal 45 degree back posture while in the hoods.
- If your stem has the proper extension, and your levers are properly placed, your upper body/back should lean forward at a 45 degree angle when you’re on the hoods. When you move to the drops, your back should be nearly flat, with your upper arms vertical, and the elbows bent at 110 degrees. If your legs make chest contact then the stem is way too low.
All these methods have significant problems however you should be able to get a guide from the different measures however;
- You should be able to ride the brake hoods with a good, noticeable bend in your elbow, so your forearm is more horizontal than your upper arm.
- You should be able to remove your hands from the hoods, stick them behind your back, and hold your upper body position without a strain.
- You should be able to grab the tops (the straight section of bar next to the stem) gently, like a piano player, and without "falling into" them.
- You should be able to reach the drops with little if any change in upper body position.
- You should be able to ride the drops comfortably on a flat road for a couple kilometers at a stretch without feeling discomfort.
Summary
The formulas and fitting systems documents can get you in the ballpark. But for most of us, a little up, a little back, a tiny shift in seat angle, etc. is still needed after your measure up adjustment. Getting the details right can make appreciable differences in performance and/or comfort.
IS THERE ONE PERFECT POSITION?
To reiterate and expand on the previous comments on tweaking, for most riders, no one position is perfect for all times, places and events. As you change, or what you’re doing changes, your position changes. For example, We must also try to allow for the possibility that during the course of a single ride your likely to slide back and forth to bring different muscle groups into play, allow other muscle to rest, maximize power, etc. however we are in pursuit to find the ideal "home Position". Knowing it maximizes performance, improves training results, and reduces the risk of injury.
