Bookmarks: [Frame Size Chart] [Compact Frames] [Saddle Height] [Longer Cranks] [Upper Body Position] [Thigh Length] [Bottom Bracket Height] [High Speed Shimmy] [Pack a bike for shipping] [Vent Holes] [More on Dave's Bike Blog]

"My framebuilding experience dates back to 1957, I retired from the business in 1993. In those 35 plus years I made an extensive study of racing bicycle frame design and how it related to the human body. Dave Moulton."

Here is some information you may find helpful in choosing the correct size frame and setting up an efficient riding position.

Human bodies do not come in standard sizes, but they do generally follow certain rules of nature. Tall people are not scaled up models of short people. The tall person has a body only slightly longer than the short person but their legs are much longer. People with long legs usually have long arms also; short legs; short arms.

The way I determine frame size is to start by saying this equals two-thirds of the rider's inseam. (This is a starting assumption, other factors need to be taken into consideration.) This means that for the taller the rider, the amount of seat post showing out of the frame increases progressively. The resulting difference in the handlebar to seat height ratio accommodates the taller rider's longer arm length. The handlebar stem also increases in length for a larger frame. The top tube length on larger frames increases at a lesser rate, because the upper body length increases at a lesser rate.

The exception to this two-thirds inseam rule is the rider with a long body and short legs. It is as if this body was designed as a very tall person, then the heel got turned further up the leg, making shorter legs and longer feet. The body and arms are as a taller person; so this rider needs a frame more suited to his overall height rather than his inseam measurement. The foot is a extension of the leg when riding a bicycle, because the toe points downward at the bottom of the pedal stroke. Therefore this rider needs to set the saddle higher to allow for their longer foot.

The longer top tube and handlebar stem recommended for the larger frame will accommodate the rider's longer upper body and arms. The reverse of this is true for the rider with extra long legs and small feet. They would need a frame smaller than his inseam would suggest.

I devised the adjoining chart to help you determine your best frame size. Look for your inseam measurement on the left. If your height is within an inch (2.5 cm.) and your shoe size within half a size of the one listed on the same line, then your frame size is a straight two-thirds of your inseam. If your height and shoe size is more or less than shown on that line, go for the frame size recommended for your height ignoring your inseam. For example, a rider with a 30 inseam, 5'8" tall and a 10 shoe (USA) should go for a frame around 54-55cm. A rider with a 36 inseam, 6'2" and a 11 shoe (USA) should have a 60cm frame.

Another way to interpret the chart below; if your height and inseam do not fall on the same line. Look at the line where your height is; then look where your inseam is. This would be the two extremes of frame sizes; your best size is going to be somewhere in between. See which line your shoe size falls on and use that to decide which direction your best fit will be.

Example: Height 5' 9 1/2" Inseam 30" Frame size between 56cm and 51cm. If shoe size is 10 1/2 (USA) choose a 54cm frame. If shoe size is 11 (USA) choose 55cm frame.

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INSEAM (Crotch to floor without shoes.)

HEIGHT (Actual measured without shoes, not estimated.)

SHOE SIZE

FRAME SIZE

*TOP TUBE LENGTH

SUGGESTED HANDLEBAR STEM LENGTH

In.

cm.

In.

cm.

USA

UK

EUR

JPN

C to C

C to T

C to C

36

6' 4"

12

11 1/2

46.5

30

35 1/2

6' 2 1/2"

11 1/2

11

46

29.5

34 3/4

6' 1"

11

10 1/2

45

29

34 1/4

6' 0"

11

10 1/2

45

29

33 3/4

5' 10 3/4"

10 1/2

10

44.5

28.5

33

5' 9 1/2"

10

9 1/2

44

28

32 1/2

5' 8 3/4"

9 1/2

9

43

27.5

32

5' 8"

9 1/2

9

43

27.5

31 1/4

5' 7"

9

8 1/2

42.5

27

30 3/4

5' 6"

8 1/2

8

42

26.5

30

5' 5"

8

7 1/2

41

26

29 1/2

5' 4 1/2"

7 1/2

7

40.5

25.5

29

5' 4"

7 1/2

7

40.5

25.5

28 1/2

5' 3"

6 1/2

6

39.3

24.5

*The above chart was prepared for frames built in my frameshop. You may not find the exact same seat tube/top tube combination from another manufacturer, so adjust the stem length accordingly.

The chart was created over the years by experience and keeping records of customers measurements and frame sizes built for them. It was not devised by any mathematical formula.

Important note: I measured all frames (Custom and Production.) from the center of the bottom bracket to the top of the seat lug. This was standard practice with English builders. Italian frames and most others measure center of B.B. to the center of top tube.

(The above chart shows C to C and C to T measurement.) There are two different ways of measuring a frame, both are widely used and both are acceptable. It becomes important when buying a frame to make sure the buyer and seller are in agreement. If one is talking center to top, and the other is thinking center to center, the buyer will probably end up with a frame the wrong size by about 2cm.

Note: This chart is designed for an efficient racing position. If your interest is in a more leisurely style of riding this is still a good place to start. Rather than give you multiple choices simply use your own judgment and increase  the frame size by up to 2cm. so there is less difference in the saddle to handlebar height and decrease the stem length by at least a centimeter.

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When you have determined your frame size, top tube and stem length from the table above transfer those measurements to the compact bike as follows:

For example suppose you have decided you need a 54cm frame with a 54cm top tube and a 11cm stem. First measure 54cm from the center of the bottom bracket and mark that point on the seat post with a piece of tape. (Or in some other way that won't damage the bike.)

Next add the top tube and stem length together in this example 54 + 11 = 65cm. Measure horizontally from the center of the seat post and 65cm should bring you exactly under the center of the handlebars as shown above. The handlebars should also be 9 to 12.5cm above this horizontal line; depending on your riding style. (Also please note because of the head angle the stem above the top tube is set back slightly so you may want to deduct 0.5cm. from your top tube plus stem measurement.)

For optimum handling ideally the center of the front portion of the handlebars should be directly over the wheel center as shown in the drawing. If you are slightly ahead or behind this position it should not be a big problem but if you are some way off this may determine what size frame you finally decide on. Also you could choose a slightly longer or shorter stem to get the bars nearer the wheel center and adjust the seat back or forward; the maximum I would suggest adjusting the seat would be a centimeter either way and don't do this at the expense of a good riding position.

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Choosing the correct size frame will place you in an area where you can then fine tune your optimum riding position.

Saddle Height.

This can be a mystery to new bike riders but it need not be if you think about what you are trying to achieve; in order to pedal at maximum efficiency it is necessary for your legs to move straight up and down like two pistons. Your hip joint like all joints has a restriction as to how far you can raise your knee. To demonstrate this to yourself; while standing up straight bring one knee forward and upward as high as it will go. Hold it in this position with one hand while supporting yourself with the other. This is the limit of your hip joint and the only way you can make your knee reach further is to move the knee outwards and you can then go another inch or so higher.

When pedaling you do not want your knees splaying outwards at the top of the pedal stroke; this is not the most efficient way to pedal. If you lean your upper body forward as you will be on your bike this restricts the height you can raise your knee even more. So if at the top of the pedal stroke you are going beyond the limit of you hip joint and your knees splay outwards; your saddle is either too low, or too far back, or a combination of the two.

A rough place to start is to place your heel on the pedal with the crank at the bottom of the stroke. I have found for most people unless they have exceptionally small feet for their leg length (See the above chart.) the saddle will need to go higher than this. A 1/4 inch higher is a good place to start, in some cases as much as an inch higher. It is easier to tell if your saddle is too high rather than to tell if it is too low. If it is too high you will feel like you are stretching and reaching at the bottom of each pedal stroke, and in extreme cases you will be rocking from side to side on the saddle. You will know after riding only a few yards if your saddle is too high; if it is lower it the quarter inch and try again.

Next check the top of your pedal stroke; support yourself by leaning against a wall or a vehicle and in your lowest riding position with your back horizontal bring each leg to the top and see if you can lift your foot slightly above the pedal. In other words you are checking to see if you are reaching the limit of your hip joint at the top of each pedal stroke. Ideally you do not want to be right at this limit of movement. Check both legs because there may be slight variations in your hip movement on either side. Moving the saddle forward just an eighth of an inch will increase the angle of the body/leg and also has the effect of shortening the distance from the saddle to the pedal so if you move the seat forward; move it up also. Make small adjustments and try it by riding to see how it feels.

The position of the knee over the pedal is generally accepted as center of knee directly above the pedal spindle with the cranks in a horizontal position. However this is not written in stone and can vary from one person to another. Someone with long legs for example will sit back and push forward, whereas a shorter person will sit more forward with their legs acting straight up and down. Once you have found a position that feels right ride it for at least a week to get used to it before making small adjustments. Each time you adjust ask yourself if it feels better or not. As you gain fitness, muscles stretch and your saddle can be adjusted slightly higher. Just remember that your legs have an upper and lower limit of movement and an ideal saddle height is one that puts you within those limits so the leg muscles can work with maximum efficiency. As simple as that; there is no big mystery and no magic formula.   

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Longer Cranks. Addendum 4/22/04

Longer cranks give more leverage enabling the rider to push bigger gears and are also a help in climbing hills. On the down side they are a disadvantage when pedaling fast as there is a greater turning circle. Generally speaking a rider needs long legs to handle long cranks, but it comes down to the upper and lower leg movement limit that I spoke of in the above piece on saddle height.

If you lengthen your crank by 5mm. then in theory you should lower your saddle by 5mm. Then at the top of the pedal stroke you are 5mm. higher, making a total of 10mm. of increased leg movement. If you follow the above exercise on saddle height, you should be able to tell if you have the upper and lower leg movement limits to handle a longer crank rather than going through the hassle and expense of buying and fitting longer cranks, only to find after the fact, they are not right for you.

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New info added 3/21/05

Upper Body Position

When making a maximum effort your legs are thrusting downwards with more force than your actual body weight. The only thing holding you down is your hands holding onto the handlebars. Power is transmitted via your arm and shoulder muscles, through the back muscles to the legs.

This is why when more power is needed for a sudden burst of speed or to climb a hill, we stand up. Not just to get our full weight over the pedals, but to get our body nearer our arms for extra leverage. Like lifting a heavy weight we lift close to our body; lifting at arms length would put a strain on the back. On a bicycle your arms need to be in direct opposition to your legs; arms stretched out too far ahead will cause back ache just like lifting a weight.

Again support yourself by leaning against a wall or a vehicle as you did for checking saddle height. With your upper body in a low tuck position, with your back horizontal and your crank arm at the two o'clock position. (The start of the power stroke.) If you draw a line from your hip joint to the pedal spindle; it should be parallel to a line from your shoulder joint to the center of your hand on the handlebars.

Get a friend to eyeball your position, or better still take a photo. That way you can draw in the lines on the picture and if these two lines are not parallel you can see where your hands and the handlebars need to be. Don't just look at making the stem longer or shorter sometimes the best position can be achieved by a combination of raising or lowering the bars as well as changing the stem length.

Bars should be tipped up slightly with the flat portion at the bottom a degree or so from horizontal. But as a temporary measure you could tip the bars more one way or the other to try a new position before going to the expense of buying a new stem. Rotating the handlebars, clockwise would make the reach shorter. Counter clockwise makes it longer. (That is if you are looking from the drive side of the bike.)

Listen to your body; if your position feels good, go by the old adage "If it ain't broke, don't fix it." But if you suspect a problem the above exercise may confirm what you probably felt all along.

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I am often asked. "Does a person with a long thigh need a shallow or more laid back seat angle?"

This would seem reasonable assumption, but the answer is. "No, not necessarily." Look at the drawing on the right. This represents two bike riders 'A' and 'B' with the exact same leg length. (Inseam) They also have the same shoe size. Because of this lets assume they ride the same size frame and their seat is set at the exact same height. 'B' has a thigh length that is 2 inches longer than 'A' but because they both have the same overall leg length, then 'B' must have a lower leg 2 inches shorter than 'A'. Shown here are the two, one superimposed on the other and you can see the effective difference in their thigh length is only a little over half an inch. So really seat angle or set back is related to overall leg length, therefore frame size rather than thigh length, because for any given leg length it follows if the thigh is longer the lower leg is shorter and vice versa.  

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Added 10/7/05

Bottom Bracket Height or Drop

This subject is often discussed among cycling enthusiasts, and here I put forward some different thoughts.

Let me first of all explain the difference between bottom bracket height and bottom bracket drop. The drop is the measurement down from the wheel center to the center of the bottom bracket. Once a frame is built this will never vary and so is probably the more accurate term, but bottom bracket height (a measurement from the ground up to the center of the bottom bracket.) is often easier to visualize and so is also widely used.

The BB height measurement will vary slightly depending on the wheels and tires you are using. Fatter tires will raise the bottom bracket height, narrow section ones will lower it. On the spec sheets for my frames I used to specify both drop and height. I would say 2 3/4 inch (7cm.) drop, and 10 5/8 inch (27cm.) bottom bracket height. If you add the two measurements together you get 13 3/8 inches. (34cm.)  This assumed the wheel diameter would be 26 3/4 inches (68cm.) an average wheel diameter at the time I was building frames.

The argument most people put forward for a lower bottom bracket is lower center of gravity therefore improved handling. My stand on the subject is that center gravity is not an issue for a bicycle. It only becomes an issue on three and four wheeled vehicles that are prone to tip over on corners due to centrifugal forces. Bicycles do not tip over on corners because the rider leans into the corner causing the riders weight to be pushed down by the centrifugal forces, through the center of the frame and wheels to the tire on the road which in most cases increases grip. If a bike crashes on a corner it is because the wheels slid out from under the rider, not because it tipped over. The rider either leaned too far, or the tires lost grip due to loose gravel, water or ice.

A bicycle and rider has a very high center of gravity anyway, so raising or lowering the bottom bracket by a small amount will have little or no effect (other than psychological.) on the bike's handling. The bike weighs less than 20 lbs. and the rider some three feet or more from the ground weighs 100 to 200 lbs. If center of gravity was an issue a bicycle would be un-ridable. Also think of the modern bicycle's forerunner, the ordinary or penny-farthing bike where the rider was some five feet from the ground.

Further proof of this theory is the racing tricycle which are very prone to tip over on corners, and it takes a highly skilled specialist rider to ride one at speed. A tricycle can't lean into a corner, it remains level and has to be steered around a corner. The rider keeps the inside pedal down and hangs his body to the inside of the curve. Thus his body weight on the inside, counter balances the centrifugal forces pushing outward. His weight is holding the inside rear wheel down preventing the trike from tipping outwards. The higher the speed the further the rider has to lean to the inside.

Left: An English Higgins Trike, cornering at speed with rider Kevin McLellan. Lean this far at slow speed and the lightweight machine will tip inwards. Trike riding is a skillful balancing act of matching weight distribution with any given speed.

The argument put forward the most often for raising a bottom bracket is more pedal clearance so a rider can pedal around corners while leaning without fear of hitting the ground. With modern clipless pedals this too is less of an issue than when I built frames in the 1980s. A track frame needs more pedal clearance because the rider may be riding slowly at times and therefore be upright on the sloping surface of a banked track making it possible to ground a pedal.

Another argument for raising the bottom bracket and one I rarely see discussed is this: By raising the bottom bracket you shorten the chainstays and down-tube, thereby making a stiffer more responsive frame.

To explain further, the wheel center and therefore the front and rear drop-outs remain constant on any frame. If you assume the front fork remains the same length, then also the position of the bottom head lug remains constant. Therefore if you raise or lower the bottom bracket shell, then you shorten or lengthen the chainstays and down-tube. And as these are the most highly stressed tubes in a frame, even a slight variation can affect the stiffness of a frame.

If you raise the bottom bracket shell, then you also raise the seat tube and top tube making the head tube longer. This is why some small track frames appear to be larger than they are, because we are used to estimating the size of a frame by the length of the head tube. The head tube is the largest diameter tube in a frame, and is also the least stressed tube. So increasing its length will have little or no bearing on the way the frame feels.

To sum up; if I built a Criterium or Track frame with a higher bottom bracket, it was not just to give more ground clearance. It was to build a stiffer more responsive frame. At the other end of the spectrum, if I built a touring frame where the main concern was comfort; I would sometimes lower the bottom bracket thereby lengthening the down-tube and chainstays.

On an all-round frame like the Fuso that could be used for racing or pleasure riding; 7cm. of drop was (and still is.) a good compromise.

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Update 3/31/06 (Originally posted on Dave's Bike Blog 11/12/05.)

High Speed Shimmy

Shimmy is usually caused by not having enough trail. To explain trail for those who don't know: If you draw a line through the center of your head tube and therefore the steering column, that straight line will reach the ground at a point (Point B.) ahead of the point where the wheel contacts the ground (Point A.)I always built my bikes with at least 2 1/2 inches of trail. Trail is common to all wheeled vehicles, cars and even a shopping cart will have it.

If you make the head angle steeper it means less trail because you move point B closer to point A. Also if you increase the fork rake (Fork offset.) you make for less trail; in this case point A moves closer to point B. The worst scenario is a bike with a steep head angle and a long fork rake; trail can be reduced to almost zero. Trail keeps the bike going in a straight line, and also assists a two wheeled vehicle in its self steering abilities.

As you lean to the left, point B moves to the left and the wheel Pivoting on point A will turn to the left. The gyroscopic action of the spinning wheel also plays a big role in self steering, but this is another subject and I only mention it because the heavier the spinning wheel, the more it keeps straight. Road bikes with ultra light wheels and tires are more sensitive to small changes in the amount of trail.

What happens in a high speed downhill shimmy the wheel is turned one way or the other by a bump in the road or a gust of wind. (Like when swinging out of a pace line.) The caster action of the trail corrects this, but if there is not enough trail it will over correct and then correct again starting the wheel fluttering back and forth. You can see exactly the same thing on a shopping cart if you run with it across the parking lot the caster wheels will flutter back and forth in the same way.

Large frames are more prone to shimmy for two reasons. Large frames are taller and also should be proportionately longer, but there is a school of thought that believes a race bike should have a short wheelbase, so the builder makes the head angle steeper to shorten the wheelbase, but in doing so lessens the amount of trail. Large frames are more flexible because the tubes are longer, also they tend to have shallower seat angles to accommodate the rider's longer legs therefore the riders weight is more over the rear wheel.

Any vehicle that has its weight towards the rear is less stable; ask anyone who has driven an old VW bus in a cross wind. So if you are a tall person with a large bike frame, try to keep your weight forward when descending. Also keep your body in a low aerodynamic tuck; if you sit up wind pressure on you chest will push more weight towards the back wheel. Finally if you should get into a high speed shimmy; try not to panic, grip the top tube between your knees, and apply the rear brake first very gently and only apply the front brake after you have come out of the shimmy.

      A bike with a shimmy problem usually has a design flaw in the frame and there is little you can do to correct it short of changing the frame. However do check that the head bearings are not loose. Also fitting a slightly heavier tire to the front wheel may increase the gyroscopic action of the spinning wheel enough to correct or lessen the problem. The design flaw will still be there but you have added and element to maybe alleviate the tendency to shimmy.

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Update 12/26/05

Shipping a Bike.

There is nothing more heartbreaking to buy a bike from someone and have it damaged in shipping. Especially if the bike was in mint condition before it was shipped. Often a shipping company will not pay up if the bike was inadequately packed, even if it was insured. The most common causes of damage in shipping are:

1. Unprotected parts of the frame rubbing against the box or another component part of the bike, such as the wheels. Result is paint damage.

2. Bikes are usually placed on the floor of a UPS truck. Sometimes a heavy box will fall from a higher shelf on the bike box. Result a dent in the top tube. If this happens and you claim it is important to keep the box and packing materials for the Insurance Inspector to see.

3. The front fork or the rear dropout pokes through the box, and get caught in one of the shipping company's conveyers. The result is a bent fork or dropout, or it may even get ripped off completely.

The following packing instructions will help avoid some of these problems.

How to pack a bike for shipping.

Go to Home Depot or other home improvement store and buy some foam pipe insulation. This looks like a black foam tube slit down one side. Also buy some plastic zip ties long enough to go around the foam tube.

Get a bike box from your local bike dealer and ask if he has any of the plastic spacers that go between the front and rear dropouts. Most bikes shipped from a manufacturer come with these and they just get thrown away.

Remove the pedals and take the wheels out of the bike. Put the foam insulation on all the tubes and attach with zip ties. Turn the handlebars sideways and fasten it to the top tube with a zip tie. (Make sure there is foam between the handlebars and top tube.)

Remove the rear derailleur from the rear dropout but leave it attached to the chain. Put the derailleur bolt in a large plastic bag (A grocery bag is fine) and wrap the bag around the derailleur and tape it. Make sure the chain is on one of the chain rings; hook it on the rear dropout, or better yet the chain hanger if the bike has one. Then tie it up to the brake bridge with a zip tie so it is not flopping around loose inside the box. Also any place where the chain might touch the frame; make sure there is foam or cardboard between to protect. 

If you could not get plastic spacers from your bike dealer; cut pieces of wood to fit tightly between the front and rear dropouts and fasten with wood screws and washers. Next and probably one of the most important things in packing a bike; put foam followed by extra cardboard on the front and rear dropouts or they will poke through the box for sure and end up bent. Also put padding and cardboard on the bottom of the chain ring.

Remove the seat post with saddle attached only if it is too big to fit in the box. Remove the quick release skewers from the wheels and attach them to one of the foam covered frame tubes with tape. Place a wheel on each side of the frame making sure there is foam between the frame and wheels. Attach with zip ties or masking tape. Make sure the freewheel cluster is on the inside and nowhere near a frame tube. You could also ship the wheels in a separate box if you wish. Place the pedals in a small cardboard box or put adequate padding around them. If necessary attach them to the frame tape. The same goes for the seat and seat post if you removed them from the bike.

Put the whole bike in the box and seal with tape. Some shipping companies prefer re-enforced brown paper tape over clear tape. The main thing is make sure the box is not going to bust open. Don't forget to check the bottom of the box. I have seen people over tape the top of the box; only to have the bottom fall out.

Ship UPS or FedEx Ground is the most economical way. Insure it for the value of the bike plus the cost of the shipping.

Printable Version Available on Download Page9.

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I saw this question asked on Bike Forums. Why the little holes in the chainstay bridge and other parts of the frame?

Answer: These are vent holes necessary during the process of brazing. They are only needed when a tube is closed both ends like the example shown above. Also the top tube (Usually vented with a hole into the seat tube or head tube), seatstays which have the fork dropout one end and the seatstay cap at the top. The front fork blades are enclosed both ends by the fork crown at the top and the fork tip or dropout at the bottom. Other tubes like the seat tube, the down tube and the chainstays are open to the inside the bottom bracket shell. These tubes and the brake bridge which has the brake bolt hole do not need to be vented.

During the brazing process the air inside the tube expands as it is heated. If the tube is totally enclosed on cooling it the air contracts sucking the molten brass inside the tube leaving a pin hole that is almost impossible to fill. Worse still pressure can build up in an un-vented tube and hot brass will blow back in your face. The novice frame builder soon learns the importance of vent holes after picking little globules of brass embedded in his face or finds them hanging like tiny Christmas Tree decorations from his mustache or other facial hair.

On most of my custom frames you won't see holes in the chainstay bridge (Shown above) they are hidden inside the bridge tube by drilling one hole sideways through the left chainstay tube, before the bridge tube was put into place. Only one hole is needed for venting but often two holes are drilled for better drainage of moisture later.

The vent hole in the seatstays on my frames is on the inside up near the seat lug. You might have to turn the bike upside down to see it. On my front fork blades I drilled one vent hole in each fork blade near the bottom, but after the fork had cooled went back and filled it by brazing a piece of wire in the hole. The heat generated in doing this was so small and the air space inside the fork blade was big enough as to not cause a problem.