Originally Posted by seely

I figured it out once, and the actually difference between a 170mm crank and a 175mm crank is something miniscule like .4"... I don't think it really makes as big a difference as some might lead you to believe. As for cornering clearance, if you are going hard into a corner, your inside leg is probably up anyways, so it doesn't really matter if you have 167's or 180's... they won't strike.

Originally Posted by seaniesharko

hmmm i am new to cycling, and i don't know much about frame sizing, but i was reading about this formula and it sounds like people are pleased with it. i read about a 5'10 1/2" persons frame size according to the forumula and he said it was perfect... 56-57cm. thats my exact height, but i know different inseams sizes can dictate the best frame size. my inseam length is 32". does this measurement seem ok for me?

Originally Posted by Dave Moulton

After measuring and studying hundreds if not thousands of customer’s measurements over the years as a custom frame builder. I came to the conclusion that although human bodies are all different; they do follow certain rules of nature.

Tall people are not scaled up models of short people. Most of the height difference is in the legs; body length differs by a lesser proportion.

If you have long legs then you also have long arms. Short legs; short arms. This makes sense since most animals are four legged; why should we be any different?

Leg length is a combination of the inside leg measurement plus the length of the foot. Length of the foot is important because when pedaling the toe is pointed downward at the bottom of the pedal stroke; so the foot becomes an extension of the leg.

People, who have a short inside leg measurement for their height, generally have longer feet. (Bigger shoe size.) It is as if they were designed as a much taller person, but their heel got turned further up their leg; making a short leg, long foot.

Imagine two people both six feet tall standing side by side; one has a 34 inch inside leg, the other a 32 inch leg measurement. Because they are the same height it follows the one with the shorter leg has a body 2 inches longer; he also has longer feet and shorter arms than the other guy. They can both fit on the same size frame, (59 cm. center to top i.e. 57 center to center.)

They will both have close to the same seat height, because the short leg guy has a longer foot so his seat needs to go higher than his inseam would suggest. They can also use the same top tube length and handlebar stem, because one has short body long arms; the other long body, short arms; making their reach the same. Minor adjustments in seat height and stem length may be called for.

It has occurred to me that with these compact frames on the market now and only available in small, medium, and large; customers are only ball parking frame size anyway. It has long been my opinion that frame size is linked to the overall height of the rider more than any other measurement because of the rules of nature I have just spoken of.

So I have just formulated this based on my own frame sizing chart. If you are 5’ 3” to 5’ 5” frame size equals Height divide by 3.3. For people 5’ 6” to 5’ 10” frame size = Height divide by 3.2 and if you are 5’ 11” to 6’ 4” frame size = Height divide by 3.1

A example would be someone 6’ 2” = 74” divide this by 3.1 = 23.87 in. (61 cm. measured center to top. i.e. 59cm. center to center. A person 5’ 7” = 67” divide this by 3.2 = 20.93 in. (53cm. center to top. i.e. 51cm. center to center.) The easiest way to convert from inches to centimeters is to get a tape measure with both on and simply read across.

Reach which is top tube plus stem length; is frame size center to top plus 10cm. If you want something more accurate go to the chart on my website (Link below) go to ‘Bicycles’ page 6 ‘Bike tech.' That chart was derived not by any mathematical formula but by records of custom frames built over many years. Most people find it pretty accurate. The above is an attempt to come up with a simple formula that comes close to this. Please don’t change your position based on this alone because this is new thinking.

What I would like to know from everyone is; is this of any help or does it complicate things further and also does it come close to what you are riding now?

Originally Posted by bccycleguy

I'm trying to size a bike for my teenage daughter as a birthday present. Your chart appears to be largely for the male figure, but any way, her sizes are: 5'2" tall, 29 3/4" inseam, size 8 1/2 ladies runner. Dividing height by 3.3 gives ~48cm (18 3/4") but I know thats way too big for her. I think something around 42 - 44 in a ladies fit might work, what do you think. She would be a recreational weekend rider.

Originally Posted by Dave Moulton

What I would like to know from everyone is; is this of any help or does it complicate things further and also does it come close to what you are riding now?

Originally Posted by skycat

I can honestly say there is a huge difference between 170mm cranks and 165mm cranks for me. I'm 5'1 and with the 170's I can't seem to get a smooth cadence and climbs seem jerky yet with 165s I have no problems with climbs or cadence. Of course, it's amazing how hard it is to get components for the small end of the spectrum, it seems like they only cater to the tall people.

Originally Posted by Snicklefritz

I'm having a hard time finding compact cranksets with 165mm crank. Do you have any ideas where to look?