Tuesday, February 7, 2012

Determining the lengths and Angles

Once I say I'm going to pickup the pace on this project no sooner than life happens, so I'm not going to say anything and jinx it.

If you get a chance to buy this book, it's pretty informative even for a book from 1988. It's main features are the chapters on bicycle fit. I know there are many custom builders that use this book's reasoning even though this book is considered old.

I have a saying, "Dazzle me with your over complication of the simple". It's real easy these days with all the digital smoke & mirrors to make something appear more mysterious than it needs to be. One thing some fit systems do is set you up with ridgid dimensions, where as this book give you some tolerances to fall between. You can have two people who measure the same, but if they have different flexibilitys, then you need to fit them differently.

These are the 4 critical dimensions for you bicycle, and the 5 body measurments you need to take.

After taking the same measurments on 3 different days to make sure I have them right. this is what I came up with. To the left are the measurements, on the top right are the ratios, and on the bottom right are the suggested dimensions.

Saddle height is your inseam x 0.883

Frame height is your inseam x 0.065

Saddle setback is open to the saddle nose being 6cm to 8cm behind the bottom bracket. This is a place to start. If your saddle is too far forward, you will find yourself riding on the tip of your saddle, then having to scoot back during you ride. You would think if your saddle is too far forward you would find yourself riding at the back of your saddle, but that is not what happens. The perfect place is when your body's center of gravity is over the pedal spindle. For every action there is an equal and opposite reaction, So when you press on the pedal, you want the opposite reaction to be projected though your center of gravity. This is a lot like doing a proper squat.

Saddle to Bar is open to 53cm to 57cm is a lot of tolerance. This has a lot to do with flexibility. You want to be extended so your back is flat, but not over extended. I like 54cm-55cm works natural for me.

Saddle to stem drop is open to 7cm to 8cm. How far do you want your bars below you saddle? (Remember this is a racing position and not touring). I'm not very flexible and will go the minimum of 6cm. Also you have to consider the drop on your handlebars, I also like shallow drops.

One note on saddles is they are not all the same size. I have two WTB saddle, they are identical but one is wider than the other. I rider further towards the front on the wider saddle than the narrow, so the wider saddle is setback about 1cm than the other.

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