Bike Forums - Bike size for commuting

Tightwad is right you need to get the bike adjusted and to see if it is in fact the right sized frame for you.

The do it yourself guideline is that the top of the seat should be a the height of your hip, or lift one leg up and the seat should be level with the top of the raised quad.

Seat position (fore/aft) is done on the bike and with some sort of plumb line also if you have a garage get yourself on the bike close to a wall so you can support yourself with one hand. With feet on the pedals position on foot/crank at the 3 o'clock position the front of the knee should line up where the crank and pedal meet.

Here's a more technical guideline from a professional bike fitter

General Guidelines:

ROAD / HYBRID / CYCLOCROSS

To determine your recommended bike frame size first you need to measure your inseam.

Do this standing against a wall in sock feet with your feet slightly away from the wall. Place either a book or a carpenter's square between your legs held right up against your pelvic bone (about 20 lbs of pressure).

Measure the distance from the floor to the top edge of the book/wood in centimeters.

Frame Size = Inseam x .657

For example if you have an inseam of 79 cm then the recommended frame size would be 52 cm

(79 X .657 = 51.9 )

Bike frame geometry is designed to fit riders of “average” proportion.

So it is therefore important to determine if your body is proportional in terms of leg/torso dimensions.

This can change the recommended frame size. To determine if you have short/long legs:

Inseam / Height= % legs are of body

If your legs are 45% or less of your body, then you have short legs and a long torso.

You therefore could use one frame size up (since you need a longer reach for your long torso)

If your legs are 50% or more of your body, then you have long legs and a short torso.

You would therefore be better on a smaller bike (since you need a shorter reach for your short torso)

MOUNTAIN BIKE

Frame Size = Inseam - 36cm

3 - 6 '' stand over clearance between the crotch and the top tube

Frame size should be around 8 - 10cm less than your road bike

Sizes may vary from one manufacturer to another.

The above are general guidelines. You are best to test ride some bikes once you have gotten a rough idea of what will fit you. This will help you determine what is most comfortable for you.

Frame size of a bike refers to the measurement of the length of the seat tube in centimeters.

Traditionally this is measured from the centre of the bottom bracket to the centre of the top tube. Some manufacturers measure to the top of the top tube or the top of the seat tube.

With a horizontal top tube this is an easy measurement. Many bikes however have compact geometry with a sloping top tube and therefore will have a different way of measuring frame size. The size is based on the virtual seat tube length. The top of the seat tube is measured at a point where a virtual or imaginary horizontal top tube would bisect the seat tube. This is often a complicated measurement. You could either consult the bike's web site or a bike shop employee should be able to translate the frame size for you.