August 8, 2013
Seat Tube angle : measured in degrees relative to the horizontal plane , they can vary from 65 degree to 80 degree.
steeper angles (75 degree – 80 degree)push the rider’s weight forward on to the handlebars and are less comfortable over long distances, but more aerodynamic ; they are common on dedicated time-trial bikes,track bikes and triathlon bikes with aero bars.
slack angles (65 degree), which place more weight on the saddle, belong on commuter or other bikes for short trips.
Conventional road-racing bikes with drop handlebars tend to be between 72 degrees and 75 degree.
The angle is partly determined by ergonomics – that is, the saddle being in the best position for efficient pedalling.
Head Tube angle : again,measured in degrees relative to the horizontal plane, it has a marked effect on steering characteristics and shock absorption and can vary from 71 degrees to 75 degrees.
steeper angles mean a bike handles more quickly – turn your head and the bike turns too.
slack angles make a bike more stable, notably on descents, and generally more comfortable over long distances.
Touring bikes have slack angles.
August 8, 2013
the geometry of a frame – that is the angles between the tubes of a frame – is largely determined by the intended application of the bicycle.
Criterium,triathlon,time trail,touring and sportive bikes are variations of the road bike, for different purposes.
They may look roughly the same shape,but in fact they each have a different geometry, giving them different ride characteristics.
Mountain and commuter bikes have a different geometry again.
Frame geometry is an important factor in how a bicycle rides,how comfortable it is, how it responds to a rider’s manoeuvres, how it corners,descends and even climbs.
Many other factors al;soaffect ride quality – from the frame and fork materials to tyre pressure – but the geometry of a frame sets the parameters.
Few cyclists ever think about frame geometry.
If you buy a mass- manufactured bike, it’s scarcely a consideration.
Along with the immaculate fit and right tubing material,geometry is an intrinsic part of buying a bespoke bicycle.
Get the geometry of the frame wrong and you end up with a bike that is at best uncomfortable, and at worst, dangerous to ride.
Get it right, and the bike will have the handling characteristics you desire.
August 7, 2013
” The main principles which guided me in making this machine were to place the rider at the proper distance from the ground …. to place the seat in the right position in relation to the pedals ….. to place the handles in such a position in relation to the seat that the rider could exert the greatest force upon the pedals with the least amount of fatigue.”