Rotational weight vs Frame/Fork weight

Bhima Posts: 2,145
edited February 2009 in Workshop
If I understand the physics correctly, a lighter bike, at a specific rider's power output will accelerate at a rate quicker than a heavier bike, at the same output. (Assuming we ignore gravitywind/rolling resistance)

...but i've been told that rotational weight - wheels/chainrings/cranks/chains/pedals - is more important...? I assume this is because the wheels are moving faster forward than the bike itself?

So, lets say we have two bikes, both 8kg:

Bike 1 - Wheels: 3kg
Bike 2 - Wheels: 1kg

Even though they both weigh 8kg, would bike two accelerate faster than bike 1 for a given power output? (Assuming we ignore gravitywind/rolling resistance)


  • balthazar
    balthazar Posts: 1,565
    I'll let somebody who knows and enjoys it do the maths, but I think it is easy to demonstrate viscerally how little impediment it is to accelerate your wheels. Try spinning them in your hand. It is easy to spin a wheel up to 15-20 mph, using just your thumb, in a couple of seconds. The strength in your thighs and the mass of your body should present orders of magnitude more force than that. Nearly all of that power is applied to pushing your body through the air.

    It is the princess and the pea, a story that perhaps was written in the long foreknowledge that cyclists would one day appear.