Big Bike = Faster?

[Fisher]

I like this thread!


Physics problem!

Get two different sized styrofoam balls and place them side by side on an inclined plane inside a wind free room. See which has lesser time to get to the bottom

layball:

Ignoring air resistance it will be the same.
The way I see it is that a heavier rider would have more momentum, velocity times mass, when braking your momentum is what comes into account of how quickly you will stop, so over an entire downhill track a lighter guy would be able to brake later assuming they are riding the same bike. This would give the lighter guy a slight edge assuming all other variables were the same.

 

[sonicusx]

Depend on the course. If you like slope style course riding?, you keep your 140mm stuff.
My friends used two kinds bike when DH race.
One is Demo8 + Boxxer, another bike is Cannondale Prophet + 140mm lefty.

 

[A.France]

the problem with being big is after certain point of height about 187-190 is that all low branches try to kill you and in corners with a leaned over tree it gets in the way

 

[Petero]

Interesting discussion.

I studies sports biomechanics, more so running, jumping and impacts, but basically on a bike, particularly DH riding skill>mass (assuming the mass of each bike is relatively similar).
I can't see how gravity can have an advantageous affect on riders of different mass, either light or heavy assuming relative fitness levels. I can see how more skilled people can carry more speed out of a corner, therefore trying to accelerate mass is a very small issue.

Although does anyone know if a lighter bike glides over obstacles better or tends to get throw off line easier?

A few considerations (I'm just going to highlight a few and not even bother trying to assess)

Friction - Higher with a heavier bike (slower acceleration, lowers top speed, more GRIP)
Momentum - Change of direction on a heavier bike is harder meaning avoiding obstacles is also more difficult, but you can also carry more speed through said obstacles
Acceleration - A lighter bike will slow down quicker but also allow you to recover speed quicker after hitting an obstacle and getiing 'thrown' off line

Probably more that I have neglected.

 

[chadly1084]

Gravity exerts the same pull on everything.
Its been a while since I studied physics but I'm pretty sure that Velocity = acceleration over time (mass is irrelevant)
having said that Momentum=mass times velocity so a heavier rider will carry speed further.
But a bigger rider has more resistance from friction caused by wind.

Obviously a while since you did physics , displacement is distance (m), velocity (m/s) is change in distance over change in time velocity also needs to have direction and acceleration (m/s^2) is change in velocity over change in time

Full marks for Momentum = mass x velocity

Hope this brings back memories I hated studying physics

 

[jumpers]

Obviously a while since you did physics , displacement is distance (m), velocity (m/s) is change in distance over change in time velocity also needs to have direction and acceleration (m/s^2) is change in velocity over change in time

Full marks for Momentum = mass x velocity

Hope this brings back memories I hated studying physics

Good see you applying all that uni to bikes Chad

 

[cramhobart]

Obviously a while since you did physics , displacement is distance (m), velocity (m/s) is change in distance over change in time velocity also needs to have direction and acceleration (m/s^2) is change in velocity over change in time

Full marks for Momentum = mass x velocity

Hope this brings back memories I hated studying physics

20 years and lots of beers thanks for the correction-But I'm correct as far as mass is irrelevant when acceleration due to gravity is concerned?

 

[stackcheddar]

20 years and lots of beers thanks for the correction-But I'm correct as far as mass is irrelevant when acceleration due to gravity is concerned?

Correct. Vertical acceleration close to the earth's surface is always going to be 9.81m/s/s (neglecting air resistance).

Given a perfect world with no friction, a bigger bike shouldn't get down a hill faster than a smaller bike. But since you are questioning, the high level reasoning can only be explained by you not going down faster on a bigger bike but you're SLOWING DOWN LESS.

The next question is why you are slowing down less and that's where all the environmental variables come into question - more confidence to plow through obstacles, less effective braking due to higher momentum... list goes on.

 

[chadly1084]

Good see you applying all that uni to bikes Chad

Too much time studying wishing I was riding. Not enough time riding not thinking about studying.


All the pros seem to be going light my reasoning would tell me this not in a quest to go slower, however could just be marketing so that bike companies sell these light components that cost a fortune too make lots of $$ from those people watching the world cup on tv, or every engineers quest to create the lightest and strongest materials known to man and throwing practicality and price right out the window. Example Bugatti Veron who can afford one and probably wouldn't make it over a speed hump.