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Areodynamics, Centre of Gravity and balance

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c-m
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Joined: 12 May 2006
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PostPosted: 07:21 - 14 Oct 2009    Post subject: Areodynamics, Centre of Gravity and balance Reply with quote
Right i have randomly been wondering the following things:

1) As the forks on a motorcycle are pretty unareodynamic, why don't they make them () that shap front to back rather than O shape? Similar to racing bicycle forks?

2) An under tray offers a nice smooth surface under the bike, surely the use of an undertray makes the bike more areodynamic? If so why don't manufacturers fit as standard?

3) The centre of gravity is pretty high on a sports bike, i'm wondering why I never see brake calipers mounted at the bottom of the disc, this would help lower the centre of gravity and improve balance. I think the Brawn formula one car has them mounted there.
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Dr. DaveJPS
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Joined: 24 May 2008
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PostPosted: 07:38 - 14 Oct 2009    Post subject: Re: Areodynamics, Centre of Gravity and balance Reply with quote
c-m wrote:
Right i have randomly been wondering the following things:

1) As the forks on a motorcycle are pretty unareodynamic, why don't they make them () that shap front to back rather than O shape? Similar to racing bicycle forks?

3) The centre of gravity is pretty high on a sports bike, i'm wondering why I never see brake calipers mounted at the bottom of the disc, this would help lower the centre of gravity and improve balance. I think the Brawn formula one car has them mounted there.


1) hossack front ends are (roughly) that shape, but people prefer forks due to feedback/familiarly/cost

3) surely with the exposed nature of the calipers on a motorcycle it would cop all the road crap and seize very quickly if it was mounted at the bottom, also i would guess you'd get reduced rigidity in the mount as it wouldn't be being supported by the fork leg

(no doubt will be corrected by later posters)[/url]
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Last edited by Dr. DaveJPS on 09:11 - 14 Oct 2009; edited 1 time in total
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DaveH
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PostPosted: 07:40 - 14 Oct 2009    Post subject: Reply with quote
1) The mudguard on my bike covers the lower forklegs and makes them more aerodynamic. I may be wrong here, is it not only bikes without front suspension that have them shaped like ()?

Also there is no point in making them more aerodynamic as any gains will be removed by the presence of an engine right behind them.

2) The aftermarket undertray is not an aerodynamic aid - it is aesthetic in purpose. It does not act like a diffuser.

EDIT: It also may be nice and smooth, but then they shove the reg plate at the end of it... Wink

3) C of G is not meant to be low on a sports bike, but centralising it helps, infact, IIRC it is meant to be high-ish - cruisers are different.
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bazza
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PostPosted: 08:48 - 14 Oct 2009    Post subject: Re: Areodynamics, Centre of Gravity and balance Reply with quote
c-m wrote:
Right i have randomly been wondering the following things:

1) As the forks on a motorcycle are pretty unareodynamic, why don't they make them () that shap front to back rather than O shape? Similar to racing bicycle forks?


Two words.

Oval. Springs.

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Kickstart
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PostPosted: 19:34 - 14 Oct 2009    Post subject: Re: Areodynamics, Centre of Gravity and balance Reply with quote
c-m wrote:
Right i have randomly been wondering the following things:


Suspect for those 3 things, any improvement is tiny. Bikes are pretty dire at aerodynamics. Forks would make no real difference considering the lump of radiator and engine behind it. Undertray might make a minor difference, but the airflow around there has probably already been wrecked by the rear wheel and suspension. The weight of the calipers is tiny compared to the weight of the bike and would make a negligable difference to the centre of gravity.

All the best

Keith
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Dibble
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Joined: 17 Jul 2007
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PostPosted: 20:28 - 14 Oct 2009    Post subject: Reply with quote
Quote:
1) As the forks on a motorcycle are pretty unareodynamic, why don't they make them () that shap front to back rather than O shape? Similar to racing bicycle forks?


I remember reading in a bicycle magazine an article by an eminent designer(Mike Burrows?) that bits of a bike needed a ratio of 4:1 to have an aerodynamic effect i.e 40mm wide forks would have to be 160mm front to back.

Forks take most load front/back but do have some side-to-side forces when cornering so ovals are a good idea from this perspective. Would 20mmx80mm air sprung forks be possible or would it be easier to reduce drag by going on a diet?

I notice Moto GP riders are now specially bred to be aerodynamic midgets.

The most important thing is that the center of gravity is in front of the center of pressure( like a c-of-g but for aerodynamic forces) so the bike is stable.

Last edited by Dibble on 22:47 - 14 Oct 2009; edited 1 time in total
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Pete.
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PostPosted: 20:40 - 14 Oct 2009    Post subject: Reply with quote
Oval motorcycle forks would have more stiction under breaking than round ones, they would also be more prone to sideways flex.
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Ariel Badger
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PostPosted: 20:49 - 14 Oct 2009    Post subject: Reply with quote
At low speeds (80-160 MPH) streamining is more efficiant at the rear of a bike than at the front as it needs to defeat the vortex of air behind the machine that is pulling against it.
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Dibble
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PostPosted: 20:58 - 14 Oct 2009    Post subject: Reply with quote
Quote:
At low speeds (80-160 MPH) streamining is more efficiant at the rear of a bike than at the front as it needs to defeat the vortex of air behind the machine that is pulling against it.


So Cafe Racer tails worked as well as looked good-form following function? Cool
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Ariel Badger
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PostPosted: 21:03 - 14 Oct 2009    Post subject: Reply with quote
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colin1
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Joined: 17 Feb 2005
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PostPosted: 00:08 - 15 Oct 2009    Post subject: Reply with quote
Not much air flow past the forks on faired bikes, so its not really a key area for aerodynamics.

Developing oval forks would cost money, and until its worth someone doing it, it won't happen.

Development costs for bicycles are lower.

As Ariel said, there are more benefits to streamling the rear of the bike than the front. You want smooth air flow, as turbulence wastes energy. You tend to get turbulence behind the moving object, so if that can be reduced by a stream lined shape, it's good.
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Old Thread Alert!

The last post was made 16 years, 336 days ago. Instead of replying here, would creating a new thread be more useful?
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