Funny shaped front Cog in the Tour De France

[rest have risen above me]

Watching the news there was a bit of footage of a front cog that appeared Oval. Is this some new technical improvement? I can't see the advantage as the drive required would be uneven. Can any penny farthing racers shed some light as google doesn't seem to be yielding much?

 

[Little Tronk]

Had one on my old mountain bike circa 1993 ish. Elliptical, apparently more efficient. In fact a mates Dad circa 1980 ish talked about them in the past tense. In essence, nowt new.

How it is supposed to work is pointy bit of cog follows pedal and therefore 'pulls' the chain round harder with no increase in effort. B0ll0cks if you ask me because still bloody knackering!

 

[Dark Helmet]

All the power from cycling happens when the pedal is horizontal and being pressed down (or on the other side being 'pulled' up). When the pedals are at 'top dead centre' or 'bottom dead centre' there is no power being generated. The idea of the oval is to accelerate the rider's leg to the horizontal position. It is supposed to give a 10% advantage. The downside is that the chain comes off more often!


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[busby1971]

It's not a new thing, I bought a Trek mountain bike many moons ago (1992 ish) that had oval rings. From what I can remember the theory is that the power is applied during the shortest bit then the cog and free wheels around the long bit then you peddle the short bit again.

Don't know the science behind it but my next Trek bought ten years later had round cogs so it may not have caught on at the time.

 

[fileeth]

As has been previously said its not a new thing.

I've still got my Dawes Scorpio road bike (purchased mid 80's) and that has still got the Shimmano Biopace oval front chain ring on it.

Not sure but seem to rememeber that it went out of fashion because it was claimed it caused damage to the knees compared to a normal circular chain ring. (I could be wrong as my memory is not so great now i've gone past 40DT_Xtremez_21: - i'm sure i'll get corrected)

 

[rest have risen above me]

Cheers for that. I've never seen it before and thought they'd come up with something new. I can see the extra power bit now, it must be wierd having an unequal force required throughout the pedal travel.

 

[Malesu]

Use to have biopace on an old racer, and preferred it. Easiest way to think of it is look at two different chain rings at the front... Use the large one for the flat, and the smaller one on hills to make life easier.

Combine the two, and you get the power from the large one on the power stroke, and the recovery from the smaller one.

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[Keyser Söze]

Wiggo' has been using oval chain-rings on his Time-Trial (TT) bikes for a while, they were en-vogue in the 80's but fell out of fashion for a number of reason all mentioned previously (chain falls off, irregular pedal stroke, etc) nevertheless the science under-pinning the 'power-stroke' (which is effectively extended when using oval chain-rings) is sound.

Followers of Armstrong et al, preferred to 'spin' the legs using a lower gear ratio to get the speed, (this style tends to increase max HR; whereas Wiggins relies on his power to turn a higher gear ratio to generate speed (tends to increase muscle lactic acid build up/cramps). All said, it depends on which method is more suited and efficient to each riders physiological strengths and weaknesses.