Michael Coldwell ([EMAIL PROTECTED]) writes: > Rod, > There is some of a sound explanation for this! It > turns out that in addition to the calculation of > appropriate ratios to maintain a certain cadence, > there is also prefered rings and cogs for efficiency > of power transfer. The larger rings and cogs are more > efficient - and the explanation has to do with the > mechanical advantage (leverage) of the larger cogs and > chainrings (due to the longer distance from the pivot > (the axle)). Bruce Timmermans once had a graph > showing the efficiency of the power transfer through > different ring/cog combinations. I never saw the > graph, but know he had one - I believe more of the > advantage can be accounted to the larger cog rather > than the large chainring (makes sense). There may > also be a teeny advantage with the large chainring in > fewer rotations of the little wheels at the rear > derailer (I forget what they are called - I once knew, > but my brain leaks these tidbits sometimes). > > The efficiency gain is small however - and the more > important factor will be to pick a ratio that > maintains an appropriate cadence - but if you have two > chainring/cog combinations to choose for the required > ratio (as there is an overlap of ratios between the > two/three chainrings), then choose the larger ring. >
The larger ring / larger cog combination operates with less tension in the chain compared to the smaller ring / smaller cog combination - due to leverage as described above. With less tension in the chain there's probably less frictional losses, although whether they are proportionately less would be difficult to say. There is another factor to consider, particularly with the wider freewheels common today - the chain alignment. When the chain is distorted laterally there are significant frictional losses - it is not designed to be flexed in this way. So all other things being equal it is the combination with the straightest chain line that will be the most efficient. With respect to the jockey wheels, you have it the wrong way around. One revolution of the big chainring will pull _more_ chain through the jockey wheels, so they will rotate faster. But I don't think that this is a significant factor. -- Peter James Ottawa, Ontario ------ To unsubscribe, send a blank message to [EMAIL PROTECTED] Club Office: [EMAIL PROTECTED], (613) 230-1064 Web/mailing list: [EMAIL PROTECTED] http://www.cyberus.ca/~obcweb Newsletter: [EMAIL PROTECTED] http://www.cyberus.ca/~obcweb/Newsletter ==^================================================================ EASY UNSUBSCRIBE click here: http://topica.com/u/?aVxiDo.a2i8p1 Or send an email To: [EMAIL PROTECTED] This email was sent to: [email protected] T O P I C A -- Register now to manage your mail! http://www.topica.com/partner/tag02/register ==^================================================================
