Johan Bornman Posted August 31, 2007 Posted August 31, 2007 xak1' date=' I tend to agree with the constant speed theory, but my assertion is that we as cyclists NEVER travel at constant speeds. We are always accelerating or decelerating on a micro level due to pedaling inefficiency, wind changes, bunch surges etc. That is why I believe it has less of an effect on ime trial bikes and riders and more on crits for instance. I also think more energy is required to accelerate a heavy wheel as opposed to a light one (apart from the obvious linear movement of the weight), even if this is quite a small force, but the weight must make a difference.[/quote'] I agree that we accellerate. What I don't agree on is that we accellerate enough for the wheel component of the accellerated body to make a significant difference. It is very, very easy to accellerate a bicycle wheel to 100kph when the bike is on a stable bike stand and you're rotating it by hand. Try it. The resistance you feel there is only partially the wheel's rotational mass, the rest of is arm, pedals and crank and chain. From some crude timing I can do so in less than 3 seconds. Accellerating a bike and rider from 0-30kph is a different story altogether. Try that and see how much effort is involved from far larger muscle groups. That's the sort of difference I'd like people to think about when they talk about the "twice as important" fallacy read in......ok lets not go there.
bruce Posted August 31, 2007 Posted August 31, 2007 xak1' date=' I tend to agree with the constant speed theory, but my assertion is that we as cyclists NEVER travel at constant speeds. We are always accelerating or decelerating on a micro level due to pedaling inefficiency, wind changes, bunch surges etc. That is why I believe it has less of an effect on ime trial bikes and riders and more on crits for instance. I also think more energy is required to accelerate a heavy wheel as opposed to a light one (apart from the obvious linear movement of the weight), even if this is quite a small force, but the weight must make a difference.[/quote'] A heavier wheel will take more energy to change it's speed from 'a' to 'b' than a lighter wheel, BUT this greater energy requirement is due to the fact that the heavier wheel will store more potential energy (momentum). So yes, you may require more energy to change a heavier wheels velocity (i.e. accelerate that wheel) but that heavier wheel will discharge more energy when it slows down. So, the heavier wheel gives back that energy to the rider. Unfortunately, in racing situations, the rider often does not benefit from this because he uses brakes to slow down, or coasts down. So I would agree, a heavier wheel is less responsive - the question is how much less. Assuming a light set of wheels is 1.3kg's, and a heavy set of wheels is 2kg's we are talking about a 700g difference. Assuming the rider + bike weighs 75kg's - we are looking at a 0.9% difference. In a race where the 100m sprint is won by 2cm's, we are talking about a 0.02% margin - so yes, I guess this is why top pro's look at these minute details. Not so sure that this applies to us lot paddling in the shallow end down here on the tip of Africa.
NotSoBigBen Posted August 31, 2007 Posted August 31, 2007 Sure I'll get flamed and insulted and and and ........ but here's my take :- Get over it guys, for most of us back to near front guys a 100g's here or there actually makes no difference (Did you go to the toilet before the race?). Take a corner as tight as possible? Only brake when it's absolutely necessary so as to avoid 'losing' time or needing extra effort to get back to speed etc. etc? I'm not saying ride a brick but a reasonably light bike is fine for most of us! For those that have no more body weight to lose (not me that's for sure!) and are missing out on winning races by seconds, hey it may and probably will make a difference! When it comes to cost it seems to me that there is a point at which it is extremely expensive to lose more weight (on the bike that is!) and you may be better off to only wear 1 sock if it's that critical (OK maybe 2 so you don't look stupid!). Or have I missed the point completely? Wasn't there a recent post that said something to the effect that pro cyclists aren't that smart so all this 'high' fallutin talk isn't helping them that's for sure!
gianni Posted August 31, 2007 Posted August 31, 2007 BiBen Yup agree fully (except for the not so smart comment. Don't quite agree there). It's human nature to look for the shortcuts rather than do the hard work. People would rather pay $1000 to loose 100g on the bike than do and extra bit fo training. That's why the guys that win DO win. THEY do the extra bit fo work.
NotSoBigBen Posted August 31, 2007 Posted August 31, 2007 Cool gianni, the smart part was just sarcastic after the previous comments made in another thread not a generalisation Should anyone have felt insulted or aggrieved by my comment please accept my most deepest humblest apologies! 2 true stories both overheard in a bike shop :- 1) 2 cyclists (neither racing snakes BTW) discussing whether to buy a C/F bottle cage How much less does it weigh than the one you got now? About 60g's why? Save the 300ZAR and rather wear just one sock! (hence the sock comment!) 2) In a famous but no longer around's bike shop Guy (largish) busy looking at the Bridgestone RB1 and RB2 (showing my age?) Bike store owner goes to answer a phone call Another customer says "what's up bud can't decide?" Buyer "this one's 1000ZAR more expensive but 1Kg lighter" Other customer "If I were you I would buy the cheaper one, lose 1 kilo of weight and put the 1000ZAR in my pocket"
Willehond Posted August 31, 2007 Posted August 31, 2007 I think I managed to convince myself (with the help of JB and others) that all weight is equal, but that rotational weight is more equal when accelerating!!! Or rather; there is a small rotational acceleration element that does require extra effort, but that this effort could well be near negligible and that the 'double the weight saving' claim is dubious. I think....
Spinnekop Posted August 31, 2007 Posted August 31, 2007 I think I managed to convince myself (with the help of JB and others) that all weight is equal' date=' but that rotational weight is more equal when accelerating!!! Or rather; there is a small rotational acceleration element that does require extra effort, but that this effort could well be near negligible and that the 'double the weight saving' claim is dubious. I think....[/quote'] Through 7 pages of mud slinging and digits rape, this is basicly what it seems like, yes....
NotSoBigBen Posted August 31, 2007 Posted August 31, 2007 http://www.33smiley.com/smiley2/communicate/everyday/10.gif
scotty Posted August 31, 2007 Posted August 31, 2007 http://www.33smiley.com/smiley2/communicate/everyday/10.gif Very good comment
Christie Posted August 31, 2007 Posted August 31, 2007 Holy ! Lots of action here since I last had a look.Some comment (sorry - I am a bit behind in the debate): 1. I dont believe in the "micro acceleration every pedalsrtoke" thing2. I dont like Burke's stuff. 3. Bike magazines / books contain nonsense, sometimes. Just because it is written down does not make it true.4. An American/European/who ever would know better than a South African - NOT. There are clever & stupid people of every nationality.5. Few people want to understand the math behind something. It is easier to believe the general truth/misconception.6. Even writing out the full equation of the forces acting on a bicycle & solving them for different cases will not convince everybody.
bruce Posted August 31, 2007 Posted August 31, 2007 Eurika!! I have the answer to the question as to why you should ride a 6.8km carbon bike with a top end groupset and deep section carbon wheels!!I have solved the complete equation describing the motion of a bicycle and I now know why!! Because it is damn nice to ride a nice bike!!
Willehond Posted August 31, 2007 Posted August 31, 2007 Eurika!! I have the answer to the question as to why you should ride a 6.8km carbon bike with a top end groupset and deep section carbon wheels!!I have solved the complete equation describing the motion of a bicycle and I now know why!! Because it is damn nice to ride a nice bike!! FANTASTIC, so we don't need fancy power meters after all!!!!
Sean Posted August 31, 2007 Posted August 31, 2007 Eurika!! I have the answer to the question as to why you should ride a 6.8km carbon bike with a top end groupset and deep section carbon wheels!!I have solved the complete equation describing the motion of a bicycle and I now know why!! Because it is damn nice to ride a nice bike!! By Jove I think you have it! BTW, thats exactly the reason I drive a BMW! (oops, is this gonna start a whole new row? )
Spinnekop Posted August 31, 2007 Posted August 31, 2007 By Jove I think you have it! BTW' date=' thats exactly the reason I drive a BMW! (oops, is this gonna start a whole new row? )[/quote'] You drive a WHAT??? http://www.advrider.com/forums/images/smilies/2ar15smilie.gif
Sean Posted August 31, 2007 Posted August 31, 2007 here we go! Before I doscovered the Hub I used to be bored on Friday afternoons.
bruce Posted August 31, 2007 Posted August 31, 2007 Eurika!! I have the answer to the question as to why you should ride a 6.8km carbon bike with a top end groupset and deep section carbon wheels!!I have solved the complete equation describing the motion of a bicycle and I now know why!! Because it is damn nice to ride a nice bike!! By Jove I think you have it! BTW' date=' thats exactly the reason I drive a BMW! (oops, is this gonna start a whole new row? )[/quote'] The assumption in this case being that a BMW is a nice car
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