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So you think your fancy new wheels are fast.


ChrisH
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This podcast has figures from a real world test published in the Journal of Sports Medicine. It is fascinating stuff when you are on an indoor trainer with nowhere to go.

 

The Podcast mp3 is 32 meg so you may need ADSL or better to download.

 

I have cut and pasted the relevant part of the transcript below for the paupers and Ludites.

 

A great study published in the Journal of Sports Medicine calculated the performance times of a light less-aerodynamic wheel and heavier aerodynamic wheel over different grades of ascent, and also comparing different levels of cycling experience. The study divided cyclists into 3 groups: novice, trained and elite. The novice had a VO2max of 48, the trained group had a VO2 of 66, and the elite had a VO2 of 80. Now, if you have a VO2max of 80, you shouldn't be listening to this show. A VO2max of 80 is extremely high, and you should be out dominating any number of endurance events. For our purposes, for us mortals, I'll be mainly looking at the novice and trained group, with a more common set of VO2 measurements. A reminder that VO2max is the scientific standard to measure cardiovascular fitness.

This study took those 3 cyclists groups, and calculated performance times using a wheelset 500 grams lighter than an aerodynamic wheelset. But they also took those sets and calculated the performance of those cyclists and wheels over different difficulties of ascent, calculated at 3%, 6%, and 12% grades of ascent. Now, a quick review what a grade of ascent or descent is. A 6% grade is not a 6% angle. A 6% grade means that for every 100 feet of travel, there is 6 feet ascent or descent. A 6% grade is therefore actually only a 3.4 degree angle, or the inverse tangent of 6/100. So when we talk about a grade of 6%, think of an ascent of 60 feet over 1000 feet traveled. By the way, that does not sound too bad, but that is pretty darn steep. That's over 300 hundred feet of ascent in only 1 mile of travel. In this study all ascents were over 20K, or about 12 miles.

OK, so here are the results. At a 3% grade, you would be slower across the board with the lighter wheel over 20K. Astonishingly, the faster you are, the worse off you would be from choosing a light wheelset over an aero wheel over that 20K 3% grade. The novice cyclist would be 10 seconds slower, while the trained and elite cyclists would be a full 20 and 21 seconds slower over that 20K by choosing weight over aerodynamics. That's because the trained and elite cyclists would still be able to produce enough speed at that grade to introduce enough drag for aerodynamics to still be a factor. OK, let's get steeper. What about the 6% grade. At 6%, the wheel weight starts to be a factor. The novice and trained cyclist would be faster by 25 and 3 seconds, respectively, but the elite cyclist would still be going fast enough at that grade that they would be at a disadvantage to give up aerodynamics, and would still lose 6 seconds. OK, what about a 12% grade? At that point, yes, all 3 cyclist groups would benefit from the light wheel, as much as 1:12 for the novice, and 35 and 22 seconds for the trained and elite cyclists.

Now, let's put that in perspective for triathlon. Based on this study, for a trained cyclist, which is where most of us will fall, it is clear that the cut-off for choosing a lighter wheel over an aero wheel is a 6% grade lasting at least 20K, or 12 miles. I am unaware of any event in North America that has any kind of ascent even close to that. 6% does not sound like much, but let me give you some data. The steepest ascent of the Tour de France, known for its brutal hills, is only 10%. That's the steepest part. Ironman North America gives the bike ascent profiles for its races, and I could not find any race that had more than a 3% grade for even 10 miles of the race. That's because triathlon race directors, the guys who pick the course, don't really want to have you grinding it out in the hills too much. They do a good job of choosing relatively flat courses. Those of us who have done difficult bike courses like Ironman Canada and Ironman USA think those are steep courses. No offence, but that it nothing. Nothing! Yes, there are portions of those races that have you going up 1500 feet over just 10 miles, and that is nothing to sneeze at, but that is still only a 2.9% grade over those 10 miles, nowhere near the 6% cut-off to choose weight over aerodynamics. Yes, there are portions of the race that exceed a 6% grade, but only for less than a mile. OK, David, you say, what about a total of 12 miles of ascent at a 6% grade over the entire 112 mile course? Not all 12 miles in one pop, but is there a race with a total of 12 miles of ascent at 6%? Yes, that is more likely in some of the steeper races, but 6% is a huge ascent. In looking at that bike course profiles, I just don't even see Ironman Canada or USA having even more than a miles at that ascent, and certainly, I don't think you'll ever find that much grade in events at the sprint, Olympic, or half-Ironman distances either.

I know that you weight weenies are probably having a fit right now. You have worked hard and spent $8,000 getting your total bike weight down to 13 pounds. Let's say just for the heck of it that there is a race that has a total of 12 miles of ascent at 6% grade. Guess what, you are going to save 3 seconds over those 12 miles. And here is the kicker: this study only did the results of 12 miles uphill and finishing. In almost any other triathlon, you are going to have an equal amount of decent. Any race that uses a loop will have equal ascent and descent, and even if you save 3 seconds by choosing the light wheel, you still have to go back down those 12 miles, which will probably then be at 30 miles per hour with that 6% grade, and then you are losing in aerodynamics the whole way down. That was not included in this report.

So in summary, the only time you would want to save 500 grams for a less-aero wheelset, is if you are doing an event that has 12 miles of 6% grade ascent, that ends at a higher elevation than you started. And if you are doing that, you are what I would call a pro-circuit cyclist.

Now, I have somewhat oversimplified this. There are wheelsets that can have both. That is one reason why Zipp 404s are so popular. The multi-spoke design gives low weight, and the deep, flared rim gives the aerodynamics. It has a great mix of both features. Norman Stadler won the Ironman Championships last year on Zipps, and Ferris Al-Saltan won the year prior on a 4 spoke. Both were great choices. I think the winds at Kona were the main reason for Norman to choose the Zipps over a higher surface aera 3 or 4 spoke, since 3 to 4 spoke wheels do not handle cross-winds as well. Also, lighter cyclists would do better on a multi-spoke aero, like Zipps for the same reason: the cross winds might push them too much with the 3 or 4 spoke wheel. But for your average heavier, male cyclist in low-wind conditions, I think that this study clearly demonstrated the superior advantages of the wheels built specifically for aerodynamics over weight.

A couple more items on weight, where I will strongly agree with the weight weenies. Let's talk about frame weight and rider weight, and how this effects performance from this same study. Which would you say was more important? Bike weight or rider weight? Let me pause while you commit to your answer, and then let's see if you are right. If you were to take a typical bike, the total weight for an average tri bike is about 10kg, or 22 pounds. That's wheels, cranks, aerobars, cassette, chain, race day ready. What if you could shave off another 3KG and get it down to 15 pounds total weight. Carbon frame, carbon cranks, titanium cassette, hollow spindle cranks, hollowed out chain links, 1000 gram wheelsets, the works! Could get it down even less than 15 pounds if you invested the time and money. Over a 40K time trial, or Olympic distance triathlon, those 3kg for the novice cyclist would save 13 seconds, the trained cyclist 7, and the elite 5 seconds. 7 seconds is pretty awesome, but would you pay an extra $5,000 to get all that stuff for 7 seconds? That's about 30 seconds over an Ironman, which at that point, may be worth it.

Now, what about the rider weight. Those same classes of riders, if they lost 3kg in weight would save 25 seconds, 21 seconds, and 19 seconds for the novice, trained, and elite cyclists, respectively. A significant difference compared to the bike weight, a saving of 3 times more for losing rider weight for the trained cyclist! This is because as you lose weight, you lose surface area, and therefore drag. Whereas, in general, losing weight on the bike frame does not change the shape or aerodynamics of the bike. Also, what this study did not include, is the physiological benefits of losing 3kg on performance. We know that each pound of weight lost on the run will equal 2 seconds per mile, because not only the reduced energy requirements, but oxygen does need to be delivered to as much of the body, and your VO2max automatically rises as a result of losing weight. I don't know of any study that confirms the performance gains in cyclist weight. Although it would not be as much as running, I'm sure there is a noteable gain in physiological performance from reduce cyclist weight in addition to the physics of rider surface area.

So, if you have choice of spending an extra $5,000 on a lighter bike, or losing a few pounds, healthy body-composition weight loss is certainly less expensive and more effective. This is why a carbon fiber frame did not make the Tri Talk Top 20. It just didn't have the bang for the buck. However, there are other important non-weight related reasons to look at carbon fiber as the primary compound of your bike. Carbon fiber has significant vibration dampening benefits that can reduce muscle fatigue for the run, but we'll talk about carbon fiber another day. So, if you can afford to the nice bike and to lose weight, by all means do both.

What's ironic about this topic is that it took me 5 hours to research and write it, and 15 minutes to say it

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What's ironic about this topic is that it took me 5 hours to research and write it' date='

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And it took me 5 secs to scan and determine that its way to much info/reading for a friday.LOL
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Take the time, its a pretty good read. Even though I'm a mountain biker, all this talk of aerodynamics has convinced me I should wash off the 2 kgs of dirt lurking on my bike, it might be giving me drag issues!

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Isn't there a shorter summary?

 

Aerodynamics is more important than weight. Although light aero wheels are obviously first choice. If you've only got a choice between a very aero wheel or a wheel thats 500gr cheaper than your current set, go for the aero wheel
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no fair, this is a con. i'm from the east rand. i was expecting an article on the spinners and chopped suspensionWink

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Whoa You are going to upset sunblock writing such long articles this is his territory you messing with

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"And we know that in ALL things' date=' God works for the GOOD of those who love Him!! (Romans 8:28)

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You're misquoting the bible... you forgot the "and are called according to his purposes". A lot of people like to use that verse to say "Why isnt God doing things for me", forgetting that they are not following His will...

 

Just because I argue against christianity, doesnt mean I dont know what I'm talking about Wink

 

Suppose this would be considered a hijack?
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