We always say that the MAX recommendation is for roadies over 200 and triathletes over 220 lbs. The only differences are that the MAX version uses a Pave laminate rim for improved impact protection since larger guys will compress a similar sized tire more in an edge impact, pothole, crash, etc. The other difference is a few extra spokes for increased lateral stiffness, which is the real thing that big guys notice while actually riding the wheels.

We worked with Guy East and the guys at Team MAX on figuring out what bigger guys wanted (their headquarters are 10 minutes from us) and basically the standard wheels worked fine for them, but for out of the saddle climbing, criterium racing and sprinting, they wanted more lateral stiffness. The penalty is roughly 100 grams per wheelset, but will result in more precise handling and a bit of impact insurance.

The lateral stiffness issue really seems to also depend on the smoothness of the rider, we see some 180lb guys who require higher lateral stiffness just because they are all over their bikes while climbing or sprinting, just as we see some 225+ lb guys who are so smooth that they don't even notice the increased stiffness of the wheel, but those nuances are so rider specific it is really difficult to say without really knowing how somebody rides.

Currently there’s a lot of discussion on 3 and 4 spoke handling being due to the way the spokes become shielded behind the fork legs in a side wind, effectively changing the surface area of the wheel depending on rotational position. The wheel is turning at a fairly high rate, so this isn't directly affecting handling, but does set up a harmonic within the system such that certain wind conditions can cause handling issues. However, I think the bigger issue is that these wheels just have a lot of surface area which leads to higher side force values for a given wind condition.

I don't have anything posted yet on the harmonic issue, but we do have info on the surface area/crosswind issues on the tech sction of our website:

at the very bottom you will see a graph of side force on the wheel during wind tunnel testing. The 808 has roughly 30-35% less side force than a 3 spoke and the 404 has less than half the side force for the same wind condition.

Rim shape has a big effect here, and the large sidewall curvatures that we use in our rims not only make them more aero but also reduce side force compared to V or U shaped rims as the airflow tends to flow around the rim instead of impinging it.

From a purely technical perspective the breakdown goes like this:

The 808 will be about 16-18 seconds faster than the 606 and the 606 will be about 12-14 seconds faster than the 404 in a 40k (the front wheel has slightly greater impact than the rear).

The 808 is essentially dead equal to a 909 in a 40k as the front 808 is faster than the front 909 by the same margin that the rear 808 is slower than the disc. So from that perspective the 808 is slightly lighter and cheaper than a 909 while being just as fast – and it’s Kona and UCI legal, so that makes it a great deal. The downside is that the front 808 exhibits ~30% higher side force in a crosswind than the 909 front (the 808 still has ~32% less side force than a 3 spoke).

The other considerations are comfort and steering torque. The 808 is the most comfortable wheel we've ever made due to high sidewall curvature and laminate design, whereas a 404 transmits about 11% less vibration to the hub than a box section aluminum rim, the 808 transmits about 7% less vibration than a 404. Surprisingly, this is the thing noticed most by customers after they notice the aero advantage of the wheel. I think with the 404 that most people write the comfort off as being related to tubular tires, or have themselves convinced that all deep rims ride harshly, but the 808 seems to have crossed that line, and most everybody I've talked to who has ridden them mentions the comfort (which is about time as we've spent untold money and 4 years on our VCLC damping technology to get the wheels to this point).

Lastly, some people will benefit from having a larger surface area wheel in the rear due to improved steering torque component. If you are smaller or nervous on the bike, you may be better off with a 606 as the aerodynamic pressure bias is rearward, whereas larger or more experienced bike handlers will be fine with the 808. Likewise, adding a disc to the 808 front (same as the 999 wheelset) will have the same effect allowing smaller riders to more comfortably utilize the faster 808 front wheels.

The weight really is not an issue so I won't discuss it, you see less than 100 grams increase from 404 to 606 and another 100 grams from 606 to 808, and for triathlon usage, that is significantly less important that the aero performance so don't let those numbers affect your decision.

I hope this helps with your decision, and doesn't just further confuse the issue.

For a few graphs on wheel aerodynamics check out our engineering white paper on rim shape.

The weight/aero debate will forever rage, but my personal feeling is that for most people aero will almost always triumph. The 202 is an incredible hillclimb TT or road racing in the Alps wheelset, but is designed for road racing, and not Tri. The reason is that a roadies need the weight and inertia advantage to make very high wattage intense efforts at key points in a race. Looking at a most any Tour stage in the Alps, the 202 is disadvantaged to a 404 for more than 80% of the course, but will be advantageous in making or following an attack at a key point of a climb.

In actuality, the 404 aero advantage offsets its weight over a 202 up to about 7-8% grade depending on rider output. So even in the hilliest of courses, the 202 at best will only be advantageous in very specific terrains. Having said that, however, in road racing, that attack coming out of a hairpin turn onto a 12% section of the climb can be critical, and just 1-2 watts of efficiency gain suddenly becomes a few seconds in a hundred or so meters. This can be pivotal tactically in this type of event. In triathlon, the power requirements are much more stable throughout an event, and will almost always favor the more aero wheel. A rider may lose a few seconds over a very steep pitch, but likely has gained many seconds up to that point and will continue to gain many more seconds after that point. When we run the computer models of the Alpe stages, the 404 always overcomes the lighter wheelsets, generally by a few minutes or so, and thus we have always recommended the 404 depth wheels, but after working with CSC last year, and looking at the power requirements on various stages, we have begun to understand exactly what these guys need, and realize that our computer models more accurately represent a TT over the stage, but do not account for tactics, attacks, or other factors. In all, the difference between a 202 and 404 at 30mph on flat land is between 10-14 watts depending on wind angle, and the advantage of a 202 to a 404 at 8% grade at 15mph is roughly 1-2 watts (the two are equal at about 7% according to computer modeling).

As for rim design, our patents on rim shape help to insure that our rims behave as if they are much deeper than they are, so many comparisons are hard to make to other rims. The 202 is in fact similar aerodynamically to the old 340 rim shape, which was that of a 'V' and the new 303 is comparable to the original 440 rim which was a 'V' shape. Compared to 'V' shaped designs, the 38mm 303 behaves similar to a 'V' shaped 55-58mm rim, and the 404 behaves similarly to a 75-80mm deep 'V' shaped rim.

The real beauty of the Zipp rim shape is that the rims maintain their aero advantage when used with tires wider than the rim (but less than 105% of the width of the bulge), which is the real difficulty with 'V' shaped rims. This allows you to have solid aerodynamics with a 21 or 22 mm tire, whereas you are losing 10-15% efficiency with one of these tires on a 19 or 20mm 'V' shaped rim. This was the real discovery, and in my opinion is the real meat behind the Zipp rim shape patent, especially for roadies who prefer the better grip of a wider tire, and ironman distance triathletes who can use the additional comfort of a slightly wider tire.

There’s one onther thing to consider in all of this: hubs. There is a tendency for people to think that the Zipp hub is not the most advanced hub on the market because they come in prebuilt wheels. But we have spent the last 4 years designing and perfecting our hubs, here are a few facts that people tend to overlook:

Zipp makes all hubs completely in house, each designed specifically for the rims they are used with. So a 404 hub has spoke angles precisely for that rim, etc, and on a straight pull hub this is very important. Every Zipp hub is made entirely in the USA in our Speedway, Indiana facility. The Zipp hub uses 4 proprietary grades and heat treatments of 7000 series aluminum, all drawn specifically for our hubsets by Alcoa in Lafayette, Indiana, each type of aluminum and heat treat is specific to a particular part or function of the hub. Zipp hubs are manufactured on dual spindled lathes with live tooling, meaning that most every part can be made in one operation, removing tolerance stackup that occurs when parts have to be removed and fixtured in multiple steps. Because of this the bearings bores are more than twice as concentric and planar as with other manufacturing technique.

All Zipp hub internals are turned on Swiss watch lathes, these machines were originally designed for manufacturing precision timekeeping components, and are generally only used to make precision aircraft fittings, bone screws and orthopedic inserts for joint replacement. The incredibly high accuracy of these manufacruring techniques allows us to use much higher grade ball bearings and races, and results in hubs that spin with lower friction and increased bearing life, while weighing less than other designs. Zipp is the only company in the industry using Swiss made ball bearings, and the only company to use grade 10 balls, which are more than twice as round and 4 times as expensive as grade 25 balls which are the highest precision balls used in the bicycle industry otherwise. There are numerous other very nice hubs on the market, but we feel that we have the finest designed and manufactured hubsets on the planet.

Whichever rim, hub, or manufacturer you go with, my suggestion would be to prioritize aero over weight. If you do go with a 'V' shaped rim, you will need a tire either equal in width or slightly narrower than the rim, in order for the rim to behave to it's potential from an aerodynamic perspective, and if you go with the Zipp products, we recommend 21mm or smaller tires for the 202 and 303 wheelsets, and up to 22.5mm tires on the 404 wheelsets. For more information on wheel aerodynamics see our engineering white paper on rim shape.

Just looking at an Excel Sports catalog which publishes actual weights of all products in the catalog, and they are showing Ksyrium ES at 1510 grams for the pair and 404 clincher at 1570 grams for the pair, so I would say weight is very similar. Look at the Tour magazine aero test on the Zipp website homepage and you see that in their wind tunnel testing the fastest wheel was the 808 at 68 seconds per 40k faster than Ksyrium and the 2nd and 3rd place wheels use proprietary versions of our undimpled 404 rim shape and are 62 and 50 seconds faster per 40k respectively.

But of course we are not at all competitive on price.

Personally I would go for the 606 setup, it gives up only about 10-12 seconds per 40k to a 909 (404 front with disc) setup but is light and legal for sprint, Olympic distance and Kona, as well as all mass start road events if you ever have a need.

Some of the answers to this question are posted in the new tech section on our website. Particularly questions regarding rim shape and aerodynamics can be found in the white paper entitled "A note on rim width"

As a roadie, I'm loving the 606 right now, I've been on prototypes for about 6 months, and won't give up that 81mm deep rear, technically the 606 gives up only 10-12 seconds per 40k to a 909 wheelset (assuming 8mph crosswind), but is UCI and Kona legal, and makes a killer road racing wheel with its 1340gm weight. The main bonus is handling to complement the speed, one of the benefits of the new shapes and dimples are the reduced side forces on the 2005 rims, the new 404 shape makes less than half the side force of a 3 spoke while being 2-4 seconds faster per 40k, while the 808 rim makes less than 2/3 the side force of a 3 spoke, while being 14-16 seconds faster per 40k than the 3 spoke.

For all out Kona legal performance the 808 is the way to go with computer modelling showing 18-20 seconds per 40k faster than any other wheelset, and for everything else, the 999 will be 8-10 seconds faster per 40k than a new 909 and 14-16 seconds faster than a disc/3 spoke setup but with added cross-wind stability (a reduction of about 2 lbs on the front wheel).

Check out those white papers, we've really opened the books up on our R&D testing programs and tried to answer some common questions such as effect of spoke count (pdf), spoke shape (pdf) and rim shape (pdf).

ABLC (Aerodynamic Boundry Layer)

There is no issue in crossing over into road with any of these three wheelsets, other than the slight weight penalties, which for anything other than a hillclimb TT or racing in the mtns is a non-issue for most athletes (it’s about 100 grams between the 404 and 606 and the 606 and 808).

The only other issue I could think of is what Jens Voigt told me at training campt this year about 'showing your hand'. His only worry was that if he shows up for stage 2 of the tour on his R2.5 with 404's and then shows up for stage 3 on a Soloist with 808's that his intentions will be all too clear and he'll have 'shown his hand'.

This is the one aspect of road that you just don't have in Tri, but at any level other than the protour I think that signaling your intentions to kick everybody's a$$ is no big deal. Personally, I put 808's on my bike 7 months ago and flat refuse to take them off. I was then on a 606 for about 2 weeks when I lent the front 808 wheel to a friend, but other than that it's been 808's all the way.

The clincher shape is totally different than the tuby shape and is optimised for clincher tires up to 23mm wide, so your Michelin's will be perfect. As for the handling effect, there will be little noticeable difference between 808 and 404 front wheel if you are using a disc, so I wouldn't worry about it. As far as drag and force in a crosswind, check out this technical white paper, you can see how the 808 performs relative to the 404 and see that it is superior to all but a disc in a moderate crosswind:

Rim Shape

The thing to remember here when comparing aerodynamics is what wind angles are you measuring the wheels at? From our historical testing as well as the testing done independently by Tour magazine and Hed's own data, modern toroidally shaped wheels like the Zipp 808 and the new Hed Stinger 90 best the H3 at wind angles less than about 20-22 degrees.

Our own design process with the 808 had a primary focused on finding speed between 10 and 20º of yaw (theoretically 60+ percent of all conditions) and secondary emphasis on 0-10º degrees (to cover a total of 80+% of all real-world riding conditions – the Aerodynamic “sweet spot” if you will), and with about 18 months of design time and 60+ hours of wind tunnel time we developed the current 404 and 808 rim shapes which are faster than the H3 from 0-~22º of yaw. Additionally, the new Hed Stinger 90 uses a slightly different shape and deeper rim and is more aero than the H3 below 15 degrees of yaw according to both Hed's own data and data we have taken on this wheel at Allied Aerospace.

The issue for us is that to achieve 22+ degree wind angles, you need considerably high wind speeds to the point that many if not most people will choose not to ride the wheel for handling considerations. This was one of the major factors in our decision to stop producing 3 spoke wheels some 14 years ago now. Statistically, the 22+ degrees of yaw condition occurs less than 25% of the time, so I really would see a wheel like the H3 or Zipp 3000 3 spoke occupying a place in the wheel arsenal as being a windy day only wheel for those who are comfortable riding it in those conditions.

For the other 75-80% of the time you will be faster on a toroidally shaped very deep section wheel (the patent co-owned by Zipp and Hed) or even a hybrid-toroidal shaped deep rim (the zipp specific patent) which will be aerodynamically faster as well as have considerably less side-force and steering torque due to decreased surface area.

As a side note to my whole rant about the Stinger 90 and 808, I am yet to test the Blackwell 100 rim, but it is interesting in that John has put some waves in the sidewall to try and control the airflow without infringing our patents for rim shape, I'm not sure if this will have the effect of recapturing the air that is described in the patent but is an interesting concept and we will be taking one to Allied in a few months with some other R&D wheels we are experimenting with.

The H3/Specialized/DuPont wheel is extremely fast, and for the longest time has been the gold standard in aero front wheels, but the last 4 or 5 years have really seen an explosion of technology in rim shapes, spokes, manufacturing techniques, etc. that allow us to produce wheels that are now faster at moderate yaw angles. Past about 22 degrees of yaw, the only thing competitive with the H3 is a disc, which is considerably faster, but you definitely won't be riding the disc as a front wheel at that wind angle! The key to this low drag is that at high yaw angles the drag is purely a function of surface area, something that a 3 or 4 spoke wheel has in spades over a deep or very deep section wheel.

Jens has been riding the 606's a lot. That was the wheelset he rode in LBL last year where he got beat out by Vino in the sprint. Riding aero wheels day in and day out, in stage races is something that we’ve been pushing within CSC since 2003, making them the first team to have every rider on carbon aero wheels every day. The biggest obstacle is the riders, they seem to have heard and believe all the rumors about the wheels being uncomfortable or difficult to ride in crosswinds, etc., but we worked with Riis, and their SRM data to show the riders individually how much power they save riding a 404 compared to a 202 or the like, and in the past two years, almost all the CSC and Phonak guys are choosing 404's and occasionally 606's.

The thing to remember about road racing and the tactics involved is that it is often not about just TT'ing off the front. In Jens breakaway yesterday, those guys are not going 100% to make that thing work, they are really trying to walk the thin line between getting enough of a gap, but not too much of a gap to freak out the peloton. But the sprinter's teams are all close enough to the yellow jersey that they aren't letting anybody go. The beauty of using those wheels and looking at the power data is that for Jens, the results would have been the same had he chosen say a 202 wheelset yesterday, but by end of stage he would have expended an additional ~600-700 calories, and that sort of savings day in and day out is the real benefit as it reduces the amount that they have to eat and aids in recovery. If you can save a few hundred calories per day, the aggregate benefit by end of the Tour can be huge, and SRM studies show that riders will save 300-500 calories per day just sitting in the peloton by using aero wheels

You can read about the relative advantages of the different wheels on our tech pages of the site.

On the wind tunnel graphs 0.1lbs of drag is the equivalent of 6 watts, so it really depends on what wheels you are comparing. Also we have a link to Tour Magazine's wind tunnel test which extrapolates time savings of various aero wheels. They predict the time savings of 808's over Ksyriums for 40k as being 68 seconds, wheels using the previous generation 404 rims came in at 62 and 50 seconds faster. These assume a rider outputting 300 watts, the time savings will increase slightly with lower wattage.

The fastest wheel for a 70.3 (half ironmans) will be the fastest wheel you are comfortable riding, the 808 is considered the fastest non-disc wheel on the market right now, but is a little deep for some people (although it does have 30% less side force than a 3 spoke and about 15% less side force than 100mm rim in a cross-wind), hence the 606 which is a 404 front with 808 rear really seems to be the setup for IM/HIM distance (winning 5 categories at Kona), for larger riders the full 808 is generally no problem (I weigh 155 and ride 808's on my road bike daily) and for smaller riders the 404 or 343 (303 front/404 rear) are very good options, but it is my experience is that the 343 is only really beneficial for riders under 120 lbs or who are VERY concerned about bike handling.

Adding a disc rear will also speed things up a bit, but the margins are small, the disc is about 4-6 seconds per 40k faster than the 808, so for some people that is more than worth it.

On the hub issue I would put ours against anybody's in the world. Mavic hubs are nice, but the Zipp hubs are considerably lighter and roll smoother with as much as 1 watt less friction due to our use of grade10/ABEC5 swiss bearings, so I'm not sure how Mavic's hubs are better other than that they are more affordable.

As for durability, the cosmic Carbones are durable because they are just an aluminum rim with carbon fairing (this also really hurts aerodynamics as the spokes enter the side of the carbon rim body making the wheel appear to be only about 2/3 as deep as it actually is to the wind.) whereas the Zipp is an actual structural carbon rim with welded aluminum hoop, and if durability is in question you only need to look to the 29er mtn bike scene where 404 rimmed wheels are all too common (don't do this as we won't warranty them if anything happens...) but guys like Mike Curiak have been setting all sorts of endurance records and winning mtn bike races on wheels built on these rims, plus the 404 holds the current record for fatigue testing on the impact drum tester at DT in Switzerland, but again we cannot compete on price as we are selling a structural carbon rim made entirely in the US with US materials, the most expensive spoke in the world, the Sapim CX-Ray, and the most expensive bearings in the industry, which are actually of higher grade and higher cost than almost anyone else's ceramic bearing upgrade – just the 6 bearing cartridges are actually more expensive than most Asian made hubsets! So again we are not competitive in the pure cost category but I think that the value represented is extremely high. And if you quit triathlon tomorrow we have the highest resale value of anybody out there according to the eBay stats. But then again that's just my opinion and I'm a bit biased!!!

Please check out tech info on our website, all of this and more is up there, and we’ve reposted the Tour magazine aero tests this week so you can see that our aero data matches identically to the Tour data, so we aren't just making all of this up.

There are a couple of factors at work with pro team selection, and I've been involved with all of them so here's my take.

One, companies like Xentis and Lightweight have people cruising the paddock during events like this offering wheels to pros. I've seen them and talked to them, and if our company were based in Europe, I'd be doing this to as it is an excellent way to get somebody on the product at the last minute and really create a buzz.

Second, one assumes that these teams and mechanics are very technically proficient and up to date on equipment, but in reality, many pro riders know less than your average Slowtwitcher about the aerodynamics of wheels. I am always amazed when I do tech presentations for the teams or wind tunnel testing with them that most of the riders will not even know what wheels their competitors are on, so I might have an aero graph comparing the 404 to a Bora and I'll generally have to say 'ok, the Bora is the wheel ridden by these teams' before they really get it. In general, I'd say 90% of these guys could care less about equipment and most of them never read cycling magazines or websites.

I was shocked last year to be talking to Jens Voigt about the Tour Magazine wind tunnel test (the largest road cycling mag in Germany) in which the 808 won the test (and Jens is quoted talking about how fast these wheels are in a crosswind) to find that he'd never even seen the test. So some of these guys are very anal about this, but by and large they just ride what they're given.

That's why we're fortunate with CSC to have Bjarne, he is super anal and reads and understands all the data, so he is generally the one selecting wheels for key stages and sometimes involving us if there are questions. Phonak on the other hand is very different, they all like 404's so they just ride them all the time (except Floyd who really likes 202's) so where you will see CSC riding different wheels every day and mixing and matching wheels for certain days, Phonak will have every rider except Floyd on 404's every day and 999's for TTs.

Third, is testing methodology. We were approached by Fluent about using fluid dynamic modeling for design and even did a research project with them and it was very enlightening, but really showed the limitations of the software at this point. The wheel models they had developed for the British cycling team were used with our rims and wheels and models and we found that this technology doesn't yet accurately reflect wind tunnel or real world data in yaw.

So for instance, they showed deeper wheels increasing in drag with increasing yaw angle, where in the wind tunnel the drag actually decreases with yaw. By their model the 202 was going to be a faster wheel than an 808, which we know from both wind tunnel and SRM data is absolutely wrong. Since the models were developed for track racing, only the zero degree condition was ever tested and deep rims compared very similarly in these models, and showed that spoke count and tire/rim width matching was the largest determining factor in drag.

However, in the wind tunnel we see that rim shape and depth are of primary importance and spoke count is secondary, but still important, although it is of primary importance if using round spokes. This computer model actually matches closely with the indoor velodrome testing done by Triathlon magazine in Germany, which showed the Vuelta wheels, which are 12 spoke wheels using a variant of our 404 rim to be faster than anything else, including 808's, three spokes, four spokes or even dual discs.

If you overlay the data this also matches the wind tunnel data as well for zero degrees, however, on the road zero degrees is pretty rare, so this test is leading people to make wheel decisions based on what may possibly be the least common wind condition in triathlon, whereas we've been telling this to the indoor track guys for years now and nobody wants to abandon their dual discs for spoked wheels because conventional wisdom says that dual discs indoors are fastest, although both wind tunnel and real world SRM testing show us otherwise.

In the end you can get in a lot of trouble by just using one testing methodology as certain variables have to be controlled or eliminated that may be very key. For instance the computational method seems to be accurate at zero degrees, but still very flawed at higher yaw angles, while the indoor track testing looks like a very real world test, but is only giving you one wind angle. Wind tunnel testing is also great, but the airflow is of very high quality which is not always true in the real world, and even so, you then have to extrapolate all of your data down to something meaningful, as companies will say 'fastest in wind tunnel testing' but maybe they were only fastest at the 30 degree data point, which doesn't occur too frequently in the real world, or maybe they were fasted at zero which is really more applicable on the track indoors. 3, 4 and 5 spoke composite wheels are another issue as these wheels can look very fast on their own in the tunnel, but can incur a 4-6 watt penalty when placed in a fork because of the boundary layer effect, so I hear from people all the time that the Mavic IO is the fastest wheel ever tested, but I guarantee you it isn't when it's in a fork, in fact it compares very comparably to a Hed3 but worse than an 808 because you have 5 pressure pulses per wheel revolution.

Tire width is another way to skew data, an H3 or Mavic IO with 18mm tire is significantly faster than with 21mm tire so people always test them that way, but in the real world, on real roads nobody should be riding an 18mm tire, so you throw on a 21 not realizing that you've compromised 20% of your aero advantage.

I see this with pro teams and amateur athletes both in the tunnel as well, people like to make tweaks to see benefits in the tunnel, but are not real world applicable. Or maybe you do three runs with a new position and one of them is particularly good, the practice is to take your best run and drop it in a model and say 'wow, we can save 50 seconds per hour' but you are forgetting that in the real world your worst case data is probably your more accurate data.

I think the best example of this was the Nike SwiftSpin suit data. I was in the tunnel that year with Lance when he was testing with it, and we were seeing drag reductions maybe on the order of 20-25 seconds per hour, but with some serious tweaking of the suit, clothes pinning it together to remove wrinkles, and having somebody physically go into the tunnel between runs to make the suit perfect before the run you could make it like 2 minutes per hour faster, but once he stood up to pedal or even moved for that matter, you were back to the 20 seconds per hour savings. But of course they went into the press saying '2 minutes per hour faster' and it just never materialized.

I have seen the same theoretical data that you talk about showing higher RR for tubulars than clinchers, but this isn't actually nearly as clear cut a case as that data would suggest. Mainly, all RR tests use a simple machined drum for testing the tires and that is not very true to real life. Some data was taken a few years ago using a different system, similar to that developed at CALSPAN in California. This system is more like a treadmill but the belt is steel with various types of tarmac surfaces bonded to the surface.

In these tests the tubular tires actually fare slightly better than clinchers on more realistic, rough road surfaces; more or less because the structure of the tire allows the tire to conform to the rough surface with fewer losses. The clincher tire on a smooth drum only needs to defore really at the contact patch and partially in the casing, but on rough pavement the additional deformability of the tubular tire carcass seems to be helping out. The other thing to remember for all the tubular bashers is that clinchers only show better or equal in these tests when used with thin latex tubes, these tubes have significantly less RR than butyl so if you want to run clinchers for racing you really have to run latex tubes, which is something that very few people do. Overall that's why the 13 minute over IM distance is not so realistic, if it were you would see it affecting results, and you would have certain pros with wildly different bike splits in similar events when they switch sponsorship between clincher and tubular wheel manufacturers and so on, but it just doesn't happen that way.

I think that the other thing generally not mentioned is that most tubular tires have a puncture resistance belt under the rubber that adds a bit of weight and RR, but improves durability of the tire. Clincher tires that test very well for RR usually don't have similar puncture resistance belts, but these are not the clincher tires most of us want to use and we certainly don't recommend racing on them as a flat will cost you way more time than any RR savings will get you.

Also, the tire bed shape is critical. Older aluminum rims (which are used in many of these older RR tests) would have a large single radius curve shaped tire bed, generally 23-25mm diameter, and eyelets that protrude into the tire bed. These rims can significantly increase RR when a tire is used that has an effective inflated diameter smaller than the rim bed as the entire casing of the tire is deflected at the contact patch. This is made worse by the stitches under the base tape which protrude slightly, requiring additional glue to fill the airspace, and further deforming the casing locally.

With some proper design the tire bed can very closely mimic the tire profile eliminating these problems, and also resulting in the need for significantly less glue as the glue can be very thin on the rim. Also the elimination of eyelets eliminates excess glue as well as what were effectively high-spots in the wheel that show up in testing as an increase in RR. The same 21mm tire will show 15-20% less RR on a Zipp rim due to these design elements than on an older GL330 or similar tubular rim, and that is not at all trivial. This is another reason we strongly recommend 21mm tires on all of our wheels.

We have probably done more work than anybody in studying the tire/rim interface in both clincher and tubular. With considerble work on both models we have ultimately ended up with nearly equal drag on clincher/tubular products. To get there, the clincher rims are generally slightly wider and have a little bit of a different shape, but at least with our product there is no appreciable difference between tubular and clincher in terms of aerodynamics.

As for the inevitable question of why the pros favor tubulars, there are a few very simple answers: 1. they flat less, since most flats in pro racing are pinch flats (the roads are generally pre-swept or somewhat cleaned) tubulars eliminate the majority of flats. Plus road pros race on all sorts of crap pavement and cobbles where clincher tires just don't hold up. 2. in a downhill or fast situation a flat with a tubular is far safter than with a clincher as the tubular flat can be ridden with much less drama. The tubular flat can also be ridden faster and longer giving the team car more time to get to the rider, so he isn't stuck on the side of the road. 3. they can be run at lower pressures. Everybody always talks about how tubulars can be run so high, but really the pros want lower pressures for better grip (particularly in the wet) and more comfort. It is common to see road pros in Europe running 90-95 psi in the rain and 100-110 in the dry, so on the roads they generally ride, these pressures would be very problematic with clinchers.

There is really no clear cut answer here, and as with a lot of things it is largely personal opinion, but there is lots of data showing the superiority of one vs the other and so on, but in reality the differences are quite small. We prefer tubulars as they are much lighter, the tires are more puncture resistant despite being lighter, can be pressure optimized to road surface (can run much lower to much higher), generally have more consistent and higher cornering grip, and when properly glued offer an extra margin of safety."

I can assure you that I and the rest of the folks have no secret reason for advocating tubulars. Nor are trying to pull the wool over everybody's eyes on this tubular/clincher debate. Since we make and sell all of our products in both, we certainly could care less what you buy or use, but from the testing I have been privy to and worked with there are many real world situations where the tubular will have equal or lower RR, specifically poor road surfaces. Having said that, even if clinchers can surpass tubulars in all RR situations tubulars will continue to be most prevalent in pro road racing due to the safety issues and ability to ride when flat, as well as the weight discrepancy which will remain indefinitely due to the necessary design limitations of clincher rims.

Also some have said that clinchers are an aerodynamic mess. They are not a mess, they are just different than tubulars, so that using the same rim shape for both will leave one of the products lacking when compared. This forces us to design the clincher and tubular versions of a rim as two different products, so that they share rim depth and marketing but from engineerings point of view they are totally different products.

All of our clincher products more or less mimic the performance of the tubulars with the 404 clinchers having a slight advantage actually over the tubies and the 808 tubulars having a slight advantage over the clinchers. To give you an idea of how different things are, however, look at our clincher disc. We really had to work some sidewall curvature into the shape to clean up the airflow off of the tire, and blend the aluminum to carbon interface so as not to have a hard lip between the two as that lip can cause 3-4 watts of drag in some designs. But you can see that the final product essentially looks nothing like our tubular disc, yet the performance is nearly identical.

It is the heat that causes the butyl inner tube to fail and not the pressure increase, although I have seen people blow clincher tires off of rims due to the pressure increase. We have seen rim temperatures in testing exceeding 325F, which can be enough to raise the air pressure in the tire by 20-25psi, so this can be a blowout risk on loose fitting tires or rims at the low end of the ISO diameter spec. On tubulars the heat is more likely to melt or soften the glue than blow the tube as the tire base tape and casing serve to insulate the tube. The tire rupture on tubulars is more likely going to be that the tire begins to rotate on the rim and the valve is ripped from the tube. I was doing a US Nationals about 15 years ago in Bear Mtn. New York and they started the race at the top of some climb and neutralized the start behind a car for the 3 or 4 mile descent and maybe 20 people flatted or rolled tires in those 3 or 4 miles due to brake heat of having to ride a steep descent at 25mph behind a car…painful.

Anyway, alternating your brake usage or at least feathering out of one brake of the other for a few seconds will lower rim temperatures considerably. Also using brake pads without any abrasive additives like the Zipp pads or even the Kool Stop Black pads will lower temps by as much as 20-30degrees and up to 60 degrees for the Zipp pad which also contains thermally conductive materials. Most pads anymore contain aluminum oxide; the same stuff sand paper is made from, to increase coefficient of friction, but that also increases heat. Also, once the pads do begin to melt they create an insulating situation on the rim where the hot pad material melts to the rim keeping the aluminum or carbon from being able to reject heat to the atmosphere, and also increases the surface coefficient of friction, so that when the part of the rim with melted pad on it comes through the brakes again it is hotter and higher friction which will make it even hotter...a sort of snowball effect.

Finally, lighter weight, or shallower profile rims will get hotter as they have less mass to act as a heat sink, and less surface area to dissipate heat for convective cooling. The more aerodynamically effective a rim is the better it will generally cool as the airflow stays attached to a larger area of rim where it can transfer away heat.

This is a difficult argument that has many facets and honestly none of us fully understand all of the interactions well enought to model them 100%, and probably never will. But here is what we know. Clearly nobody wants to trust wind tunnel data from a manufacturer, but the stuff we have on the web was completely taken and graphed by the wonderful folks at Texas A&M with us only there watching it. There is no possible manipulation here, and to improve the results this was the first known bicycle wheel test where every wheel was run a minimum of 3 times and averaged to take out any anomolous data (and it does happen). So you have my word that it is not bogus marketing material, and if you want you can always contact the guys and gals at A&M and they will verify.

Having said that, there are changes in tunnel protocol that have changed the apparent aero properties of some wheels over the years. The whole lenticular vs. flat disc thing got started when the lens disc guys (and a prominent university) started testing wheels at various angles by starting at 0 and slowly yawing out to 30 taking measurements along the way. This is how aircraft wings are tested and makes a lot of sense. However, with aircraft wings they then start at some higher angle and come to zero to check hysteresis. Doing this in the late 90's with wheels (it adds time and cost to the testing) we noticed that the lens discs would not track their initial data as well on the return. What was happening was that the discs from 0-30 was maintaining relatively attached flow, thus generating lift on the leeward side which appears in the data occasionally as negative drag. This would not happen every time, but many times. However, if you start the wheel at 30 and yaw to zero, the flow is detached and does not reattach to nearly 0 degrees, so the data looks much more like that of a flat disc. Once there is a bike and rider in the way, there is enough airflow disturbance that the flow cannot ever reattach so the 30-0 trip much better mimics the real world performance of the disc.

Of course, when all of this was being learned we really started to see bigger differences between discs and frames. Good example, the Trek TT frame was designed when the team were using lens discs and hence has pretty wide seatstays to keep the disc and seatstay boundary layers from coliding. A cervelo P3 on the other hand has very narrow seatstays that work ideally with a flat disc and can cause air damming when used with some lens discs. This effect is now seen to be greater than the lens vs. flat shape debate. The dimples simply help the air remain attached longer to our disc, thus somewhat mimicing the 0-30 attached flow scenario of the lens disc, and also the dimples lower the wattage to spin. The effect is small, but on the order of a few watts, which for some folks is not small at all.

As for deep vs 3, 4, 5 spoke wheels the question is really where do you want to be aero. We have now developed 4 shape revisions of the 404 in 5 years to best the Dupont/Hed3 wheel, and with the last two generations of 404 are faster than them at most real world wind angles. The 404 will be faster from 0-22 degrees, while the 3 spoke will becomes faster at 22+ degrees. The 808 is an entirely other beast, and when we first published our aero data showing the wheel to mimic a disc to 12.5 degrees we were really criticized for making so bold a claim.

Fortunately Tour magazine in Germany did their own wind tunnel test and found essentially the exact thing (in their test the 808 was actually slightly FASTER than the disc between 0 and 12 degrees!). This is not a factor of depth so much as shape, which really comes from much of what we learned doing the 404. Both of these wheels, however, are less aero than the H3 at high wind angles, but it is our feeling that it is these high wind angles (read: strong cross-winds) where people are least likely to actually ride the products so we have thus far not developed a wheel using these shapes with any more surface area as it is of no value at the lower wind angles and only adds speed at wind angles where very few people seem to be likely to actually use the wheel.

OK, having said all that. Weight is important, but is generally always trumped by aero. The analytic cycling calculator helps out with this, although we are now understanding better from our work with CSC and Phonak, that on steeper grades weight is more important than these models show. The theory is that since nobody really makes constant power, the dead spot in the pedal stroke allows for a slight deceleration that then requires a re-acceleration during the power stroke. These fractional acclerations really can sap power, and weight definitely affects this quite considerably, although aero has a small affect as well.

The smoother you pedal the more accurately the analytic cycling model becomes, but anybody using and SRM or a stroke scan on a computrainer will know that most of us are anything but round. This is partially why Lance's high RPM stroke kills Ulrichs low RPM power stroke on steep climbs the faster stroke is smoother and has fewer losses due to this fractional accleration issue. This is the stuff we are really trying to understand now so that we can have better answers in the future, but the advice we give people right now is that for everything short of hillclimb TT'ing, get the most aero stuff you can ride, and if you have the money buy the lightest version of what you want. You really can't have it all in every situation (which is why we now have 7 wheelset options), but you can have most everything 90% of the time. :-)

For more information on rim shape and aerodynamics check out our engineering white paper on rim shape.