The Numbers Game


I get a lot of questions from readers about purchasing dilemmas, and I do my best to answer them all. The questions range from what saddle is best (I have a favorite, but unless your pelvis is a clone of mine, you might not like it), to clothing sizing issues (hard to do without being in the same room with samples in hand), to the typical frame selection and sizing questions.

The single most recurring question that I get from friends and readers is what wheel to choose. For someone purchasing a single set of high-zoot wheels, what would I recommend? And because I’ve reviewed more wheels from Zipp than Enve, Easton or other manufacturers, the question is often framed as, would I recommend the 202, 303 or 404?

It’s not a tough question for most riders, at least in my opinion.

For the purpose of this piece, I’m going to use Zipp wheels, but I think a number of wheels, such as those by Enve or HED, could be substituted for Zipp in this comparison. The point isn’t the brand, it’s the category. And frankly, getting a handle on the competing aerodynamic claims from one manufacturer to the next isn’t something I care to undertake—the marketing claims prove each brand is faster than their competition.

Before I get into the considerations that lead to the choices I would make, I want to lay out a few assumptions that guide my thinking. The first is that because I’m aware that a set of Zipp wheels are more expensive than some bikes, I don’t really see them as something I’d routinely take to a race, even if I was still racing. Sure, I’d use them in a time trial, and I might have been willing to use them in some road races, but the average crit isn’t a place I’d be willing to risk a $10,000 bike, unless, of course, I was sponsored to ride it—and even then I’d have a fair amount of trepidation. So while a great many people think you ought to save your most expensive equipment for race day, I think if you’ve got good stuff you ought to go ahead and ride it.

The second assumption is that fast is fun, and faster is more fun. So while I may be riding long training rides with a select group of friends or the occasional gran fondo, I want to ride as fast as I’m able. To that end, I want aerodynamic wheels for all the free speed I can get. Third, if I’m going to be on aero wheels, I don’t see any point in being frightened when riding in a crosswind; I want wheels that offer handling as close to that of a box rim as possible.

So now for a bit of objective data. The images that follow I got from Zipp. They offer a fairly objective comparison of several different wheels against the 202, 303 and 404.

For me, there a few takeaways from these images. The most striking is how a traditional box rim is aerodynamic equivalent of an elephant. The improvement of the 202 offer over a box rim is significant, but considered against the 404, I can’t help but wonder why a greater effort hasn’t been made to make a relatively lightweight aluminum rim that offers better aerodynamics (and handling) than the box rim. To my eye, the industry has given up. The best offerings I can see in the sub-$1500 range are HED’s Jet series wheels which mate an aluminum rim with a carbon-fiber fairing. What else is noticeable is how much more crosswinds affect the box rim and traditional V rims, and while I’ve seen how Firecrest (and other similarly rounded rims) handle better in the wind than V rims, it is interesting to see that phenomenon illustrated.

The basic wisdom on rim depth is that the flatter the course, the deeper the rim, and vice-versa. It’s the single easiest way to choose, but it leaves out all the nuance that causes lunatic cyclists like me to actually fret over these decisions. The discussion that follows isn’t about the obvious choices, it concerns the nuances that make you second guess.

The big knife
For riders across most of the world, where flat land dominates, the wheel that makes the most sense is the Zipp 404. That’s the simple truth. The weight penalty is more than overcome by the aerodynamic gains. Why deny yourself that aerodynamic advantage? Now, that said, there is a caveat to that selection. If you’re a light rider and you live in a place where the wind is a frequent training partner and if gusts are an issue, you may want to consider selecting a different front wheel, such as a 303 or 202.

There’s a lot of new technology that addresses the wind’s input on steering. Zipp’s Firecrest, Enve’s SES and HED’s Jet rim shapes have all used a rounded spoke bed that has fundamentally changed how the wind affects the wheel. Not only are the aerodynamics better, but the handling, as I’ve written previously, is much better than the previous generation of V rims. My first experience with Firecrest was on a pair of 808s and the on-shore breeze in the afternoons here can push me around as easily as a pro defensive lineman. The 808s were so easy to deal with in crosswinds I wondered if I was on Punk’d. It’s worth noting that Tom Boonen told me he starts every race, except for cobbled ones, with a 404 front and an 808 rear.

Where the 404 becomes an issue is on climbs. Its aero advantage disappears at speeds below 20 mph and then there’s the extra rotational mass of the deep rim to consider. But the issue the 404 faces is less going uphill than dealing with changes in terrain. When I’m on climbs that change grade the liability I encounter is in trying to accelerate the bike when the grade lessens. It’s not a huge issue, but the 404 flat-out doesn’t accelerate as easily as the 202. I think if I were riding in the Rocky Mountains consistently, where downhill speeds can easily eclipse 50 mph and the grades on climbs can often hover around 5 percent, I’d still go for the 404, but in the undulating grades of California’s coastal mountain ranges, there’s another wheel I prefer.

Mountain goat
The 202 Firecrest is a wheel I was excited about even while it was still on the drawing board. It features the same 16.25mm clincher bead width as the 404, giving the tire a bigger footprint for superior traction in corners (handy when descending), but at only 1343g for a set, as opposed to 1562g for the 404s. That’s not a huge difference in weight, but as all of the difference can be found at the rim; you notice it any time you start winding up the wheels. The combination of aerodynamics and low weight make it a climber’s dream, but only if your heart is set on clinchers.

The 202 does feel faster than a traditional box-rim wheel, but I can’t say that I sense the difference between it and the 303. However, on the flats and on descents, I hit higher speeds with the 404. I also notice a difference on descents between the 202 and the 404: The shallower 202 is more maneuverable in turns. By contrast, the 404 feels more stable and gives me confidence at speed.

I can’t stress enough how impressed I was with this wheel’s strength when I went down back in October. I went from 30 to zero in about the amount of time it takes to sneeze. The front wheel, which is what did the stopping, didn’t even come out of true. While Zipp wheels do flex some side-to-side, the incident did a lot to confirm for me how much stronger their rims are than they once were.

The wheel of all trades
And so what of that in-between depth of 40 to 50mm? If your home terrain has got a few sustained climbs of at least 5k, hills like politics has liars or roads bumpy as a bipolar’s emotional life, then the 303 may be your ideal choice. It’s a wheel that is light enough to climb well and yet still packs a powerful punch on the flats. It has gotten great play as a stout wheel for cyclocross and races involving pavé. Featuring the widest rim in the Zipp stable, the 303 yields the broadest tire footprint if any Zipp wheel, making it preferable for anyone concerned about tire adhesion in corners.

At 1478g, the 303 isn’t much lighter than the 404, but I’ve experienced them as being much easier to accelerate, or at least what passes for me accelerating. It makes them more cooperative on climbs while still lending a powerful aerodynamic edge on the flats and descents.

It’s worth noting that Enve has taken a slightly different approach to their SES-series wheels. Rather than using the same rim front and rear, Enve uses a shallower rim in the front. The 3.4 wheels use a 35mm-deep rim front and a 45mm-deep rim in the rear. Practically speaking, it’s like running a front 202 and rear 303. The 6.7 wheels use a 60mm-deep rim in the front and a 70mm-deep rim in the rear. The front is effectively a 404 while the rear splits the difference between a 404 and an 808.

If you’re only going to buy one set of Zipp wheels, chances are the 202 won’t be the best choice. I can only see buying the 202 if you live in a place that is binary—either up or down. I know there are people out there who think about purchasing high-zoot wheels for race day and saving them for special occasions. I’m not down with that thinking. Any day you put a great set of wheels on your bike is a special occasion. They, after all, are not like a bottle of wine which is destined to last but a single night. You don’t have to work very hard to take care of any of these wheels, so you can do consistent miles on them without fear that each ride is death by yet another paper cut.

I can’t claim that can always feel the improvement in aerodynamics of the 4o4 over the 303 or the 303 over the 202. On long, fast flats, my sense is that I’m just faster. I’m usually going too hard to reason my way through it at the time. But I seem to have a lot of good days with the 404s. What I can say for sure is that the 404 is noticeably faster than the 202; I’ve swapped the two out and been able to note the improved speed, even when the switch was one day to the next.

For me, the 303 is the best all-around choice. It’s a wheel I can climb well with, handles well on descents and still provides a killer aerodynamic edge as compared to the standard box rim. But my preference depends heavily on the terrain where I ride. Where I live, I do plenty of miles on the flat. Any time I’m riding to Malibu, I’ve got about 18 miles of flat just to get to the foot of the nearest climb. I’m going to have to ride that flat getting home as well. My weekday training rides take in plenty of flat miles as well; I’ve got a half hour of riding just to get to the hills in Palos Verdes. That’s why the easy choice would be the 303, even though our roads are a good deal smoother than a Congressional hearing.

Coastal California isn’t like most of the rest of the world, though. The world is, for cycling purposes anyway, flat. Most places I’ve ever visited merit the 404. And that’s a handy thing. Whether you consider the 404, Enve’s SES 6.7, HED’s Stinger 5 or any of a host of other options, the real point is that once you have a chance to ride with your friends over known roads, you’ll be amazed at the advantage the wheels give you. Granted, some of these flat places experience a lot of wind. Even with the rounded profile of a rim like Firecrest, there can still be some steering input. For lighter riders who want some aero advantage with as little steering input as possible, I’d suggest a front 202 with a rear 404 or a set of wheels like the Enve 3.4.

There are a great many products that might increase your enjoyment on the bike, but very few I can swear will make you faster. For purely selfish reasons I should probably shut up so that the guys I ride with don’t all start buying aero wheels, but that would really violate the spirit of this site. We want you to have fun out there, and there’s no denying that more speed is more fun.

, , ,


    1. Author

      Dave: The Zipp 101s are great wheels, but they’ve been in relatively short supply. That said, I was thinking of something with a greater rim depth, say more in the 40 to 50mm range.

  1. LesB

    Do you know what the air speed was for the Zipp images?

    And to get all techie on you, does air resistance progress linearly with air speed? I think I’ve heard that air resistance increases as the square of air speed.

  2. Jeff

    Am about 135 lbs and live in pretty gusty Hawaii and don’t have any problem with front 303 and rear 404 – and these are pre-Firecrest.

    Drag goes as velocity squared – twice as fast has 4X the drag.

  3. Neil

    It would have been interesting to see a comparison of the 202 with a 32mm V section rim, instead of a box section. Obviously side winds are going to be less of a problem anyway with a rim of this depth, so I wonder if there is really a significant advantage to the firecrest profile here (and it would also be interesting to see the difference between a box section and a 32mm V).

  4. Steve

    Padraig, I’m a bit confused by the numbers in those pictures. Drag is a force. Grams are a measure of mass. I suppose Zipp is simplifying things for those of us who don’t normally think in newtons: we can use the numbers to think about the relative drag of each wheel. Still, I wonder what the values really mean.

  5. MCH

    OK, you’ve convinced me – aero wheels for everyday riding are the way to go, even if they are a bit heavier. I may be slow, but I catch on eventually ;-). So which ones? If I was interested in carbon clinchers and had a fat wallet, one of the Zipp options would be tempting. However, I don’t want the hassles of 100% carbon wheels. Maybe the new DT RRC Dicut H wheelset. Should be interesting to see what these are like when they’re released early next year.

  6. Dave

    Steve, I think you are right. It’s prob shown as forced generated by the quoted mass in earths gravity. In otherwords, just multiply by gravitational acceleration to get newtons. Similar idea to how lb-force and lb-mass are sometimes used interchangeably but often incorrectly.

  7. Rod

    @ Steve –

    The confusion is on how we use units. Grams are a unit of mass, but since we are on planet earth under consistent gravitational forces for convenience we also use them as a force which we usually call “weight”. Formally, they should be referred as “grams-force”, which is defined as the force exerted by an object with mass of one gram when subject to the normal gravitational acceleration (9.8 m/s).

    So, for this example wind tunnels standardize drag measurements to the force presented to resist the wind pressure of given equipment at a stipulated speed (40 or 45 km/h are some “normal” speeds used). So as a visual example, using weights to “counter” the drag of the best wheels presented above you could tether 67 grams of mass accelerated to the normal gravity to balance the bike and preventing it from going forward or backward. So, 67 g of “weight”, which formally should be referred as 0.067 kg x 9.8 m/s2 = 0.66 Newtons. We rarely use N colloquially, and use instead “grams-force” (or your reference system units) which gets shortened to “grams”.

    If you think about it, when you step on a scale you’re really measuring the force you exert on it (LBf, pounds force), not your body mass directly. If your ceiling is low you can push against it with your arm and your weight will read higher, even though you’re really not more massive. You’re simply exerting more force on the scale.

    I studied engineering and a few of my professors were real picky on the use of units, but really who refers to their weight in N?

  8. tinytim

    This is a interesting analysis of the Zipp and Enve wheels. But what about evaluating a more modestly priced/durable wheel? There are numerous options out there that cost a fraction of the above mentioned wheels. I’ve got a set of Velocity A23 rims ($40 each rim) laced to White hubs, shod in a 25mm tire. The parts for this wheelset cost me a total of $300 + tires (i built them up myself). The wide rims with a large tire are proposed to be more aero than traditional deep dish aero rims. @Rod, I think the best describing formula of force would be newton meter seconds, converted into joules and then into the holy watts.

  9. Steve

    @Dave, @Rod, thanks for the explanations. I’m curious: Anyone know what units the display on a wind tunnel’s computer screen reports? (That’s the problem with a Computer Science degree: they never let you close to the real hardware.)

  10. Dave

    Hey Steve, it pretty much is whatever the facility wants to use… most US commercial tunnels will use british units (lbf), while academia and the rest of the works tends to use SI (Newtons). Software usually allows conversion to allow the user to custom function whatever units they want on display.


  11. A Stray Velo

    @Padraig – Have you had chance to try the new Reynolds AERO/DET wheels yet? I’m wondering how those compare with the Zipps, HED and ENVE wheels.

    If you did and you wrote about it, sorry for asking. I searched the site but only found some comments from interbike that you would be getting a pait to test in fall.

  12. Chris

    What are peoples thoughts on buying the Zipp wheels stock vs a custom built set of Zipp’s from the builder of your choice?

  13. Andy

    For a deep (50mm), modern profiled aero rim with an ally brake track I’ve been very impressed with the Bontrager Aura 5 – very stable feeling in cross winds.

  14. naisan

    As a rider of pre-firecrest 303 and firecrest 404s, both in tubular, I believe the 303s are the best bang for the buck for any wheel: they are almost as light as the lightest, and almost as aero as the most aero.

    Furthermore they seem to retain their aero advantage with a wider tire like a veloflex arenberg/roubaix (25mm?).

    I mostly ride the 404s these days, but it is pretty difficult to determine if there is any advantage vs the 303s just by feel or the statistics that I have access to.

    BTW: I have read studies that say that having a more aero rear isn’t much benefit, so perhaps staying with a full 303 set if there are wind issues will be best.

    Also, I have heard that some are riding 808s full-time as they also have about the same sidewind feel as the 404s, but I wasn’t brave enough to try out that theory.

  15. Mitch


    Agree with the key points, but you may want to check on some of the assumptions you’re making. For example, I think aero is much more important than you assume at speeds under 20, and the flywheel effect can make the objective cost of acceleration smaller than a rider’s subjective experience (in other words, light wheels “spinning up faster” is often a psychological benefit).

    There are lots of variables in the formulae on the energy “demand” side. And the you have to consider the “supply” side…. the rider’s specific physiology and riding style, the specifics of the event, fatigue level, etc. etc. etc. So it can get pseudoscientific pretty quickly without doing the actual calculations, which are behind the capabilities of most of us because we lack the data, aren’t engineering PhDs, are too lazy.

    But if your key point is that aero beats weight in almost all cases (it seems that it is), I don’t think you can go wrong with that. My conclusion is just ride the most aero wheel you can safely handle given wind and road conditions. If you’re choosing among top tier wheels (zipp, enve, etc.) and you’re not riding a pro in a climbing stage, the effect of weight differences are going to be overrated.

    1. Author

      Everyone: Thanks for the comments. I apologize for taking so long to respond. In addition to the fun/demands of the holidays, I’ve been wrestling with serious computer issues for the better part of two weeks. It has eaten up crazy amounts of time.

      MCH: I’m interested to ride those DT wheels. I’ve had previous experience with aluminum/carbon clinchers (most recently the Roval Rapide 40) and found them to be pretty darn good. That said, I’m not one who switches wheels out a lot, so I don’t mind setting up brakes for carbon clinchers and then just leaving them that way for a while. The gains you get in both aerodynamics and handling with the Zipp Firecrest and Enve SES I think do a lot to justify the increased investment over an aluminum/carbon aero wheel.

      Rod: Thanks for that explanation. I could never have explained it as well as you did.

      Tinytim: The more affordable wheels will definitely offer a great improvement in aerodynamics, but won’t handle as well in crosswinds as Zipp Firecrest and Enve SES wheels.

      Stray Velo: I’m supposed to ride the Reynolds wheels this winter. Just waiting on their arrival. I’m told their handling is way better than previous iterations; I am eager to find out.

      Chris: I think a strong case can be made for buying Zipps from a company like Wheelbuilder. You’ve got the ability to substitute hubs (though Zipp’s hubs are terrific) in favor of, say, a Powertap rear, and their build quality is legendary, and if there’s anything that Zipp can be criticized for it is the build quality of some wheels. They seem to be much better in this department these days, though.

      Naisan: The pre-Firecrest 303 is not a particularly quick wheel. The Firecrest 303 was a big improvement, aerodynamically. The numbers regarding the 808s suggest that running a rear 808 will result in measurable gains. My experience riding them was such that I would be more than willing to do what Boonen does and run a front 404 and rear 808 if I was both racing and sponsored by Zipp.

      Mitch: I’ve had the sense that I’m still getting noticeable benefits aerodynamically at speeds below 20 mph with both the 303s and 404s, but because there hasn’t been much data to back that up, I haven’t bothered to make the claim. There’s a lot to consider on the acceleration front, more than I wanted to chase in this piece. I think the greater truths there will be found out on the road after riding a thousand kilometers on different wheels; there’ll come a point when you just know which wheels work better for you and that realization is independent of math. My bottom line is as you put forward, that in essentially all cases aero beats weight.

  16. John Marrocco

    I’m still unsure about whether to get the 202 or 303. I live on the east coast of FL and we definitley get wind here, all year round. In fact its rare to have a day with wind below 10 mph. Though there are no prolonged climbs there are short but steep hills in the central portion of the state, and I do travel to more hilly terrain. My primary use will be for ultra events, 12 and 24-hour events. I am wondering if there is any validity to the idea that a wheel with longer spokes will be more comfortable over the long haul, which is why I would choose the 202 over the 303.

    Like you said, its one of these things we obsess over, for weeks, even months, on end.

  17. Sdp

    A great write up. I agree, there is a right tool for any job and the nature of where and how you ride play large into any choice of wheel upgrade. After way too much reading and a lot of lucky test rides, I chose the 303 tubular. As someone else mentioned, at less than 1200 grams for the pair, they’re lighter than many of the best aluminum lightweight climber wheels. As well, the aero advantage is only just slightly less than the 404. I also agree that fast (either measured or felt) is inherently good. The measured advantage of the 303s on the flats is significant. Get into the drops and watch the miles roll by quicker than they did before. The seat of the pants feeling of quickness and speed is immediately apparent with these wheels. The feather weight lightness means jumping on the pedals rockets you forward with every stroke. I’ve never driven a Porsche Cayman S but I’m guessing the 303 tubulars are a close comparison…snappy, light, immediate. It might fall just short of the 911 but it feels so good to drive. That’s the 303 tubular. Throw in the genuine magic carpet ride comfort of tubular tires and these wheels are a game changer.
    The 404s felt almost the same but didn’t quite have the snap immediacy of the 303s. Love them, plain and simple.

  18. Clark


    While Watts are a great yard stick, they actually can muddy the water a bit more when you’re talking about aerodynamics. As described above, aerodynamic drag force is a quadratic relationship (drag force proportional to square of relative wind speed).

    So that tells you how much the air is resisting your motion in terms of the force you have to apply. But power (Watts) is calculated by multiplying that force by velocity yet again, meaning that the relationship between power and velocity is actually cubic (double your speed, and the power required to overcome drag multiplies by 8). This is why when you see claims of drag reduction in terms of Watts, it should be combined with a speed (“Skin Suit X saves Y Watts at Z kph.”). Incidentally, that is also what the iBike power meter attempts to calculate. It essentially takes wind speed measurements and computes the power required to overcome it. Since power varies greatly with speed, small changes in wind speed measurement can amount to big inaccuracy in reported power output.

    So all-in-all, it’s just a question of representing the same information in different ways, but just remember that to get the same Wattage or drag force reduction as claimed, you have to be going the quoted speed.

  19. Bikelink

    So, for the flat crit/track racer (ahem), I’m actually considering 808s vs Stinger 9s (hills? not my race then). More crosswind means harder to handle, but also increased aero advantage of deeper wheels (stall out at larger yaw angles). I raced a friends pre-FC 808s and the front wheel handling felt a little less snappy though the weight isn’t higher than my 1500gram American Classic 420s. I commute with front panniers even in strong winds. Sure, there is more margin for error when you aren’t in a pack, but unless we’re talking 30-40+mph cross winds, it doesn’t seem to be a problem.

  20. Mike

    Yes the 404’s might be the best for the flats, with little penalty going up…
    But as a racer I’m not going to get dropped on the flat, i want all the help i can on the climbs, that’s where the difference counts.
    You could argue that in a breakaway or solo effort the deeper wheels are better, but how often does that happen as compared to climbing and hanging on for dear life.

  21. Alex TC

    This post came in good time as I´m considering a new wheelset and was eyeing the 303 FC. I´ve owned a couple of Zipps, a Reynolds and an EDGE (pre-ENVE) carbon hoops for years (tubulars and clinchers), then I got tired and came back to regular, alu-rimmed wheels for everyday use and also racing.

    For the last couple of years I´ve been on a pair HED´s Ardennes SL wheels. It´s not a common wheelset out there, hardly ever mentioned in articles or forums, much less a hyped-up one. And of course it´s not as aero as a deep carbon rim but overall a good-performing wheelset, I really like these.

    Wide scandium rims, aero spokes, sub-1400g for the set. External, regular spokes make it easy to touch-up or fix on the road, though I´m yet to need it. I find them pretty good for climbing and descending, and they´re comfy too since I can pump 5-10psi less than usual and still avoid snakebites. Makes it excellent for rainy rides and incredible on curves.

  22. MSuria

    A great and helpful write up indeed. Currently, I’m on 404 for both wheels on my SuperSix. Thinking of switching to a 303 front & 404 rear??? …or maybe like you suggested, a 404 front & 808 rear? But, could this give me significant difference? Think like a one click multi-purpose set-up for the windy, hilly, all type of weather/terrain.

Leave a Reply

Your email address will not be published. Required fields are marked *