Choosing aero (race) wheels

So onto probably the next major purchase a lot of triathletes consider. Race wheels.

On the whole this is a bit simpler than the tri bike discussion.

Similarly to tri bikes, race wheels, or deep rim wheels, or aero wheels or whatever you want to call them are more aerodynamic than your normal wheels. They are often lighter too and that weight reduction is usually on the rim, where, because of angular momentum, it makes the most difference. The improved aerodynamics combined with the weight reduction adds up to the aero wheels being quicker than your normal wheels. All this is physics and so not really in question.

So what to consider when looking to spend your hard earned cash on a set of aero wheels.
 Well first thing to consider is that the benefit you get from aero wheels is nowhere near the benefit you get from something like a tri bike, or even clip on aero bars. They sure look good and make you feel like a star, but the benefit you are getting from them may not actually be that great.
The reason for the above is that, similar to a tri bike, the reduction in drag that you get from aero wheels is proportional to how quickly you are riding. Don't get me wrong, no matter what speed you are riding, aero wheels will have less drag than normal wheels. However, at 30km/h that reduction in drag may not be that great. I remember reading somewhere that at speeds less than 32/33km/h the reduction in drag probably isn't worth it. What proportion of the field ride at less than 33km/h in an Ironman, the answer is most of it. What proportion of the field in an Ironman have aero wheels, the answer is most of it. Hmmm...

To be honest I am not sure how true that 32/33km/h statement is, I read it on the internet, so who knows. But what I can say is that if you are pushing along at 26km/h in your tri, then you are probably better off saving your money and spending it on something else.

So say you have decided that the aero benefit you are going to gain is worth your money and so you make the decision to buy a set. What should you look for?

Well a few years ago I would have said you look for a sticker that says Zipp, but I don't really think that is so true anymore. Certainly in a triathlon field you will see more Zipps than anything else, but that is as much due to people wanting to follow the herd as it is to any particular advantage that Zipp wheels have.

So a bit of history, as I understand it anyway. Going back a while, Zipp and HED were at the forefront of aerodynamics. They shared the patent for the rim shape that they both used. There certainly were other deep wheels around, but they typically used simpler shapes. A few years ago that patent expired and everyone had access to those designs. Around that time Zipp came out with Firecrest wide rims. A little while before that HED had released their own wide rims. These days every man and his dog produces a set of wide race wheels. They all have their minor differences of course to give the marketers something to work with, but the basics of the rims are pretty similar. Wide wheels, with quite a blunt looking rim shape.

With the advent of wide race wheels the playing field has become a lot more even. These days it is a bit like tri bikes, once you have made the decision to use aero rims, the differences between particular wheels is probably coming down to a couple of percent. If you look hard enough you can still find non wide aero wheels (Zipp still makes them), which generally aren't going to perform as well. However, if you stick with the wide ones, it is pretty hard to go wrong.

At this point I should add that if you do go wide rims (which I recommend) make sure your bike can fit them. A lot of older bikes were never designed for such wide wheels. When I first got mine I had to change my brakes on my P3 to ones that would adjust wide enough. Several bikes are known to not have the clearance around the seat stays for wide wheels (Cervelo P4 is one I think). My old P5 was specifically designed for wide wheels and even then the clearance was pretty small. Something to be aware of and check before you pay your money. Most modern bikes are designed with them in mind.

So if all the wide wheels have similar aero qualities, what should you look for?

Well cost is a big one. Zipps cost quite a bit. Other more exotic brands cost even more. HED is usually a bit cheaper. The cheapest brand that I have seen with a convincing product is called FLO. If you are after a set of wheels then I would certainly give them a look. You might have to wait for a while though (they are in the US and they don't carry stock, instead you have to wait until the next batch are made and then hope that you are quick enough with your order to snag a set. They explain the order process very clearly on their website).

The point is that aero wheels are expensive, no way around it, even 'cheap' FLOs are around $400 for a wheel. For a Zipp you are more likely to pay $1500 to $2000 per wheel. So before you spend the money, you want to be sure that they are going to benefit you and that they will satisfy your requirements.

So what exactly do you get for the money, particularly if they are all aerodynamically similar? Well generally for more money you get slightly better engineering and more advanced products. Not necessarily more aero, but possibly better made and almost certainly lighter. FLO wheels might be cheap, but they are made by mounting an aero carbon cowl on to a alloy rim. It is a bit hard to picture, but basically the carbon aero bit is hollow. They make very aero wheels, but they tend to be a bit heavier. In comparison Zipp wheels are beautifully made and even the clinchers are completely made from carbon. These days the average carbon clincher gives up very little in terms of aerodynamics and weight to a tubular.

So to a certain extent by paying more you get a better product. Do you get your money's worth? Hmmmm... I guess that all depends on how much you value a handful of seconds. You could be paying about $1000 for it? Is that worth it? That handful of seconds could be the difference between finishing 1034th or finishing 1032nd. However, that handful of seconds could also be the difference between a Kona slot and not a Kona slot (looking at you Stu Fitch). You could also argue that you could save yourself the money and get the weight reduction by eating less pies. In the end it is a personal decision.

So once you have made the decision to spend the money and have found a product that fits your price bracket, then what?

Well there are a couple of things to consider. Firstly, tubular or clincher. I am not going to go into the differences between a tubular tyre and a clincher and the perceived benefits of one over the other. That is what the internet and endless forum flame wars are for. Needless to say, both are available and if you are unaware of what they are, just know they are quite different.

It used to be that most aero wheels where tubulars. The only way manufacturers could make the rim strong enough to hold the bead of a clincher was to build the wheel around an alloy rim like FLO do. That bought with it sacrifices in terms of weight and aerodynamics. Therefore, nearly everyone used tubulars since they where lighter, cheaper, more aero and generally considered to ride better.

Then came along carbon clinchers, which is, as the name suggests, a clincher rim made entirely out of carbon. It depends on the brand, but carbon clinchers are usually only a bit heavier than a tubular and just as aero (also quite durable). At the same time clincher tyre and tube technology has gotten to a point where the 'better ride' of a tubular is considered to be largely neutralised. And then of course you have the big advantage of a clincher which is that repairing a flat doesn't cost $100 and can be done using the same spares and tools that you use to repair a flat on your training wheels.

So the downside? Well carbon clincher wheels cost more than tubular wheels (about $200 more per wheel or so) and as I mentioned they are still heavier. Having said that a couple of years ago I made the switch from tubular over to carbon clinchers, first Zipp and then Caden. I have never regretted the change. For me the convinience of the clincher far outweighs any disadvantages.

So you have decided on the brand and type of wheel, now what? Well now you need to decide on the depth. You see not all aero wheels are created equal. They come in a range of depths. By depths I mean the height of the aero section of the rim (ie the distance from the braking surface to the inner edge of the rim). Typically most manufactures make something around 30mm deep (Zipp 303), something around 60mm deep (Zipp 404) and something close to 80/90mm deep (Zipp 808). The general rule of thumb is that the deeper the rim, the more aero it is. They used to go even deeper (Zipp 1080), but with the advent of wide rims, they don't seem to do that anymore. According to the drag figures a Zipp 808 Firecrest (wide wheel) is as aero as a non Firecrest (skinny) 1080. So there isn't a lot of point dragging around the extra weight of an 1080 (which also handle horribly in wind). Why didn't they apply the Firecrest shape to a 1080? I have never heard a reason, but my speculation is that the advantages of the wide shape don't transfer to ultra deep rims, therefore a wide 1080 may have very little aero benefit over a wide 808 (plus they would probably still be a handful to handle). If that is the case what would be the point of the ultra deep rim? That is my theory anyway.

Okay so that aside, deeper is better right, why don't I just chuck on a couple of 90mm deep wheels and be done with it then? Well it isn't quite as simple as that, not for your front wheel anyway. You see the deeper the rim on the front, the worse it will handle in a cross wind. You are effectively putting a sail on your front wheel after all. The new wide rim shapes supposedly handle cross winds better. But if that is the case then I never want to ride on a skinny aero rim. I have ridden in strong winds where I was scared to get down on my aero bars since my front wheel felt so unstable. Not often, but it has happened (not in a race I should add). Take the advertising about the wide rims with a pinch of salt, if you are riding a 90mm deep front wheel, it WILL be effected by cross winds. That isn't to say it will be unmanageable, I know plenty of people who do it, you just need to be aware is all.

A rule of thumb is that the bigger and more powerful a cyclist you are, the deeper a front wheel you can handle. Most men I know who are competent on a bike could handle a 90mm rim in anything but the worst cross wind conditions. A lot of women often choose to go smaller, 60mm, or even 30mm for really bad conditions. Have a look at photos of Kona and see what the pro women are riding, you will see many of them are on very low profile rims. That is why. Having said that, I know several women who are happy riding an 808 on the front. I am not going to tell you what you should ride on, my point is just don't go into the decision blind.

So if you have to be careful about your front wheel, what about your back wheel. Well to be honest you can go with whatever you want. Since the back wheel isn't doing the steering, and has more weight over it, it is a lot more stable. Most people could get away with a disc if they wanted to and probably wouldn't feel any less stable. For the back wheel the rule of deeper is better really is pretty true. However, there are a few other things that should be kept in mind. The main one is that deeper wheels are heavier, more material means more weight. If your course is particularly hilly, or you aren't particularly strong, lugging around more weight may not be the best decision. For you the extra weight might outweigh the aero benefit of the deeper wheel. That is one of the reasons that only the strongest women tend to use discs (discs are usually the heaviest type of wheel, although some lightish ones are available). Once a course starts getting to around 400m or 500m of elevation gain I think twice about a disc. If the course is a flat one though, deeper is better, it is free speed.

I think that is about it.

So to summarise:

• Be honest about your capabilities. The benefits of an aero wheel are smaller than those of an aero frame. Depending on your speed the wheels may simply not be worth the money.
• The aero differeneces between the various brands of wheel are minor (don't believe all the advertising).
• Choose a product that fits your budget, there is a wide range out there, all very aero.
• Clinchers or Tubulars?
• How deep?

Well that was a lot longer than I thought it would be. I am not sure what I will look at tomorrow. Possibly something a little shorter. TT helmets perhaps.