Friday, July 09, 2010

Equipment - How to "Do" Aero Wheels

Okay, yeah, you really want some of those sexy carbon aero wheels. The pros use them all the time, they go really fast, and they make a really cool "whoosh-whoosh" noise when you sprint on them.

So you just buy them, right?


The following is a mini dissertation on how to approach buying those sexy carbon aero wheels. It's my ideal way of getting the best aero return for the buck while maintaining "bike handling fluency". Since aero wheels handle a bit differently than non-aero wheels, it benefits everyone if you get on the bike and feel totally at home when you have an aero front wheel.

This whole thing helps you from looking ridiculous in your first race on your "race wheels". At one of the early Bethel Spring Series races, perhaps even the first one ever, a guy unveiled his precious new aero wheels for their trial by fire - his first ride on them would be in a mass start race. He floundered at the back in the (typical Bethel) extremely gusty conditions, unable to handle the wind hitting his front wheel. He finally crashed himself out, breaking some bone/s in his body. He threatened to sue (he was a lawyer) because, well, I'm not sure why.

Eventually someone talked him out of suing everyone involved. Can you imagine the testimony?

"Well, your Honor, I, um, just fell over."
"You 'just' fell over?"
"Well, the wheels caused me to fall over."
"So you filed a suit against the race promoter?"
"Well, he let me race the wheels."
"You said earlier though that he uses the same wheels too. Did he fall over in his race?"
"No, but he trains on them!"
"And you don't?"


See, that's what this post is about - you need to train on equipment that you'll use in the race. Racers spend some good amount of time making sure they have the right position on the bike, the right shoe alignment on the pedals, stuff like that. They also need to make sure they feel comfortable with their bike as it would be set up on race day. If it means using an aero front wheel, then it means the racer should feel comfortable on an aero front wheel.

Now, let's take a little detour and talk about tubulars and clinchers. If there were no functional differences between the two, my recommendation would be to get an aero clincher wheelset and be done with it. But there are a couple differences, enough to convince me to spend a bunch of money to buy tubulars.

I prefer to use tubular tires in races - they're lighter overall (as a system, not necessarily the tire itself), they don't pinch flat, and tend to be very durable for a given weight. Tubular tires don't need much rim material for support, so the wheels can weigh a lot less. It's typical to see over a pound difference between matching tubular and clincher wheelset weights.

On the other hand, I prefer clinchers when I train. They're cheaper if I flat ($7 for a tube versus $80 for a standard race quality tubular tire). Clinchers are easier to change. With furious pumping, it's possible to change a tube in under 2 minutes while on the side of the road (biting mosquitoes contribute to motivation). Even a leisurely flat fix will take only 4 or 5 minutes (no mosquitoes). And once the tube is replaced, a clincher tire returns to 100% performance - you can brake or corner on it as hard as you normally do.

Changing a properly glued tubular is time consuming at best. It takes me a good 5 to 10 minutes to remove a tire if I want to reuse it - a flat one might take a few minutes to remove. And although it takes about 10 seconds to install a spare tire, it'll roll off pretty easily. When you get rolling on that spare tubular, you have to take it easy, else you'll find the tire rolling off at some inopportune moment. I consider a "post on-the-road-replaced tubular" to be about 10-20% functional use. I wouldn't want to corner or brake hard on that tire for a while, not until I got home and glued it on properly.

Therefore it's better to train on clinchers, race on tubulars.

Now that we got that out of the way...

One of the most significant things you can do to a bike to negatively affect its handling is to slip in an aero front wheel. That sexy, beautiful, tall, (usually) carbon fiber (shrouded, sometimes) wheel is fantastic in the wind tunnel but can really wreak havoc with your straight line stability in gusty wind situations.

If you think a tall profile rim catches a lot of air, a disk wheel is insane. I had a 24" front disk wheel on a TT bike and a gust of wind took me across a full lane of road. I was on cowhorns (this was before time trial bars as we know them) so I had a relatively strong grip on the bars. It didn't help. If there'd been a truck there... I literally creeped home on the bike, arms rigid with tension, hoping the wind wouldn't spontaneously teleport me sideways 8 or 10 feet into a bus or a lamp post.

In fact, at the Hawaii Ironman, they had to forbid competitors from using disk wheels up front. Riders were getting blown off the road, blown off their bikes, due to the wind catching their front disk wheels.

See, aero wheels act as a rudder. And rudders don't belong up front in a normal bike with normal geometry. Standard bike geometry works when the front wheel wants to point straight forward. But when wind hits a wheel with a lot of surface area, the wind turns the wheel. Suddenly the geometry works against you - instead of stabilizing the bike, it (along with the aero wheel and some wind) destabilizes it.

Aero front wheels require more steering input from the rider. Steering with your hips doesn't work too well - you have to turn your bars a bit too. If you don't get used to this concept in training, you'll enter a race with sub-par bike handling skills. In extreme situations, this can literally throw you over the handlebars, like the example rider above. And in less extreme situations you end up simply a squirelly rider. Neither is good.

Of course we all want to avoid that, but how?

Funny you should ask. Here's how.

Step 1

Buy both a clincher and tubular front wheel with similar (aero) profiles. For example, I have two Specialized TriSpoke front wheels (now sold as a HED3) - a tubular and a clincher. I got the clincher first, since I could train on it. Later I bought a pair of tubular TriSpokes. I never bought a clincher rear TriSpoke. Later I repeated the idea of buying matching front wheels, one for training, one for racing. I did this with Spinergy Rev-Xs, Reynolds DV46s, and now the HEDs (Stinger 6 and Jet 6). I'd use the clincher for training, the tubular for racing.

Note: the newest HED spoked wheels (Stinger/Jet series) have an additional variable, and I note it at the end of the post. However, they (as well as the TriSpokes, Rev-Xs, and Reynolds) handled similarly in wind front and rear. I imagine the Williams, Eastons, Neuvations, and other profile matching carbon clincher/tubular front wheels will handle similarly as well.

Advantages of buying two front wheels, one tubular, one clincher:

1. Similar profile front rims handle similarly in wind; you can use the clincher in training, the tubular in races. You'll be intimately familiar with the wind-handling aspects of your race wheel.

2. Front wheels are universal (no cassettes, no weird spacing). Okay, except for disc brakes and rim width. But in general, if you buy two front aero road wheels, you can use them on virtually any road bike, with any drivetrain set up. You can even use a road front wheel on a track bike (note use of TriSpoke in pictures), if you use appropriate skewers or convert to a bolt-on axle. With rears you can't - Shimano/SRAM vs Campy, 8s vs 9s vs 10s vs 11s, frame width, fixed gear versus not, etc.

3. Number 2 above means that front wheels are cheaper because manufacturers don't have to stock umpteen combinations of hubs and such, and the spokes are all the same length (except weird wheels like the G3s or the FSAs).

4. Front wheels are stronger, usually last longer, etc, due to the even spoke tension and lower loads it sees.

5. Aero front wheels affect handling the most, so if you're going to get used to one wheel in training, get used to the front one.

6. Front wheels affect aerodynamics the most (2/3 of aero effect of wheelsets comes from front wheel), so it makes sense to get two front aero wheels if you can only afford to buy two wheels. This way you get the best bang for the buck in races.

Step 2

Buy matching rear tubular wheel for races so now you have 3 wheels - a clincher front and a tubular set.

1. Lighter rotating weight in the rear (tubular rear).

2. Looks cool (matching wheels). You gotta look cool, right?

3. Stabilizes rear of bike (rear aero wheels do that).

4. Tubular rear wheel typically more durable - no pinch flats, stronger rim for a given weight, or, conversely, lighter for a given strength. Except for super-wide rims (Stinger 6, the new Zipps), it's also much easier to ride on a flat tubular than a flat clincher.

Try doing that on a clincher...

5. Doesn't affect handling much beyond that stabilization - you don't have to train with an aero rear wheel if you don't want to.

Step 3

If budget allows, buy matching rear clincher for training and spares for racing. Now you should have 4 aero wheels - a set of aero clinchers and a set of aero tubulars.

1. Two pairs of wheels that handle similarly in all aspects (twitchy up front, stable in the rear).

2. You can work on speed a bit more in training (i.e. using aero wheels to your advantage in going faster on, say, group rides). Remember, training on clinchers is easier than training on tubulars - on the wallet and also quicker to fix a flat.

3. Typically clincher aero wheels are heavier so they require more work to get up to speed - you can work on your jump/acceleration, which is about the only thing the wheels will significantly affect. Unless one pound is a significant portion of your combined bike/body weight, it won't affect steady speed climbing that much.

Step 4 (optional)

Finally, you should keep a box section front wheel for really windy days. Most riders start with a box section clincher so just keep that wheel for training. When you feel like it, get a box section tubular front wheel (or one that's relatively "un-aero") for those really gusty race days. I don't have one at this point, but on those really gusty days I'll prepared to use my box section clinchers front and rear. I'll sacrifice aero for stability in gusty days as well as any kind of major road race with 50+ mph descents (not that I've entered any, but if I did, I wouldn't use an aero front wheel).

So that's that.

Now, to get to that exception I mentioned earlier in the post.

HED clinchers and tubulars have wide rims for different reasons.

The clinchers are wide to get the wheel/tire to be more durable and more comfortable. The wider rim allows you to run lower pressures, resulting in better comfort, while still avoiding pinch flats. I run about 10-20 psi less than normal on my HED clinchers compared to normal box section clinchers (95/105 psi, vs 115/120 psi). I find the lower pressures corner a bit differently, so that's something I have to account for when I swap wheels. However, the aero handling aspect (catching gusts, cornering as far as wind goes) stays pretty constant between the HED aero clincher Jet 6 and the aero tubular Stinger 6.

Keep in mind an important factor: HED tubular rims are wider ONLY FOR AERODYNAMICS, not for anything else. You need to use the same air pressure as on normal width tubular rims.

On my HED tubulars (Stinger 6s), I run 120-140 psi, depending on my mood. At 105/110 I thought my tires were sliding everywhere on smooth pavement; at normal pressures I'm fine. That's my preference in tubular tire pressures in general; yours may be different.

Questions? Comments?

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