Technical Q&A with Lennard Zinn: Getting aero’

By Lennard Zinn

Dear Lennard,
So there are two Giro TT helmets, right? (The round one that everyone has and the square one that Lance rides.) In the Vuelta I noticed that David Millar was wearing the square variant. What’s the deal with this? Is one faster in certain conditions? Why David and Lance?
– Geoff Dear Geoff,
As far as I know, Lance’s helmet is not available for sale, whereas the other one is. Lance’s was designed specifically for him and works well with the hump in his back. Apparently, Millar has reason to believe that it is fast for him, too. When I was at the final time trial in the Tour in 2001, John Cobb gave Lance’s second helmet of that shape to Roberto Heras and followed him in the team car with video, thinking it would encourage him psychologically as much as anything else. But, as Cobb had been in on the design and testing of every item of Lance’s aero’ equipment, he must have known that it would be at least as fast for Heras as the standard aero’ Giro, or he would not have given it to him.
– Lennard

When does a nicked disc become unsafe?
Dear Lennard,
I recently purchased a used Hed disc wheel, and upon inspecting it, I found a few minor nicks and scratches. The nicks number less than five (depending upon the depth of the nick as to whether it should actually be counted), and all are very small in length (less than a quarter-inch) and depth (not more than about an eighth of an inch). In my opinion, none of these nicks and scratches gives me any major concern about using this wheel (both on the track and road TT’s up to 40km in length), but they make me wonder about a few things. At what point would such nicks place in doubt the structural integrity of a disc wheel? Do disc wheels have a lifespan at which point, no matter what the surface damage may appear to be, the disc should no longer be used? What are the things a person should watch for when inspecting a disc wheel for safe operation?
– Bob

Answer from Hed:
Our discs, (and I assume other ones also) are very durable. Nicks or dents won’t hurt anything. I would start worrying if you had a cassette-body-sized hole in the side, but even then it probably would not be a big deal if it were in the middle of the wheel. Compared to a wire-spoked wheel, a disc has a lot of material between the hub and the rim. Losing some of it would not be good for aerodynamics, but it would not hurt the integrity of the wheel.As for lifespan, all I can tell you is what we have seen here at the factory. We get about half a dozen 10-year-old and older discs back every year for inspection, and they are nearly always fine. If one of our discs fails from age, it delaminates either at the hub, or at the rim. If the hub breaks loose, the cassette body will spin in the disc side instead of propelling the wheel forward. If the rim comes off the disc side it will do so gradually, and the wheel will start to get very whippy. Most of the delamination I have seen is on wheels that are more like 12-15 years old. It is not common, but if one of our discs fails, this is likely how it will go.
– Andy Tetmeyer
Hed Design

Old disc, new spacing
Dear Lennard,
I have an old Hed disk (126mm spacing/freewheel), and it seemed a shame that it was not being used, so I found an eight-speed freewheel on eBay and am ready to use it in the coming year. The only problem is that I need to fix a spacing issue. I need about an additional 5mm on the freewheel side and 5mm less on the non-freewheel side to make it work. The frame I’m using is an old steel (Tange?) frame set up for 126mm spacing (but a 130mm Shimano 105 freehub fits fine). My question is, do you know if the disk has to have the same amount of space on both sides, or can I go ahead and give the freewheel side the 5mm and take it away from the non-freewheel side? Will this make the bike tack funny?The only other option is to add 5mm to both sides, which will make it about 135mm spacing. Will this damage the frame? And another issue is where to get the spacers. I contacted Hed via their Web site and got a response that I could buy directly from them. When I re-contacted them I got no response.
– Joe

Answer from Hed:
We made and still stock seven- and eight-speed end caps for our discs. Seven-speed end caps are 28mm wide; eight-speed are 32mm wide.If I read Joe’s letter correctly, he is trying to do something that will not work. One of the things he asks is whether he can add 5mm on the drive side and take five off the kickstand side. This won’t work because the wheel will end up way out of dish and the tire will likely rub the kickstand-side chainstay. He can put on eight-speed end caps , but that will increase his wheel width from about 126mm to 134mm. It will be a stretch to muscle the rear triangle open that far, and the derailleur hanger will probably end up sitting at an angle, causing problems for indexed shifting. A frame builder should be able to cold set a steel frame to wider spacing, but I would think about going with seven-speed instead of eight – it is a TT wheel, after all, so I think seven speeds would be enough for most courses.Joe, I apologize if you have had a hard time contacting us. You can always call – we only use voice mail nights and weekends, so you should get a real human if you call during the day. 888-246-3639.
– Andy Tetmeyer
Hed Design

How ’bout those new aero’ bars?
Dear Lennard,
Time trialing is one of my best areas of racing, so aerodynamics is fun to work on, but I cannot find any data on the newer flat aero’ bars like the oval A700TT. My question is, are they any faster than cowhorn bars with clip-ons?
– Dan

Answer from Oval:
In the simplest terms, pure handlebar aerodynamics have not changed in a significant way since Boone Lennon brought the aero’ position from skiing to cycling. The biggest improvements in aero’ bar design are the number of adjustments available on the latest generation of bars to improve rider aerodynamics.

Improvements from 1993 to 2003 in wing shape, brake/shift lever integration and internalizing cable runs have reduced bike drag by less than 20 seconds in a one-hour time trial at 50 kph. The current ability to adjust a rider’s position to maximize speed over distance has taken minutes off hour time trial times in the same 10-year period.

The biggest change from when Boone Lennon, Steve Hed and John Cobb worked with Greg LeMond and Mark Allen in the late 1980s until today, when they are working with Lance Armstrong, is the realization that the function of the aero’ bar is really optimizing the drag, cardiovascular and power (DCP) equation to maximize speed over distance. Boone used to say he would put you in the best aero’ position and you had to learn to breathe and pedal in that position. Now aero’ positioning on the bike is a bit more nuanced.

John and Steve found that the most important function of the aero’ bar was the ability to adjust the position of the rider on the bike – to minimize the drag and cardiovascular load while maximizing the power output to the pedals. You can be super aero’, but if you can’t breathe or apply consistent power to the pedals, you will not be moving very fast.

We have gone from wind-tunnel testing to a process of finding the DCP optimum. This type of testing requires adding heart-rate monitors and power meters to the wind-tunnel session. The massive data output (including multiple speeds, cross winds and positions) of one of these sessions can create an interesting challenge to decipher. That is why the aerodynamics guys make the big bucks.

Interestingly, road cyclists have two significantly different concerns than triathletes. First, pure cyclists do not have to worry about swimmer’s shoulders or running off the bike. Second, they spend 300-plus days per year on a road bike with a traditional 72- to 74-degree seat angle. This means the optimum DCP position for a pure cyclist is going to be much closer to their standard road-bike position than a forward “triathlete” position. John Cobb’s extensive work with both road cyclists and triathletes has made him a champion of the SLAM position, which moves the optimum DCP slightly back from a standard road position instead of far forward. The theory is that you are not going to make a pure cyclist more comfortable and powerful by radically changing his or her position for 10 days of time-trialing per year.

The ability to move the bars, elbow pads and aero extensions a significant distance on multiple axis is critical to being able to find the optimal DCP position.

Within this new DCP optimization process are two other interesting (and ongoing) questions. First, does the optimal DCP for a given bike and rider change with course type? Second, what is the optimal position of the bar ends – low to minimize drag (like the former ONCE squad) or flat (higher) to maximize power and cardiovascular capabilities (like U.S. Postal)? These questions are what make our sport interesting – but both studies require aero’ bars with maximum adjustability in order to reach an accurate conclusion.

Now I can answer your A700 question. The Oval Concepts A900 carbon (845 grams) and A700 alloy aero bars (825g) and the A700 SLAM/Cow (695g) or SLAM/Drop (710g) clip-on combo bars have ultra low frontal area, proper brake- and shift-lever positioning and internal cable routing, making them as aerodynamic as anything else on the market. However, far more important is their incredible adjustability. I have worked closely with both Steve Hed and John Cobb on these designs, and I feel we can now provide you with the best tools available to optimize aerodynamic performance.

In summary, the pure aerodynamics of an aero’ bar is a much smaller factor in today’s bars than the ability to optimize a rider’s position to maximize speed over distance. An aero’ bar with great adjustability is the tool necessary for the aerodynamic fit guys to create superstars. – Morgan Nicol
President, Oval Concepts

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VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.