Wheel cover question
I raced yesterday with a power tap wheel and wheelbuilder cover. My tire flatted in transition just a few minutes before transition was closing. I didn't have a tire pump in transition, so rather than mess with changing the tire myself, I just ran it to bike support.
As the guy was changing my tire, he said that given the course that I was riding and the wind conditions of the day, that cover was going to do nothing but slow me down. He recommended I take it off, or not ride it in the future when on a windy and hilly course. This was an Olympic distance tri which was mostly flat with one steep descent into a river valley, followed by a steep climb out. It's an out and back course, so you ride through the river valley twice. It was windy, but I'm not sure of the exact wind speed. He was talking about yaw angles, and wind and climbing, and I honestly didn't pay any attention to the specifics. I just wanted my wheel fixed and to move on with my race.
So are there circumstances in which you should not race with it? Would I have been faster on that course without it? It was not a bike PR for me, but I'm not in PR shape so I was relatively happy with my day. Just curious, so I can make sure I decide on the right gear for future races.
Comments
It's the deepness of the rim on the front that can have serious impacts, especially if you're not used to handling it in windy/gusty conditions.
I always ride with a disk cover when racing.
As you know, I'm well acquainted with the course and the wind in the area - that part of the course is part of my almost-every-weekend route. Other than that hill (well, really it's a river valley), the course is only modestly rolling like you say. I hit 50 mph descending yesterday without my aero gear except a helmet...no doubt that a disc cover is faster going that fast. No doubt that the disc cover makes only the gravitational difference when going back up at 6-8 mph.
I haven't ridden with my disk cover yet this year because I typically don't until a week or two before I race, but I have ridden that hill and those winds over and over and over. I cannot specifically tell you that the disk cover speeds you up or slows you down because of the difficulty of running the proper control experiment, but I CAN tell you that when I ride that area with the disk cover on, I generally ride the course a few minutes faster. (I have occasionally gotten lazy and not taken the cover off for a couple weeks after racing, too.) I have never felt that the disk cover hurt my ability to control the bike. As Scott mentions, the front rim makes a much bigger difference in handling.
If you go to any of the wheel company sites (HED, Zipp, etc), you will see graphs like the one Tom points out, except the X axis will be labeled something like " effective yaw", which is the effective angle of the wind. (The effective angle of the wind obviously changes with your own velocity...the faster you are going, the closer the wind is to going exactly in your face...) Because of this bit about yaw angles and steering it is NOT always better to run an 808-depth wheel vs a 404-depth wheel IN THE FRONT. That said, I'm unaware of circumstances where the disk isn't at least as good as (and generally better than) any other wheel in the back...again assuming it doesn't affect your handling.
Incidentally, another person commented on my cover in transition and said that it wouldn't do me any good unless I was going 30mph. I have no idea who he was or why he felt the need to tell me that, and I had nothing much to say except that I was quite sure I would be topping 30 at least twice that day.
The short answer is that both guys you talked to, especially Mr 30mph, are just wrong. Politely say thank you and walk away
, the come in here and ask us for the real scoop.
Many don't know this, but the benefits of aerodynamic gear and setup are more valuable at lower speeds because the benefit has longer to express itself of the ride. We always recommend that everyone races with an aerohelmet (~$150), wheelcover ($89), address their bike fit, and pay close attention to things like bottle placement, cockpit setup, etc.
Race helmets are much, much more common these days. I was wearing one before they were cool and I was uber dorky in my '05 LG "Kazzoo" the Martian helmet.
Also very cool to not be a fast athlete but with a very clean, well thought out setup. TONS of people hanging 10lb of crap on their $$$$ bike because they haven't done due diligence to learn about clean, efficient setups.
And nothing wrong with being smugly frugal when you race your bike and $89 wheelcover next to the $1200 Zipp disk wheel. Same benefits for a fraction of the cost.
If everyone were riding for a fixed period of TIME, there would be truth to the "don't bother with aero gear beneath XYZ mph" business. But everyone is riding a fixed DISTANCE, and that makes all the difference. Even if you are helped by a smaller percentage, it's a smaller percentage of a bigger number and the balance works out in the slower rider's favor in terms of absolute time saved.