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12/17/2010

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Eric D.

There is only one problem here and perhaps it's the camera angle but I don't think so. The rider in the above photos appears has anything but a good aero position. I have to think someone with a more aggressive aero position may see some different results. No?

Nick

Joe, I had a similar experience after visiting the wind tunnel last year. Lowering the head, or sticking your neck out and 'lowering' the ears and still keeping the tail of the helmet down, coupled with narrowing the pads took two and a half minutes off my 40km time, simple but effective. We also raised the stem by 20mm which increased power and made it easier to see and lower the head. Seating the helmet on the back of the head makes it easier to see too. Drag down, power up, massive savings, safer position. 45W saved by spending 2hrs in the wind tunnel. In total 4:50 off 40km time, 9min off 50M TT. Race proven!

Joe Friel

Eric D--The rider does have a rather high shoulder position. He does some ironman distance races which may be the reason for this. But all of the tests were relative to the bike set up you see here so his position was not a variable.

Susan

Love that you call it the turtle -- it's the term I use to remind myself to tuck my head between my shoulders, assuming it would be faster. Good to know it really is. Wonder if turtles really do that....

Trevor

Joe,

First off I'd like to say thanks for your blog and the information you provide in it. I own the training bible and ordered your new book yesterday. I'm sure I will enjoy. The aerodynamic question I have is did you happen to test different water bottle options (i.e. - Front (handle bar) mounted v/s an aero version on the seat tube)?

Joe Friel

Trevor--Several different types of drinking systems common for triathlons were tested. The testing was paid for by www.PowerTri.com so they own the data. I was given permission to comment on head position. They will publish the remaining in due time. Keep checking in with their website.

Bert

When drag is lowered by 1.5%, then 1.5% power is saved at that speed. Power (phys) needed to drive a bicycle increases as the third power (math) of speed. This means that for small variations the speed increases by a percentage approximately 1/3 of the percentage extra power (phys) you can spend. In this case this means a speed increase of 0.5%. This rule is illustrated by Nick's findings above: assuming that his 45W power savings are about 21% of his total power, his speed should increase by about 7 percent, which corresponds quite closely to his improvement of his 40km time: something like 4:15 on a presumed 60:00, although this increase may be a bit too large to apply this simple rule of a percentual speed increase being equal to 1/3 of the percentual power (phys) increase.

Michael Paul

Do you have wind tunnel data, actual numbers, on the new helmets compared to the old? I have an old Troxel (the plastic one) with the dimples--I also still have an old Bell Stratos that I pulled out of moth balls in the mid 90's and beat all my best times. How do these two compare? What about riding with a normal helmet, like a Giro Ionos? Trying to decide if it's worth my $$ to get a helmet newer than my 12 year old Troxel.

Joe Friel

Michael P--power Tri has the data. Start by searching their site (http://www.powertri.com/). At one time they posted the data there. If that search doesn't produce it then write to them directly. Good luck.

Michael Paul

Thanks Joe! I love messing around with numbers. I used to be so delicate with the aerodynamics, back when I was pretty darn good at time trials.

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