Aero helmets
fire tri
Posts: 173
in General Chat
hi all,
heres a question for you,
Aero helmets, how much benefit do they give over a standard one, read some articles saying they can give minutes worth of difference!!!
Is this true???
They seem a cheapish way of saving time on tt and tri bike legs
heres a question for you,
Aero helmets, how much benefit do they give over a standard one, read some articles saying they can give minutes worth of difference!!!
Is this true???
They seem a cheapish way of saving time on tt and tri bike legs
0
Comments
You can get a big time benefit. Also, I find if I am motivated to push harder on the bike as well - to avoid looking "all the gear and no idea" in my silly hat.
Alternatively, use the Fabian Cancellara method of speed increase and hide an electric motor in your downtube (allegedly)
I can manage 20mph average on a 25miler
Actually did 21 mph for tatton olympic on sunday!!
So would a helmet benefit me do you think???#
Really would like the proper tt bike but too expensive at present for my budget, and credit is a long time paying for it!!!!
I've posted before on this, could only find this one
pointy-helmets-yay-or-nay-t47894-10.html#p59575
Can't find my best ref as I have some of them bookmarked (sad git I am ) but also here:
http://www.pponline.co.uk/encyc/cycling ... mina-33073
Get a pointy hat
I may be wrong but shouldn't the helmet
Benefit The slower rider more as a percentage
Gain over time because they are gaining aero
Benefit over a longer amount time?
Again I posted on this a couple of times but can't find my links now - sorry
Another link
http://www.cyclingtipsblog.com/2010/04/ ... equipment/
Friction, or more correctly drag, is inversely proportional to velocity for low viscosity fluids (eg air)...I think the key factor being that it increases by the square of the velocity, or in plain English as speed doubles, the drag quadruples.
Therefore at low speeds the amount of drag impacting the rider is much lower than at higher speeds, so although the rider will take longer they won't gain as much benefit. In fact due to the proportional nature, if you're really slow, then aero equipment may not benefit you at all, as the actual resistance (drag) is minimal, therefore any percentage gain is negligible.
...but having said all that, some equations for drag state it's proportional to velocity, which changes everything, and the actual improvement for aero stuff is usually given at a set speed, or it's a flat percentage gain...neither of which help work out what the real world benefit would be.
So all in all, I think there’s a benefit regardless of your speed, but it becomes more important the faster you go.
However what it doesn't take into account is the friction of the bike (rather than wind resistance). So I think at low speeds there's still less of an overall advantage due to inherent friction, but so far I'm not sure how low those speeds need to be...
Again as I remember the problem is not only the friction caused by air passing at or close to the surface but of the turbulence caused by non streamlined objects hence dimples etc to create near surface drag - laminal flow is that the term? - to slow down the air and reduce turbulence
Drag does not have a constant value in terms of watts required but does have a fixed coefficient (unless the body changes) and the power output required to overcome it increases at the square of velocity as I recall and the power output required at any velocity is the cube.
Found this
http://www.mne.psu.edu/lamancusa/ProdDi ... ecalc1.htm
I used settings of:
Gear ratio .269 14/52 (unrealistic I know but closest I could get)
Air Resistance Full Crouch 0.0032
Rolling resistance .004 racing clinchers
So little old me at 20mph needs 144.12watts, 76.007% (109.45w) of which is to overcome air resistance and 18.992% (27.37w) to overcome rolling resistance.
The elite at 25mph needs 261.24watts, 81.902% (213.96w) to overcome air resistance, 13.097% (34.21w) rolling resistance
Let us say my pointy hat saves 10 watts at 20mph that equates to me having the equivalent output of 154 watts and achieve a speed of 20.52 mph. The elite rider at 25mph to get the same increase in speed to 25.52mph needs the equivalent of 276.34watts or a 15.1watt saving. The elite therefore needs to achieve a 150% saving over my 100%
My brain now is about to explode so can someone step in to finish this off (where are those damn links??)
After posting a 1hr 7 minutes at Allerthorpe tri last month on a std road bike with no aero helmet, no carbon aero wheels, and no tri bars fitted, im interested on how much time i could save. Obviously with a few tweaks without buying a TT bike (yet) i should save time but im not sure how much?
http://www.cyclingtipsblog.com/2010/04/ ... equipment/
Ah here we go, very own 220 mag
http://www.220triathlon.com/train/aero-biking-part-two
You will loose all the advantage if you tip your head forward too often. On a hilly course consider the extra weight. You also need to be careful you do not overheat.
There's a good calculator here http://www.exploratorium.edu/cycling/aerodynamics1.html that you can plug figures into.
Overall it's basically down to the law of dimishing returns, ie the faster you go the less actual time savings you get.
Simplifying things, the two factors that will reduce the power required/ increase speed (however you want to look at it...) are the surface area and the drag factor. Both work in the same way in the calculation
So to maximise your speed, reduce your body's frontal area as much as you can (free), and then it's down to the bling/ pointy/ dimpled things to reduce the drag afterwards (expensive).
You still get the same percentage power saving regardless of speed, however as the power output goes up by the cube of your speed, the power saving in terms of raw power increases drastically. That's why it doesn't feel like aero stuff benefits you at lower speeds, becuase the watts saved are low, however the faster you go the greater the watts saved are.
Hope this helps someone else get their head round it...it's been bugging me for ages!!
For me getting 6KG's off is far more important than a pointy hat, no matter how much aerodynamics i got on me noggin carrying too much weight is no goood
so i may invest once i get the weight off and get over the OMG!!! i look like a cock factor.
But awesome thread and obviously a lot of time spent on research for this nice one guys.
Zac you must be single
Good luck with the weight loss. Just before I started out 4yrs ago I was about 13st - 82Kg and now 66kg and most of that happened in 18mths - had always been active but just crept up
Good luck and get a pointy hat.
I gave up smoking in jan when i decided to train properly for my first year of tri's.
I have gone from 13.5 stone to just under 15!!!!!
Try carrying all that when cycling up hill and running, not good!!!
I know some will be muscle as hadn't done any real training of any kind for years, just hoping i can lose it again for next year!
If I can keep my power output, and drop weight, which will also reduce my frontal area, then I'll be unstoppable on the bike next year....
Muscle atrophy is hard work.