Get pics of time trial position reviewed for aerodynamics of position?

Discussion in 'Triathlon' started by stowy, Mar 15, 2011.

  1. stowy

    stowy New Member

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    Hi,I've recently tweaked my TT position on the TT bike, after reading adam topham's book about time trialling ( highly recommended - you can get it from www.timetrialling.com)


    So I've taken some pics of my position and was wondering, my friend told me there is somewhere I can post pics of my position and get some suggestions on how to improve it.

    Does anyone have any ideas of places that offer this service? I've come to the opinion that positioning on the TT bike is vital for a given power output if you want to maximise your speed, given that 90% of the force against a rider is drag, which is a product of speed, shape, slipery-ness and frontal area.

    Any ideas would be awesome

    Cheers

    Stowy
     
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  2. swampy1970

    swampy1970 Well-Known Member

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    You could always post on here and get some critique for free...

    There's a chappie on here that pretty much wrote the book on training with a power meter that somehow manages to get 29mph out of 230 to 240 watts. Staggering... Personally I reckon there's no bearings in his bike and everything is suspended via opposing magnets and his carbon frame is actually one huge AGM battery.

    ... and a few other people who have made significant contributes to working out aero bits n bobs as well as training etc etc.
     
  3. stowy

    stowy New Member

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    You are joking! 29mph from 240watts? I wish i could do that! I think my size is a factor (I'm 75kg, 181cm ~6ft), but i can't seem to get over 25mph (40km/h) for a 1hr TT, even though my FTP is 330watts!

    Would love some help. Here are some pics:

    [​IMG]

    So from right to left is oldest to newest, i tweaked the setup twice. The first two i averaged 39.6km/h for 1hr, little wind and out and back, very different seat heights (2nd one was much lower). I don't have a PM so don't know power. The last one i haven't tested yet. This is with normal riding gear, no aero helmet, etc. I lowered seat and bars for 2nd one, then have raised seat for third one, and extended the extensions out further. This can be seen in this next shot:

    [​IMG]

    So top to bottom is oldest to newest, same positions as the previous picture but from side on. I am trying to get flatter and more laid out in the final position, which as i said i haven't test yet. Would love some opinions on this! I really think that 41-42km/h should be easily acheivable with the power i can average for 1hr. Any ideas?

    Cheers

    Stowy
     
  4. swampy1970

    swampy1970 Well-Known Member

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    Clarify those two points in bold will ya... ;)

    First thing to try and do is get your head out of the way. The bottom pic looks like you're getting there but you still have to make that position work with your helmet. Think of it as shrugging your head down. Keep the head angle the same just try and tuck your chin down in front of your chest more. It's uncomfy but you'll either get used to it or get over the discomfort but it'll take some effort initially.

    I wasn't joking about the 29mph. Apparently "narrow shoulders" and massive amounts of aero testing (regression analysis outdoors I believe - could be wrong though) to figure out what works and what doesn't with regards to his position.

    If you did have a power meter you could use something like Golden Cheetah and use the "Chung Method". It's a pretty darned accurate way to figure out your drag and once you have a baseline you can start changing stuff and actually see what works and what doesn't.

    If you really can put out 330watts for an hour in that position you should certainly be doing more than 42km/h. You should be doing about that in the drops on a road bike for that power output.

    Is there any particular reason why it looks like you're leaning over to your left side in all the frontal pics - and do you really need that 6" of strap dangling off your helmet. Chop 'n sizzle (cut and then melt the ends slightly to prevent fraying)
     
  5. stowy

    stowy New Member

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    thanks swampy for the tips.

    Yep, i'm starting to wonder how accurate that power test was, i did it on an indoor cycle meter, they took off the rear wheel and put the chain around a wheel that was resisted by a magnet, it was and indoor 40km TT, it said i averaged 40.3km/h and 333watts.

    but i don't have a PT or anything to get consistent readings and feedback.

    The angles of the photos aren't good, it was just a quick snap by my GF at home, so prob i could be straighter.

    not sure what i can do on a road bike for an hour, but it obviously wouldn't be over 40km/h based on the TT tests i've been doing on the TT bike. so maybe i need to get a PT and do some outdoor real life testing. just need to collect the $$ together.

    thanks again

    Sam
     
  6. bidaci

    bidaci New Member

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  7. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Stowy,
    I second Swampy's advice, especially about shrugging or 'turtling' your head. You can think of it as sagging your neck and head down between your shoulder blades, you can think of it as shrugging your shoulders up towards your ears or you can get there through the 'head drop, chin lift' method. While riding on the trainer let your neck go totally slack and let your head fall till you're looking back at your rear cogs. Then without lifting the top of your head, rotate your head back up leading with your chin till you can see far enough ahead (which doesn't have to be very far in your most aggressive race position, just enough to scope the white line and see road obstacles but you don't have to see a quarter mile up the road like we're used to on the road bike, just be careful riding in this position and train in a more conservative head position on busy roads with intersections or driveways).

    I also second his observation on power and speed. You have the body type of someone I'd expect to be very 'aerodynamically gifted', long torso not a lot of excess on your frame and based on those photos a flexible lumbar region that lets you get very flat. 300+ watts should take you through 40K in well under an hour. I've broken an hour in the 40K half a dozen times in the past few seasons with anywhere from 260-290 watts and I'm not the most aerodynamic rider with less flexibility and not as lean and long overall. But I have spent a lot of time working on my position and field testing various candidate positions.

    If possible reshoot some images taken directly from the side with the camera at least eight feet away and ideally about three feet off the ground and not pointed side to side or angled up or down. So IOW, place the camera on a sturdy table, bookshelf, tripod or some other support and try to set it up so you can recreate the same fitting studio for additional shots as you make changes over time. If you're serious about dialing in your position you should also get an inexpensive spiral notebook and keep a record of key measurements along with things like field testing results, general impressions on comfort and speed and any race or hard training day results. Over time it's what let's you identify patterns and figure out what really works, it also helps you avoid chasing your tail and going back to positions you've already dismissed or getting back to positions that were better if you make some changes that don't work.

    Here's an image from some recent TT fitting where I was playing with a longer 'faux superman' style position. You can learn a lot from measuring angles and comparing things like helmet height, torso angles, hip angles, knee angles, etc. Try to shoot something like this and post it here. Having said that, images can be misleading and I've definitely chased some ghosts in terms of ultra low positions that looked incredibly aero but turned out to be pretty slow even though I could ride them and even generate decent power in them. Sometimes looks can be deceiving and even though we can optically measure frontal area with very careful camera setups we can't optically measure Cd and both matter. BTW, videos are better than stills for fitting as we tend to move around when putting real power to the pedals and it allows us to extract frames for things like top and bottom of the pedal stroke or compare deep head tuck with more relaxed positions.

    [​IMG]

    BTW, in terms of field tests if you don't have a power meter than go old school and do roll down tests. Try to find a low traffic street that goes downhill long enough to get you up to or beyond race speeds from a dead stop coasting but then either flattens out for a long distance or ideally goes back uphill. If you find one with a dip followed by a hill then mark your start spot, always start from a standstill and see how far you can coast up the final hill in the aero position before putting a foot down or till you reach a predefined very low speed. If it's flat either see the speed you hit at a certain landmark like a certain telephone pole or streetsign or see how far you coast in your aero position before you drop down to some defined low speed. You can learn a lot by testing positions with this simple test. You still want a calm low to zero wind day and ideally no car traffic during your test runs. Do several runs in each position to reduce testing errors.

    -Dave
     
  8. coneofsilence

    coneofsilence Member

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    You need to clean your work bench.
     
  9. stowy

    stowy New Member

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    Hey Swampy,

    Thanks heaps for that post, some good stuff in there. Like the idea about roll down tests.

    Do you have any ideas about other tweaking i can try? Should i try moving seat forward, or angling bars up,
    stuff like that? Should i change seat height, bar height?

    I did another TT effort with the 3rd position today, and I think I've definitely made an improvement with that one.
    I didn't do the full hour because my legs were cactus, and don't know what my power was, but i did average over 40km/h
    steady state.

    And this was without aero gear and not in race conditions, so traffic, etc. So I reckon in TT mode i could
    probably do ~42km/h with this position, which would be a major win for me based on my current best for 40km being 39.5km/h in training
    and 38.7km/h in a race.

    Also, I have a question, if my threshold heart rate is ~175bpm and I could only hold 160bpm today because my legs were tired, would that
    indicate a lower power than I could normally put out? Or is it possible to put out your FT power on a lower heart rate after hard training?
    Will try and get some more pics done in the way you asked and post them up.

    And I agree about the workbench! Nice superman tho.
     
  10. swampy1970

    swampy1970 Well-Known Member

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    It's a workbench and not a work "fancy storage unit" - it looks like Dave has other priorities and quite rightly so. ;)

    Don't thank me - thank Dave for most of the good stuff so far in this thread.

    I wouldn't change too much at one time because you'll have no reference of what change actually did make a difference and most importantly, whether the extra speed did come from a change and not just feeling a bit fresher and pressing on the pedals harder or because the wind was a bit more cooperative.

    Project: skunk stripe.
    [​IMG]

    High quality photos nabbed from a single frame shot of an iPhone video of some not so serious positional fiddling on the very old TT bike. Darkness, suspect quality and careful shadow placements hide the important details ;) Note the super hubless front wheel.

    15 years ago, that bike saw a bit more action, outdoors...
    [​IMG]

    ... and from what I recall my nether regions suffered as a result. A good TT saddle may be a good option - the nose of a San Marco Regal is not a good place to spend more than 5 minutes on.

    It sounds like you're getting all gung-ho about getting aero but oddly enough probably the best 'device' to have right now for you to eek out some free speed would be a power meter. Sure, a set of good wheels will get some extra velocity for nothing more than a dent in the check book but a power meter will help stick you in a position that's verified to work and be very aero and you'll have data to back that up.
     
  11. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Without better side on shots that show the bike all the way down to the bottom bracket and ideally at least one with leg at full extension it's hard to say too much, but first impressions:

    - The most recent side shot photo is getting pretty close to as low as you'll likely want to get. You might try going down another cm or so, but pretty soon your upper back will start to slope down a bit which trades torso exposed to the wind for upper back exposed to the wind and generally costs you power from the resulting tight hip angle. I can't get a good read on your current hip angle from those photos because they're chopped to exclude a bottom bracket or fully extended leg reference point and they're shot at such an oblique angle which skews things. But from the basic neanderthal fitting starting point you're closing in on the point where 'your acromiom process is level to the origin of your latissimus dorsi' or the point below which you start exposing upper back to the wind. IOW, it's probably plenty low and at most you might play with a cm or two lower but I wouldn't go there unless your current position or higher doesn't get you where you want to be and then I'd only try lower along with some form of field testing to make sure it's worth it.

    - The arm position is much better in the most recent shot, you look way too cramped in that middle shot. Conventional (non superman) positioning shoots for roughly a 90 degree angle between your torso angle and your upper arm. The middle shot definitely looks too tight to me, the bottom one better but you might stretch a tiny bit more with your pads a bit further forward if possible.

    - Hard to say without the helmet on, but the latest shot looks better from a head turtling perspective. Wear the aero helmet in any new shots you take to see how it all lines up and how well you keep your head turtled. In the upper two shots the helmet is nice and flat which is good but it's still adding a lot to your projected frontal area as the highest thing hitting the wind as it's well above the high point of your back.

    - The front shots look pretty good from an elbow width standpoint. Again hard to say with the off center shooting angle in the photos but your elbows appear to be sheltering your knees nicely. Your hands however are pretty far apart. The British pursuiters played with something like this for really short events with some success but conventional TT fitting wisdom is to have the hands very close together even if the elbows are a bit wider. You can generally get a position like that even if your aero extensions don't rotate laterally by rotating S bend or ski bend extensions along their long axis. IOW, you spin the extensions in their holders so the tips rotate in towards each other. It's kinda hard to explain but works nicely if the brackets don't allow you to angle the extensions inward in the horizontal plane. In terms of field testing positions I'd compare a hands in with current elbow width to a hands in with slightly narrower elbows if possible.

    Without better photos or video it's hard to say more but you mentioned some saddle height concerns. Maximum knee angle determined by saddle height and setback is one of the easiest things to validate with fitting photos. See if at least one of your aero position photos includes a capture of your pedal stroke at full extension ideally shot in motion to capture your actual foot position during the pedal stroke.

    -Dave

    P.S. Can't figure out why dudes on these boards care about the cleanliness of my basement but for the record that's not my workbench, just an unused work surface that tends to be a catchall for stuff, my workbench has my truing stand and tools and yes it's typically a mess as I use it a lot, tools go in the toolbox and I don't get off on painting outlines for all my tools on the wall and hanging everything up for display but I can't see why anyone cares...
     
  12. swampy1970

    swampy1970 Well-Known Member

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    For that side shot that Dave suggested have it taken while doing a hard effort. You'll likely pedal differently tootling around for a couple of minutes at 150watts than you would after 15 minutes of threshold work. Heck, you'll probably do everything differently after 15 minutes of on the rivet, full gas riding - the way you sit on the saddle, the way your shoulders probably end up hunched, head straining because your arms and shoulders are fatigued.

    Oh... I'm such the bringer of happy, happy, joy, joy.
     
  13. stowy

    stowy New Member

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    Thanks guys for that feedback, lots of info there, i will take it on board, do a bit more testing in current position and try and get some more pictures up here when i can.

    Stowy
     
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