"Obviously if you push forward and low and cramp yourself - you will lose power."

Not sure I follow here. I can see slide back and go low might lead to cramping yourself, but I find sliding forward and going low works.

Define "power output".....

There are many different data points...max power output, sustained, etc. Not the mention the aero factor...which is key because most of a cyclist's power is lost fighting resistance.

Be a bit more specific in your question or give a situation.

If you sit up like a sail and ride slack, you should have no less power than forward and moderately low, assuming the minimum hip angle for both is the same. Of course, this is not totally true in that some people have musculation adapted better to one than the other and there are a few other factors

A 73 angle and 80 angle are only the same relatively (basically you are rotating your frame of reference by 5 degrees) if the level saddle on 73 degree is dropped by 5 degrees tilt when you move forward to 80 (assuming same open hip). Even then it is not identical, since gravity has a different interaction with your body and pedalling dynamic when your saddle is pointed 5% down vs level.

So the answer is similar, but not identical.

My question revolves around the idea that your seat should be in a certain position relative to our pedals. How do you fit a rode bike? Should you ride with your seat slammed back - in the middle - slammed forward. How about seat angles of bikes at 73 vs. 75. Does it matter at all? Why do smaller frames tend to have steeper seat tubes?

I ride my tri bike - P3SL at about 80 degrees. I can ride a CT and do 2x20 min as hard as possible without a significant fade. Lets say I can average 230 watts for that set. Now I get on a road bike and sit at 73 degrees - should my power be similar if I am equally adapted to each?

Why is the convention to ride road bikes at 73? Why do people say you climb better on a road bike vs. tri bike (I assume they feel that they can produce more power in a road position - why?). Hence my question about seat angles....

Does that help?

Dave

I can't seem to find the article....but read one a few months ago that (in your example) a slacker seat angle produces more power due to the (fractionally) lower center of mass...and its impact on the pedal stroke. I'll find it after my swim....

" Lets say I can average 230 watts for that set. Now I get on a road bike and sit at 73 degrees - should my power be similar if I am equally adapted to each? "

I would guess to say that you could produce the same power but the tri bike would require less cadense...[i tested this on a spin bike]

Why is the convention to ride road bikes at 73? Why do people say you climb better on a road bike vs. tri bike (I assume they feel that they can produce more power in a road position - why?). "

Slacker seattube angles seem to suit a more up-right seating [now i know some of the fastest TT riders use 74 degree angles] and use a different muscle group as well...Tri angles seam to mimmick a closer to running position [this is from what i've watched in the motion comparison....i could be wrong though]

The road bike is easier to climg with because the pedals tend to be forced in the forward motion compared to the TT/Tri bike which pushes the pedal down toward the ground more....

My understanding, as an expert armchair quarterback :-) is as follows:

1) a Standard Road Position has been arrived at since it puts the body in the optimal position (for most people blah blah blah) for power output, oxygen uptake and also deals well with bike handling issues.

2) Since competitive cycling generally happens in bunches, with sacrificial riders sent to the front, aerodynamics is not a critical issue

3) A Tri Position (presumably on a tri bike) aims to keep the power output and oxygen uptake, equal to a road position (through the same body angles)

4) A Tri Position also gains an aerodynamic advantage as this is important to a solo triathlete. Being a solo triathlete, bike handling is less critical.

5) A Tri Position is NOT simply dropping your elbows onto a set of aero bars. That is more of a TT Position (as determined by UCI rules) While a TT position is not as favourable as a true Tri Position (body angles and oxygen uptake are compromised slightly compared to a true Tri Position), it still gains most of the advantages of the Tri Position as the improved aerodynamic gains more than offset the reduced power and oxygen uptake.

6) In theory, a properly set up Tri Position does not reduce ones power output since body angles and oxygen uptake remain the same. For the same power output, speed increases due to reduced aerodynamic drag on the rider and bike combination.

The above is a simplistic overview but conveys most of the important issues.

If you are getting lower power output while on the aero bars, it is likely that your positioning is not correct and you are getting reduced power through poor body angles or poor oxygen uptake from impeded breathing.

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

yes there is a relationship between power and seat angle, but the real question is, what in the heck is the relationship?

there is a huge no. of physiological, biomechanical, and power variables affected by rider hip angle/frame seat angle. and these can variables can also be affected by sliding the seat fore/aft in the rails; by using rear, zero, or forward setback seatposts; or by a rider just sliding on the saddle during riding. there are likely a few optimal seat angles for various body types and for different types riding and different levels of effort and duration.

however, nobody knows what such "optimal angles" really are, as they have been studied pitifully little.

nobody seems to want to do such studies, as doing a series of good studies on this question with a decent no. of subjects would quite expensive and not easy. a few tiny and extremely limited studies have been done, but the weak conclusions one can really draw from them only hint that there may be some advantages to a somewhat more forward seat postion in some situations for some people in some types of riding. but good luck at quantifying that angle for yourself based on any of these studies.

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but an interesting question is why are so many road bikes at 73 deg.'? i have asked this question to numerous bicycle science experts and have yet to get a satisfactory response that is backed up by data or historical records.

my guess is that there is no real reason for the 73 deg. seat angle, other than it is an approximate selection that puts most riders with 170 mm cranks in the ballpark of a passably comfortable and stable road position and it is aesthetically pleasing (a surprisingly powerful draw in bicycle design) as it matches the 73 deg. head tube angle used by most modern bikes. beyond that, to my knowledge, there is absolutely no hard science behind the selection of the 73 deg. seat tube angle.

there is also a very powerful copy-cat culture and basic "historical inertia" within many industries, including the bike business. many companies and builders do something (like pick a particular seat tube angle) just because that is what they were taught, and because that is what everybody else is doing.

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Where would you want to swim ?

No.

seat angle - no

hip angle - yes

Exactly.

and with the USCF abandoning their UCI rules for 2007+, I'm moving forward in my position, keeping the hip angle the same but rolling forward and down for next season, except for the extension, which will look something like: (except my saddle will be forward since I don't have to conform to UCI rules any longer)



http://grahamwatson.com/...phineSt3/$file/7.jpg

but i think he is really asking WHAT is the relationship between power and hip angle.

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Where would you want to swim ?

there is no calculation for that, each rider had different size bones, body and such

a general rule of thumb, the more open the hip angle, the more power producing ability a rider has

that's why we climb in the tops when we do not have aero restrictions, open up the hip angle

ok, but then so what's with cobb's "big slam" postition which he claims a lot of success for (on certain athletes)?

it seems that type of rear position should work for no one if "the more open the hip angle, the more power producing ability"...

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Where would you want to swim ?

Remember - a key part of the traditional roadie ("Slam") position is that the seat drops down and the handlebars stay up high. The hip angle doesn't close down if it's done right.

Besides, there are always exceptions. Pantani climbed in the drops for cripesakes.

nothing wrong with climbing in the drops, its a powerful position, probably one of the most powerful positions, you just have to practice it

as for the SLAM position, Rick has it right, the rider is rolled backwards, keeping the same hip angle, yet reducing pressure on the neck, back, shoulders

if frontal area is king, the best way to know what position works best, for you, is to set up a bike on a trainer, take photos in various positions, and test power in those positions, as well as comfort

then take a look at the frontal area photos and overlay them with photoshop ... and pick the photo with the least amount of area exposed/lowest position