Rappstar, Slowman: What am I missing

Triathlon Forum
1

I’m usually the first (or fifth) person to chime in and tell someone not to buy a bike that doesn’t fit. Typically what I am advocating is to purchase a frame with the correct stack height, without consideration for reach, because I’ve never been particularly sold on concept of sitting ON a bicycle seat, and thus being forced to rely on moving the seat angle forward in order to open up the hip angle. I am 5’10" tall, but with an inseam just short of 37".

To begin with, I have a lot of bikes. A collection of bikes might be an accurate description. They are all 650c.

Aegis Trident 54cm (15cm head tube, external headset)
Kestrel KM-40 Airfoil 57cm (17cm head tube, external headset)
Softride Rocket TT Medium (16cm head tube, external headset)
Zipp 2001 Large (13cm head tube, external headset)
Cervelo P3 54cm (14cm head tube, internal headset)
Cervelo P2 58cm (15cm head tube, external headset)
Mongoose RX7 60cm (18cm head tube, external headset)

I fit on all of these bicycles very well, except for the Mongoose. The top tube is just too long for my torso, even with a forward seatpost. I used it as a road bike for several years, but now it’s stored in the attic along side the P2, which I found not to be as fast as Gerard claimed.

I have recently acquired some smaller frames for my girlfriend who has surprising TT abilities. She is 5’5", and has a 30.5" inseam.

The first bike I put her on is a 2007 52cm Kestrel Airfoil Pro. It fits her like a glove with a Profile FF seatpost to help push her forward a few degrees further than the 76 degree standard geometry. When I was building it for her, I also made a pit stop along the way and adjusted it for me using a set of Ritchey Probiscus bars that allow you to set the stem and extension length quickly and easily. I can ride this bike with no problems in the 77-78 degree range with ~105mm of stem. No power loss, no power gain at this angle compared with most of my other bikes that are setup at 82-86 degrees.

Then a couple of weeks ago I picked up a 50cm Felt B12 on eBay for super cheap. I was very excited to build that for her so that we could use the Kestrel as more of a road machine with drop bars and sti levers for going on long weekend rides, while the Felt would be a pure TT machine. When I received the frame and started doing measurements, I determined that I could make it fit me! The seatpost was extended about 2mm past it’s “maximum extension” line, but with several inches still inserted into the frame. I set it up UCI legal (5cm behind the BB) and with a 100mm stem it fits beautifully. Same thing, no power loss and no power gain at that angle. I didn’t measure what the actual angle was though.

What I want to know is how I can fit on all of these bikes from 50-58cm from various manufacturers and never really be compromising anything. Sure I put on the right amount of additional stack by using the right aerobars, but none of these bikes have ergo stems on them to make them fit properly. The only thing I have done is invest in lots of seatposts that allow forward positions, and lots of San Marco Azoto seats that allow that perfect nose position. I never lose or gain power when moving between 76 and 86 degrees as long as I stay on the nose of the saddle.

So what gives? Am I a weird special case with a highly adaptable body? Am I fooling myself into thinking that all of these bikes fit, and that I am in fact compromising something I’ve not noticed? Talk to me, fit gurus. I want to know.

2

I feel the same way. I assume I just don’t know what OPTIMAL is and can contend with various frames. Finished my first century on a bike that hasn’t been fitted to me and bought the frame on a total guess because I had tried another one with the same dimensions and felt fine on it (no professional advice).
I’m 5’11" with a 57cm top tube…You can see how lax I am on the subject as I have no other measurements to give.

3

because the “buy a bike that fits” manta here is massively overblown.

between stems, seat tubes and bars you can make almost anything fit.

4

if you buy a 52cm bike and pull the seatpost out all the way, it’s going to fit you just like a 58cm bike with little seatpost out. it’s a telescoping construct, like the radio antenna on your car. no mystery there, is there?

now, let’s talk about the front end. consider the difference in elevation between, say, a syntace and a vision aerobar. it’s about 4cm. that height variance has the same impact on the height of a bike as does changing the head tube length. the specialized transition has a 100mm head tube length in its size S, and 120mm in its XL. so, a small transition with a syntace aerobar is a “taller” bike than an XL with a visiontech aerobar.

it’s all a matter of math.

you said you set up your new 50cm felt in a uci legal position, correct? but your other bikes are set up in 82° to 86° seat angles. correct? so, you’re moving the saddle from, say, 4cm in front of the bb on your other, larger bikes to 5cm behind the bb on your new tiny felt. that’s 9cm of fore/aft change.

again, specialized transitions: only 4.5cm difference in reach throughout the entire size run. so your abrupt, schizophrenic decision on your saddle for/aft placement is equal to twice the reach delta between the S and XL transition.

did you not know all of this already?

5

i think what he’s saying is that he produces the same power with a saddle position at -4cm and at +4cm relative to the BB, and wants to know if he is unique or everyone can do it.

My n=1 experience is that my power output varies with my saddle position relative to the BB.

6

i think what he’s saying is that he produces the same power with a saddle position at -4cm and at +4cm relative to the BB, and wants to know if he is unique or everyone can do it.

My n=1 experience is that my power output varies with my saddle position relative to the BB.

There is also bike handling to be considered when you go with the extrem stem/seatposts setups.

It is something those of us in flat areas never consider, but because a big deal bombing down a hill.

7

Of course I did. Maybe I did a poor job, but the idea was to get people thinking about reality of the required contact points instead of the 6mm of additional stack that bike A has over bike B. I want someone to explain why a bike that doesn’t fit by 1 or 1.5 cm needs to be sold off in favor of a smaller or larger machine when there are so many other variables that could be adjusted with no real cost to the functionality of the bicycle. Your example of a Syntace vs. Vision Tech bar is perfect; in the extreme, you can even introduce the Profile Sonic CSX which adds virtually no additional stack.

I also want to talk about sitting on a seat properly. 100 years of bicycle seat design has lead us to seats that can be nose ridden for hours without ill effects. Nose riding allows easier adoption of a high cadence and significantly more drop because you rotate around the bottom bracket as you move down in front instead of closing the hip angle. I’ve done weeks of testing on a Velodyne to determine if there are any effects on output power from differing seat angle (for me) when moving between 73 and 90 degrees with a “nose riding” style. There are none (again, for me). I have also tested this sitting “properly” on the saddle and the results are very different…so why would someone want to do that?

Chris

8

because the “buy a bike that fits” manta here is massively overblown.

between stems, seat tubes and bars you can make almost anything fit.
Hear ye, hear ye!

9

I could be wrong here, but isn’t a major component of bike fit (virtual seat tube angle) about muscle recruitment and the impact of muscle fatigue for the run? you could be preducing the exact same wattaage @ 73 deg and 83 deg, but how is your run affected?

10

My favorite is the “custom” bikes people have round me which still have tons of spacers…

11

When sitting on the seat, I believe you are correct. When nose riding, my run ability has remained unchanged. All of the testing I have done on the Velodyne has included run bricks to make sure I wasn’t missing something. Saddle to bar drop was adjusted with the seat angle to create a constant hip angle while moving forward (and then back again, because I am thorough like that)

Chris

12

So regardless of saddle positon reletive to the BB you saw no difference in power output or ability to run off the bike? (assuming that hip angle remained the same)

13

Are you perhaps automatically sliding more or less onto the nose so that the actual ‘seat tube angle’ your body is at remains the same as you slide the seat around under you?

also how do you people ride on the nose of a normal seat comfortably? lol

Of course I did. Maybe I did a poor job, but the idea was to get people thinking about reality of the required contact points instead of the 6mm of additional stack that bike A has over bike B. I want someone to explain why a bike that doesn’t fit by 1 or 1.5 cm needs to be sold off in favor of a smaller or larger machine when there are so many other variables that could be adjusted with no real cost to the functionality of the bicycle. Your example of a Syntace vs. Vision Tech bar is perfect; in the extreme, you can even introduce the Profile Sonic CSX which adds virtually no additional stack.

I also want to talk about sitting on a seat properly. 100 years of bicycle seat design has lead us to seats that can be nose ridden for hours without ill effects. Nose riding allows easier adoption of a high cadence and significantly more drop because you rotate around the bottom bracket as you move down in front instead of closing the hip angle. I’ve done weeks of testing on a Velodyne to determine if there are any effects on output power from differing seat angle (for me) when moving between 73 and 90 degrees with a “nose riding” style. There are none (again, for me). I have also tested this sitting “properly” on the saddle and the results are very different…so why would someone want to do that?

Chris

14

That is correct. As long as I was “rotating” around the BB, everything was constant. I wouldn’t call it confusing, but interesting would definitely qualify.

Chris

15

No, the saddle position relative to the seat is constant. There is a place on the San Marco Azoto Ti (the heavier model, but with Ti rails) that is optimal for nose riding. You can feel when it’s in exactly the right spot.

Chris

16

i’m just not following you. you’re asking this question:

“when moving between 73 and 90 degrees with a “nose riding” style… there are no effects on output power] (again, for me). I have also tested this sitting “properly” on the saddle and the results are very different…so why would someone want to ?”

is this your question? but just above this paragraph in your post, you answer your own question:

“Nose riding allows easier adoption of a high cadence and significantly more drop because you rotate around the bottom bracket as you move down in front instead of closing the hip angle.”

maybe i don’t understand your question. if you’re saying that you can maintain the same power riding shallow and sitting on your sit bones instead of your taint, fine. i can too, for a period of time. but there are various forms of fatigue, neuromuscular as well as aerobic, and it’s hard to isolate the two when sitting aboard a computrainer with a HRM. and, of course, you aren’t in a wind tunnel.

some stuff is hard to test absent that test being the entire race experience. that’s why tim noakes’ studies, using the ironman, or comrades marathon, is of value. i think if riders could sit up and sit back and go just as fast, they would (who wouldn’t?). but they don’t, so they don’t.

17

Chris,

Are you able to maintain the same aerodynamic drag numbers across the range of seat angles? Even though power output may be unaffected, drag will be if you have to raise/lower the bars to accomodate your hip angle, or are you saying you are able to maintain the same power output across a wide range of hip angles as well?

Edit: sorry you already said that you vary your bar drop. Well that sort of explains everything doesn’t it?

You should choose frames based on reach, because you want to be able to achieve as low a front end as possible, while maintaining your ideal hip angle.

So yes people will change frames because the reach is not optimal. I don’t think that +/- 2cm is a big deal but beyond that i think it starts to affect handling.

I don’t think one should choose frames based on stack, unless the stack on the frame is too low such that it becomes dangerous to have that many spacers, or you need a very negatively angled stem, that negates the engineering efforts of the manufacturer to make an aerodynamic headtube.

18

Maybe I worded something improperly, but the question I was asking actually asking is, "why would someone ride on a seat properly and have seat angle significantly impact performance and limit front end drop when they could nose ride and get much lower in front while maintaining hip angle?

Don’t get me wrong, I believe in riding steep, in fact, significantly steeper than most. What I am challenging is the idea that actually sitting on a saddle as originally designed is useful for achieving maximal speed.

Chris

19

for me when i nose ride on a normal seat, its extremely uncomfortable

but then its extremely uncomfortable to ride in an aero position on the normal part of the seat too

sigh

Maybe I worded something improperly, but the question I was asking actually asking is, "why would someone ride on a seat properly and have seat angle significantly impact performance and limit front end drop when they could nose ride and get much lower in front while maintaining hip angle?

Don’t get me wrong, I believe in riding steep, in fact, significantly steeper than most. What I am challenging is the idea that actually sitting on a saddle as originally designed is useful for achieving maximal speed.

Chris

20

Buy a few new seats.

Blackwell Flow or whatever the new Cobb offering is.
San Marco Azoto Tri (titanium rails, not the cro-mo version, it has foam instead of gel in the nose)
Profile (with the cutout) if you insist on using the sit bones and have wide-ish hips
ISM Adamo Typhoon

One of these will work and end your pain. It will be worth every penny for ALL of the seats just to find the ONE that works.

Chris