Bike Fit and Knee Angles (Page 2)

Yes, unfortunately, I based my purchase on prior experiences... if I had the small, I'd have another 2.5 cm of drop available, as it is... going to a 160mm cranks would do nothing for me, it would theortically raise my seat 5mm, so I'd get another 5mm drop, but I'm pshychologicaly uncomfortable going that small, I can spin well, but I think that I'd miss the leverage to mash big gears too for short periods... both have their place. But, it might be in my mind.

By the way, does anyone know of the PRO triathletes that use shorter cranks: I read that Craig Alexander uses 167.5 (equal to 165 for me).. Miranda went 1cm shorter for KONA and busted out a PR... and Jordan Rapp uses 170 for his tall size... that'd equate to 160mm for me. What about Keinle, FVL, Luke or Starky... my biking heros and role models?

Speaking of Starky, there's a picture of him at KONA and mashing away on the gears up hill and I notice substantial BB flex... that's freakin' power... his arms are wide open too (he's a big dude), compared to Luke McKenzie, another picture perfect position and model to emulate.

Edited by tomspharmacy 2013-12-27 2:23 PM

If I posted my swim... I'd be laughed off the forum... a coach once said... I'm a surfboard with arms.

Do you know what that will buy you in terms of wattage savings ? Really


This from Damon Rinard, Senior Engineer at Cervelo

"In general though, you're calcs agree with my experience. Based on 14 runs in the wind tunnel where drop was the only position change, I get (drawing through the data points with a BIG crayon!) about 20 g/cm.

Lots of scatter in the data and lots of caveats in the protocol, so I'd say your 1.5 W/cm are roughly "in agreement" for now."


1.5W/cm !!!

I would focus on power generation but that's just because you are not in my AG. If you were I'd say keep on going lower :-)



Edited by marcag 2013-12-27 3:10 PM

I trust your advice, you guys steered me to the contis and latex... it definately benefited my last race... you're probably right about the extra 5mm, I just need to clear out the prior biases and noise from the membrane between my ears and trust it.... but that's tough to do when I felt the 170mm were right.

As it is... I've lowered my side and front profile even though my angles may not have changed much, I've dropped down about 1.5 cm, sitting more into the bike, than looking like a giraffe on top it, as some of my race pics look to me.

so you'd advise on the 160's?

I guess what I am really saying is you are at a point where *i* would worry about losing power than trying for for very marginal gains. That quote from Damon really resonated with me.

Seats going forward, hip angles getting closed will change muscle recruitment and ability to generate power.

Some of this you feel immediately, some of it you feel over long rides. I would just be very careful and sensitive to power production at this point.

You will probably get more gains with head position more than anything at this point. Make sure your changes don't change the ability to turtle for example.
Not sure if swapping out cranks is costing you anything, but if so, that money would probably yield bigger gains if you went to see Jim @ Ero.

Just being the devil's advocate that at the point where you are, lower may not be better.
I spent all last winter going forward and down just to have a fitter bring me backwards, more powerful and more aero.

Edited by marcag 2013-12-28 4:36 AM

Out of curiosity... at what point does it level off to 1.5/cm? And how do you know when you reach that point?

Obviously it's not 1.5 from sitting up to X... otherwise it wouldn't be worth it to work on an aero position at all...

Tom, a good guy to talk to about short cranks is Dave Luscan (he used to post here and still does a little on ST I believe) he has went VERY short lately and he raves about it on FB.

(Not that it makes his advice better or worse, but he's a fast dude too.)

- also, might get Thomas (Gerlach)'s thoughts... he rides 160 or 162's I think.

Edited by Leegoocrap 2013-12-28 8:07 AM

I hear you loud and clear... it would be on my mind too, since I'm aware of this possibility and I'd say when I had the Valdora I was past the point, when I had 4.25 inches of drop on 172.5mm cranks, I don't think it was the drop but the hip space since my thighs would crash into my abdomen and at some point about after 10 min of riding hard my breathing would be labored... so I'd lose power... then I put 170's it opened me slightly, but it's when I went to the SHIV with more relaxed geometry (that even though I was less aero), it was instantaneous improvement... I gained 1 mph avg, from position alone, even though more relaxed... it hit me right there that I had good power but a bad position... I was faster b/c I wasn't all bent over and had a closed off hip at the top.

But my estimated CDA with the SHIV this past season is about .280 on avg... and that's kind of bad for a 5' 9.5" person weighing only 146 lbs during race season, don't you think? That's why I have to produce 290-300 watts just to maintain a 25mph avg. speed. I've dropped down vertically 1.5cm...that with a lower yaw profile and lowered front profile... my new estimated CDA would be closer to .260 and 300 watts would be 25.75 - 26 mph avg. My goals are extreme, but since I worked a very hard year of cycling training to break 2hr 20min mark and finally did it, my new goal is to break 2hr 15min and lower, so that requires either to produce a sustained 310-320 watts in the old position, or only the 290-300 in the new theoretical position.

The drop distances gone like this: Valdora 4.25 inches with 172.5mm cranks... to SHIV 3.75 cm with 170mm... to now 4.13 inches with 165mm cranks (and 160mm cranks would give me 4.25 inches)... the dimensions between the latter 2 are the same... the torso came down from about 101 degrees to 96 degrees. It's the hip space that I gained with the SHIV that gave me more usable power since my hips could obviously get over the top easily and my back and hips weren't squawcking after after about 30 miles. I'd just have to be assured that shorter crank arms really keeps my power the same.

At the moment... my angles are exactly the same (ie current comfortable and powerfull) with my hip angle after this repositioning while sitting a little bit lower. A 160 would give me more hip space of 1 cm while raising me only another 5cm... theoretically. It's only if my back can take being hunched over that much... or whether I can train myself to accept that position... it my be ok over a 20 ro 40k TT, but how'd it be over longer distances.... if my back starts to ache (which it did on the valdora), then power drops anyways b/c you want to avoid further pain and have to still run.

But it seems that within the tri community, accepting shorter cranks is happening, eventhough the pro cyclists haven't (either b/c of UCI rules or biases). If I could afford to own 2 sets of rotor cranksets at $500 each and run tests, then I'd know which length to use.

Edited by tomspharmacy 2013-12-28 9:49 AM

You can check out Cobb Cycling's website... they have short cranks (down to 145) a bit more reasonably priced ($299)

How did you measure your cda ?

Have you seen what the guys are ero are doing ? Jim is a very knowledgeable fitter and he has the technology (thanks to a brilliant Montrealer) to test his fits. Ever thought of using that service ?

Thanks for the help... I like this over the other since I can get good feedback w/o the dickish comments.

It's funny.The guys that can put down the big numbers are the ones that abstain from the dickish comments.

I would bet that dickishness is inversely proportional to performance over there. It does make it easy to figure out who to ignore :-)

The reverse chung model via Golden Cheatah... I have an Ibike power meter and it estimates cda too.

Here is my charts from the same race but 2 different bikes and setups...

2012 - Valdora - 4.5 inches drop - 2hr 29 min - est. CDA .271 (I used also a friend's 60/90 aero wheels)

2013 - SHIV - 3.75 inchese drop - 2hr 19 min - est. CDA .280 (I used my 58mm chinese open design aero wheels)

2014 - SHIV - 4.13 inches drop - ???? - est. CDA - .270 with using a 60/90 again ???

A subsequent file: 2013 Ironman St. George - Valdora 4.5 inches drop - rented Firecrest 404/808 combo - est. CDA .272

What should I infer?

Does Jim have a website?









Attachments
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Aero CDA est. St George Valdora 2013.jpg (72KB - 4 downloads)
Aero CDA est. SOMA Valdora 2012.jpg (83KB - 5 downloads)
Aero CDA est. SOMA SHIV 2013.jpg (86KB - 5 downloads)

http://ero-sports.com/

He works with all the top triathletes in the world. He is a great fitter and has access to some very cool aero measuring technology that he applies on a track without the "noise" from outdoor. The technology was developed by one of the guys that did the GC virtual aerolab.

I think Desert Dude, who is in Tucson is doing an aero camp with them in January.

The 2nd and 3rd Aerolab plots look to me like not an ideal fit.

I think Jim at ERO is doing great stuff. I think Desert Dude (Brian Stover) and Heath Dotson are doing a 2-day clinic in Carson in about two weeks but there were limited spots. I think the clinic was going to include a few presentations in addition to the fitting, plus you'd get to see other riders getting fitted and testing on the track so attendees could learn a lot.

DP

Edited by marcag 2014-01-01 11:26 AM

What shows you that in the 3rd chart for example ?
It almost looks like a 3 loop course with much better aero on the first lap than the other 2. I am reading this wrong ?

Looking at the flatter sections on the actual elevation it looks like a climb on the virtual elevation. Is that a sign ?


Edited by marcag 2014-01-01 11:26 AM

No, that's what I see, too. Could position or wind have changed (or could something have re-zeroed the power meter)? I might have tried to fit the first lap separately from the last two. (If you held the Crr constant, that would imply lower CdA for the first lap and higher CdA for the last two).

Note also that the "estimate CdA and Crr" button tries to fit the parameters assuming the start and end elevations are the same. You can see the issue at the very right hand edge of the 2nd plot, where the VE is forced to match the start/end elevation.

The wind picked up dramatically, so I guess during the 2nd and 3rd laps... I remember a pretty nice head wind on the 3rd lap.

Wow, what an honor to get input from you, thanks... the wind picked up during the ride, I remember a headwind, and going across the bridges over Tempe town lake knocking me sideways, some gusts here and there... it was all probably 5 to 10mph, nothing dramatic but affected things I guess. My position didn't change from each lap, I stay down all the time, except on the sharp hills.

Regarding the CRR estimate... that was put at .5 by me for these models above... I did this for 2 reasons... 1) my bike was a Valdora with a Michelin Pro 3 / butyl tube combo in the first 2 analysis, and 2) the bike for the SOMA 2013 this october was a SHIV with Conti GP4000s and latex tubes and different wheelset. I wanted to make the CRR's the same so as to not let that affect the CDA, unless I did something wrong? What is your take on this?

Whoa, I'm just a rider like everyone else. OK, maybe I'm a little geekier than most riders, so I've got that going for me.


Cool. It's pretty interesting how you can see wind affecting things, eh? Anyway, in that case I'd think the first lap might give you a better picture of your aero drag than the last two.


Well, the Michelin Pro3/Butyl combo is going to have higher Crr than the 4000S/latex combo but exactly how much higher would depend on the road surface. Ballpark, I'd say maybe a bit less than .001 (that is, if the Michelin/butyl combo was around .005, the Conti/latex would still be above .004). However, at your speed a difference of .001 in Crr might be "worth" a difference in CdA of .01. They're inversely related so if you overestimate Crr you're going to underestimate CdA, and vice versa.

Apparently, still some spots left:
https://a3hdcamps.wordpress.com/aero-camp/

FWIW: I'm not affiliated with these guys. I just think it's cool that they're doing this.