Bike Fit = Free Speed
Bike Fit = Free Speed
A fellow IMLOU participant and I have been PMing back and forth this topic. I thought I would pull this together and share it with the team.
The question we were working on was how did I get around the LOU bike course 32 min faster with the same power (177w vs 178w) as my friend? The likely answer is differences in bike fit making a significant impact on aero dynamic drag. We are all painfully aware that the majority or the watts we produce are to push our bodies through the air. The smaller the hole we can make, the faster we will be for the same watts. We all intellectually know this but we may not appreciate how important bike fit is in this equation.
In a our back and forth on the question I commented that this season I had dropped the front cockpit of the bike ~2.5 cm and saw that this small change made a noticeable improvement in my speed (~.5 mph) on a flat road with no with wind.
So to see what this change did for my 2010 race I compared numbers form LOU 2009 and 2010. To eliminate the impact of Bio breaks and stopping at special needs I will use the ride times recorded on the bike computer.
LOU 2009
Bike time official 6:06:26, time riding on the Powertap head 6:03:18
NP 161w, avg 152w VI = 1.06
My FTP was 230 so IF .693, TSS 290
LOU 2010
Bike time official 5:43:44, time riding on the Powertap head 5:37:13
NP 178w, avg 168 VI = 1.06
My FTP was 260 so IF was .684, TSS 261
So the difference in average watts (those are what move you around the course) is 16w between the 2 years. The difference in time riding time is 26 min.
I use the following web site to estimate impact of watts on bike time. The nice thing about this site is it has a bike course data base that adjusts for the amount of hills.
I drop in my numbers and let it calculate a bike time. I note what avg watts it says I will be riding at to hit that time. It gave a time of 5:43:57 with 187 watts. Note it thinks I need more watts than I used for roughly the same time. This indicates to me that I am more aero than the assumptions in their model.
Next I go back and lower my FTP number until I see resulting avg watts that are 16 lower. Doing this I get a new time of 5:58:44 with 171 watts. So all else being constant, the 16 watt difference between 09 to 10 accounted for ~15 min. The other 11 min is due to being more aero. So if you do the math, this 11 min was a speed improvement of 0.58 mph! I would need roughly another 20 watts added to my FTP number to pick the equivalent speed.
Four things were different this year on the bike fit / gear. The front cockpit was 2.5 cm lower. My arm pads were brought in closer together to be right in front of my thighs, reducing my overall frontal area to the wind. I ran a wheel cover on the rear 808 this year no cover last year. My aero helmet was a Spuik last year this year a Specialized. Of these changes my view is the 2.5 cm drop and arm placement accounted for at least 9 min of the 11.
My bike position last year was pretty aggressive already. This year I rotated forward even more to get the back flatter, the head and shoulders lower and a small hole to punch through the air. My seat angle is now an aggressive 81 degrees and I have a 15cm drop from seat to arm pads. This 2.5 cm drop has my back almost flat. As others in the team have posted, when you get your head down this low, seeing becomes a challenge.
Does this lower position have an effect on my FTP? No. Compared to last year – no impact due to the movement to my seat forward which rotated my whole body and allowed my hip angle to stay constant. Closing down the hip angle usually impacts power generation.
As I review what I have written, I see 3 messages that RnP keep hammering home to us.
1. An aero bike position is free speed!
2. Get a good bike fit. It can help generate more power and also get you more aero. Continue to work the fit as your flexibility increases and your body adapts to being comfortable in more aggressive positions.
3. Raise that FTP in the off season. My 30w pick up in the OS improved my bike time but I think more importantly my TSS dropped due to being on the bike less time. It went from a TSS of 290 last year to 261 this year. The impact of that was I negative split the run this year. Last year NOT.
Don’t underestimate the impact of sitting up on a bike and catching a chest full of air!!
Matt
Off topic.
My bike – Oh I love that machine. She was my mid life crisis reward for losing my 67 lbs and running my first marathon. For me she is perfect. I have a leg length difference and the carbon crank set allows one to adjust crank lengths from 170 to 172.5 to 175. So I run 170 on one side and 172.5 on the other. Also the crank set accepts either standard chain rings OR compact rings. I run the compacts. Also the there is huge flexibility in the positioning of the front cockpit. Say I want to race a sprint or an oly distance, it simple to adjust the cockpit even lower. Then there is the Shimano DI2 electronic shifting. It is totally unbelievable and having shift points in the drops and on the bull horns just rock!
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Comments
Thanks for sharing your bike fit info. You sure look very aero on the bike position. Was there a difference in the wind conditions at IM Lou between 2009 and 2010? Also the temperature difference between years was significant. (Cooler air being more dense).
Bret, Good question on the wind.
Matt, I know you're a stickler for data. As I've been following this and you comparison to MJ and yourself last year, I've wondered what the w/kg figures are. IF and NP are tough to compare between people, and across races for the same person if the weights are different.
That said, I think I told you how impressive your position was when I saw you at IM CDA on the Ohio Match loop section of the course. You were going up hill, but you still looked as if you were magnetized to the top tube.
Al, I agree that that it is difficult to make comparisons between different people.
For me my weight was the same for both years at 160 lbs. This year’s ftp gives me a 3.58 w/kg. MJ I believe posted his was a 3.46 w/kg. So a bit over a 3% difference, pretty close. I think average watts is the better indicator for how fast a person will move over a given course. As you know NP just dials in the impact to our body of how smoothly we deliver those average watts. The wind and the hills don’t care.
Why don't we just go ahead and promote Matt to a WSM!!!
I just looked at my ASI photos online and my bike position, even though in the aero position, looks like my back is not even close to being flat like yours.
Just sent off my video to TTBikefit.com.
Im only at a 7cm drop, compared to Matt's 15cm,
Let the fitting begin......next year Im known at Mike "The Turtle"
I second.
Matt,
Great post!! I can think of one more way to gain free speed:
LEARN HOW TO PISS YOURSELF ON THE BIKE!!!
Doode, you are giving up way, way, way too much time
. The Pointy End don't stop...ever. 7th degree black belt ninja execution is to do the deed while pedaling, and running, without dropping watts or pace 
Rich, I agree. Looking at the bike roll times vs total time sure made that point loud and clear. I just need to get pissed!
I have been racing in white tri shorts – they sure are the wrong color for that mission. It’s time to get back to dark shorts that won’t show the results of a golden shower.
White tri shorts are not a good call for any mission.
Your position looks great. No way to really tell without tunnel time but can't be too bad. As mentioned it is really hard to compare person to person using power data. See Rich's thread about a new PM.
Whatever you are doing, its working...and most importantly, your bike looks very cool!
Matt - another thought on peeing on the bike. In CDA, I took three stops and my saddle time was only 1:30 less than my official bike time. Done efficiently, stops may actually *help*, just as walk breaks do during the run. More important, there are anatomic considerations with age which make things more difficult (prostrate enlargement, specifically). While seconds CAN make a difference (I once got a Kona slot by 9 SECONDS) I'd suggest first finding free time in T1and T2 and getting more efficient at bio breaks before trying to fight nature and ruin your nice trisuit.
Example: in CDA, in M50-54, the top three qualifiers were in the top five T1 times, about 3 minutes faster than you; you gave up about 4 minutes in T2. The top guy did T2 in under a minute!
So there are about 10 minutes waiting for you in transitions and in more efficient stops on the bike.
Al as always you point smartly to the area where one can improve. For all my anal attention to numbers and detail, my approach to transitions has been way to Laissez Faire. It’s time to get this portion of my race under control. To force me to focus on this I will do some timed transition simulations over the next few weeks and report back what improvements are made.
On the pee on the bike vs efficient stops very good points – let me see what I can get in place on the front in the next few weeks.
OH to find 10 free min!!!! I’m motivated.
Matt
A better picture with your helmet on is something we need to see. I'm sure your not racing in that hat. I agree with removing that " pesky obstruction " your thighs are beating the crap out of your stomach.
Did you set this position up yourself or have someone fit you ? If you were fitted I'm sure that fit was based on how THIS/THAT feels at the time. Sure you can stretch out some / go lower add wheels get the aero helmet etc, ect.. but the most important thing to start with is like you said " pesky obstruction " needs to go ! Read above Matt lost 67 lbs. In his aero picture posted above his thighs are hitting an empty shirt with no belly.
http://members.endurancenation.us/Training/TrainingForums/tabid/101/aft/5710/afnp/105178/Default.aspx