TT bike fit progress

Just remember not to make too drastic of a position adjustment in the beginning. Always try to work your way into the new position in small increments in order to help your muscles and joints become used to it. Making the entire position change at once can lead to some soreness or even injury when you begin to really push yourself on a ride.

Can we sorta toss aero-TT-setup questions/concerns here? :-)

so the story that most of us know is that the PM (plus analyticcyling & some spreadsheets) can give you a reasonable CDA value.

here's some questions:

-is it best to install your aerobars then go test your CDA right away to get a ballpark #?

-or should you study pictures/articles/yadda yadda, tinker with the aerobar setup first.......then go do a CDA test run?

-we know that best aero position vs. best power position is often a compromise. how to settle on a point in that compromise...should you do a bunch of test runs in diff. positions, analyze the CDA/speed data, and test how long & what power you can hold in the positions?

-the Coggan & Allen book speaks of the regression & constant power methods for CDA derivations. in practice are the results much different? regression seems like it has more points so in theory more accurate slope of the line but is that true in your exp.?....

Thanks to the OP for starting this thread 😉

Good thread, and I'm glad to see other folks working on their setup too!

flapsupcleanup said:

I'm actually fairly pleased with the results so far. If it would just warm up so I could ride it outside!

Curious if you are using a powermeter to check your progress, or are you hoping to get there by looks/speed/RPE?

I've had the TT bike on the trainer for a month now, getting used to the trainer feel again and tweaking for a comfortable, powerful position. I'm definitely interested in the how's and why's of people's quests for TT perfection. 🙂

DancenMacabre said:

Can we sorta toss aero-TT-setup questions/concerns here? :-)

Yes! 🙂

DancenMacabre said:

-is it best to install your aerobars then go test your CDA right away to get a ballpark #?

-or should you study pictures/articles/yadda yadda, tinker with the aerobar setup first.......then go do a CDA test run?

I'd say a combination of the two if that's not too much of a cop-out. :o Riding on aerobars takes a little getting used to, from a safety as well as comfort perspective. You'll need to be pretty comfortable on the bars, cornering with them at speed, etc. before you'll be able to hold that position long enough to do a meaningful CdA run series. I think looking at some pictures and feeling the reach, pad width, angles, etc. to find a comfortable, secure starting position before trying to gather data would be a good idea. Will you be using the track for your CdA runs? The biggest challenge for me is getting out of the Kansas wind long enough to test anything.

DancenMacabre said:

-we know that best aero position vs. best power position is often a compromise. how to settle on a point in that compromise...should you do a bunch of test runs in diff. positions, analyze the CDA/speed data, and test how long & what power you can hold in the positions?

Not sure I can speak to best method, but I'm using the winter trainer rides to acclimate to a position that is comfortable, powerful and looks good to the eye. Then when the weather improves I will try tweaking that setup to something that looks good to the wind and doesn't hurt my power or comfort too much.

My question is whether anyone has tried to evaluate saddle position fore/aft versus sustainable power? The biggest issue for my pedalling seems to be an inability to powerfully kick forward at the top of the stroke because of the sharp knee angle. I'm thinking of pushing the saddle back to help this, but that will likely close my hip angle somewhat. I was wondering if anyone else had solved that issue differently?

flapsupcleanup said:

French's comments on the "it's killing me" thread made me want to start this one......

You beat me to the punch, I was thinking of launching a 'TT Training and Preparation' thread after frenchy's good comments last night. Too much gets buried in the big ongoing threads and the boards seem dead when there's some good discussion happening. I figured the thread could be a catch all for a bunch of time trial thoughts like how to train, positioning thoughts and maybe stuff like whether Tony's still givin' 'em hell in the indoor TT series as motivation for the rest of us during the off season.

Great goal of a sub hour 40K flapsup, that's always been a big breakpoint and one that typically takes some solid training and preparation to hit. It's easier now with aero bars but that still takes some dedicated effort to figure out.

I figure it takes a tad over 1000 watts/m^2 (watts/CdA) to get under an hour in a 40K TT. That can be 300 watts at at CdA of ~.3 or 200 watts with a CdA of ~.2 or for a lot of folks around 250 watts with a CdA of ~.25. It's not trivial, but not unreasonable either with some effort.

Good luck,
-Dave

frenchyge said:

....My question is whether anyone has tried to evaluate saddle position fore/aft versus sustainable power? ...

I played with this a bit last season when I was working hard to close the gap between my road bike and TT bike power numbers. I tried a lot of different saddle positions but in the end more or less took Andy's neanderthal advice and set up my saddle pretty close to my road position then rode hard in my aero position and paid attention to how much I scooted forward under load. I rode with wrenches in my pocket and after a few miles moved the saddle forward (and up to maintain the same effective seat height in the more forward position) since I was constantly tipped out on the nose and repeated the process a few times. I ended up in a position that isn't UCI legal unless I cut down the nose of my saddle but I finally finished some TTs with my power within a couple of watts of what I'd expect for the same durations on my road bike.

This thread is timely for me because my coach wants me to do at least one of my L4 sessions each week on my TT bike. I've resisted it so far as I hate riding aero bars on the trainer and my outdoor rides have been awful wet and sloppy and better suited to the cross bike. But I've got an indoor L4 CompuTrainer session tonight (not a TT, just structured group training in ergo mode) and I'll ride the TT bike for the first time in several months. I'm curious to see if my power numbers will still be close to my other bikes or whether I'll have to re-adapt.

-Dave

DancenMacabre said:

...-the Coggan & Allen book speaks of the regression & constant power methods for CDA derivations. in practice are the results much different? regression seems like it has more points so in theory more accurate slope of the line but is that true in your exp.?....

Ideally the results shouldn't be much different, but the constant power method is an average so it glosses over things like speed changes (and the associated kinetic energy changes) and it doesn't break out CdA and Crr separately.

Regression testing is the most rigorous outdoor method and it's nice to be able to separate rolling resistance from CdA but it typically requires dedicated testing days with numerous short runs at differing speeds and ideally it's a day with little or no wind on a road with little to no car traffic. So it's not exactly an everyday sort of thing.

The average power vs average speed method is a decent ball park and good for confirming other tests but a third method not mentioned in Hunter and Andy's book is VE (Virtual Elevation) or Chung method aero testing. In it's simplest form it also won't break out Crr and CdA separately but it's relatively easy to perform as long as you have some sort of loop or out and back course with gentle turnarounds that allow you to stay in your aero position and avoid your brakes. You don't have to hold constant speeds or any particular speed although it makes sense to do spend at least some of your time up near race speeds.

I had a great long course for single lap VE testing back in Wyoming, it was just shy of 20 miles, some mellow rolling hills along the way and no forced braking or time out of the aero bars. Trouble was it was long enough that winds could shift and weather could change in the 45+ minutes it took me to ride the loop. But I still got a lot of good data that converged nicely and let me easily estimate CdA, Crr pairs for my TT bike in various set ups, my road bike in the drops, on the brake hoods, etc. I'd just ride a Tempo or SST day around that loop, ideally early morning with little wind and just make sure I stayed in the same position for the whole ride and stayed off my brakes. When I got home I'd plug the data into one of Alex's very convenient spreadsheets and play with the CdA, Crr pairs until the VE plot closed (same elevation at start and end of ride). Some days it didn't and I could usually see where the wind changed direction or air density changed by the way the curve deviated from previous rides and actual terrain.

I haven't found a good long 'Chunging' venue since moving to Seattle but have used the parking lots and loop roads in the industrial park near my work for some position comparison testing. Last fall I spent a quiet windless evening rolling laps around my work building at varying speeds to assess the point of diminishing returns in terms of lowering my aero bars. I started with all my stem spacers underneath my stem for the highest position, did six laps, swapped a spacer then repeated the test until I'd lowered my stem all the way then reversed the process and worked back up to full stack height. Then I plugged the data into Alex's VE spreadsheet and it definitely showed the point where going lower in the front end wasn't improving my CdA any further so that's where I set my stack height.

You can get Alex's VE and regression method spreadsheets in the files section of the Google Wattage Group.

-Dave

<snip>

frenchyge said:

I'd say a combination of the two if that's not too much of a cop-out. :o Riding on aerobars takes a little getting used to, from a safety as well as comfort perspective. You'll need to be pretty comfortable on the bars, cornering with them at speed, etc. before you'll be able to hold that position long enough to do a meaningful CdA run series. I think looking at some pictures and feeling the reach, pad width, angles, etc. to find a comfortable, secure starting position before trying to gather data would be a good idea. Will you be using the track for your CdA runs? The biggest challenge for me is getting out of the Kansas wind long enough to test anything.

see & the pros on TV sure make it look like a snap to ride with these things (aerobars)! I hadn't thought of how controlling the bike might get hard - 'specially on a technical course instead of a flat/curveless parcours.

i have noticed that riding in the drops for long periods is not as comfortable. guessing that means in the aerobars will be less so, but maybe with practice you tolerate it better. gotta think to do the aerobars right & hold the position then you are gonna have to tinker with the bike setup (move seat forward/up) because you are changing the dynamics of your body on the bike.

<snip>

frenchyge said:

Not sure I can speak to best method, but I'm using the winter trainer rides to acclimate to a position that is comfortable, powerful and looks good to the eye. Then when the weather improves I will try tweaking that setup to something that looks good to the wind and doesn't hurt my power or comfort too much.

sounds hella good to me :-) may as well figure out if you can stay in a ballpark aero position for a period first before bothering to do much aero testing. seeing as many of us are on the trainer anyway, why not practice it there some too?

<snip>

frenchyge said:

My question is whether anyone has tried to evaluate saddle position fore/aft versus sustainable power? The biggest issue for my pedalling seems to be an inability to powerfully kick forward at the top of the stroke because of the sharp knee angle. I'm thinking of pushing the saddle back to help this, but that will likely close my hip angle somewhat. I was wondering if anyone else had solved that issue differently?

ok ok, a little dichotomy here. i read that hip to torso angle is key for optimal power production. make the hip-torso angle too acute and you start giving up power.....but.........having torso angle be as close to zero (parallel to a perfectly horizontal line) is more aero. sounds like a tradeoff to me?

biketechreview has lotsa aero details & compares positions. many of them look near the same to me, but show up as diff. cda values:

#1 - cda = .294
[IMG]biketechreview.comimg1D4.gifOpen ↗[/IMG]

#2 - cda = 0.318

[IMG]biketechreview.comimg1DC.gifOpen ↗[/IMG]

#3 - cda = 0.315

[IMG]biketechreview.comimg1D8.gifOpen ↗[/IMG]

so they look similar but the aero diff. is a few percent & that means seconds if not minutes i think.

*****************************************************************

yeap, i asked a lot of questions earlier (& on many threads!) so maybe i can share some info rather than ask for it. hope this helps:

1)
aerodynamic testing using regression method spreadsheet

this is not some DM hack job special. it is by Alex Simmons so you know it is quality.

2)
40k < 60min probably requires w/m^2 of 1000 or better yet 1050 (it might be windy you know 😉 )

this table gives ballpark figures.

please dont send the attack dogs (advocates/lawyers) on me as this table is the work of Dr. Coggan, all rights reserved, copyright, yadda yadda
just trying to share some stuff with fellow CF's 😄

DancenMacabre said:

...so they look similar but the aero diff. is a few percent & that means seconds if not minutes i think....

Given the CdA differences listed for Kirk's frontal views the difference in time for CdA of .318 vs .294 works out to about a minute and a half for an 80kg rider (total rider plus bike) holding 300 watts for a 40K TT.

-Dave

Our local cat1 who is an excellent TTer says he rides his TT bike an hour a week, year round. I like that idea and have been trying to do the same. Plus it helps justify the money I invested!

A couple of schools of thought on position changes: Make the tweaks bit by bit to let your body adapt. Or make the big change all at once and do shorter sessions on the bike and slowly lengthen them over time. I've made the big change and am working the duration/intensity up.

And I can't imagine doing a TT without a powermeter. The temptation to go out too hard is overwhelming... speaking from experience! I've got a pretty good idea of the power I can deliver for an hour (260-265 btw) so my plan is to get my position dialed in so that power will do the trick. And then I have to actually put it down on race day. Another non-trivial thing!

Just purchased my clip-ons a couple of hours ago. I decided to go with the Profile D. Jammer GT. I know the T2+'s are better for TT's, but for now I felt very comfortable on the Jammers. I'm also just looking more towards comfort for now than aerodynamics, as I'm only getting my feet wet as far as any sort of TT-ing. The price was right also at $35. 🙂

gman0482 said:

Just purchased my clip-ons a couple of hours ago. I decided to go with the Profile D. Jammer GT. ...

Cool, great price and from what I can see they've got all the essential position adjustments of the T2+ bars. Hard to say on aerodynamics without testing, the different hand position is directly in front of the body so it's not obvious whether you'll see any real performance differences and plenty of folks go fast with upturned aero bars.

Let us know how the positioning and trial rides go.

-Dave

FWIW, I've noticed that adjusting riding position indoors may not be optimal, since the forward momentum when riding outside plays a role in how balanced one feels on the bike.

For an experiment try riding in a normal position with the hands on top of bars and then while keeping your torso still remove your hands from the bars. With a decent fit, you should be able to stay in that position fairly comfortably outside, but indoors you'll likely start falling forward (this may very between individuals depending on their legs to torso ratio). Forward momentum should be taken into consideration when making bars and saddle adjustments. This is probably one of the reasons why riding indoors feels different. I suspect that it also applies to riding a TT bike indoors.

I just thought I throw it out there.

ecandl said:

...What do you all do with your seat? Do you move it up and forward or do you leave your seat where it is? I hate to get my bike setup and then start switching things around but if it makes me faster, I might do it....

When I rode TTs on my road bike I tried what Dancen suggested:

DancenMacbre said:

...you got a cheap or 2nd hand seat post + another saddle, mark the seat height, aft/forward position, yadda yadda - then use this combo exclusively for TT's, and keep your original seat post + saddle for regular road/all-around use?...

I took it a bit further and used a Profile Fast Forward seat post to effectively steepen the seat tube angle like you'd get on most TT specific frames. It worked pretty well and marking both seat posts with electrical tape made it easy to swap back and forth without changing my bike setup. Realistically though I only got around to this method after a season and a half of riding my road bike with clip on bars and no changes to the seat position for time trials and my performance measured in time, placings or sustained power didn't really change with the forward seat position. I suspect that's because my position wasn't all that aggressive with clip on bars on my road bike, I just couldn't get the front end ultra low with my stock road stem and road bike front end geometry. It was still plenty low enough to get well under an hour on my limited power and to get my CdA down around .26.

I finally picked up a decent dedicated TT frame sized down a bit (51cm vs. 54 cm road frame) with its ultra short head tube (95mm). I got my CdA down around .23 with the new bike but my power dropped a bunch and I spent a good portion of last season trying to find the balance point. That's when moving the seat further forward really started to pay off. So I'm guessing the hip angle thing and power loss only starts to kick in at some fairly acute angle and I wasn't getting that closed up on the road bike with clip on bars and didn't really need to move my saddle at all.

-Dave

daveryanwyoming said:

I tried a lot of different saddle positions but in the end more or less took Andy's neanderthal advice and set up my saddle pretty close to my road position then rode hard in my aero position and paid attention to how much I scooted forward under load.

I have never really spent any time trying to adapt to a TT position and have always ended up far on the saddle nose during any races as a result. My current saddle position is actually about 1-2mm in front of the BB center (shhh.... don't tell the UCI). The concern that I'm feeling now is that being so far forward is destabilizing my hips and fatiguing my arms and shoulders. I'm looking pretty neanderthal, except that my shoulders are over my pads, rather than my ears. I'm not sure if that's worth trying to fix, or what I could really do about it.

DancenMacabre said:

<snip> see & the pros on TV sure make it look like a snap to ride with these things (aerobars)! I hadn't thought of how controlling the bike might get hard - 'specially on a technical course instead of a flat/curveless parcours.

You'll get used to it, but higher speeds + not wanting to brake + head over the front axle + steering with elbows = pucker factor. 😉

DancenMacabre said:

<snip> ok ok, a little dichotomy here. i read that hip to torso angle is key for optimal power production. make the hip-torso angle too acute and you start giving up power.....but.........having torso angle be as close to zero (parallel to a perfectly horizontal line) is more aero. sounds like a tradeoff to me?

That's right, but if you can comfortably roll the hips forward on the saddle then it doesn't close the hips up as much as it might seem. I had just finished reading The Myths of KOPS and was wondering if there wasn't something to the fore/aft weight distribution and CoG over the power stroke after all.

DancenMacabre said:

biketechreview has lotsa aero details & compares positions. many of them look near the same to me, but show up as diff. cda values:

Those do a good job of showing the frontal area differences due to head position, but you can't see the relative Cd (shape) differences from the sillouettes. Still, interesting to see the magnitudes. Anyone have a good technique for measuring frontal area from a digital photo?

Piotr said:

FWIW, I've noticed that adjusting riding position indoors may not be optimal, since the forward momentum when riding outside plays a role in how balanced one feels on the bike.

For an experiment try riding in a normal position with the hands on top of bars and then while keeping your torso still remove your hands from the bars. With a decent fit, you should be able to stay in that position fairly comfortably outside, but indoors you'll likely start falling forward (this may very between individuals depending on their legs to torso ratio). Forward momentum should be taken into consideration when making bars and saddle adjustments. This is probably one of the reasons why riding indoors feels different. I suspect that it also applies to riding a TT bike indoors.

That's an excellent observation and one that I considered as well. I'd probably attribute the greater degree of torso support to the relative amount of pedal force applied vertically outside vs. tangentially across the top/bottom while indoors, but it's exactly what Bontrager is talking about in his KOPS essay that I linked above.

Getting some forward kick at the top of the stroke so I can start the power-phase sooner is exactly what I feel is lacking in my current position, but maybe that won't be as much of a problem when I get back outside. Still, rearward and lower should be benficial over forward and higher if there's not a resulting sacrifice of power, so I figured it'd be worth asking if anyone had any experience there.

'i have noticed that riding in the drops for long periods is not as comfortable. guessing that means in the aerobars will be less so, but maybe with practice you tolerate it better. gotta think to do the aerobars right & hold the position then you are gonna have to tinker with the bike setup (move seat forward/up) because you are changing the dynamics of your body on the bike.'

Not really becuase the arm pads support your weight better than your arms do on drop bars, thus you can get lower with more comfort, becuase there is no weight being born by the hands and wrists.

The best primer on tri/tt fit can be found at the slow-twitch website:

Tri Bike Fit

frenchyge said:

The concern that I'm feeling now is that being so far forward is destabilizing my hips and fatiguing my arms and shoulders. I'm looking pretty neanderthal, except that my shoulders are over my pads, rather than my ears. I'm not sure if that's worth trying to fix, or what I could really do about it.

That's right, but if you can comfortably roll the hips forward on the saddle then it doesn't close the hips up as much as it might seem. I had just finished reading The Myths of KOPS and was wondering if there wasn't something to the fore/aft weight distribution and CoG over the power stroke after all.

You might find these interesting. These are Steve Hogg's notions on bike fit. This link is his general perspective. This is for TT in particular.

frenchyge said:

Anyone have a good technique for measuring frontal area from a digital photo?

There was a guy - years ago - on the WATTAGE list that had a method. You might want to search the archive over there.

Dave

frenchyge said:

Anyone have a good technique for measuring frontal area from a digital photo?

maybe
-get bike mass
-get rider mass
-figure out center of mass for rider & for bike
-take a weighted avg of those
-have fun doing lots of linear regression

why not start with a set of frontal photographs like the ones from the biketech website - then use a known scale with your pic & compute the frontal area with the information above?

then you can always go out & do some field testing to get another data point & see how well your eyeball-photo-calc experiment lines up with some r/w data?

pub-med's got a link for a study on dig. photography cda calcs, you can find it here

key for me would be (if i had to prioritize) precision more than accuracy - at least then i would know i'm headed in the right direction towards lower cda.
i prefer both but a wind tunnel session seems to end up somewhere between space travel & buying a 6-figure car on the priority list.

you are a rocket science type if i remember right so whatcha waiting for to punch up a cda?