Best Aero Position?

RapDaddyo said:

Can anybody provide a link or pdf to a technical discussion of optimal aero positions, for both TT and standard racing bar bike configurations? I'm looking for both analytical discussions and empirical studies, something for example that might have come out of the wind tunnel work at Trek for the USPS/Discovery teams. I'm more interested in positions, but am somewhat curious about frame and wheel and helmet data. Thanks.

Bit of a brief reply Daddyo...

my suggestion if you aren't able to get to a wind tunnel is for TTing to get pretty low. If you're viewing yourself from a side view you should aim to have your your acromion process at the same height (or with a 10% up slope) as your greater trochanter, see (if you're unsure of these bones) http://ect.downstate.edu/courseware/haonline/figimgs/5_1.gif

your greater trochanter is located on your thigh bone (femur) and can be felt also as a 'knobbly' bit (although to a lesser extent on ladies) as the point where you can rotate your thigh

see http://www.sportsinjuryclinic.net/gallery/hip/femur.jpg

Your should try to get your forearms parrallel to the road or pointing slightly up and your elbows probably under your ears.

a deep front wheel, and a deep rear or a disc will also be 'essential', as will a skinsuit and an aero helmet.

I've probably missed stuff out, but i'm shattered after training! Andy would be good to have on this thread as well

Ric

ric_stern/RST said:

Bit of a brief reply Daddyo...

my suggestion if you aren't able to get to a wind tunnel is for TTing to get pretty low. If you're viewing yourself from a side view you should aim to have your your acromion process at the same height (or with a 10% up slope) as your greater trochanter, see (if you're unsure of these bones) ect.downstate.edu5 1.gifOpen ↗

your greater trochanter is located on your thigh bone (femur) and can be felt also as a 'knobbly' bit (although to a lesser extent on ladies) as the point where you can rotate your thigh

see sportsinjuryclinic.netfemur.jpgOpen ↗

Your should try to get your forearms parrallel to the road or pointing slightly up and your elbows probably under your ears.

a deep front wheel, and a deep rear or a disc will also be 'essential', as will a skinsuit and an aero helmet.

I've probably missed stuff out, but i'm shattered after training! Andy would be good to have on this thread as well

Ric

Thanks, Ric. I did find on my own the following link to some of Jim Martin's aero work. cervelo.comarticle5.htmlOpen ↗
Do you concur with his numbers? Are you aware of any fitting models specifically for TT bikes? I'm primarily aiming to be in shape and have the right bike for next spring, so I've got some time to sort everything out, including best position. But, you can't get in the right position on the wrong bike, so I'm starting with optimal position.

RapDaddyo said:

Thanks, Ric. I did find on my own the following link to some of Jim Martin's aero work. cervelo.comarticle5.htmlOpen ↗
Do you concur with his numbers? Are you aware of any fitting models specifically for TT bikes? I'm primarily aiming to be in shape and have the right bike for next spring, so I've got some time to sort everything out, including best position. But, you can't get in the right position on the wrong bike, so I'm starting with optimal position.

I haven't checked that link (yet) - too busy/tired. But Jim's work is good, very good. If you're not sure who he is you can do a Pub-Med search on him. He is an expert.

I'm not sure what you mean by "any fitting models"? It could be that i'm over tired though!

Ric

ric_stern/RST said:

I haven't checked that link (yet) - too busy/tired. But Jim's work is good, very good. If you're not sure who he is you can do a Pub-Med search on him. He is an expert.

I'm not sure what you mean by "any fitting models"? It could be that i'm over tired though!

Ric

Well, maybe I should have worded my question, "fitting systems" rather than fitting models. I am looking for a system that translates detailed body metrics into a bike setup (frame geometry, seat height, bars, bar height, etc.), specifically for a TT bike. This would be for a starting point, not a final solution. Here are some fitting "systems." cyclemetrics.combike fit links.htmOpen ↗

RapDaddyo said:

Well, maybe I should have worded my question, "fitting systems" rather than fitting models. I am looking for a system that translates detailed body metrics into a bike setup (frame geometry, seat height, bars, bar height, etc.), specifically for a TT bike. This would be for a starting point, not a final solution. Here are some fitting "systems." cyclemetrics.combike fit links.htmOpen ↗

I thought you may have meant that, but wasn't sure...

anyway, i (personally) don't buy into the fitting systems -- or at least i haven't been exposed to anything here (the UK) that i would be happy with (note, that there are more fitting systems in your neck of the woods).

Personally, i use my eye and a tape measure and go from there

ric

community leader.............ric I like it😄

One thing though and I just found this out from finally riding a TT with a power meter is that it is possible to be too low.
I have tried over the years to get as low as I can on a 'standard' TT bike with a drop stem,low aerobar pads etc.
But after finally doing a TT and comparing with power generated in a standard RR position I can see that I have over done it to the point where I cannot fully recruiting all my power.
I don't think that there can be any sort of fitting model, because if you have a quick flick through Cyclesport or Procycling and look at any of the TT pictures you can see the differences. Some guys ride long in the bars(CSC) some short(gerolsteiner). Some ride extremely low(chris boardman, Big Jan), some ride high(Lance, Big Mig).

Bear

Bear the Bear said:

community leader.............ric I like it😄

One thing though and I just found this out from finally riding a TT with a power meter is that it is possible to be too low.
I have tried over the years to get as low as I can on a 'standard' TT bike with a drop stem,low aerobar pads etc.
But after finally doing a TT and comparing with power generated in a standard RR position I can see that I have over done it to the point where I cannot fully recruiting all my power.

to let you know: even though a very low position may reduce your power output, your drag may still be decreased sufficiently enough that it more than makes up for the small loss of power (i.e., you'll still be faster than a more upright powerful position).

Of course the only way to test this is either in a wind tunnel, or most likely an indoor velodrome where conditions can be held constant, but you'd need to complete multiple trials.

Additionally, even with the lower position if you train sufficiently in that position your power will come up to your more upright position.

Furthermore, you can go to low where there is no further decrease in drag and a lower power output. but you would need multiple trials or a tunnel to confirm what *exactly* is happening.

Quoted post said:

I don't think that there can be any sort of fitting model, because if you have a quick flick through Cyclesport or Procycling and look at any of the TT pictures you can see the differences. Some guys ride long in the bars(CSC) some short(gerolsteiner). Some ride extremely low(chris boardman, Big Jan), some ride high(Lance, Big Mig).

Bear

Do 'bear' in mind (!) that some of the pros aren't tunnel tested or fitted for a TT bike and rarely use one (e.g., only in a GT where they have to ride a TT) so some of their positions are dire.

ric

Bear the Bear said:

I don't think that there can be any sort of fitting model, because if you have a quick flick through Cyclesport or Procycling and look at any of the TT pictures you can see the differences. Some guys ride long in the bars(CSC) some short(gerolsteiner). Some ride extremely low(chris boardman, Big Jan), some ride high(Lance, Big Mig).

Not that such a fitting system is available, but I would think that one could get to a good first approximation of the bike geometry with a highly adjustable (cranks, seat, bars) trainer equipped with a PM and cameras (front & side). I mean, what you're after is the best tradeoff between reduction of frontal area and power. You're not going to order a TT bike without being pretty certain of the efficiency of your position on it.

Plenty of people do, I did:o Geometry for TT bikes is fairly standard but on the steeper side useless your are talking about triathlon bikes. You can get all the adjustment you need by moving the seat forward and back(within reason), an adjustable stem, and a good set of adjustable aerobars. The other thing to remember is that over time your body changes, becoming more/less flexable and this can have a big impact on your positioning so it is always good to have that adjustability there to begin with.
Most people(95%?) don't own a power meter, and no one barring pro's(or higher level national riders) tries for this level of adjustment. And when they do they use a wind tunnel. For most people it is trial and error, whack a set of aerobars on and if they arent fast enough they blame their fitness.
IMHO I think that all you really need is a powermeter and sometime on the velodrome to really get your position dialled.

Bear

Bear the Bear said:

Plenty of people do, I did:o

Okay, let me re-state. I don't plan to spend $5K or so on a TT bike with the hope that the geometry is going to allow me to get into a good position with full power. So, any suggestions about TT bike fitting approaches would be welcomed.

RapDaddyo said:

Okay, let me re-state. I don't plan to spend $5K or so on a TT bike with the hope that the geometry is going to allow me to get into a good position with full power. So, any suggestions about TT bike fitting approaches would be welcomed.

There's generally quite a lot of movement available in most bikes (as Bear suggests above). However, that said, i'm not sure there's any *good* way to work this out first (as you want). There's quite a few fit methods (which likely range from the good, the bad and the ugly), but i'm not sure how good a position they'll get you in. They may just offer some 'standard' aero position.

You're presumably asking for a bike that fits you well, and is aero. The latter may only be determined as i previously mentioned via e.g., tunnel testing or testing it on an indoor velodrome to eradicate any 'noise' (i.e., gusting winds or changes in barometric pressure).

With regards to the former (i.e., fit -- is it the correct size for you) it maybe that you're best off either taking someone with you who is experienced in good aero fitting or perhaps your current road bike company make an aero bike and you could test this out in the shop. obviously, you'll also need to be aware of any UCI limitations if you enter races that are subject to these rules.

Ric

ric_stern/RST said:

There's generally quite a lot of movement available in most bikes (as Bear suggests above). However, that said, i'm not sure there's any *good* way to work this out first (as you want). There's quite a few fit methods (which likely range from the good, the bad and the ugly), but i'm not sure how good a position they'll get you in. They may just offer some 'standard' aero position.

You're presumably asking for a bike that fits you well, and is aero. The latter may only be determined as i previously mentioned via e.g., tunnel testing or testing it on an indoor velodrome to eradicate any 'noise' (i.e., gusting winds or changes in barometric pressure).

With regards to the former (i.e., fit -- is it the correct size for you) it maybe that you're best off either taking someone with you who is experienced in good aero fitting or perhaps your current road bike company make an aero bike and you could test this out in the shop. obviously, you'll also need to be aware of any UCI limitations if you enter races that are subject to these rules.

Ric

Well, I think I'll start with Cervelo, because they seem to have given the subject some thought and they have several TT bikes (most are UCI approved). Their website has the discussion by Jim Martin. I don't kow if he is a technical consultant to them or what. Ideally, I'll find a Cervelo dealer (probably in Los Angeles) that has several sizes that I can go in and ride on a trainer and at least get some photos from the front and side so I can study my position on each frame. Once I get my bike, I will do either some velo work (we don't have a velo here, but there is one in Los Angeles) or wind tunnel work (they have one in San Diego) to find my best position on the bike, but I am curious to see how close I can come with digital video taken from the front. I would put a white background behind me and wear a black skinsuit (leotard, basically) to create a clear contrast with the white background. My frontal area will be everything that isn't white.

RapDaddyo said:

Well, I think I'll start with Cervelo, because they seem to have given the subject some thought and they have several TT bikes (most are UCI approved).

they have some nice looking bikes (as do other bike companies)

Quoted post said:

Their website has the discussion by Jim Martin. I don't kow if he is a technical consultant to them or what. Ideally, I'll find a Cervelo dealer (probably in Los Angeles) that has several sizes that I can go in and ride on a trainer and at least get some photos from the front and side so I can study my position on each frame. Once I get my bike, I will do either some velo work (we don't have a velo here, but there is one in Los Angeles) or wind tunnel work (they have one in San Diego) to find my best position on the bike, but I am curious to see how close I can come with digital video taken from the front. I would put a white background behind me and wear a black skinsuit (leotard, basically) to create a clear contrast with the white background. My frontal area will be everything that isn't white.

with the last idea i'm *sure* there must be plenty of info at Craig's site: www.biketechreview.com (i think that's the correct url). Dunno, why i didn't mention that before (brain must have been mush after training too hard :eek:!)

ric

RapDaddyo said:

Well, I think I'll start with Cervelo, because they seem to have given the subject some thought and they have several TT bikes (most are UCI approved). Their website has the discussion by Jim Martin. I don't kow if he is a technical consultant to them or what. Ideally, I'll find a Cervelo dealer (probably in Los Angeles) that has several sizes that I can go in and ride on a trainer and at least get some photos from the front and side so I can study my position on each frame. Once I get my bike, I will do either some velo work (we don't have a velo here, but there is one in Los Angeles) or wind tunnel work (they have one in San Diego) to find my best position on the bike, but I am curious to see how close I can come with digital video taken from the front. I would put a white background behind me and wear a black skinsuit (leotard, basically) to create a clear contrast with the white background. My frontal area will be everything that isn't white.

Not to be picky but what are you riding at the moment for TT's and how does it "Feel"?

ric_stern/RST said:

with the last idea i'm *sure* there must be plenty of info at Craig's site: www.biketechreview.com (i think that's the correct url). Dunno, why i didn't mention that before (brain must have been mush after training too hard :eek:!) ric

You're right -- that's a good resource. Thanks, Ric. Actually, I think Kraig lives north of San Diego (about 5 hours from me). I may go see him about my idea of using digital video images to derive frontal area and impute speed, given power. Wind tunnels are kind of pricey (and noisy).

Bear the Bear said:

Not to be picky but what are you riding at the moment for TT's and how does it "Feel"?

I'm not riding anything for TTs at the moment because I'm not riding TTs (or any other races) until probably next Spring. I'm riding a Merlin Extralight for training, which I will use for RRs and crits (I'm not much of a crit fan, but there are lots of them). I won't enter a race until I can ride at race-pace at about 65% or so of my 20K TT power. I've only been back on my bike for 3 months after a long layoff. When I enter a race, it won't be to just fund the trophies and get dropped. I figure I've got about 9 months to sort out the right TT bike and position. In the meantime, the hills and wind here will allow me to get in racing form.

I would start by looking at the dimensions of your roadie and work from there. A TT bike isnt alot different.
If you look at alot of the faster pro riders, they go for a smaller frame size to get a shorter toptube and more of a drop in the front.This is the biggest challenge even with a custom TT bike, getting lower in the front.
As I mentioned with an adjustable stem and good aerobars, you will be able to get 85% of your position dialled on a standard roadie. It just takes time, which as you mentioned you have alot of.

Bear

Bear the Bear said:

I would start by looking at the dimensions of your roadie and work from there. A TT bike isnt alot different.
If you look at alot of the faster pro riders, they go for a smaller frame size to get a shorter toptube and more of a drop in the front.This is the biggest challenge even with a custom TT bike, getting lower in the front.
As I mentioned with an adjustable stem and good aerobars, you will be able to get 85% of your position dialled on a standard roadie. It just takes time, which as you mentioned you have alot of.

Bear

Hey, Bear. As I have been investigating the frame geometry options for TT bikes, I have found that most mfgrs. only offer about 3 sizes -- basically, small, medium and large. I think they basically don't sell enough of these frames to justify offering more sizes. So, it may be easier to come to a frame size decision than I thought. Then, it'll be a matter of tinkering with the seat and bar locations and experimenting with positions on the road with a PM or in a wind tunnel if I can hook up with some others and share the cost of the wind tunnel in San Diego. The problem with my road bike is that I can't get very low due to my thighs hitting my rib cage. Not that getting lower is the optimal TT position for me, given power and frontal area tradeoffs. There are some pretty interesting theories about optimal TT position floating around. Paul

You will find the same problems on a tt bike.
You are physically limited by how low you can get yourself because you start to press in on your diaphragm.
A TT bike gets around this by having a steeper seattube allowing more rotation of the pelvis, and therefore a lower frontal area. You can also do this on a standard road by moving the saddle forward.
With this issue there is a large amount of debate about seattube angles and where you actual sit on the saddle, because by moving forward you effectively are increasing the seatangle. There was quite a large discussion about this on slowtwitch awhile ago.
But as you noted, and I have just found out, it is possible to get so low that you start to rob yourself of power and the trade-off is not worth it.
After my last TT and running a powermeter for the first time I have raised my bars about 2cm. I have a 25k TT tomorrow on the same course so will let you know how it goes.

Bear