I’m under the impression that while the aerodynamics of a TT bike might save you a couple few minutes at HIM-IM distances, its principal benefits are that it “saves the legs for the run” via the steep angle, and conserves more energy via the skeletal support offered by the armrests.
Is this accurate?
Can anybody who’s done a HIM and/or an IM on both setups comment on this?
The search function left me swamped.
Thanks
You ask three things:
a. the aerodynamics of a TT bike might save you a couple few minutes at HIM-IM distances
b. its principal benefits are that it “saves the legs for the run” via the steep angle
c. it conserves more energy via the skeletal support offered by the armrests.
a. is true. I saved 20 minutes (!) at a hilly HIM on a TT bike vs. on a road bike with clip-ons.
b. is not true. I don’t have access to PubMed here at work, but I read an article that measured running speed after cycling with different seat tube angles, and found no difference.
I’ve never seen c. measured, so I can’t assert whether it’s true or untrue. It seems like it might be plausible, but I have my doubts how significant it is. But I have no data on the matter.
I always thought what you said on B) was correct, but a quick search of PubMed turned up this article which seems to indicate otherwise. But as I said, I am prepared to be proved wrong, as I had always thought what you said to be true.
http://www.ncbi.nlm.nih.gov/sites/entrez
It is perceived that, during the triathlon or duathlon, cycling with a steep (> 76 degrees) rather than a shallow (< 76 degrees ) frame geometry might attenuate the fatigue associated with progression from the cycle to run disciplines and improve subsequent 10-km running performance. This is based on anecdotal testimony from athletes purporting to have experienced improved performance; no empirical evidence exists. To evaluate this view, eight male triathletes completed a counterbalanced, 40-km cycle ride at two frame geometries (73 degrees and 81 degrees) at approximately 70% VO2peak. Immediately after completion of each 40-km cycle, a self-paced 10-km treadmill time trial was undertaken, during which physiological, kinematic and performance variables were measured. The 10-km run performance (mean +/- s: 42:55 +/- 4:19 vs 46:15 +/- 4:52 min; P< 0.01) and combined cycle and run performance (1:45:49 +/- 5:45 vs 1:50:33 +/- 6:08; P< 0.001) were faster in the 81 degrees than the 73 degrees condition. Improvements in performance were most prominent during the first 5 km of the run (21:41 +/- 2:15 vs 24:15 +/- 2:31 min in the 81 degrees and 73 degrees conditions respectively). These improvements were not evident during the second 5 km of the run. No differences in physiological variables were noted, although heart rate, stride length and stride frequency were increased during the 81 degrees condition (P < 0.05). Modifying frame geometry from a seat tube angle of 73 degrees to 81 degrees improves 10-km running and combined cycle plus run performance. These improvements in performance might relate to alterations during the cycling phase, which minimizes the ‘residual effect’ of this (i.e. the adverse changes in substrate availability, thermoregulatory, cardiovascular and biomechanical factors felt immediately after transition from cycling to running) and attenuates negative changes in physiological and kinematic responses during the 10-km run.
I based this on my poor memory and on another study mentioned on ST:
http://forum.slowtwitch.com/gforum.cgi?post=1717616
It turns out that that study only measured VO2, not speed. I’d read the article mentioned in that thread, and its references, as well as yours to try to form an opinion. Unfortunately I can’t read anything more than the abstracts here.
the primary purpose of the steep seat angle is to allow you to get area without smashing your thighs into your stomach.
to preserve the hip angle you would normally ride with in a road position
if it also allows you to run faster of the bike has not been demonstrated clearly.
Ok, I read the other thread and associated articles and I’m now down the rabbit hole. Thanks for the links.
I guess here I’d just like to hear anecdotal evidence, which despite it’s inconclusiveness I always find valuable and entertaining.
Rubberband, you said you made up 20 minutes on a TT vs. roadie? Was that over the same course? That’s a significant number.
ETA: It appears that as long as the hip angles are preserved, one may switch back and forth between tri and road bike during training. So the “train the bike you’ll be racing” argument falls flat (notwithstanding handling characteristics).
Yeah, on the same course. It was only in training, but that has the benefit of allowing a week-over-week comparison, so there’s no increase in fitness to confound it. I consistently rode a 50 mile loop from a HIM course in around 3:20 on my road bike. Then I got a TT bike, and the very next ride there I rode the same course in 3:00. I can’t have gotten that much fitter in a week, so I can’t chalk it up to anything else but the bike.
Another data point on TT bikes: my girlfriend dropped 2 minutes on the same 10-mile TT from her road bike to her TT bike.
So yeah, reducing drag leads to pretty dramatic improvements in times. See also the book of Mott: “Always ride a rear disk…”
I don’t deny that a TT bike is faster but when you say you “got a TT bike,” was it really a new bike? I ask because thoroughly cleaning my drivetrain and overhauling my bike has given me some significant time improvements. Then again, maybe I just had a really dirty bike.
It was a new (to me) bike. I got it on a Wednesday. I rode it at the local 10-mile TT that night, and at the HIM course on Saturday. I keep my bike’s drivetrain pretty clean, so it wasn’t the difference in drivetrain 
I’ve made the same comparison on other hilly training rides too. The TT bike is pretty much always faster, even on very hilly rides.
While we like to say that a forward seat position preserves the hip angle, it doesn’t. It helps, but it doesn’t cover the gap.
When going from the tops to the aero bars, I drop 8 inches at the shoulder, moving my saddle forward by a few degrees does not move me forward enough to totally preserve the hip angle.
a. is true. I saved 20 minutes (!) at a hilly HIM on a TT bike vs. on a road bike with clip-ons…
I have a really hard time with this. Perhaps YOU gained 9 to 12% in speed, but across the board I question the gains.
While we like to say that a forward seat position preserves the hip angle, it doesn’t. It helps, but it doesn’t cover the gap.
When going from the tops to the aero bars, I drop 8 inches at the shoulder, moving my saddle forward by a few degrees does not move me forward enough to totally preserve the hip angle.
…only if you attempt to contact the same point on the seat in both positions.
You have a hard time with what, precisely? Believing that I saw that increase in speed? I did. Believing that anyone else would? I never said that.
Or is there something else you’re having a really hard time with?
Jeez - you get defensive, don’t you.
Here, let me spell it out for you. I don’t doubt YOU may have seen that increase in speed. I do doubt that OTHERS would find an increase of this magnitude normal.
Feel better about yourself now?
Not trying to be defensive, I was trying to be clear. In answering your unstated question, I risked putting words in your mouth.
As I already said in my first reply to you, I never claimed other people would see a ~10% increase in speed. I just said that I had.
a TT bike might save you a couple few minutes at HIM-IM distances
“a couple few minutes” is selling it WAY short. I raced the iron distance in a relay last year in what I’d estimate to be quite nearly a full hour under what I could have done on a road bike riding solo. That’s fully aero’d out … TT helmet, aero shoe covers, skinsuit, disk rear/deep front … the whole nine yards. Maybe if I’d adopted some of the aero gear on the road bike I might have shaved 10 minutes or a little better off of that hour discrepancy. Even if I give myself credit for an amazingly good average speed for the full IM distance on a road bike, I still come up 42 minutes shy of what I actually did on my TT bike.
its principal benefits are that it “saves the legs for the run”
Well … maybe and maybe not. Some would make a distinction between a true TT bike and a Tri bike based on seat tube angle. A true TT bike would be more slack and wouldn’t have exactly the same impact on the run as a modern tri bike. But then this discussion bogs down in discussions of the UCI and a bunch of weird crap. I believe there’s probably some benefit to the run, but I believe the “principal benefits” are that hour of time savings I mentioned above … the aerodynamic benefits which you can convert to speed, or energy savings, or some of each.
conserves more energy via the skeletal support offered by the armrests.
I believe this is true for people who fit their bikes properly and not true for those who don’t. It’s a tough comparison. I can ride my TT bike and be comfortable on it for 5 hours and I can ride my road bike and be comfortable on it for 5 hours. One bike will allow me to have completed a good bit over 112 miles (with full aero regallia) in that amount of time. The other won’t. Conservation of energy is relative to conservation of time, no?
Here, let me spell it out for you. I don’t doubt YOU may have seen that increase in speed. I do doubt that OTHERS would find an increase of this magnitude normal.
This is undoubtedly true. I see some people who go from a road bike to a TT/Tri bike and it’s like magic happens. They get it. They engage a few new muscles and they like it and … off they go. I see others who just don’t seem to get the concept. They try to force their TT/Tri bike to ride like their road bike. They can’t stand any discomfort and won’t tolerate a little soreness in the neck or anything long enough to adapt to it, so they never achieve the kind of aerodynamic benefit the bike was intended to help them achieve. I feel sorry for their poor bike … fated to be ridden to nothing more than a MOP split. How people respond when you put a TT/Tri bike beneath them is probably a good indicator of what their personality type is … type A, type B or total doormat.