I was watching a TT race on the Vs. channel and all the riders were in the aero position sitting on the front of the saddles. That looks very painful to sit on the skinny part of the seat. Struck me as odd. Is this a "TT thing"?

Not always a TT thing...but known as "riding on the rivet". Basically getting the hips as far forward to drive the pedals. Not much weight on their seat as it's all on their legs and arms. Maybe not so painful on their butt...but the rest of their body is screaming at 'em, I'm sure.

Saddle position is limited by UCI rules, so when they're forward on the aero bars, they often don't have much saddle left.

Next time you are on the bike, go as hard as you can for 30secs to 1min while staying seated. See where your butt ends up on the saddle.

Yep, not strictly TTs, but usually reserved for "short" efforts and rarely a favorite position for things like recreational centuries.

With the right saddle it's not bad at all, with the wrong saddle it's pretty damn awful. I'm going to assume that most pros ride the right saddle for them and don't deal with too much discomfort.

Most TT saddles are designed to be ridden (relatively) comfortably on the nose, you wouldn't be riding the same saddle that you would on your road bike.

Ding Ding Ding, this is the main answer

There is a hard compromise between aerodynamics and producing power. Triathletes fix this by moving there saddle forward, as much as to have the nose "in front of" the bottom bracket, which maintains an open hip angle. UCI constrained cyclists have to sit as far forward on their saddles as possible to achieve the same effect.

It's not terribly uncomfortable to do this when you are going hard and racing under one hour. As some pointed out, it's also an effect of the effort and getting weight on to the legs.

Does anybody know what the UCI's reasoning for this rule is?
I've never been able to think up a line of reasoning for a rule like that, it seems so arbitrary.

If you are hammering hard like in a TT your butt is only brushing the saddle, there's not a lot of weight on it, your legs are lifting you off it.

UCI arbitrary? No, couldn't be. lol

Seriously though, it seems whenever an outsider uses an innovation to start winning, that innovation will be banned post-haste (see for example https://en.wikipedia.org/wiki/Graeme_Obree)(PS, on Obree's riding position "... a very forward position on the bike, on the peak of the saddle. The Obree position isn't advantageous simply aerodynamically, it also allows, by pushing the point of pedalling towards the rear, to benefit from greater pressure while remaining in the saddle.").

Many pro cyclists surgically remove their ding dongs to help them make this riding position more comfortable.

Sheldon once said you don't sit on a saddle. You want most of your weight over the pedals.

As others have also said, you can produce greater power by sliding up on your saddle.

When racing, I find that I spend much of my time on the front of my saddle.

i agree with the previous comments on shorter/faster TT races.

but for longer efforts on a tri/time trial bike/saddle (such as IM distance) you just have to find a saddle that doesn't put much pressure on your perineal(sp?) vein. and you have to just train your sit bones to endure pressure in a different (more forward) area.
many triathlon specific saddles have massive cutouts such as:

During last years TdF final time trial, I remember Contador scooting back onto his saddle after 2 -3 revolutions of the pedal. It was extremely unattractive style and looked like he would be robbing himself of power....but he did well enough to hold his lead. Yesterday, watching Criterium Int'l, FSchleck was doing the same thing...although he had more pedal revolutions before he'd scoot his butt back again.

Maintains the traditionalism of cycling. The real problem is that it isn't just arbitrary but also has greater detriment to smaller cyclists because they are riding a much more effectively slack time trial position unless they get an exemption.

Sometimes they care about "traditionalism", sometimes they don't- I think it is more of a post-hoc justification than the real reason.

This does not look even vaguely traditional:

+1

Weighing 135 lbs does not hurt either.

I haven't been 135lbs since 8th grade.

Those Adamo ISM saddles most of those guys use are designed to have contact with the so-called "sit" bones instead of the perineal tissue. If you watch their seat setup video you are supposed to have several cm sticking out from the back on their seats.

UCI banned the position after Graeme Obree broke records with his personally fabricated bike and unique riding position which was more aerodynamic than orthodox positions. The common tri-bar is an innovation from Obree's efforts.

My understanding is they had triathlon bars long before Obree came along. Both of Obree's positions were eventually banned in favor of the traditional aerobar.

You can complain about the UCI all you want, but at some point, they have to define what, exactly, a "bike" is. You can argue about whether this saddle position or that saddle position is allowed or not, but in the end, there will always be people pushing right up to the limits. At some point you just draw the line and riders aren't quite as aero as they possibly could be.

Apparently pretty much everyone gets an exemption these days, that allows the saddle to be right over the top of the bottom bracket. The 5cm rule really only applies to bigger riders. Most riders can figure out how to sit on their saddles and stay within the other angle/length constraints.

That was a personal fit issue more than anything saddle related.

https://www.cyclingnews.com/news/riis...-and-armstrong

If you watch the last TT he did he only scoots back maybe once or twice the whole time compared to every 3-5 seconds he used to.

Why not just make the seat a little shorter? Doesn't make sense to design a seat that is supposed to have a couple of inches of seat poking out the back. These guys are so obsessed with weight, I bet you could shave a significant amount of seat weight by eliminating unneeded size.

When you are descending, you need to sit back on the saddle for control. When climbing, you need to sit back on the saddle for power.