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Trying to understand triathlon bicycles(17 posts)

Trying to understand triathlon bicyclesstinkfoot247
May 19, 2003 11:11 PM
I can't see why all triathlon bikes have steep seat tube angles. I was reading about the relationship of handle bars to seat tube angle, but I just can't figure out what is so different about the roads a triathlon rides, roads are roads to me.
It's because...Dwayne Barry
May 20, 2003 3:03 AM
the steeper seat tube angle allows you to get into an aero position (essentially low with a flat back is the goal) and yet maintain a relationship to the bottom bracket good for generating power. To get that on a normal road bike is difficult and uncomfortable.
re: Trying to understand triathlon bicyclesdivve
May 20, 2003 5:05 AM
It facilitates a reasonable aero position without having to bend your back down as much as you have to with a time trial bike - also makes running easier after you've cycled.
To elaborate....ClydeTri
May 20, 2003 6:55 AM
Moving forward in your position changes the ratio of muscles used while cycling. A forward position seems to be more advantageous for a person who also runs alot, with a rearward position better for a strictly cyclist. Moving from the gluts to the quads shalll we say as you go from the rear to the front. Thus, as divve says, makes running easier after you have cycled.
If it works for those who do triathlons it's fine with me.dzrider
May 20, 2003 6:08 AM
People new to cycling complain about the set-up and geometry of road bikes. I tell them the position has evolved and is what it is because it enables bike racers to ride long distances comfortably and efficiently. Triathletes, because of aero bars and the need to run after they get off the bike, have found a different geometry and set-up. If they're happy, I'm happy.

Interestingly, some have started questioning the steep seat angle, having observed that road racers ride long and really fast. I've seen two articles about bikes for triathletes that talk about "slam" positioning, which I believe is more like the typical road riding posture.
If it works for those who do triathlons it's fine with me.ZeGopha
May 20, 2003 6:28 AM
Part of it is, road racers who ride a lot faster train a lot more. But there is some evidence that riding the shallower angle seat tube "slam" position helps; however, I would argue that at slower speeds (i.e. 25-30 miles an hour the benifits are going to be minimal. If you read up on John Cobb he does also agree that the slam isn't for everyone. I personally used to have a road bike I road more in the slam position, I couldn't get comforatble at all. Now I ride a somewhat steeper angle tri-bike and I can go aero for hours on end. Ultimatly the "tri bikes" and "adapted road bikes" come down to a matter of fit.
aero, muscles, breathingDougSloan
May 20, 2003 6:17 AM
In a timetrial, you want to get as low and flat as possible. If you got really low on a conventional geometry bike, your legs would be slamming into your chest, it would be harder to breathe, and your hips would be cramped. The steeper seat tube allows you to get low and still have a wider hip angle.

For dedicated time trial and tri bikes, this is fine, for relatively short distances. I tried it on for a bike set up for 24 hour time trialing, and it was a little hard on the neck and upper body. Also, if you body is used to conventional angles, you might be better off not going quite so radical for a time trial bike used only occasionally. That's why, aside from rule constraints, typically you see pro time trial bikes with more conventional angles. Since tri bikes are usually used for shorter distances and tri geeks usually don't ride other bikes, too, they can be set up to optimize the seat tube angle for higher speed, shorter, solo efforts.

Have you ever been "on the rivet?"QuentinCassidy
May 20, 2003 8:52 AM
When you see someone on a solo break in a race (doesn't matter if it's TdF or Cat 5s), or someone doing a TT, they're probably "on the rivet" as Phil Ligget would say. Years ago, before plastic was everywhere, the old leather saddles used to be riveted along the edges, and there was a rivet right on the nose of the saddle. In other words, they're in an aero position, on the front of the saddle, really hammerering for all they are worth.

The point is, strong riders who are forced to hammer at a fast pace naturally move to the front of their saddles in order to produce more power. Check out the next TT in the Giro, and some of the guys will be so far forward that they appear like they're about to fall off the front of the saddle! Do a little trig, and you'll see that effictively they're increasing the seat tube angle by a few degrees. Triathaletes are in the same boat as Jackie Durant doing a solo flyer or Tyler doing a TT... they want steeper seat angles so they can produce more power.

Why steeper angles allow you to produce more power, I don't know. But it does.
Why not just move the seat forward for a TT?LC
May 20, 2003 9:30 AM
Using a zero setback seatpost and sliding the seat forward on the rails should do the same thing? They even have seatposts that move you even further forward if you need it.
we can, but not prosDougSloan
May 20, 2003 9:40 AM
UCI regs prohibit the saddle nose from being in front of the bottom bracket.

For us peons, we can do anything we want, including what you mention, as long as your weight balance on the frame and effective top tube length aren't all screwed up.

So Mr Doug....ClydeTri
May 20, 2003 9:55 AM
is that rule, not letting the saddle nose be in front of the bottom bracket a safety rule? or...another case of UCI with their nose up....ah, you know where...
May 20, 2003 10:05 AM
Don't know what it would have to do with safety. I think it's more of a "keep the bikes looking like traditional bikes" rule.

If i recallsctri
May 20, 2003 11:38 AM
It was to avoid the so called "superman position" which was gaining popularity in the track world.

yep - or turn a layback post around 180 deg.rockbender
May 20, 2003 12:25 PM
Here's my 'TT' setup for an annual multi-sport race I participate in:

take 1 regular roadbike and...
*add aero bars
*drop bar height 3" (not done yet in this pic)
*turn layback seatpost 180 deg and shove saddle all the way forward
*add aero wheel cover
*swap 53-39 rings and 12-23 cassette for 60-48 with a 11-21 (I'm a grinder)

you're right Doug - wouldn't want to hold my head up for much longer than an hour!
Why not just move the seat forward for a TT?dotkaye
May 20, 2003 3:09 PM
changes the handling of the bike significantly by putting more weight on the front wheel. The bike becomes noticeably squirrelly , in my experience. Add aero bars to this and you get a rolling accident-waiting-to-happen. The steep-angled frame changes the geometry so that the bike remains stable. has a number of articles by the guy who invented the steep-angled frame for tris, Dan Empfield.
... go to
May 20, 2003 11:43 AM
... and click on their tech link...

Be the bike.
How about I draw you a picture. . .js5280
May 20, 2003 1:06 PM
or just link to one. I think this explains it all. The rest of the page is worth a read too and has great photos of good and poor bike fit.