All of the riders I see have a stem that looks like a 120mm. Why is this?
I was thinking because they ride small frames, but then I remembered that they have frames custom made for them. Could it be to change the handling, or have a more aero position?

Another thing I noticed is their handlebars almost always move side to side in unison with their pedaling motion. This is when they are in the saddle. It's like they are making tiny "S" turns instead of holding a straight line. Any ideas?

Most riders seem to prefer a smaller frame: less weight, stiffer, [allegedly] better handling... ...but I suspect it's more because we all want to look more like the TdF thoroughbreds.

Me (6'2"), I prefer to stretch out on a big 63cm (or in the case of my Schwinn, 25-inch) frame and just a 90mm stem. I've noticed that the bike does tend to waddle back & forth more with the 110mm stem installed, but this only increases your mileage, so it's a win-win.

The long stems are a function of riding smaller frame sizes. The major reason to ride a smaller frame size is that it results in a lower position, i.e. its easier to get a significant drop from the seat to the bars with a 56cm top tube, and 120mm stem, than it is with a 58 top tube and a 100mm stem.

Other reasons, stiffness and weight don't really matter for tDF riders ( you can make any frame acceptably stiff theses days, and they're all at the UCI weight limit anyway)

So the answer is aerodynamics.

As for "S turns" with pedal strokes, that happens to everyone riding a bike. Take a look at yourself with an aerial shot. You just don't notice it, without that viewpoint.

I guess I will have to watch the rest of the bike rides from the helicopter camera. Usually I just watch the town sign sprints, where I am out of the saddle. I know the helicopter is expensive but I like to see me destroying the rest of my group to the town signs.

^ Good point. What I'm trying to say is that we would look like that or worse if there was an aerial shot available.

By pulling up on the handlebars at the same time you are pushing down on the pedal, you are using arm muscles to oppose the pedal stroke about the roll axis. By using the arm muscles to pull/push the bike about the roll axis-it is a way of supplementing your leg muscles with arm motion. The S-turns become necessary component of achieving that aspect when in the saddle as your body moves with the bike. If you are standing the S-turns diminish as the movement of the bike along the roll axis is fully independent of the rider.

Why do you ride with such a short stem?

Incorrect.

They ride bikes with quite short chainstays for whatever reason. When you shorten the chainstay you also have to shorten the front center to keep the weight distribution from getting too rear biased. So short TT/long stem.

In this age of monocoque carbon fiber I'm not sure any of them actually have have custom frame geometry -- a custom mold for CF has an incredible price. Even Johan Vansummeren at 6'5" just looks to be on the largest, 60cm stock Felt with a 140mm stem and about three miles of seat post showing:




Of course Johan isn't a GC contender, maybe if another guy like Indurain comes around he'll get a custom frame. Then again Indurain himself rode a 59cm, albeit with another 140mm stem and a silly looking headtube and steerer extension:

"Another thing I noticed is their handlebars almost always move side to side in unison with their pedaling motion. This is when they are in the saddle. It's like they are making tiny "S" turns instead of holding a straight line. Any ideas?"

Look at their arms - they are small people with big legs - but arms like twigs. Its easier to wobble along than to fight bike into a straight line.

This doesn't make sense. The chain stay length doesn't change as the frame size goes up. For example all Cervelo R3SL's have 399 mm chainstays regardless of the lenght of the top tube from 48cm to 61cm. By your theory the larger frame sizes would be horribly out of balance.

Moreover the weight distribution is going to be the same regardless of whether the reach to the bars is made up of 56cm of TT and 12cm of stem, or 58cm of TT and 10cm of stem.

What is different is that the bike with the 56 cm top tube typically has a shorter head tube, and than the bike with 58cm top tube.

Hence my point, the smaller frame tends to facilitate a more aero position, i.e. more drop from seat to bars.

These guys aren't wobbling. I guarantee you they can hold at least a straight of line as anybody you've ridden with. You can't be wobbling about, not holding your line, and ride a couple of inches off the guy beside you at 30+ mph in a pack of 190 guys.

It's simply a view that you don't see when you're riding, and its points out movement that you don't notice when you're following a bike in front of you.

Many people who have studied bicycle dynamics at the quantitative level do indeed agree that chainstay length should increase with front center. Better designs at least compensate for rear weight bias by increasing the trail, using less fork rake on larger frames. And I can testify personally that YES, large frames DO typically have poor handling the way most manufacturers design them. My most agile, intuitively handling bike has 47cm chainstays.

I'm talking about weight distribution at the wheels not the rider contact points.. When you shorten the top tube, the front wheel moves back, hence more weight on front wheel.

Also having a short head tube doesn't explain why the bike is made with a short top tube.

Bike have top tubes appropriate for their size. We're just saying that people size down to get the associated shorter head tubes to be able to get a lower position. I picked the smaller of two sizes that would have worked for me mainly to get the bars as low as possible, and also got the special "team geometry" version with an even lower head tube than normally found on that size. (Althought o be fair it only restored the head tube heights from prior years before jacking them up )

And the people at Specialized, Cervelo, etc do not understand this, and make poor handling bikes for their sponsored riders. Perhaps the handling charecteristics they are looking for are differnet from the ones you are.



But its a fact, as you go to bigger frames (i.e. longer top tubes) the head tubes get longer and the handlebars get higher. Smaller frames tend to come with shorter headtubes, and the minimum height you can set the bars at is lower in relation to the seat height.

Look at Andy Schleck's bike. He rides with the handlebars as low as they can practically be set on the frame (no spacers, stem angled down) If he went with a larger frame, (and therefore a shorter stem) he could not get the drop he needs from seat to bars.

Its a quite common setup for pro riders, no spacers, stem angled down. A guy riding a bike with that setup can't ride a larger frame size and still get the necessary drop. They simply put on the stem that gives them the necessary extension to the bars.

^^^

Merlin, you always have such a way of putting things so clearly and succinctly. I guess it's all that lawyerly training.

If you need any evidence of this look up at Vansummeren's bike again.

Then vs. now: Similar rider position (i.e. just as "aero",) but the newer bike has shortened chainstays, and shortened front center and increased trail to match.

In his case it sounds like he is already on the largest size frame so he didn't really have much of a choice. Lots of post, and spacers under a long stem. But in general, you see most pro bikes with slammed stems, indicating that they picked the frame size to get their bars low.

I am pretty sure the short chain stay might also have something to do with aerodynamics. Most of the aero road bikes not only have the short chain stay but also the seat tube built around the tire.

Because, like many out here they fit a bike using a picture from a magazine. Which on a longer ride probably feels like drilling your own tooth, without painkillers.