There are a few possible reasons:
1. You’re leaving gaps and surging. When you get to the back and it’s your turn to jump in the fast lane you might not be doing it smoothly or possibly not be paying enough attention that it’s your turn. If you need to jump hard to get on the wheel ahead of you this is extremely annoying for the guy behind you. It only takes a few of these before the rider behind you says “forget it” and waits for another wheel. That means you’ll be the last wheel in the fast lane and when you pull off you’ll be left on the front with no one rolling through from behind.
Example: Cadel (BMC Red) is leaving gaps in the fast lane and Renshaw (HTC yellow/black) behind is getting fed up with Cadel’s surging to get on Schleck’s (yellow) wheel. Sooner or later Renshaw will say “f#$@ it…I’m getting off this wheel and waiting for a better one”.
Remedy? Pay attention and make sure you change into the fast lane when it’s your turn and get on the wheel in front smoothly. Don’t let any gaps open so you don’t need to surge.
2. The other mistake that people often make in a paceline is rolling through too hard. You’ll roll past the front rider at a much faster speed than he’s travelling, leave a gap, then force him to close it. This is probably the biggest mistake that people make. This is not the time to flex your muscle. If you do this more than a couple times you’ll find that the riders behind will quit following and hang you out to dry on the front.
Example: Cadel rolls-through hard on Schleck and Renshaw says “f@#$ this”, and pulls off in-between Schleck and Cadel. Cadel is hung out to dry.
Remedy? Rolling through in the fast lane should be smooth and only marginally faster than the slow lane. You then start pulling over ahead of the lead rider just after your back wheel is slightly ahead of his front wheel. Then you slow down about 1km/hr and let the fast lane come through.
3. To add to the point above, if you don’t slow down after you switch into the slow lane it makes it extremely hard for the rider on the front of the fast lane to roll through ahead of you. If you keep doing this, the riders will eventually just pull over and sit behind.
Example: Cadel rolls-through nicely but keeps the gas on while in front of Schleck. Renshaw needs to do a 1500watt Cav-style lead-out in order to get past Cadel. Reshaw eventually backs off after a couple times of this and says “f#$% this…” and again Cadel is left at the front.
Remedy? When you make your way to the front be sure you slow down so that guy on the front of the fast lane can easily make their way past you. Only about 1km/hr slower is all it takes. Sometimes I’ll even shift down a gear when I get to the front.
Now, if you’ve made any of these mistakes and you’re now caught at the front and no one is rolling through, whose responsibility is it to get the paceline running smoothly again? Answer: The rider either on second or third wheel behind you.
Let’s pretend in the photo above that Cadel (BMC red) is messing up the paceline again. He’s having a bad day and is leaving gaps in the fast lane and is now left on the front.
Matty Lloyd on second wheel (in polka dot jersey) is getting yelled at by the guys behind to “Roll Through!”. Even though it wasn’t Lloydy’s fault that Cadel is messing up his turns, it’s up to Lloydy to roll another turn since it’s the least amount of effort out of the bunch for him to do so. Gerro is on 3rd wheel (Sky blue). In order for the bunch to start the paceline again it’s up to Gerro to get on Lloydy’s wheel and others will follow suit. If Lloydy hadn’t pick up the extra turn, it would have been up to Gerro to roll past Lloydy to get the paceline moving again. Knowing Gerro, as soon as he gets to the front he’ll blow the group to smithereens up the next climb. Nothing wrong with that. Respect.
Now Lloydy will roll to the front, smoothly pull off in front of Cadel, Gerro will do the same, and so on. The paceline has been kickstarted again.
Of course the fact that Cadel was always left at the front in these examples could be nothing more than a lazy guy in behind (perhaps a sprinter like Renshaw) and refused to roll-through!