Issues shifting under load
 

I am trying to learn to do the maintenance on my bike myself. I am having an issue when i am climbing and go to shift from the big ring to the smaller. Any other time shifting its fine but under heavy load the chain pops off completely. I can shift up and recover if im moving fast enough, but other wise its a real issue. Im riding a cervelo RS with full Dura Ace 7900 group

Thanks

Front shifting under high load is alway iffy so learming to anticipate is useful. That said, try tightening the low limit screw a fraction of a turn and install a "chain watcher" for insurance.

Ill give this a try. Thanks

Front ring shifting under load is kind of a no-no. It's totally normal to have to let up pressure on the pedal stroke during a front ring shift in order to get a smooth shift. Eventually, over time it becomes second nature and you don't even really think about it when you do it. That being said, it could also need an adjustment.

You have discovered the often talked about but never claimed to be at fault of front shifting under load. In a word "DON"T" shift under load if you can help it. Of course far more time will be spent seeking der adjustment/replacement and or ring blame then taking a mirror to their aspect of the situation. As time goes along the manufacturers are making front shifting more positive and able, at the same time the newer riders are not being taught the basics as to how to ride WRT shifting ease. Andy

Get ahead of the gear so the Load-strain on chain comes Off , and then ask it to down shift

You shouldn't be having much difficulty shifting down up front even under modest load. Check your low limit adjustment setting of the front derailleur. First confirm that the side plate of the derailleur cage furthest from the frame is parallel to the big chainring. Then shift into the low ring in the front and check the position of the inside side plate. When shifted into low (I'm assuming a double setup), the inside side plate of the cage should be about 1mm away from the edge of the inside chainring. It can get really close because the lowest gear combination, large sprocket in the back with small ring in the front, are pretty close to being aligned with each other which provides a straight chain run. Test it in this combination and if you're getting any rubbing on the inside cage plate, back the low limit screw out, counter clockwise 1/4 turn, to open up the gap just a bit.

Adjusting the low limit of the front derailleur has the added benefit of restraining the "leap" the chain has to make to drop down to the low ring. A shorter leap is less likely to result in a dropped chain.

By double step do you mean that to shift down i need to shift twice despite the fact I am only going down 1 gear? Why is that? To be honest i inherited this bike and was riding something far inferior before so i do not fully understand Dura Ace completely. It is like i am shifting through 3 gears when i only have 2 up front.

I will get the bike adjusted for sure but i just gotta learn to shift right i guess. It was never an issue before but i think they cheaper claris groupset i was riding on before wasn't so sensitive maybe

Patient to doctor while demonstrating, "my shoulder hurts when I lift my arm like this".
Doctor to patient, "well, stop lifting your arm like that".

It' an old joke, but very apt in your situation. Shifting the front under load will cause chain drop. That's because you usually do so when on the inner half of the cassette, and the chain is coming to the chainring at an angle. As soon as the chain disengages from the larger ring, the tension makes it snap inward like a rubber band, and overshooting the smaller ring.

There are fixes as Hillrider noted, and they do help, but the right fix is to not shift under load in the first place. Anticipate your needs and when starting a climb, downshift the front soon in the sequence while your pedal cadence is still high, and the load lower. This also has the advantage of shifting while the chain is feeding straighter, so that "rubber band" snapping is reduced.

I think I got quoted by mistake. But, a double shift with half-step gearing is one step down and one step up. Or one step up and one step down. The first shift is of the front derailleur and the second shift is of the rear derailleur. For example, as you approach a hill you drop from the 52T ring in the front to the 42T ring. At the same time, you shift the rear derailleur from the 17T cog to the 15T cog. One advantage of a double shift is that it yields a gear combination very close (measured in gear inches) to that of the previous combination, just a little bit lower (80.5 inches goes to 73.6 inches). A second advantage is that it sets up the bike's gearing for climbing which you do in the smaller front ring (the 42T ring in my example).

I'm wondering if an electronic FD would minimize this result, if not eliminate it. If I understand correctly, an electronic FD doesn't use spring tension to move the chain toward the frame.

It'll help, not because of spring tension, but because the system is smart. When you're riding on the large ring and outer half of the cassette, the system makes a crisp downshift. But when you're riding on the middle or inner half of the cassette, it compensates for the chain angle by shifting slowly and hesitating a fraction of a second so the chain can't suddenly snap inward and overshoot.

But you might have misread my post. I wasn't referring to the FDs spring, but the issue of the chain's tension when under load. The electronic system may be better under these conditions, bt don't expect a miracle. The key is NOT TO DOWNSHIFT THE FRONT UNDER LOAD.

I didn't completely understand, so thanks for clarifying. Seems there is both chain tension and FD spring tension in the equation.

Yes, there are two things working in concert. At any time, throwing the lever, releases the cable and the FD's spring moves it inward. But the variable here is the chain tension. When it's low the FD cage gently pushes the chain over, but when it's higher, it initially resists disengaging from the larger ring, and when it finally does it snaps the chain inward much faster. In fact if the tension is high enough, it can hold the chain so tightly to the larger ring that it won't shift at all.

So as I said, the character of the shift is different under load. You have a bike that shifts well under normal conditions and overshifts when under load. So, like the doctor joke, the solution is to not shift that way. It takes very little thought to anticipate FD shifts, and change the sequence and avoid FD shifts under load.