tbkfan

I am new to road biking. My mountain bike is a 1x narrow-wide chainring setup that is bullet proof. There isn't anything that will make that chain drop.

I just got a brand new Specialized Sirrus Pro Carbon as my foray into road. As far as I can tell everything is set up optimally. I have messed with front derailleur quite a bit and I think it's about as good as it gets. No worn parts of course as the bike is brand new.

When I am on the big ring in the front and one of the smaller cogs in the back, and I really stand on the pedals and lay down the power the chain skips right off the chainring. I can pretty much do it on command.

I am a bigger guy, 230 lbs (but with this bike, well on my way to below 205) and I am an avid XC mountain biker so when I need to, I can put out some power.

I am assuming that the chain is dropping due to frame flex. Is this kinda normal for an all carbon road bike? Should I have perhaps picked a stiffer aluminum bike given my size? Are there tweaks, adjustments, or modifications that might improve the situation? Or do I just need to learn to ride with a bit more finesse? This road bike thing is all new to me...

justin70

May need to adjust your derailleur limit screw.

HTupolev

The height of the front derailleur is also a place to look. Too high and it won't block the chain.

Campag4life

Not normal, you don't need finesse. You need adjustment to the FD as mentioned. You didn't mention which way the chain jumps off the big ring. I will presume it jumps inboard onto the small ring. A good way to get hurt as no doubt you know as well.
The outboard stop on you front derailleur needs to be loosened and then there has to be enough cable tension to hold the FD against the stop which is being competed against with cable tension to draw the FD inboard toward the inner ring.
Either learn how to do this...youtube is your friend to learn pretty much anything...or take it back to bikeshop where you got it.

PS: carbon is generally stiffer than Al in the BB although new designs are changing this. Also, since you went carbon with your Sirrus, you should have bought the drop bar Roubaix which has a comfortably high handlebar like your flat bar Sirrus only with many more hand positons. If not too late to trade in your new Sirrus consider this if discussing with your bike shop.

tbkfan

Thanks for the replies. The chain falls off outboard.

I have the derailleur about as low as I can have it without making things pretty noisy. I also have adjusted the high limit so that the derailleur is almost touching the chain. The cable tension is dialed right in too. I took it back to my LBS and had him setup the front mech too but it ended up being crazy noisy because he had the limit and height set even closer.

I probably should have taken a good look at the Roubaix but I really liked the idea of a flat bar. I may regret that one day and be looking at a drop bar bike. Does the Roubaix offer anything more in terms of bb stiffness though that I wouldn't be having this sort of issue? I understand that the Roubaix and Sirrus are essentially the same frame.

Should I look at better chain rings/cranksets? I think the FSA hollow carbon crank and chain rings that are on it are pretty decent stuff though.

What is a chain watcher and would something like that be a good thing?

Or should I just demand that my LBS deal with this? Like I said, avid mountain biker, new to road and not sure what's normal and what's not.

PepeM

Take it to the shop.

Bah Humbug

At this point, that's the answer. It's not your rings, or crank. Either the FD is installed wrongly some other way (rotated?), or the adjustments that are correct to your eyes aren't working. Worse, it could be something like a hairline crack somewhere that lets things move, under power, just enough to let the chain go. Get it looked at.

tbkfan

Thanks for all the advice. I'll take it in and have it looked at again.

Maelochs

Chain too long?

tbkfan

Just got back from the shop. Set up is as good as it gets, nothing wrong with the bike. The mechanic took it for a ride and couldn't get it to drop, I hopped on and rode to the end of the parking lot and on the way back really stood on the power and popped the chain right off. The mechanic said he could see how much I was bending the cranks and basically said I need to ease up.

I can certainly accept this as well. I get that road biking is more about lighter load and higher cadence. As I said, I am a big guy and my only frame of reference is a pretty indestructible MTB XT 1x11 drivetrain.

For the next few rides, I'm going to think more about maxxing out my cadence before I shift up to the next higher gear. I think it's just a frame of mind thing that I need to adjust to.

The mechanic suggested a Dura-Ace crankset, but I'm not so convinced that that would be the solution to my problem.

Campag4life

It isn't a frame of mind thing OP. You probably have outlier strength interacting with your bike set up.

1. yes, check chain length to ensure your derailleur cage is under tension. Should not be an issue in the big ring however.

2. Question: can you get the chain to jump if in the small ring?

3. Identify what manufacturer and model no. crank

4. Request the shop double check your crank installation....chainring bolt torque and readjust crank axial preload. Chainring maybe shifting fractionally under load.

My suspicion is...you have a low spec crank...maybe FSA on the bike and the big chainring is flexing under your considerable power. Let us know what crank you have on the bike. They are not equal in term of chainring stiffness.

All said, next step is...because you paid at least a couple of grand for the bike and likely more....request the shop install a Shimano 105 or Ultegra crank on the bike on their nickel. Insist. Powering the crank is not about finesse. It should take your power. There are pros that have more power than you make no mistake without this issue. It is most likely your crank which would probably work fine for a medium strength rider like me, but not for you. BB stiffness is probably adequate. Likely the big ring is flexing. Specialized btw had this identical issue noted by strong riders on their factory cranks a few years back. Not unheard of...especially if you have a lower spec crank on the bike.

PepeM

That still doesn't sound right.