grumpus

Sure there is - sometimes it's too much effort to downshift the front and upshift the back, if you're not going to cross-chain for long just use the forbidden ratio. It's likely going to wear your transmission faster, drag more and maybe make noise, so don't make a habit of it, but occasionally there's no great harm.

smd4

Sorry...I should have said there's simply no good reason to do it. Being too lazy isn't one of them.

But of course, you're correct--momentarily doing something wrong isn't going to ruin things--but will result in the effects the OP has brought up. If he doesn't want those effects, most of us know what the solution to that problem is.

Eric F 

Operating both levers is too much effort? If your shift levers are hard to operate, maybe it's time for some maintenance. For me, doing simultaneous double shifts is not an uncommon occurrence on my road bike, same with my MTBs back when they had multiple chainrings.

smd4

And you don't even need to operate both levers; one will do.

grumpus

Is that derailleur rated for the size of sprocket you have there? It looks too close, but also wound back pretty far. Maybe it's just because the chain is at the limit, could do with a couple more links if that won't make it too long for small-small. Or just don't use big-big, or indeed small-small. But it's nice to have all the gears, just in case you go there. Sometimes the front doesn't shift cleanly under load and you need to push hard to keep going ...

Eric F 

There are times when I drop to the small ring and a small cog simultaneously. It gets me roughly the same result as the next lower gear with the same chainring.

smd4

Ah. Good point.

AndreyT

Something is definitely out of alignment. I'd guess this is a problem with RD hanger, but you said that you have already aligned it. Are there any signs of damage on the RD itself, especially around attachment point? What about the jockey wheel cage?

And no, there's no such thing as "cross-chaning" (and hasn't been since 1990s). Every time someone tries to tell you to "stop cross-chaning" they are simply trying to troll you. Your drivetrain is designed with one purpose in mind: to permit you to use big-big combination - the most important objective of all bicycle drivetrain design in the world for the last 30 years. If you can't use big-big with a modern drivetrain, your drivetrain is broken. If you are avoiding use big-big with a modern drivetrain, you are doing it wrong.

It appears that you are using a RD with a fairly large capacity, i.e. with a long jockey wheel cage. So, given your chain length and chainstay length, in the big-big configuration the lower jockey gets pulled far forward (fairly close to the chainring). This results in the lower jockey "feeling" the effects of chain skew, which might be what's causing the problem. I'd guess that if you installed a [slightly] longer chain, the lower jockey would end up being a bit further away from the chainring and the problem would go away. Or, alternatively, if you used an RD with a shorter cage. Having said that, I'd still note that your chain length looks fine to me.

smd4

So why don’t you explain the revolutionary technological changes in chain-driven, front-and-rear derailleur-equipped bikes that happened 30 years ago that eliminated the concept of cross chaining? And how “chain skewing” is different?

grumpus

It's a good enough reason for me. But apart from that, it may be that I'm already pedalling too slow and hard to manage a clean shift up front, and that one last sprocket at the back makes the difference between riding and stalling.
I'm not sure his problem is caused by cross-chaining, or at least I think there's something else going on too.

smd4

Maybe. As a former mechanic, it’s hard to diagnose problems through a device/computer/monitor. We tend to go with the most logical solution with what little information is available.

grumpus

Further back than that: the Sedisport bushingless chain with chamfered side plates was introduced in 1978. Since then riveted pins have been added to the mix to make narrower bendier chains that don't fall apart, but which require special joining links. Those are the major evolutionary steps that saw chain go from 2x5 transmission to 1x12. The narrow-wide chainring may also merit a mention.

79pmooney

And - a few posters here will get very bent out of shape and go to extremes to point out that you broke some universal rules should they learn you went big-big, especially if it was by choice. I try not to but I don't loose sleep over it and I do make sure it can happen at any time on my bikes and no damage ensues outside minor excessive wear.

In one of my better races, state champs, I arrived at the finishing stretch in a field of about 25, very few of whom I could beat in a sprint. My bike was over-geared and I rode much of the race on the small ring but I double shifted to the big-big as we came on onto that stretch about 2 miles from the finish. Mile to go I quietly shifted to mid cog and went from the glass strewn right side of the road and pulled it off. (No, not the win. The break was long gone.) Riding the big-big meant that I didn't have to do anything attention getting when I wanted no one to even notice I was there. I was even with the first rider and going much faster when finally someone said "he's going!"

grumpus

A text forum is not the best place when diagnosis can require looking at something from a very specific angle, or feeling how loose or smooth something is ... what could take ten minutes IRL can last days here and still not get fixed. Why do we even bother?

smd4

Maybe you would have had a better chance to win if you weren’t in one of your slowest gears while at the same time being in one of your fastest.

Jeff Neese

Is that like when you're riding in dense fog and can't see the road ahead of you, and all of a sudden you encounter a hill that you didn't know was there? I don't think I'd ride if visibility prevented me from seeing the road ahead. Forget being in the right gear for the upcoming hill - I'd be afraid of running into something.

Kai Winters

To me it looks like it's just the load on the chain on that gear combo...pulling the chain away from the idler pulley. I think the reason it seems to track properly when pedaling backwards is because the load or pressure against the chain is from the bottom of the chain ring, not the top as it is when pedaling normally. I think the chain length is borderline a link to short which is the cause of the mis tracking. It's not a problem because it is unlikely you are in this gear often or for very long...such a degree of cross chaining isn't good for the drivetrain but most only do it for brief periods. Sometimes you just have to do it...
Try adding one link and see what happens.
You're not really hurting anything an in such cases most people in the same circumstance...chain length, gearing...while riding don't notice it because you are riding and not many put the bike in this gear while it's on a stand except to check chain length.

smd4

Evolutionary. Sure. But our friend Andrey seems to think there was some monumental technological breakthrough 30 years ago that somehow eliminated the possibility of the chain going from the extreme inboard cog on the wheel to the extreme outboard chainring on the cranks. Without a hint of incredulity, he even calls this major development "the most important objective of all bicycle drivetrain design in the world for the last 30 years." Not more gears. Not smoother, more-accurate shifting. The ability to cross-chain has been the gold standard of drivetrain component engineers for three decades.

Iride01 

No, it's like when you're riding up a constant grade for a long time and have your near max effort dialed in and then you reach a section that is suddenly just enough more grade for just a brief time to make you want a lower gear.

Fog isn't involved. Knowing and not knowing that the rise is there isn't involved either. It's just not wanting to do most of the climb in the smaller ring and larger cog and willing to shift into the bigger cog briefly then go back to the smaller cogs after hitting that brief rise. If I'd arrived at that hill in the smaller ring, then I'd stay in the smaller ring. But obviously since we are talking about the large ring, I was coming into the hill with some speed and it'd make little sense to slow down before hand losing all that inertia and shift to the small ring for the climb.

While some try to make this out as what gives less friction, that we know is marginal gains. For those riding their bikes and not competing against and losing to others, it really doesn't matter if they are using a less than perfect combo.

smd4

The more I read posts here, the more I think people just don't understand how to properly use their gears.

Kapusta

You abso-freaking-lutely should be able to go big-big on a dedicated 2x system like the OP has. And while it might not be something you want to stay in for long periods (thats open to debate) there is no reason you should need to avoid it for short periods,

I would check if the cage or the hangar is bent. Also, check the length of the chain.

smd4

So do it, but just not for too long. I'm guessing you don't want to do it for too long because it's detrimental in some way. If that's the case, why do it at all??

Black wallnut 

What's your crankset? What are your cogs? I just can't see a combination that says the most efficient gear is big + big-1, when little + big -3(or 4) is nearly the identical ratio and a straighter chain line.

Iride01 

None of this is about being in the most efficient gear combination. It's just about those that want to say never ever X chain in the big/big.

While I agree with the reasons to avoid that combination, those aren't valid reason to tell someone to never ever use that combination. Nor is it helpful for the OP's issue.

It's about as useful as when some say their bike makes noise when they pedal backwards and I tell them not to pedal backwards.

Black wallnut 

Okay but when you write:
You seem to be saying that big +big-1 is the most efficient gear combination. It's not and using that as an example of why one would use big + big is nonsense. Much more believable is that riders of lesser skills or awareness do not know which gear they are in. Those that mash as opposed to those that spin.

If the OP only has the issue in big + big then the easiest solution is don't do that. Problem solved.