Kontact 

Again, you must not be on this subforum much.

I gave you multiple links to articles and forum discussions about the big ring rubbing and even picking up the chain in small/small. I presumed you would read one or two and see that the manufacturers acknowledge this is as designed.

Do your own reading. Stop being a troll like SMD4.

Jeff Neese

Of course you'll find plenty of articles and discussions about chain rub on the internet, and that's all you've done. What I'm talking about is an actual bicycle manufacturer that acknowledges that chain rub is "as designed". You don't need a whole list of articles. Just one will do.

Since you only work on bikes after "reading the instructions", you should be able to provide an example from a technical or installation manual that says that chain rub is unavoidable and as designed. Show that to us.

smd4

HEY! That's a pretty low blow coming from the smartest man in the world!

Kontact 

The first article quotes Campagnolo. I suggest you read it instead of acting like you have any reason to demand people dance for you

Jeff Neese

OK, if you think that article says that chain rub is part of the design, and the solution to chain rub when cross-chained is to just not do that, then you really don't understand.

It doesn't matter. I think the OP has his question answered by more knowledgeable members of the forum. Your responses are mostly just noise, things you read somewhere, or whatever pops into your head. Carry on.

Kontact 

Why don't you pretend I'm smart enough and articulate what you're talking about.

MyRedTrek

3 front, 8 on the cassette.

choddo

Yeah, so a triple then, as you surmised.

oldbobcat

2x10 SRAM Doubletap doesn't do low trim. They figured that the chain's giong to rub on the inside of the big ring if you do small-small so it wouldn't matter if it rubbed on the derailleur, too. Throughout its history, derailleur-equipped bikes are just a plethora of compromises.

Jeff Neese

I'm not sure exactly what components you're talking about, but I looked at least one technical manual for SRAM Doubletap and did NOT see any reference to cross-chaining or chain rub. I do see a lot of people reporting that they have chain rub on their particular bike, but that just tells me the bike is not stock or that they haven't spent enough time adjusting things. Or they don't know how.

My position stands. Bicycles are designed and components specified such that they do not have chain rub in any gear. If you were to examine the bicycle in AutoCad, there is no chain rub. This is pretty basic mechanical engineering - an object will either pass through an opening without contact or it will not, and that will be revealed in the design drawings. If a particular bicycle has chain rub, it's a difference between the engineering drawings and the assembly and setup of the bicycle.

I'm willing to be wrong, but I have not seen anything in writing by any manufacturer that says otherwise. It would be in the form of "You will experience chain rub when in the Small-Small or Large-Large gear combination, so we recommend not using those combinations. Our product is not designed for that."

I believe that given enough time I can eliminate chain rub on any stock bicycle. If I put a bike on the stand with the goal of eliminating chain rub, I would definitely want to see something in writing that says that it's impossible and that I shouldn't waste my time. I don't think that exists. I'm going to continue to eliminate chain rub on all of my bicycles not because I want to cross-chain, but simply because I can. I'm a bit finicky when it comes to bicycle setup and I can take all the time I need to get everything as close to perfect as possible.

I acknowledge that a shop cannot do that, and so a lot of bicycles are delivered with minor variances in installation and adjustments. If I worked in a shop, the owner would tell me that I can't take that much time with each bike, and that "good enough" is good enough. Just tell the customer not to cross-chain and call it good.

Eyes Roll

If your chain is rubbing front derailleur something is not right, bruh.

But, you've got it right.

Kontact 

Now you're just telling two people reporting the exact same thing that they are idiots and you know better. But you don't have any experience, so I don't know why you are so insistent that the world works like you think it does.

The standard double front chainring spacing is old - at least back to 5 speed if not older. But the step between the chainrings has changed, since the inner and outer used to be 10t or less (52-42) and has grown past 14t (53-39) to 16t (50-34). At the same time rear freewheel/cassette width has grown from 24mm wide 5 speed to 40mm wide 11 speed - all on the same 43.5 chainline. With the small chainring retreating forward and the small cog moving outboard by 8mm, the chain getting 1.2mm narrower per side isn't going to make up for how much the cross chain angle has increased. And that's ignoring chainstay length, which has shrunk to a minimum spec of 405mm, but is often less than 400 on Tri/TT bikes due to their long front ends.

So modern drivetrain geometry is based on geometry from the '50s that has been made simultaneously shorter and wider, grossly changing chain angle at the extremes without compensating with greater chainring spacing or sufficiently narrowed chains. However, Shimano did increase the spacing from the standard 5mm when 11 speed came out to counter this, and used a curved outer ring to prevent the chain wedging between rings. This spacing change is obvious to anyone who has used an aftermarket crank (Praxis, Rotor, etc) on Shimano 11 speed front shifting, because you lose the outside trim position once you have the Hi limit set. I don't know if Shimano 11 speed cranks completely solve the problem or not, but the change acknowledges that the standard spacing still used by Campy, SRAM, Rotor, Praxis, Zipp, etc is beyond the limits of cross chaining.

Or you could look at a bike.

Kontact 

Took a moment to confirm on my 2x10 speed bike. 53-39, 410mm chain stays, correct crank chainline - it rubs the outer chainring in the low-low crosschain. And not just rubs, the lifters and teeth on the 53 ring keep snagging the chain.

That's with a pretty conservative set up.

​​

Jeff Neese

All that prattling on by you is irrelevant. I'm looking for something by a manufacturer, that acknowledges that chain rub is unavoidable and cannot be adjusted out. And again (third time?), we're talking about a stock bicycle, as designed by the manufacturer. Your mention of aftermarket cranks indicates you do not understand what you're trying to argue against.

You said you can't get your setup to work without rubbing. If your bicycle is bone stock, as designed by the manufacturer, you may not be able to but someone could. If you've changed anything on the bike, all bets are off.

Kontact 

What are you failing to understand? It's a stock SRAM Rival 10 speed drivetrain. The chain rubs the big ring. As multiple people told you it would.

But now you don't want to look at bikes, you want a manual (not a quote from SRAM) that admits to a deficiency?

I only mentioned aftermarket cranks to illustrate how Shimano (and only Shimano) went to wider chainring spacing. Please reread.

Do you have a road bike with greater than 7 speeds?


And please post the document you are using that says that a 10 speed drivetrain can be set up for no rub.

Jeff Neese

Well, you're the one that needs to "read the instructions" in order to install a derailleur. I would think if there is the verbiage I'm looking for, you'd know about and would have posted it by now.

There wouldn't be a document that says that a drivetrain can be set up for no rub - that's assumed. Just like there's no document that says that you can turn the wheel on your car all the way in either direction, without tire rub on the inner fender. It's designed not to rub. If you install bigger tires there could be, but that's not what we're talking about.

There doesn't seem to be any document that says chain rub is unavoidable on any stock bicycle. You seem so desperate to come off as knowledgeable, I'm pretty sure you would have found it by now.

My position stands. Any chain rub is the result of using aftermarket components different from stock, and/or installation and adjustment issues. A stock bicycle can always be adjusted to eliminate chain rub.

Kontact 

So you don't have and haven't worked on a a road bike with more than 7 cogs.

Thanks for your ignorant opinions.

smd4

He didn't answer your question, one way or the other. Stop making assumptions.

hokiefyd 

You ought to be able to get it pretty close. I'd start with trying to get the whole cassette without rub in the middle ring. In my experience, if you can get this, you're 90% of the way there, and the low and high positions, in terms of propensity to rub the chain, are as much a function of limit screw settings as they are cable tension or adjustment, assuming you don't have any cable tension when resting against the low limit screw.

I've found that you can sometimes get no rub, but have slow or inconsistent shifting. In these cases, you sometimes have to accept chain rub in a certain combination to achieve good shifting. This also assumes your front derailer is rotated/clocked correctly on the seat tube. This is a good point made earlier - it's possible it wasn't perfect from the factory or whomever might have been there before you.

HTupolev

No, because in order to absolutely guarantee that rub does happen in specific combos, the drivetrain manufacturers would have to put some very odd over-specifications in place. Such as having strict restrictions on maximum chainstay length.
They do, however, often specify (in both user and dealer manuals) that rub is "likely" in the extreme combinations (from either chain contact with sprockets or with the front derailleur). And what Shimano generally specifies as a solution to this problem is not to perform additional drivetrain adjustment, but shifting to less-crossed gear combinations.

Or in other words: it's often explicitly stated that cross-chain rub isn't incorrect drivetrain behavior.

Drivetrain manufacturers specify things like chainline and how the derailleurs mounting points should be placed, and frameset makers follow those requirements.

Bicycle frameset designers generally aren't going to model drivetrain dynamics unless it's relevant to the stuff they're doing, like how pedaling tension along the chainline can affect the behavior of a rear suspension, or ensuring that the drivetrain parts and frameset parts will clear each other.

KCT1986

Here is the older spec (2005) that Shimano presented for chainstay length in their 'frame requirement'.

Kontact 

Yeah, they all use 405.

HTupolev

Yes. They specify minimum chainstay length, because allowing shorter means having to tolerate more and more oblique angles. It's geometrically simpler to tolerate unconstrained long chainstays, because the chain angle asymptotically approaches straight.

choddo

I think they misunderstood why (or indeed that) you were saying they’d have to specify a maximum length to guarantee rub when cross-chaining.

Road Fan

Not too long ago, Campy used them on Recoed fronts.