oldbobcat

On road bike doubles, yes, sorta. On small-small the chain might rub on the inside of the big ring. If it's rubbing on the cage, too, it probably can't be helped. On road bike triples, in spite of trim, there might be some cross-chaining situations where rub is inevitable. Also, with triple-chainring mountain and city bikes with no trim.

MyRedTrek

By doubles, triples you mean the number of front chainrings?

In my case it's a 24 speed.
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choddo

3x8 or 2x12?

oldbobcat

If you're talking about 3x8, yes.

My rule of thumb for tuning and using triples is to be able to work the entire rear cluster from the middle front ring. To get big-big to work without rub would be a bonus, meaning, I wouldn't knock myself out trying to get it to work because this could cause problems on another part of the spectrum and that's what you have two other rings for. But if it does, don't complain, and don't use it all day because the cross-chain border patrol will detain you. And forget about small-small. The chain is going to be too flappy, and the small ring is for climbing, period, so why would you want to use it with a sprinting cog in the rear?

hokiefyd 

I think this is a great approach, and one I use myself.

Most of my bikes are 3x7/8/9, most are flat bar index-shifted, most can use all combinations without rub, all can use reasonable combinations without rub. For fun (and learning, ODC, etc.), I do enjoy trying to tune the drivetrains so that you don't have any rub, ever, regardless of ill-advised gear selection. This is possible on some bikes and I have most of mine there...but it doesn't seem possible on a few of them.

One trick is to use an externally narrower chain than intended. For example, use a 9-speed chain on a 6/7/8-speed drivetrain. You can sometimes escape the rub in certain combinations. Of course, a counterbalance to that is some gear changes (especially front indexed gear changes) can be more sluggish.

maddog34

I dialed in a Specialized Crossroads for a new customer today.. It had Horrid Ft. der. noise at either end of the cross-chain world when i started.. It left here silent and shifting better than it ever had.. 3x9 Shimano, Altus front, Deore rear..chain is now a SRAM pc-951.
This "miracle" was performed as part of installing the new chain.

Jeff Neese

All of my triples work without chain rub, even when cross-chained. It's more difficult to achieve with a triple, but a bike doesn't leave my stand if it rubs in any gear combination. I only go up to 3x8 though, so maybe it's different when you get beyond 8 gears in the rear.

I just bought a 1997 Specialized Sirrus which is a 3x7 road triple, and it rubbed a little in small-small. It took a little time. I ended up having to rotate the front derailleur body by just a hair in order to achieve no rubbing. I agree that's a gear combination that you'd never use, but I wanted it to work without rubbing just as a matter of principle.

Germany_chris

I can get my 2x to run the whole cassette without rubbing but I can’t on the 3x

Kontact

So you sacrificed the way the derailleur is designed to be adjusted - and presumably shifts best - to make sure you can ride in the granny and 12t cog without noise?

Sound like greasing brake pads to reduce squeal.

oldbobcat

Chain rub is a function of number of chain rings, width of rear cog cluster, shortness of chain stays, width of chain, and width of front derailleur cage. I just follow manufacturer specs. If you think you can do better, by all means experiment.

Jeff Neese

No, I was correcting a minor assembly error, or call it a "variance" if you like. When this bike was built, whoever installed and adjusted the derailleurs would never have taken the time to get things perfect, like I can and do. Not only does it not rub now, it shifts a little better too.

Kontact

So you are following the manual and it was designed not to rub in crossovers, or you are taking credit for improving the system?


Generally speaking, FDs work best when the instructors are followed, and way too many people don't follow them. Just like chain line, FD adjustment is not art.

Jeff Neese

It was not "improving the system". Nothing was modified - this was adjustment of the existing system. And many of us don't need to read instructions for adjusting derailleurs.

I'm getting the impression you haven't worked on that many bikes. Have you ever even installed a FD, yourself?

Redbullet

For sure it is possible with higher quality systems well assembled. I use SRAM Force 22 - mechanical and Rival axs (2x12 - electronic) with no rubbing regardless the combination. There is a big noise around "big-big" position, but it comes from "cross chain" contact with teeth. For lower systems or brands there might be problems at extremes.

Kontact

I get the impression you don't spend any time on this board. I have been the service manager at several high end shops going back to 1990 and have posted a ton of innovative solutions to a range of mechanical, hydraulic and electronic problems that people have requested here. There are maybe 4 or 5 people on this forum that are as knowledgeable and skilled as I am.

It is simply impossible to correctly mount and adjust several of the recent Shimano road derailleurs without the directions. Same to an extent with SRAM Yaw derailleurs. But even older derailleurs, like the first gen 105, have alignment procedures that you won't guess correctly.

smd4

AH-HAHAHAHAHA!! That’s why I wouldn’t let you touch my bike with a 10 foot pole.

Jeff Neese

I'm sure it would be fine. He'd read the instructions first.

smd4

Jeff Neese

To me, that's the key. I don't know for sure, but I tend to believe that bicycles are all designed and components specified such that they do not have chain rub in any gear, on paper. I find it hard to believe that a bicycle would make it into production if the design had chain rub built in. But the tolerances are so tight (especially on a triple) that when a human being installs and adjusts the derailleurs, even a small variance in derailleur height, rotation, or adjustment can cause rub. I can always achieve no rub, but they don't always come that way.

Once you start changing crankset, derailleur, rear cluster, or shifters, all bets are off.

Kontact

Many modern doubles with 11 or 12 speed cassettes will rub the inside edge of the outer chainring in the small/small crossover. Shimano combats this by moving the chainrings further apart than Campagnolo and SRAM, and using dish shaped outer chainrings.

And that's before you even install the front derailleur.

But maybe you believe different.

Jeff Neese

The question is whether there is chain rub while the bicycle is still in AutoCad (or whatever they use). I tend to think that no, the design does not have chain rub built in. I think if you give me any stock bicycle, I can adjust things so there's no rub. But I may be wrong.

Kontact

Correct: You are wrong.

Jeff Neese

Maybe you should provide some evidence and examples. I don't think anyone is going to think something's true just because you say it. Especially you.

Kontact

Who are you, again?

https://www.google.com/search?q=camp...e-gws-wiz-serp

Jeff Neese

OK, you've shown that you can put random words into Google, but failed to address the actual question. Nothing there supports what you're saying, at all. Completely irrelevant list of Google search results.

You seem to be one of a handful of posters here that desperately want to be a real bicycle mechanic, but in fact are simply posing as one on the internet. I'll reiterate what I said before - I don't think you've ever actually installed a FD, or done much actual wrenching on bikes in general. You don't seem to actually know what you're talking about. Judging by other responses, I see I'm not alone in that belief. I wouldn't let you within 10 feet of my bicycle, either.