Motorad

BikeForum has a ton of discussion about chainring-cassette setups, cross chaining, and advice on how to avoid cross chaining. One point, although I have no experience with, seems to make sense: With a compact, the circumference of the big chainring far outshadows the circumference of the small chainring ... the point being that when using the small chainring of a compact crankset, there would be a good potential of the chain to rub on the inside of the large chainring if cross-chaining on the small rear cogs.

To find a good double crank that would be good on club rides, I offer more discussion about cross-chaining:
< https://www.bikeforums.net/showthread...t=double+crank >.

A lot of people make reference to the "Rule of Three", as far as cross-chaining with triple cranks. This triple crank Rule of Three means you should not use the 3 smallest cogs when using the small inner chainring ... and should not use the 3 biggest cogs when using the big outer chainring.

What is not clear is whether there is a "rule", as far as cross-chaining with double cranks. One discussion that a gentleman provided, is that both chainrings of a double crank are closer to the center of the cassette ... than would be the inner & outer chainrings of a triple crank. He and others indicate that it would be okay to adopt a "Rule of Two", as far as avoiding cross-chaining with a double crank. In the BikeForum thread that I pasted above, someone is quoting a Shimano representative about considering a "Rule of Three" for triple cranks ... and considering a "Rule of Two" for double cranks.

For 10-Speed Cassettes: Any thoughts about following a "Rule of Three" for triple cranks ... and a "Rule of Two" for double cranks?

Rutnick

The rule of two still seems to apply on my compact in either combination but not as bad in big big.

cedricbosch

Cross-chaining is a myth that originated several decades ago. Today's chains are designed to be flexible enough to handle much more than a few centimeters in each direction. Anti-friction coatings, along with better materials, makes cross-chaining a thing of the past.

However, most people (myself included) tend to avoid it due to pre-concieved ideas, which is alright too.

mpearson76

I go with a rule of one with my 9-speed double. Never had a problem, but then again, it's rare that the cross-chained combos will be advantageous for more than a few minutes, because if it is, you'll switch rings. So my rule of thumb is to just shift rings when I'm running out of cogs--most people do this without thinking about it, so I don't think there's any need to worry, especially if cedricbosch is correct.

ks1g

I recently swapped my Ultegra 9-triple for a U-9 double, still using the same BB so my chainline is already slightly too far outboard. 30 years ago (10-12 speeds, friction shifters) when I was flying sailplanes when I should have been biking (could've had a sweat custom ride for just what I was spending on tow fees, let alone my 1/2 of the glider), cross chaining was a BAD THING (TM) and following the rule of 2 (or at least 1) on a double was gospel.

Today, I am not so sure. As cedricbosch observed, modern chains and derailluers (the capacity or range of the derailluer is also a factor) appear to be more forgiving of chain angles and especially with the ability to trim my front derailluer with the extra positions the triple gives me, I pretty much have use of all 9 cogs. That said, I also agree with mpearson76 and tend not to use the extreme one or 2 positions (small-small or big-big) unless I think it'll be for just a moment to deal with the terrain. I prefer to use the chainring that will give me the broadest range of cogs.

You can check for yourself by watching how and when you decide you need to shift, and by watching your chain for wear. Another thing you can do is see if you feel you are running out of cogs at one extreme and not using the ones at the other, and replace all or part of your casette to get a more useful range for the riding you do (I am quite happy with a 12-27, while my racer friend can make much better use of a 11-21 or -23).

recursive

Rubbing the chain on the big chain ring is not a myth. It makes a sound.

sfrider 

I go with the 'rule of noise'; if it rattles I don't do it. Otherwise I couldn't care less, chains are cheap.

Camilo

Functionally, with a triple I use 1/2 of the rear range with the outer and inner chain rings, and the whole shi++in' shebang with the middle.

With a double, I use approximately 2/3 of the gear range with each, shifting the front ring when I think of it.

Or, keep shifting until I hear the chain rubbing on the front der. cage and it won't go away with trimming.

re-cycler

I'm a year late, but hey...

Bingo, Camilo. I have a 53/39 double, with a changed-out 8-speed 11-28 in the back. The limits of the rear derailleur, 8-speed shimano 600 (ultegra), mean that I can't run big/big. This forced me to pay attention to the issue.

As you said, the chain will rub against the front cage in extremes in either direction. I avoid that. Also, watching the chain in the extreme positions, it's obvious to me that the chain is wearing on the cogs because the angle that it comes off of them becomes steep. Regardless of whether the chain can handle this, it does cause more wear on the teeth, which over time will degrade drive train performance.

With this 8-speed, I use the 5 rear gears on either 'side', and leave off the extreme 3 rear ones. (Btw, technically it's an 8-speed because you divide it 4 and 4, no?) Check Sheldon Brown's gear ratio calculator. Using the extreme rear gears is redundant; the same gearing can be had at some point by shifting up front and going from there. That switch-over in shifting up front just becomes natural. I believe it is still good practice, both for decreased wear on the whole drive train, and most efficient and intended use of the available gearing.

nitropowered

I hardly ever go down to 39/12 but I always find myself in 53/25. I try to stay out of it but sometimes its just how it is. Chains are strong enough to handle it, especially if you change your chain at regular intervals. The only fear I have is the chain dropping off the 53 to the 39.

merlinextraligh

+1

If it's causing enough friction/wear to be a concern you can hear it.

rbart4506

+1

akatsuki

+2

AEO

exactly