Bicycle Mechanics - Which gears not to use?

Using the large chain ring with the large cog on the cassette, for example, is what I’ve always called “cross over”. It is unnecessary because it probably duplicates a gear ratio or range that is obtained by a more normal combination. However if you think about it, this cross over puts a strain on the chain and also on the cogs involved because of the large angle involved as the chain changes direction on joining or leaving the gear. On my last bike with Shimano 105 components the chain would make loud noises as it drug over the derailer when you made a cross over. I didn’t discover that. It was my son in law to whom I gave the bike who did.

It is unnecessary because it probably duplicates a gear ratio or range that is obtained by a more normal combination.

So how would I know which combination is most efficient or most normal? ??? - did I just say 'most normal'? I think this first all-night shift of the week is wearing on me.

Middle ring, any cog.

Big ring, 4 smallest cogs

Small ring, 4 largest cogs

You could only go 3 cogs even bump it up to 5 cogs but 4 is what I use.
Actually I only have one bike that has more then one chain ring so I usually do not have a problem.

:beer:

I think it's somewhat a matter of preference. On my Shimano 9 speed doubles (53/39) - I prefer to only use the 6 smallest cogs with the 53 and the 6 largest cogs with the 39. Sometimes I "crossover" for a brief period.

55/Rad

I use an "all-but-one" rule for double chainring and an "all-but-two" rule for triple chainring. My reasoning is that if the chainrings are reasonably centered on the cassette, there will be just as much chain deflection from the big ring to the 8th cog (9-speed) as there is to the 1st (smallest) cog and just as much chain deflection from the small ring to the 2nd cog as there is to the 9th (largest) cog. So if I have 53/39 and 12-23, I use the 53 with 12-21 and the 39 with 13-23.

Sometimes I cross-chain when I'm in tricky traffic, but I try to avoid it.

The gear you use for "normal" riding depends on your power output, pedalling style, and the various drag factors, such as gradient, aerodynamic profile, tyre pressure , road surface, luggage. You will pretty soon find out which rear cog you use most often, in your middle ring.

I believe that the Shimano web site says if it would realy hurt things they wouldn't have sold it, but it is better not to cross chain too much. On my 10 geared I ignore it, on my 21 geared I leave off 1 cog on each end, and usually 2 on my 27 geared.

Joe

in determining which gear combinations are best, there is a formula to determine the "inches" of a chainring/cog combination. The bigger the "inches" the bigger the gearing (harder to spin). That formula is (Chainring teeth/sproket teeth)wheel circumference. A 27" wheel has a circumfrance of about 84.1 inches. A few examples are:

cog 53 ring 39 ring
11 405 298
12 371 273
13 343 252
14 318 234
15 297 218
16 278 205
17 262 193
18 248 182
19 235 173
20 223 164
21 212 156

This shows that a 39/11 is about the same as a 53/15 and a 53/21 is close to 39/15. So you get the same gearing with less stress on the equipment at 53/15 or 39/15. If anyone cares, the "inches" refer to the circumference of the front wheel on the old "Penny Wheelers". The bigger the wheel, the faster you could go ... limited, of course, by your ability to spin and the length of your inseam.

Using the large chain ring with the large cog on the cassette, for example, is what I’ve always called “cross over”. It is unnecessary because it probably duplicates a gear ratio or range that is obtained by a more normal combination. However if you think about it, this cross over puts a strain on the chain and also on the cogs involved because of the large angle involved as the chain changes direction on joining or leaving the gear. On my last bike with Shimano 105 components the chain would make loud noises as it drug over the derailer when you made a cross over. I didn’t discover that. It was my son in law to whom I gave the bike who did.


http://www.paul-lange.de/nl/2002/TT_1_02.PDF

Two birds, one stone

Fixed gear, single speed.

You only need one.

:D

Fixed gear, single speed.

You only need one.

:D

We should have expected that. . . . :D

Marty

We should have expected that. . . . :D

Marty

I could not resist.

Though, tommorrow, I'll be on a bike with gears, and it coast. How scary is that?

Well that just means that if you're riding a geared
bike then you're not "shiftless"

Marty

My rule is: if the chain makes noise under pressure it means that it is under additional friction due to cross chaining, both between the links and on the cogs..

Friction is wasted energy, Friction is extra wear on the chain and cogs..
So I do it by ear...

I think it's somewhat a matter of preference. On my Shimano 9 speed doubles (53/39) - I prefer to only use the 6 smallest cogs with the 53 and the 6 largest cogs with the 39. Sometimes I "crossover" for a brief period.

55/Rad

Holy crap, you got a lebenty seven speed! The way I figure it, you have six small cogs, six large cogs, a total of 12 cogs, then you have two chain rings, that means you have 2 factorial times 12 factorial times the number of wheels, or two, for a grand total of a lebenty seven speeds!

Man, is it Shimanono ???

P.S. for as long as I have been riding and as many miles as I have covered, I just recently figured out this cog/ring thing. My wife says I am slow. I will have a comback ready for her in about a week.

This looks like about the right place. ;)

Campa told me that with my original 3x9, they advise not using the top or bottom three sprockets with the small or large chain ring respectively. And they suggest it is OK to use all of them with the middle ring.

I am about to enter the world of 3x10, so have asked them for their advice for that situation. In the meantime, what do you do with this setup?

My guess is to leave four alone in the extremes, but how about the middle? Maybe the middle eight? ???

Cheers...Gary

Here is Campa's reply to this question:

As general indication, please be informed that it is better not to use extreme gear combinations (for instance: inner 30t with 12 and 13 or medium 42t with 23 and 12) in order to avoid noise, excessive wear of the drivetrain components and to get the shifting optimal performance.

Cheers...Gary

I believe that the Shimano web site says if it would realy hurt things they wouldn't have sold it, but it is better not to cross chain too much.

Joe
What do you expect from a company that sells driveline components?