Basic gear question

(Fx199) said:

This is a real basic question, hopefully not a target for petdowns from
know-italls but here it is.

On a bike with many speeds, three chainrings, it is not mechanically good to
cross chain.
Do you have the same ratios with cross chaining?
I mean obviously you work your way in for low gears and out for high gears.

Do the ratios cover crosschaining, or is it that much different depending on
the crank gear you use?

No reason to cross chain is there?

Someone asked me, that's what I told them, just so they wouldn't crosschain,
but what do you guys say?

Thanx

It will depend on the chainring sizes and the back gear sizes, but you
are pretty well correct. There is usually some significant overlap.
For example, I have one bike with 48/38/28 up front and 12-25/9 speed
in back. Away from the two extremes- small/large or large/small- I
will have the same gearing on two adjacent chainrings if I move the
rear up or down three cogs.

If you go to this gear calculator-

http://www.sheldonbrown.com/gears/index.html

you can enter various combinations of chainrings and gears. The
resulting chart will show you the overlaps, etc.

In article <[email hidden]>,

(Fx199) said:

This is a real basic question, hopefully not a target for petdowns from
know-italls but here it is.

On a bike with many speeds, three chainrings, it is not mechanically good to
cross chain.
Do you have the same ratios with cross chaining?
I mean obviously you work your way in for low gears and out for high gears.

Do the ratios cover crosschaining, or is it that much different depending on
the crank gear you use?

It really depends on the gearing. A very typical road double (52-39)
with some mess of gears like 12-25 will probably have substantial
overlap, such that the middle gears will all be the same, and yes, if
you are tempted to use the 39-12, you'll get about the same ratio on the
52-14.

I think on my race bike (52-39, 13-26 8-speed) I figure that
downshifting on the front is about the same as picking up two gears on
the rear, ratio-wise. So that means I can find equivalent ratios to any
of the middle four cogs on either front ring (albeit some with wretched
cross-ups like the above-mentioned 39-12), but the two highest and two
lowest ratios are only available on the big and small rings.

A triple changes things very little, except that it is often a very
steep drop from the middle ring, so there is less overlap. But don't use
that as an excuse to try the 26-14. Bad ratio.

You can figure this out very precisely (which I am not doing above) for
your own setup by using Sheldon Brown's excellent gear calculator:

http://sheldonbrown.com/gears/

Quoted message said:

No reason to cross chain is there?

In general no. Sometimes, it is momentarily more convenient to get to a
gear without an alpine (both front and rear together) shift, so in race
situations I sometimes find myself in the big ring and the second
biggest cog.

Quoted message said:

Someone asked me, that's what I told them, just so they wouldn't crosschain,
but what do you guys say?

Don't crosschain. The ratios, even if unique, are effectively
meaningless, and it's less efficient and hard on the drivetrain (mainly
the chain, though in marginal circumstances you can bend a derailleur).

--
Ryan Cousineau, [email hidden] http://www.wiredcola.com
President, Fabrizio Mazzoleni Fan Club

I'll second Dan's and Ryan's comments but add that if you go to Sheldon's gear
calculator, don't be put off by that crazed look in his eyes. He really does
know what he's talking about. <g>

Regards,
Bob Hunt

Quoted message said:

Subject: Re: Basic gear question
From: [email hidden] (Hunrobe)
Date: 7/17/2004 2:19 PM US Eastern Standard Time
Message-id: <[email hidden]>

I'll second Dan's and Ryan's comments but add that if you go to Sheldon's
gear
calculator, don't be put off by that crazed look in his eyes. He really does
know what he's talking about. <g>

Regards,
Bob Hunt

That is a very good site ! (Sheldonbrown)

Let me ask this further then...

How many gears should one crosschain with the middle cog if we are talking 3
front cogs?
How many from the outside ones?
When does it "become" crosschaining and not simply shifting?

Ryan Cousineau said:

In article <[email hidden]>,

(Fx199) said:

This is a real basic question, hopefully not a target for petdowns from
know-italls but here it is.

On a bike with many speeds, three chainrings, it is not mechanically
good to
cross chain.
Do you have the same ratios with cross chaining?
I mean obviously you work your way in for low gears and out for high
gears.

Do the ratios cover crosschaining, or is it that much different
depending on
the crank gear you use?

It really depends on the gearing. A very typical road double (52-39)
with some mess of gears like 12-25 will probably have substantial
overlap, such that the middle gears will all be the same, and yes, if
you are tempted to use the 39-12, you'll get about the same ratio on the
52-14.

I think on my race bike (52-39, 13-26 8-speed) I figure that
downshifting on the front is about the same as picking up two gears on
the rear, ratio-wise. So that means I can find equivalent ratios to any
of the middle four cogs on either front ring (albeit some with wretched
cross-ups like the above-mentioned 39-12), but the two highest and two
lowest ratios are only available on the big and small rings.

A triple changes things very little, except that it is often a very
steep drop from the middle ring, so there is less overlap. But don't use
that as an excuse to try the 26-14. Bad ratio.

I have to agree with this as I have a 48/40/26 front and a 14-39 on the
back.
26-14 makes no sense and 48-39 hangs since the system does not have that
much play. Again both of those combinations are kind of silly, as are
others, so my 15 speed really has about ten speeds thatmake sense and
don't overlap. 9 x 3, 27 speeds are probably just as bad. I did a
small excel spreadsheet and found that some gearchanges were only
about 1/2 % so why even bother.
Bill Baka

Quoted message said:

You can figure this out very precisely (which I am not doing above) for
your own setup by using Sheldon Brown's excellent gear calculator:

http://sheldonbrown.com/gears/

Quoted message said:

No reason to cross chain is there?

In general no. Sometimes, it is momentarily more convenient to get to a
gear without an alpine (both front and rear together) shift, so in race
situations I sometimes find myself in the big ring and the second
biggest cog.

Quoted message said:

Someone asked me, that's what I told them, just so they wouldn't
crosschain,
but what do you guys say?

Don't crosschain. The ratios, even if unique, are effectively
meaningless, and it's less efficient and hard on the drivetrain (mainly
the chain, though in marginal circumstances you can bend a derailleur).

--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

In article <[email hidden]>,

(Fx199) said:

Quoted message said:

Subject: Re: Basic gear question
From: [email hidden] (Hunrobe)
Date: 7/17/2004 2:19 PM US Eastern Standard Time
Message-id: <[email hidden]>

I'll second Dan's and Ryan's comments but add that if you go to Sheldon's
gear
calculator, don't be put off by that crazed look in his eyes. He really does
know what he's talking about. <g>

Regards,
Bob Hunt

That is a very good site ! (Sheldonbrown)

Let me ask this further then...

How many gears should one crosschain with the middle cog if we are talking 3
front cogs?
How many from the outside ones?
When does it "become" crosschaining and not simply shifting?

As a rule of thumb, never fully cross up (biggest cog and biggest ring,
or small-small), and avoid using the adjacent combos. So with an 8-speed
rear wheel, try to use about 6 gears per ring (highest 6 with the big
ring, middle 6 with the middle ring, lowest 6 with the granny ring).

Your system may vary,
--
Ryan Cousineau, [email hidden] http://www.wiredcola.com
President, Fabrizio Mazzoleni Fan Club

"Fx199" wrote: My bad, I use low-low and high-high all the ime. (clip)
^^^^^^^^^^^^^^^^^
Do you understand why "cross chaining" is bad?

1.) You are using useless combinations--the big ring in front is trying to
make you go fast, and the big cog in back is trying to make you go slow, so
they cancel each other out. Likewise with the small ring in front and the
small cog in back.

2.) Since the chain runs at an angle to the plane of the rings and cogs,
you lose a few percent due to the "cosine law."

3.) Since the chain is running at an angle, the efficiency is lower due to
friction of the teeth on the sides of the links, so you lose again.

4.) The friction referred to in 3.) causes additional wear on both chain
and sprockets.

None of these effects is disastrous, and you could ride for a long time and
maybe never notice the difference. Like revving or lugging your engine,
riding your clutch, or eating unwisely.

(Fx199) said:

How many gears should one crosschain with the middle cog if we are talking 3
front cogs?
How many from the outside ones?
When does it "become" crosschaining and not simply shifting?

The only hard-and-fast rule is not to be on the extremely crossed
combinations. Beyond that, just try to be reasonable. I use the
middle chainring with all of the rear cogs; I use the small ring
with 4 or 5 of the rear cogs (the larger/easier ones); and I use the
large ring with 4 or 5 of the rear cogs (the smaller/faster ones).

That is for a 9 speed rear end. Use less combinations if <9 speed.
--
Rick Onanian

Quoted message said:

Subject: Re: Basic gear question
From: "Leo Lichtman" [email hidden]
Date: 7/18/2004 11:30 PM US Eastern Standard Time
Message-id: <[email hidden]>

"Fx199" wrote: My bad, I use low-low and high-high all the ime. (clip)
^^^^^^^^^^^^^^^^^
Do you understand why "cross chaining" is bad?

1.) You are using useless combinations--the big ring in front is trying to
make you go fast, and the big cog in back is trying to make you go slow, so
they cancel each other out. Likewise with the small ring in front and the
small cog in back.

2.) Since the chain runs at an angle to the plane of the rings and cogs,
you lose a few percent due to the "cosine law."

3.) Since the chain is running at an angle, the efficiency is lower due to
friction of the teeth on the sides of the links, so you lose again.

4.) The friction referred to in 3.) causes additional wear on both chain
and sprockets.

None of these effects is disastrous, and you could ride for a long time and
maybe never notice the difference. Like revving or lugging your engine,
riding your clutch, or eating unwisely.

I think you misunderstood me.
When I meant was farthest in farthest out combos (nearer and farther away from
the bike)
I try not to crosschain, once in awhile it happens. My chains last at least a
few thousand miles, but I'm not quadzilla.