Question on gearing

Jeff said:

Which chainring/gear combinations should be avoided on a road bike with
a triple chain ring and a 9 speed cassette? If the specifics matter, I
am thinking of a 52/42/30 with a 12-25 cassette. In particular, how
low can you go with the big ring and can the middle ring go all the way
up to the highest gear?

If you have enough chain and the right derailleur, you "can" use all 27
combinations. How much cross-chaining you want to tolerate is a gray
area, though - the more you cross-chain, the faster things wear.

I usually avoid the two largest cogs with the big ring, and use the
third sparingly. I use all nine cogs with the middle ring, though it's
probably not a good idea. Shift to the big ring and avoid the 12-13-14,
unless it's just for a minute or so before shifting to bigger cogs. I
usually only use the 4-5 biggest cogs with the granny ring.

FWIW, this is on Campy equipt, Shimano may have different tolerances.

Mark Janeba

Jeff said:

Which chainring/gear combinations should be avoided on a road bike
with a triple chain ring and a 9 speed cassette? If the specifics
matter, I am thinking of a 52/42/30 with a 12-25 cassette. In
particular, how low can you go with the big ring and can the middle
ring go all the way up to the highest gear?

Only avoid the extremes: 52-25 (and next one or two cogs) and 30-12 (and
next one or two cogs). I use all 9 gears with my middle ring (39 now but 42
originally) -- just trim the FD to keep Neil Brooks happy. (I recently
installed a DA BB and my trimming requirements have increased compared to
the old 105 BB. Slight change in driveline maybe?)

As long as your chain's long enough (and it should be), it won't /hurt/
anything to be fully crossed (52-25), but it's noisy and probably causes
some excess wear.

Shifty Bill

Jeff said:

Which chainring/gear combinations should be avoided on a road bike with
a triple chain ring and a 9 speed cassette? If the specifics matter, I
am thinking of a 52/42/30 with a 12-25 cassette. In particular, how
low can you go with the big ring and can the middle ring go all the way
up to the highest gear?

Thanks,
Jeff

If I couldn't use all gear combination on a triple, I'd be disappointed.
I can't figure out why people say it shouldn't be done, but then there
are lots of things that I can't figure out.

I'm an old fogy, who's been around for quite a while, and have set up a
reasonable number of bikes -- I have three just now, and one of which is
a Campy triple, with the largest cluster available. On hills up to about
7%, I generally crosschain with the largest chainwheel and largest rear
cog -- I seem to loose less momentum by shifting the rear when spinning
up a hill. I seldom crosschain the other way, which I guess
theoretically could wear the small rear cog a bit, but mechanically
shifting into that combination is no trouble -- if it wasn't I'd fix it.
My chains seem to last as long as anyone else's, but even if they didn't
who cares, they are cheap.

--
Bob Wheeler --- http://www.bobwheeler.com/
ECHIP, Inc. ---
Randomness comes in bunches.

Jeff said:

Which chainring/gear combinations should be avoided on a road bike with
a triple chain ring and a 9 speed cassette? If the specifics matter, I
am thinking of a 52/42/30 with a 12-25 cassette. In particular, how
low can you go with the big ring and can the middle ring go all the way
up to the highest gear?

As another responder has said, it's not that you can't use any of the
combinations, but you don't have to use them all, they gain you very
little, and the chain and gears will wear out more quickly if you do use
"cross-chained" gears.

It's instructive to figure out your gear ratios. sheldon Brown's site has
a calculator. In terms of "gear inches", the effective diameter wheel
correponding to a given set of gears, you have the following ratios:

52: 113 105 97 91 80 72 65 59 54
42: 91 84 78 73 65 58 52 48 44
30: 65 60 56 52 46 41 37 34 31

This is assuming that your cassette is a 12 13 14 15 17 19 21 23 25,
which I think is standard.

What this means is that only the biggest three gears on the big ring are
unique to that ring. all the others are duplicated elsewhere. This is
common. In fact, every gear in the middle ring is repeated elsewhere.

So, you might as well use the gears that _don't_ involve cross-chaining
(like big-big and small-small combinations). Your chain, cogs, and
chainrings will last longer, and you lose a bit less of your energy to
friction. Of course, if you need to use one in an emergency, or
accidentally shift into one, it's no big deal.

--

David L. Johnson

__o | Accept risk. Accept responsibility. Put a lawyer out of
_`\(,_ | business.
(_)/ (_) |

Jeff said:

Which chainring/gear combinations should be avoided on a road bike with
a triple chain ring and a 9 speed cassette? If the specifics matter, I
am thinking of a 52/42/30 with a 12-25 cassette. In particular, how
low can you go with the big ring and can the middle ring go all the way
up to the highest gear?

Thanks,
Jeff

A triple should be able to go big ring, big cog to small ring, small
cog w/o breaking anything altho cross chaining in these will wear
things out. On A properly setup triple, you should be able to use the
whole cogset in the middle ring. You should use the smallest 6-7 cogs
in the big ring, the largest 6-7 in the small ring. Going past those,
you should shift to another front ring.

In general, you know your gearing is right when most of the riding you
do, you are in the 'center' of your cogset, unless going uphill or
downhill.

Thanks to everyone for your reply. One thing that prompted my question
was that after I set up a spreadsheet to see at what speed I would be
riding in various gear combinations using my favored cadence, I saw
that when riding at my most common speeds (about 19-23 mph) I would be
either at the upper end of the 42 or lower down on the 52, and was
wondering if that meant I would have to do a lot of front shifting.

Quoted message said:

From what most of you tell me the answer is no, I can actually do all

riding in that range on either ring. Probably the thing to do is to
mix it up to wear things evenly.
Jeff

Jeff said:

... I saw
that when riding at my most common speeds (about 19-23 mph) I would be
either at the upper end of the 42 or lower down on the 52, and was
wondering if that meant I would have to do a lot of front shifting.

Maybe you should consider an 11-23 when that 12-25 wears out. Then most
of your riding will be centered in the rear cluster while in the 42,
optimizing chainline and minimizing front shifting. This assumes, of
course that a 30-23 lowest gear is low enough...

--
Dave
dvt at psu dot edu

That is a good suggestion, thanks, Actually I don't have the bike yet
- am planning to upgrade from a 7 speed hybrid and am thinking about my
options, assuming I can swap cassettes when I buy the bike if the
standard one isn't right. I live in flatland (chicago) so I don't need
a triple, but the bikes I am looking at all seem to have them and I
suppose its not a bad idea to have it since I plan to keep the bike for
a long time.
Jeff

Jeff said:

Which chainring/gear combinations should be avoided on a road bike
with a triple chain ring and a 9 speed cassette? If the specifics
matter, I am thinking of a 52/42/30 with a 12-25 cassette. In
particular, how low can you go with the big ring and can the middle
ring go all the way up to the highest gear?

It's always best to avoid cross-chaining, such as the big-big and small-small
combos, because of increased friction and wear. There's no hard and fast rule
though.

When I find myself approaching the big-big combo I drop down to the middle ring
because I can actually feel the decrease in friction. I also know I should be
in the middle ring when my speed drops below 18 MPH or so. I generally jump up
to the big ring before I'm in the middle-small combo too. BTW, I have the same
gearing you do, with a stock Ultegra triple.

Matt O.

Jeff said:

I live in flatland (chicago) so I don't
need a triple, but the bikes I am looking at all seem to have them
and I suppose its not a bad idea to have it since I plan to keep the
bike for a long time.

A stock triple gives better gearing for flatland riding, because of the 42T
middle ring vs. a 39T. There's a smaller gap between middle and large rings,
making front shifts quicker and smoother. The small chainring will be handy too
if you ever go to the mountains, especially as a flatland rider.

Matt O.

One problem that has not been mentioned wrt big-big and small-small: You
are in a middle ratio, but your next shift may have to be at the front. For
example, suppose you are in big-big, having downshifted in response to a
hill that keeps getting steeper. Your next downshift will HAVE to be at the
front, and it is usually equivalent to about two steps in the rear. This
will likely be a bigger change than you want, so you have to shift both
front AND rear. I always prefer to do the front shift before I really have
to.