compact crank gear ratio question

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss?

You must be living in a flat area. 50/36 or 48/34 gives you lower gears,
without the direct need to go triple.

Lou

--
Posted by news://news.nb.nu

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss?

The point is to use a regular cassette and thus gain lower gears. If you
don't understand the point behind this, you're either in top shape or
don't live near mountains.

-as

The idea is not to maintain the same set of gear ratios you already have. It is
to gain a broad range of gears thereby simulating having a triple crankset
without all the fuss (wider BB, longer arm RD, possibly different FD, possibly
different left shifter, etc). You would likely use the same gear cluster that
you already own. If you don't have hills or are always in great shape, you may
not be interested in this. If you are not considering a move to a triple, you
may not be interested in this. However, it can make sense on an early season
training bike, a commuter, etc.

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss? TIA - Bill

"Bill" <[email hidden]> wrote in message

Quoted message said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used
by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss? TIA - Bill

As additional to prior posts:

Much has been written about how the typical road "racing" bike sold these
days, has gearing that is appropriate to those who actually race these
bikes, but not much use to folks who don't, which is probably the greater
percentage of users..

As example, a typical 53 front ring when combined with a typical 12 tooth
cog yields a gear inch of 116 inches (distance bike moves forward for every
turn of the crank). This is typically useful when attempting to accelerate
while doing 35 mph, but might not have much use at any other time. Ditto the
13, 14, & 15 when in the big ring.

One concept put forward is to change the front crank to a 110bcd, which
allows the use of smaller front rings (down to a 34 small), allowing better
use of that racing cogset. The existing 130bcd road cranks don't allow a
small ring with less then 38 teeth.

Another way would be for the manufacturers to build cassettes starting at 14
or 15, but they don't, SO..... the smaller crank is the next best choice.

SB

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss? TIA - Bill

What has long puzzled me is the utility of a 53/39 set of chainrings with
an 8,9, or 10-speed cassette. With a typical 12-23 cassette, you get only
13 really distinct gear ratios, and overlaps (if you count the long
reaches) on 5-6 of the 9 cogs, on each chainring. Now, certainly you
shouldn't use the long reaches of the 53/23 or the 39/12, but there is no
advantage of having 2 73-inch gears (the 53/19 and the 39/14). If you
really want to keep the jumps between chainrings where they are, then
there is no real use in having a 9 or 10-speed cassette.

The original Campy chainrings usually came in 52/42, which gave as good a
set of gear ratios as you could achive -- with a 5-speed freewheel. When
6-speeds came along, the cranks evolved to 52 (or 53)/39 to give a good
set of gears with overlaps only for the long reach combinations. But
since then the number of cogs in the back has grown, with no change in the
chainrings.

Compact drives not only take better advantage of a modern cassette, but
give you lower gears to boot. Now, a good racer can find a use for a
53/11, but it's been a long time since I had any such hopes. If you don't
need those super-high gears (racers in the 60s and early 70s had nothing
bigger than a 52/14. A 48/12 is bigger.), then a compact, with lower low
gears, tends to make a lot of sense.

--

David L. Johnson

__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkein

Quoted message said:

"Bill" <[email hidden]> wrote in message

Quoted message said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used
by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss?

Steve B. said:

As additional to prior posts:
Much has been written about how the typical road "racing" bike sold these
days, has gearing that is appropriate to those who actually race these
bikes, but not much use to folks who don't, which is probably the greater
percentage of users..
As example, a typical 53 front ring when combined with a typical 12 tooth
cog yields a gear inch of 116 inches (distance bike moves forward for every
turn of the crank). This is typically useful when attempting to accelerate
while doing 35 mph, but might not have much use at any other time. Ditto the
13, 14, & 15 when in the big ring.
One concept put forward is to change the front crank to a 110bcd, which
allows the use of smaller front rings (down to a 34 small), allowing better
use of that racing cogset. The existing 130bcd road cranks don't allow a
small ring with less then 38 teeth.
Another way would be for the manufacturers to build cassettes starting at 14
or 15, but they don't, SO..... the smaller crank is the next best choice.

well done overall except:
"a gear inch of 116 inches (distance bike moves forward for
every turn of the crank)."

In the English speaking countries, we use "gear inches"
which express the gear in highwheeler equivalents ( front
t/rear t *nominal diameter) ex:52/13*27=108inches.

The rest of the world uses 'development' or distance
traveled in meters per crank turn. (front t/rear t * nominal
circumference) Example 52/13*2.1=8.4meters

Other systems exist including our own Mr Brown's "gain"
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"Steve B." <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

Another way would be for the manufacturers to build cassettes starting at
14 or 15, but they don't, SO..... the smaller crank is the next best
choice.

I know that there are cassettes that start with 14 for Shimano, and assume
for Campy. The rules for junior racers in the U.S. require that one
revolution for the highest gear must be less than 26 feet. Both of my boys
run 14 - 25 Shimano Ultegra 9-speed cassettes and I know that they make 15 -
25 and 16 - 27 10-speed cassettes.

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss?

As has been pointed out, the point is to achieve lower gearing for
people who ride in hilly terrain.

Those who opt for compact chainrings aren't running 12-23 in the back.
They're running 12-25, 12-26, or 12-27 (the Ultegra version of the
latter so popular that you can't find them, see:
http://sheldonbrown.com/harris/k7.html#9cassettes) and still want/need
lower gearing.

Converting to triple is much more expensive and complicated than
converting to compact double (50/34 is the most popular) and keeping
the same cassette used with the 53/39.

The problem is that using the compact double and keeping a 12 tooth as
the smallest cog necessarily sacrifices the highest gear. The
solution is building a custom cassette that has an 11 tooth to prevent
spinning out on flats and downhills (50:11 is a slightly higher gear
than 53:12) and goes up to a 25, 26, or 28 (Shimano doesn't make a
loose 27) to maintain the super low gear. You have to live with some
3 or 4 tooth jumps in the big cogs (which can be slightly minimized if
you have a 10 speed) and you will have a very slack chain in the
seldom used combos of 34:11 and 34:12.

But with these small sacrifices, you will be able to stay seated and
spin on monster hills, save your knees and legs, and ride longer and
stronger.

My prediction is that the market demand commanded by such consumers as
aging baby boomers will cause the compact double to become the
standard front ring choice and that 53:39 will become an option for
racers and young bucks. It happened with mountain bikes less than 10
years ago.

Steve B. said:

Another way would be for the manufacturers to build cassettes starting at 14
or 15, but they don't, SO..... the smaller crank is the next best choice.

SB

But they do, Shimano sells a 14-25 9-speed cassette in Ultegra. I've
been using one for the last couple of years.

Life is Good!
Jeff

Bill said:

Can someone point me in the right direction for a site that explains the
rationale behind the 50/36 or 48/34 chainring setup currently being used by
folks? I'm assuming if you use that configuration, you would use an 11-21
instead of a 12-23 with a 53/39. What is gained besides a modest weight
loss? TIA - Bill

With a 50/34 and a 11-23..bigger high gear and lower low gear, when
compared to a 53/39 and 12-25...'triple' type gearing with a double.

Quoting Doug Taylor <[email hidden]>:

Quoted message said:

Those who opt for compact chainrings aren't running 12-23 in the back.
They're running 12-25, 12-26, or 12-27 (the Ultegra version of the
latter so popular that you can't find them, see:
http://sheldonbrown.com/harris/k7.html#9cassettes) and still want/need
lower gearing.

.... or 13-34, but I guess not everyone with a 110bcd double likes to fill
a trailer up with stuff and pull it up hills.
--
David Damerell <[email hidden]> Kill the tomato!
Today is Teleute, Presuary.

Doug Taylor said:

My prediction is that the market demand commanded by such consumers as
aging baby boomers will cause the compact double to become the
standard front ring choice and that 53:39 will become an option for
racers and young bucks. It happened with mountain bikes less than 10
years ago.

Aging baby-boomer checking in! I use 45:32 rings on my 1970s vintage
Stronglight 99 crank with 13-21 freewheel. 48:36 1970s vintage Zeus
crank with 13-24 freewheel on another...

--

John ([email hidden])

Point yourself over to:
http://www.jbarrm.com/cycal/cycal.html

Compact cranks are gearing the bike lower without the need for a triple
chainring setup but the sweetspot where most people find their natural
cadence (ie. 42-15 ~73GI) gets sacrificed in the compact fitment. In a
compact setup, you are either overspinning the small gear or
underspinning the big gear.

Stronglight make chainrings here:
http://www.zefal.com/stronglight/BASES/PRODUIT/imgHR/prodTableaupltxrouteImgHR.jpg

These fit 110bcd compact cranks. This is one way to fit traditional &
compact configurations on the same compact cranks. Buy'em and try'em
till you find a compromise you can live with...

-r