Wondering about transmission ratios . . .

Stan Shankman said:

Greetings newsgroupers,

Quoted message said:

Okay, so each chainring is able to provide a certain number of different ratios depending on the
number of gears on the freewheel.

Quoted message said:

But I'm wondering this:

Quoted message said:

Do bicycles with multiple chainrings have (or ever have) ratios that "overlap" - so that if a
rider wishes to go through the gears in a linear progression he is force to activate both
detailers for the next shift? Or is it that each chain ring offers a completely different set of
always-higher (or always-lower) ratios?

Almost all bicycles with multiple chainrings have overlapping ratios. In practice, you have multiple
overlapping sets of gear ratios for different conditions. With modern bicycles with 7-10 cogs on the
freewheel you usually just use the rear derailer for shifting, and only use the front derailer when
you run out of gears with whatever chainring you're using.

My own bike is an extreme example of this, as it has ten cogs on the freewheel, which offer a wide
range of gear ratios. The two chainrings are quite close to each other in size, so the two sets of
10 gear ratios overlap almost completely. In practice my "20-speed" bicycle has 12 different gear
ratios, but it works great for the kind of riding and terrain it's used for.

Quoted message said:

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill? Or what?

That's pretty much it.

-as

Stan Shankman said:

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill? Or what?

Thanks all,

- Stan Shankman

Stan

Don't know what other people do, but here is what I do: On my bike, I have a triple chainring - 30,
42, 52, and a 9s cassette 13,14,15,16,17,19,21,23,26.

If you try using the big chainring with the big sprocket, the chain has to go at quite an angle, and
it doesn't run as smoothly as it might, similarly fron the small ring to the small sprocket. I spend
90% or more of my time on the middle chainring, when I am going up a hill, and having a hard time
keeping my cadence up, I switch to the small chainring, and move down two or three sprockets. As it
flattens out, rather than switch to smaller sprockets, I move back to the middle chainring. A
similar thing happens when I want to go faster than the 42-13 combination allows me - I switch to
the big chainring and pop up a couple of sprockets. The result is that out of 27 possible
combinations, I really only use about 15 of them.

Mark

Stan Shankman said:

Do bicycles with multiple chainrings have (or ever have) ratios that "overlap" - so that if a rider
wishes to go through the gears in a linear progression he is force to activate both detailers for
the next shift?

Almost always. Normally the rear ratios are expected to be close enough that you don't ordinarily
double-shift; for instance, my usual shifting sequence (if for some reason I was shifting through
the entire range) would be 52x13, shift the back through 15,18,21,24,28, double shift to 39x24,
shift the back to 28,34.

However, if you _are_ going to do this a big overlap is kind of pointless, which is why I have a
52x34 crank coming; the ultimate answer is a Schlumpf Mountain Drive, which provides a roughly 2.5:1
reduction at the bottom bracket (or a straight-through drive), which can actually reduce the overlap
to nothing.

Quoted message said:

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill? Or what?

Most of the time I ride in the 52 large ring. On a huge hill I drop into the 39 small ring; then
I'll stick with it until things flatten out and I go back to the 52.
--
David Damerell <[email hidden]> flcl?

With the new nine and ten speed clusters, my experience is that you do exactly as you stated in your
last paragraph. There is enough fine tuning in the cluster that you can generally find the gear you
are looking for, However, on my tandem, I have 1/2 step plus granny gearing. The chain rings are
52/48/28 with a six speed freewheel in back, 13-28. The set up is such that a shift of between the
two large chain rings is equivalent to half way between the other two. Hence you basically get 12
non-redundant gear ratios, better than current clusters.

"Stan Shankman" <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Greetings newsgroupers,

Okay, so each chainring is able to provide a certain number of different ratios depending on the
number of gears on the freewheel.

But I'm wondering this:

Do bicycles with multiple chainrings have (or ever have) ratios that "overlap" - so that if a
rider wishes to go through the gears in a linear progression he is force to activate both
detailers for the next shift? Or is it that each chain ring offers a completely different set of
always-higher (or always-lower) ratios?

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill? Or what?

Thanks all,

- Stan Shankman

Most definitely. Especially on "factory engineered" systems. And the more gears, the more overlaps.

You can try to engineer your own ratios, but with the limitations of "Hype"glide and it's various
clones, it can be a frustrating endeavor

I have two pages on gearing, both written so that even the novice can understand. For the
gearing itself:

geocities.comtech5.htmlOpen ↗

For how it's used (and why it's there):

geocities.comhtmlOpen ↗

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": geocities.comczcornerOpen ↗

Stan Shankman said:

Do bicycles with multiple chainrings have (or ever have) ratios that "overlap" - so that if a
rider wishes to go through the gears in a linear progression he is force to activate both
detailers for the next shift? Or it that each chain ring offers a completely different set of
always- higher (or always-lower) ratios?

Yes, some or many do. I suspect that most bicycles have this issue.

There's a good article on Sheldon Brown's site about gear ratios. I remember reading it with just
this issue in mind. I just looked at sheldonbrown.comindex.htmlOpen ↗ and didn't find
the article I remember, but I'm sure it's there. There's useful info to be found there on this
subject, anyway.

Quoted message said:

How do people shift a fancy multi-chainring bike? Is it like; one ring flat land, one ring for
uphill, and one ring for downhill? Or what?

On my mountain bike, I'm almost always in the middle ring; I go to the smallest or largest when I
_require_ it. This is a bad habit because, if nothing else, I wear the hell out of the middle ring
instead of distributing the wear evenly.

On my road racer, with only two rings, I use them approximately evenly, and avoid crossing them up
(that means running big front with big rear / small front with small rear). The ratios in the rear
are so small, I doubt I can get any smaller ratios by going back and forth in the front, and if I
could, I'd lose more time shifting than I'd gain in pedalling efficiency. My weak, wimpy legs don't
get up hills on this bike anyway, at least, not since they got weak over the long winter...

On my latest bike, a triple road bike, I can't begin to guess what I'll do, because I never get to
ride the damn thing. I really thought I had it ready, but adjusting the brakes, I broke a necessary
washer in them and have to chase one down now. I suspect the non-STI, downtube shifters will
discourage me from shifting as frivolously...

Quoted message said:

Thanks all,

- Stan Shankman

--
Rick Onanian

Stan Shankman said:

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill?

Yes. So although double-shifting* is extra work, it's not very important because it is not done very
frequently. I prefer having widely-spaced chainrings (to get a wide overall gear range) to a
wide-range cassette for this reason.

But double-shifting is not often required on typical chainsets anyway (eg.
22/32/42 or 30/42/52) because the rings are reasonably close in size and front shifts are often
made when major changes in speed are needed. However, I do often find double or even
triple shifting is required on chainsets where the rings have been customized to something
like 26/39/53.

Try Sheldon Brown's gear calculator to see where the ranges and overlaps are - probably all not as
awkward as you think, bearing in mind that certain crossed-over combinations are not used.
Typically, for instance, one changes up or down on the cassette to the end of the reasonable range
on it (for the chainring) first, and only then the ring is changed if higher/lower gears are
required - but that's not strictly necessary and it's sometimes better to front-shift well in
advance when a sudden change in gradient or speed looms.

* Shifting rear and front gears at the same time (actually one just before the other for safety).

~PB

Stan Shankman said:

Do bicycles with multiple chainrings have (or ever have) ratios that "overlap" - so that if a
rider wishes to go through the gears in a linear progression he is force to activate both
detailers for the next shift? Or is it that each chain ring offers a completely different set of
always-higher (or always-lower) ratios?

How do people shift a fancy multi-chainring bike? Is it like; one ring for flat land, one ring for
uphill, and one ring for downhill? Or what?

Yes and no. Back in the days of 5 and 6 cog freewheels, there were gear patterns that required many
double shifts (e.g., half-step gearing). The idea was to get as many different and evenly spaced
ratios as possible from the limited number of gears.

Now that 8, 9, and 10 cog cassettes are popular, most everyone uses "crossover gearing." For a
double, while on the small ring, you would use the large and medium gears in back. When you get onto
the two or three smallest cogs, you shift onto the big ring. Similarly, when on the big ring, you
avoid the two or three largest cogs in back.

On a triple, you use the smallest front ring with the three largest cogs in back, the middle ring
with the middle cogs, and the big ring with the little cogs. Using the big-big or small-small combos
puts the chain at an extreme angle and increases drivetrain wear.

One front shift may have the effect of two or three rear shifts. So when you shift up on the front,
you may have to shift down a gear on the back.

You don't have to work through all the gears in a straight progression like in a car. Just pick one
that feels comfortable. See:

sheldonbrown.comgloss cn z.htmlOpen ↗

sheldonbrown.comgloss h.htmlOpen ↗

Art Harris

Thanks for the reply Chris!

Quoted message said:

geocities.comtech5.htmlOpen ↗

For how it's used (and why it's there):

geocities.comhtmlOpen ↗

corrected link: geocities.comtech4.htmlOpen ↗