Formula for actual # of usable gears



A

Ablang

Guest
Due to cross-chaining issues, I came up w/ a formula for the actual #
of usable gears on a bike, which is less than the stated number by the
manufacturer.

For instance, on my bike, which supposedly has 24 gears (3 in front, 8
in back), I only actually have 16 usable gears, and not 24.

The formula can be expressed in this form:

(# of speeds by manf) - (# of rear sprockets) = actual # of usable
gears
ex. 24 - 8 = 16 usable

Note that this formula only works if you have 3 sprockets in the
front, and any number in the back.
 
On Jun 19, 12:18 am, Ablang <[email protected]> wrote:
> Due to cross-chaining issues, I came up w/ a formula for the actual #
> of usable gears on a bike, which is less than the stated number by the
> manufacturer.
>
> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
> in back), I only actually have 16 usable gears, and not 24.
>
> The formula can be expressed in this form:
>
> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
> gears
> ex. 24 - 8 = 16 usable
>
> Note that this formula only works if you have 3 sprockets in the
> front, and any number in the back.


I think it's a great idea to come up with a formula but I think that,
with all due respect, what you have come up with might be too easy.

Kind of like " if it sounds too good to be true, it probably isn't ".

Lewis.

*****
 
L

Leo Lichtman

Guest
"Ablang" wrote: (clip) The formula can be expressed in this form:
>
> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
> gears
> ex. 24 - 8 = 16 usable
>
> Note that this formula only works if you have 3 sprockets in the
> front, and any number in the back.

^^^^^^^^^^^^^^^^^^
With the limitation to bikes with front triples, the formula reduces to

Useful speeds = 3N - N = 2N.

Would you explain by what reasoning you arrived at this? Obviously, you
eliminated the two cross-chain positions, which would give you 3N - 2. It
seems to me that from that point on, you would have to consider the
individual ratios obtainable, and look for duplications. Your formula
doesn't consider the actual ratios, so it couldn't possibly do that.
 
R

Roger Zoul

Guest
"emanon" <[email protected]> wrote in message
news:[email protected]
>
> "Ablang" <[email protected]> wrote in message
> news:[email protected]m...
>> Due to cross-chaining issues, I came up w/ a formula for the actual #
>> of usable gears on a bike, which is less than the stated number by the
>> manufacturer.
>>
>> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
>> in back), I only actually have 16 usable gears, and not 24.
>>
>> The formula can be expressed in this form:
>>
>> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
>> gears
>> ex. 24 - 8 = 16 usable
>>
>> Note that this formula only works if you have 3 sprockets in the
>> front, and any number in the back.

>
> If it works for you, great, but I'd like to know your definition of
> "usable".
>
> I have 9 freewheel cogs and 3 chainrings. I can physically actually use,
> without undue chain angle problems, any of the 9 freewheel cogs with any
> of the three chainrings. Therefore, I do have 27 "usable" gear
> combinations.
>
> I have yet to count the free wheel teeth for the cogs, but I have no doubt
> I have duplication in gear ratio (gear inches). In fact, I'll even allow I
> have more than three probably very close (2 inches or less) gear
> combinations.
>
> What this means to me, though, is that I do not have to keep changing my
> front derailleur to find my desired gearing. I use this to my advantage,
> by making most of my changes only on the rear. If I'm on the road, I use
> mostly the large chainring; mild off road / not too hilly a course, the
> middle and when it gets really tough, I do hit the granny gear and bounce
> back to the middle when the hills flatten out.


Thank you for taking the time to point this out. I always wonder why people
go through the exericse of trying to minimize the value of duplicate gears.
It's silly and indicates how poor of an understanding some people have about
gears. As long as you aren't be weighted down by excessive gear
duplication, this is a good thing.

Of course, I've always read that the big-big and small-small combinations
should be avoided due to the cross chain issues. Indeed, it does seem that
one could easily avoid these combinations for the most part to avoid a
possible breakdown on the road.
 
M

Mike A Schwab

Guest
On Jun 19, 6:28 pm, "Roger Zoul" <[email protected]> wrote:
> "emanon" <[email protected]> wrote in message
>
> news:[email protected]
>
> Of course, I've always read that the big-big and small-small combinations
> should be avoided due to the cross chain issues. Indeed, it does seem that
> one could easily avoid these combinations for the most part to avoid a
> possible breakdown on the road.


I sometimes notice issues as I am downshift the cassette, I then
downshift the chainring. I don't notice any issues upshifting to the
highest cassette gear, then I shift the chain ring.

And in actuality, I like to figure, for my Sun Bicycles EZ-1 with a
triple chainring and 3*7 SRAM rear wheel, that I don't actually have
63 gears. I start by considering the internal hub and chainring are
in the middle. I can change the cassette up and down over 7 gears,
about 10% difference each. If I hit the limits, I can change the
chain ring, for a 20% change or 2 gears on the cassette. If I am at
top speed, using the hub overdrive adds more resistance and ends up
slowing me down. If I am climbing, I can use the underdrive for about
a 25% drop in effort, about 2 more gears. If I rush to stop without
downshift, I will use the under drive to get started and downshift the
derailers and go back to hub direct drive.

So even though I have a hugh number of gears, the hub just gives me a
25% lower range in gear ratios. I think a more accurate calculation
would be to count the # of cogs (7), + 4 additional gears for the two
additional chainrings, + 2 for the hub underdrive.
 
E

emanon

Guest
"Ablang" <[email protected]> wrote in message
news:[email protected]m...
> Due to cross-chaining issues, I came up w/ a formula for the actual #
> of usable gears on a bike, which is less than the stated number by the
> manufacturer.
>
> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
> in back), I only actually have 16 usable gears, and not 24.
>
> The formula can be expressed in this form:
>
> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
> gears
> ex. 24 - 8 = 16 usable
>
> Note that this formula only works if you have 3 sprockets in the
> front, and any number in the back.


If it works for you, great, but I'd like to know your definition of
"usable".

I have 9 freewheel cogs and 3 chainrings. I can physically actually use,
without undue chain angle problems, any of the 9 freewheel cogs with any of
the three chainrings. Therefore, I do have 27 "usable" gear combinations.

I have yet to count the free wheel teeth for the cogs, but I have no doubt I
have duplication in gear ratio (gear inches). In fact, I'll even allow I
have more than three probably very close (2 inches or less) gear
combinations.

What this means to me, though, is that I do not have to keep changing my
front derailleur to find my desired gearing. I use this to my advantage, by
making most of my changes only on the rear. If I'm on the road, I use mostly
the large chainring; mild off road / not too hilly a course, the middle and
when it gets really tough, I do hit the granny gear and bounce back to the
middle when the hills flatten out.
 
P

Paul M. Hobson

Guest
[email protected] wrote:
> On Jun 19, 12:18 am, Ablang <[email protected]> wrote:
>> Due to cross-chaining issues, I came up w/ a formula for the actual #
>> of usable gears on a bike, which is less than the stated number by the
>> manufacturer.
>>
>> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
>> in back), I only actually have 16 usable gears, and not 24.
>>
>> The formula can be expressed in this form:
>>
>> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
>> gears
>> ex. 24 - 8 = 16 usable
>>
>> Note that this formula only works if you have 3 sprockets in the
>> front, and any number in the back.

>
> I think it's a great idea to come up with a formula but I think that,
> with all due respect, what you have come up with might be too easy.
>
> Kind of like " if it sounds too good to be true, it probably isn't ".
>
> Lewis.
>
> *****
>


Imagine a 10spd triple: 30 - 10 = usable gears? nah...

Try Ncr * (Nc - 2) = Nug

where N = number of...
cr = chainrings
c = cogs
ug = usable gears

--
Paul M. Hobson
..:change the f to ph to reply:.
 
T

Tom Keats

Guest
In article <[email protected]m>,
Ablang <[email protected]> writes:
> Due to cross-chaining issues, I came up w/ a formula for the actual #
> of usable gears on a bike, which is less than the stated number by the
> manufacturer.
>
> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
> in back), I only actually have 16 usable gears, and not 24.
>
> The formula can be expressed in this form:
>
> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
> gears
> ex. 24 - 8 = 16 usable
>
> Note that this formula only works if you have 3 sprockets in the
> front, and any number in the back.


What if the bicycle has half-step gearing?

Or Alpine gearing?


cheers,
Tom

--
Nothing is safe from me.
I'm really at:
tkeats curlicue vcn dot bc dot ca
 
B

bluezfolk

Guest
On Jun 19, 12:18 am, Ablang <[email protected]> wrote:
> Due to cross-chaining issues, I came up w/ a formula for the actual #
> of usable gears on a bike, which is less than the stated number by the
> manufacturer.
>
> For instance, on my bike, which supposedly has 24 gears (3 in front, 8
> in back), I only actually have 16 usable gears, and not 24.
>
> The formula can be expressed in this form:
>
> (# of speeds by manf) - (# of rear sprockets) = actual # of usable
> gears
> ex. 24 - 8 = 16 usable
>
> Note that this formula only works if you have 3 sprockets in the
> front, and any number in the back.


I don't know how many usable gears I have nor do I care. I'm only
concerned with which ones I use, which on my road bike is probably
about 6 and on my mtb about 10.
 
A

Aeek

Guest
On Sat, 21 Jun 2008 12:41:24 -0700 (PDT), bluezfolk
<[email protected]> wrote:

>I don't know how many usable gears I have nor do I care. I'm only
>concerned with which ones I use, which on my road bike is probably
>about 6 and on my mtb about 10.


I use all 20 gears on my latest road bike. Yes, some are redundant.
This is a good thing, means I don't have to change rings.
If I had a 53-11, that would be unusable, I'm not strong enough.
My tourer's big-big 48-32 used to just lock the chain if I was
exhausted enough to try it, that was unusable.
 
I

It's Chris

Guest
I have 21 "advertized" gears (3-front, 7-reqar). With my seventeen inch
chain stays that reduce chainflex, combined with the half step granny
configuration I have 17 useable and different, evenly spaced gear ratios
(18, if you count the one redundant ratio shared by the granny and
middle rings).

How do you figure that into your theory?

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"Your Friendly Neighborhood Wheelman"

If you want to E-mail me use:
ChrisZCorner "at" webtv "dot" net

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