Gear ratios

[Pete Whelan]

Bob wrote:
> Pete Biggs muttered:
>
> [snipped...]
>
>> 55 is very unusual. It'll certainly be worth changing that for a smaller one. I suggest 52 or
>> smaller for the outer ring.
>
>
> I was quite surprised when I found out that it was 55 as I'd just watched a time trial on the tely
> and one of the pros was running 55:11. I think at that point I realsied I should have paid more
> attention in the shop...
>
>> More informtation is needed to make more suggestions. Please check and tell us what all the
>> ratios are: How many rings in the front and how many teeth do each have? What cassette/freewheel
>> (rear sprockets)? What is the smallest and largest cog, and how many cogs? You can physicically
>> count the teeth if you don't know.
>
>
> I got down on my hands and knees this morning and counted the teeth on the rear cassette, it's a
> 12-22, 8 speed, dunno the make as it's caked in **** and really needs a good glean (which I shall
> be doing this evening). There are two front chainrings which I've managed to get off, with the
> help of copious quantities of WD40 and the biggest screw driver I own. The outside ring is a 55,
> while the inside ring is a 44.
>
>> This gear calculator is handy for making comparisons (gear inch units are best for this):
>> http://www.sheldonbrown.com/gears/
>
>
> He only goes down to 650c x 23mm, I'm currently running 650c x 20mm road wheels. I don't know how
> much of a difference that'll make, but since I switched back to 20mm Continental Grand Prix tyres
> from 23mm Michelin slick tyres, the bike handles so much better.
>
> Cheers,
>

650C wheels explains a lot, and a 55 is now not necessarily excessive. Going down to a 53 or 52
would give you a lower gear if you really want
it. it also looks as if the whole gearing is set up for tri-athlon/ time trials.

--
Pete

interchange 12 for 21 to reply

 

[Arthur Clune]

Bob <[email protected]> wrote:

: I got down on my hands and knees this morning and counted the teeth on the rear cassette, it's a
: 12-22, 8 speed, dunno the make as it's caked in **** and really needs a good glean (which I shall
: be doing this evening). There are two front chainrings which I've managed to get off, with the
: help of copious quantities of WD40 and the biggest screw driver I own. The outside ring is a 55,
: while the inside ring is a 44.

Ah. Was this a second hand bike? I'd suspect that this was someones time trial bike with
those gears.

Replace the rings with 39/50 or 39/52 and you'll have a much more sane setup.

Arthur

 

[Dave Larrington]

Sky Fly wrote:

> I've often wondered about the different gears that are out there in the market. I know that
> different riders will want different gearing, but I can't help feeling there must be a demand
> for a 9 speed cluster that has such a range that you only need one chainring up front. Something
> like 11-13-16-19-23- 27-32-38-44 with a ring up front of 42 would would give you a range of
> gearing to be found on most average bikes, and the single ring would simplify the chain
> transmission system, yes?

What Pete said about the jumps, plus one would need to redesign the rear derailleur so the upper
pulley would clear the big sprocket. If one really wanted something of that ilk, consider the
Rohloff 500/14 Speedhub. But one would have to /really/ REALLY want it at that price...

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

[Doobrie]

> I agree that more derailleur bikes should come with single chainrings - they're at lest useful for
> flat areas, but double and triple chainsets exist for good reasons.

yes, ive got a single chainring at the front with a 6 gear derailleur at the back and could do with
gears above and below, although the spread of gears feels fairly reasonable to me.

 

[Bob]

Arthur Clune muttered:

> Bob <[email protected]> wrote:
>
> : I got down on my hands and knees this morning and counted the teeth on the rear cassette, it's a
> : 12-22, 8 speed, dunno the make as it's caked in **** and really needs a good glean (which I
> : shall be doing this evening). There are two front chainrings which I've managed to get off, with
> : the help of copious quantities of WD40 and the biggest screw driver I own. The outside ring is a
> : 55, while the inside ring is a 44.
>
> Ah. Was this a second hand bike? I'd suspect that this was someones time trial bike with
> those gears.

Nope, brand new out a shop some time around autumn 1997 as someone pinched my old bike.

> Replace the rings with 39/50 or 39/52 and you'll have a much more sane setup.

I'm off to LBS in a couple of minutes to see what I can get...

Cheers,

--
bob [at] bobarnott [dot] com http://www.bobarnott.com/
----------------------------------------------------------------------------
"Crash programs fail because they are based on theory that, with nine women pregnant, you can get a
baby in a month."
-- Wernher von Braun

 

[Frank X]

"Pete Whelan" <[email protected]> wrote in message news:[email protected]...

>
> the jump between gears is smaller if you reduce the chainring and keep the rear the same,
> otherwise you will end up with the same widely spaced gear ratios with the 55 and changing the
> rear cogs
>

I'm not sure what you mean? The jump between gear ratios due to shifting the rear cassette would be
smaller with the big chainring. e.g.the jump from
50/12 to 50/13 is bigger than the corresponding jump from 55/13 to 55/14.

Or did you mean the jump between the big chainring and the little chainring is a problem?

Obviously all the ratios on the small chain ring would also be lowered if the rear cassette
were changed.

 

[Pete Biggs]

Bob wrote: /snip
> He only goes down to 650c x 23mm, I'm currently running 650c x 20mm road wheels.

Yes, the 650 wheel does make the 55T more sensible. I was assuming you had 700c or 27" wheels.

Both your cassette and inner chainring are quite tall. Personally, I would change both to get some
lower gears - but the choice is yours.

> I don't know how much of a difference that'll make

Hardly enough to affect choice of ratios - but maybe you could do the sums manually or find another
calculator to check.

~PB

 

[Pete Whelan]

Frank X wrote:
> "Pete Whelan" <[email protected]> wrote in message news:[email protected]...
>
>
>>the jump between gears is smaller if you reduce the chainring and keep the rear the same,
>>otherwise you will end up with the same widely spaced gear ratios with the 55 and changing the
>>rear cogs
>>
>
>
> I'm not sure what you mean? The jump between gear ratios due to shifting the rear cassette would
> be smaller with the big chainring. e.g.the jump from
> 50/12 to 50/13 is bigger than the corresponding jump from 55/13 to 55/14.
>
> Or did you mean the jump between the big chainring and the little chainring is a problem?
>
> Obviously all the ratios on the small chain ring would also be lowered if the rear cassette were
> changed.

no, the incremental step from 55/x compared to a 52/x

55/12 to 55/13 is bigger than 52/12 to 52/13

--
Pete

interchange 12 for 21 to reply

 

[Dave Larrington]

Pete Whelan wrote:

> no, the incremental step from 55/x compared to a 52/x
>
> 55/12 to 55/13 is bigger than 52/12 to 52/13

Bigger in terms of gear inches, yes, but I'm told that the legses tend to think of things in terms
of the percentage difference between ratios instead. And that's 8% in both cases, if my
gear-crunching spreadhseet SCIENCE is correct.

55-12 with a 25-571 gives about 112". Personally I rarely get above 75" on the road, which leaves me
a couple in reserve for emergencies and plummets. The race bike goes up to 106", but that only gets
engaged once or twice a year too.

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

[Bob]

Pete Biggs muttered:

> Hardly enough to affect choice of ratios - but maybe you could do the sums manually or find
> another calculator to check.

To tell you the truth, I haven't got a clue what those two calculators that were suggested are
supposed to tell you...

Cheers,

--
bob [at] bobarnott [dot] com http://www.bobarnott.com/
----------------------------------------------------------------------------
"Crash programs fail because they are based on theory that, with nine women pregnant, you can get a
baby in a month."
-- Wernher von Braun

 

[Bob]

Thanks to everyones input, I've just been to Ben Hayward's in Cambridge and picked up two TA chain
rings of 52 and 42 teeth respectively. Bit shocked at the prices though, £34 and £28, but they're
way better quality than what was on the bike and the bloke said they'd last ages.

Hopefully this will make my life a little easier next time I'm out on the bike.

Cheers,

P.S. Anyone got any good tips on cleaning rear cassettes and chains...?

--
bob [at] bobarnott [dot] com http://www.bobarnott.com/
----------------------------------------------------------------------------
"Crash programs fail because they are based on theory that, with nine women pregnant, you can get a
baby in a month."
-- Wernher von Braun

 

[Frank X]

"Pete Whelan" <[email protected]> wrote in message news:[email protected]...
> Frank X wrote:
> > "Pete Whelan" <[email protected]> wrote in message news:[email protected]...
> >
> >
> >>the jump between gears is smaller if you reduce the chainring and keep the rear the same,
> >>otherwise you will end up with the same widely spaced gear ratios with the 55 and changing the
> >>rear cogs
> >>
> >
> >
> > I'm not sure what you mean? The jump between gear ratios due to shifting
the
> > rear cassette would be smaller with the big chainring. e.g.the jump from
> > 50/12 to 50/13 is bigger than the corresponding jump from 55/13 to
55/14.
> >
> > Or did you mean the jump between the big chainring and the little
chainring
> > is a problem?
> >
> > Obviously all the ratios on the small chain ring would also be lowered
if
> > the rear cassette were changed.
>
> no, the incremental step from 55/x compared to a 52/x
>
> 55/12 to 55/13 is bigger than 52/12 to 52/13
>

No the choice was between changing either the chainring or the cassette, to achieve a new set of
lower gear ratios.

When we compare gear shifts gaps we should compare shifting between similar gear ratios not between
shifting between identically toothed sprockets.

I mean he wouldn't even have a 12 sprocket on the new cassette the smallest sprocket would be 13 and
each corresponding sprocket would have more teeth. .

This is why we should compare the shift from 55/13 -> 55/14 against the shift 50/12 ->50/13. The
change from top to second top gears.

 

[Pete Biggs]

Bob wrote:

> To tell you the truth, I haven't got a clue what those two calculators that were suggested are
> supposed to tell you...

No problem. Even if you don't understand what the numbers actually represent (there will be a full
explanation on the S Brown site somewhere: try the Glossary), they're still useful for comparing one
set of gear combinations to another. If the "gear inch" is the same then the gear will be the same.
It's just a way of translating each gear ratio into a nice chunky single number.

Basically, a small chainring + a small rear sprocket can equal a large chainring + a large sprocket
- so there are lots of ways to crack the nut. A gear calculator is useful for comparing all the
various available possibilities to each other and what you have now. So you start off with existing
gears then repeatedly enter different options, print out, don anorak then pore over the tables
comparing them to each other and working out compromises.

The percentage differences between the gears can be used as a guide to guess what is required
outside the existing range, and you'll get more of an idea of what the numbers "feel" like with more
experience.

The 42 won't make a big difference - I expect you'd benefit from different sprockets at the back as
well. An option for the future anyway.

~PB

 

[Anonymous]

"Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
news:[email protected]...

> The 42 won't make a big difference - I expect you'd benefit from different sprockets at the back
> as well. An option for the future anyway.

Well, I'm currently getting annoyed by having a 38 rather than a 36 as my middle ring (where I spend
most of my time)...

cheers, clive

 

[Bob]

Pete Biggs muttered:

[snipped great explanation...]

Thanks for that, I'll look at them a bit more closely now.

> The 42 won't make a big difference - I expect you'd benefit from different sprockets at the back
> as well. An option for the future anyway.

I thought I'd use that for a starting point, I didn't want to end up going to other way to something
that was too easy... I can always buy a few more rings to suit what sort of terrain I'm on, like if
I go back home and actually have some hills to go over.

Cheers,

--
bob [at] bobarnott [dot] com http://www.bobarnott.com/
----------------------------------------------------------------------------
"Crash programs fail because they are based on theory that, with nine women pregnant, you can get a
baby in a month."
-- Wernher von Braun

 

[Pete Biggs]

Clive George wrote:

>> The 42 won't make a big difference - I expect you'd benefit from different sprockets at the back
>> as well. An option for the future anyway.
>
> Well, I'm currently getting annoyed by having a 38 rather than a 36 as my middle ring (where I
> spend most of my time)...

I definitely appreciate one or two teeth can make a difference in that way but I'm thinking more
about the bottom gears for getting up the steepest hills (the OP has a double chainset). If that's
the main problem then larger rear sprockets would help even more.

ps. I've just re-read the original message and notice that only the top gear was mentioned. Sorry
Bob for going off on a tangent. Ignore the extra waffle about inner ring and cassette if hill
climbing is not a problem.

~PB

 

[Arthur Clune]

Bob <[email protected]> wrote:

: P.S. Anyone got any good tips on cleaning rear cassettes and chains...?

One of those chain cleaner whatists from Halfords works well for me.

Cassettes - spray with de-greaser and then get a rag and work between the cogs.

Arthur

 

[Pete Biggs]

Bob wrote:
> Pete Biggs muttered:
>
> [snipped great explanation...]
>
> Thanks for that, I'll look at them a bit more closely now.

You're welcome. Cheers.

>> The 42 won't make a big difference - I expect you'd benefit from different sprockets at the back
>> as well. An option for the future anyway.
>
> I thought I'd use that for a starting point, I didn't want to end up going to other way to
> something that was too easy... I can always buy a few more rings to suit what sort of terrain I'm
> on, like if I go back home and actually have some hills to go over.

That's very sensible. It's what I've done myself - gradually tweaking the gears over the years
rather than make any huge changes in one go.

~PB

 

[Pete Biggs]

Bob wrote:

> P.S. Anyone got any good tips on cleaning rear cassettes and chains...?

Chain: Clamp-on chain bath cleaner thing if don't want to remove chain. Better is to remove chain
and soak in a jar of white spirit. A Powerlink (see www.sram.com) makes removing and refitting
chain a doddle.

Cassette: As Arthur's method except I think it's safer to spray degreaser or whatever* on rag rather
than directly onto sprockets.

* I use WD40.

~PB

 

[MSeries]

I take mine apart and wash them in Diesel, brushing them with a toothbrush. Wipe of the excess, refit then re-lube with Finish Line