Bottom gear on a Dawes Galaxy

[Pete Biggs]

druidh wrote:
> My old MTB has 28/38/48 and 14/16/18/21/24/28/32 gears. I was hoping
> to use it for touring now that I've acquired a full suspension rig
> for the hills. I was a bit worried that, with road tyres, I'd not
> have a high enough top gear for decent speed.

It is on the low side, but you should only need a higher top gear to pedal
down fairly steep descents. Maybe you could change the big ring for a 50.

> However, I'm now also
> worried that the weight of any luggage will result in not enough low
> gear either. Am I missing something?

Take it for a test ride with some luggage, might be OK for you. Again,
you could use a different (inner) chainring if needed.

> (and where do these 17"/16" figures come from?

That's "gear inches" (for handy comparisons): Number of chainring teeth
divided by sprocket teeth, times tyre diameter in inches.

~PB

 

[druidh]

Pete Biggs wrote:
> druidh wrote:
>
>>My old MTB has 28/38/48 and 14/16/18/21/24/28/32 gears. I was hoping
>>to use it for touring now that I've acquired a full suspension rig
>>for the hills. I was a bit worried that, with road tyres, I'd not
>>have a high enough top gear for decent speed.
>
>
> It is on the low side, but you should only need a higher top gear to pedal
> down fairly steep descents. Maybe you could change the big ring for a 50.
>
>
>>However, I'm now also
>>worried that the weight of any luggage will result in not enough low
>>gear either. Am I missing something?
>
>
> Take it for a test ride with some luggage, might be OK for you. Again,
> you could use a different (inner) chainring if needed.
>
>
>>(and where do these 17"/16" figures come from?
>
>
> That's "gear inches" (for handy comparisons): Number of chainring teeth
> divided by sprocket teeth, times tyre diameter in inches.
>
> ~PB
>
>

Thanks. That means that my shortest gear is about 25" - (28/32)*28 and
my longest is about 97" - (48/14)*28 ??


druidh

 

[Pete Biggs]

druidh wrote:

> Thanks. That means that my shortest gear is about 25" - (28/32)*28 and
> my longest is about 97" - (48/14)*28 ??

27" is a more realistic size to the nearest inch for 700C tyres despite
them sometimes being called 28"!, or even 29"!! Confused? You will be
...... www.sheldonbrown.com/tire-sizing.html

So your range is about: 24 to 93".

~PB

 

[Peter Clinch]

druidh wrote:

> Thanks. That means that my shortest gear is about 25" - (28/32)*28 and
> my longest is about 97" - (48/14)*28 ??

That'll be right, and that's a fair range for cargo over roads.

"Gear inches" refer to the size of the wheel you would be using if you
were turning it directly with no gearing. It's quite a preposterous way
to measure the gear in many respects but if you've got a feel for what
the units translate to on a bike it works okay. Note that gear meters
are rather different, telling you how far you'll go for one turn of the
cranks, so the conversion is Pi times more than the simple inches to cm
multiplier.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[druidh]

Peter Clinch wrote:
> druidh wrote:
>
>> Thanks. That means that my shortest gear is about 25" - (28/32)*28 and
>> my longest is about 97" - (48/14)*28 ??
>
>
> That'll be right, and that's a fair range for cargo over roads.
>
> "Gear inches" refer to the size of the wheel you would be using if you
> were turning it directly with no gearing. It's quite a preposterous way
> to measure the gear in many respects but if you've got a feel for what
> the units translate to on a bike it works okay. Note that gear meters
> are rather different, telling you how far you'll go for one turn of the
> cranks, so the conversion is Pi times more than the simple inches to cm
> multiplier.
>
> Pete.

That's the bit that confused me. When I first worked it out, I was using
circumference instead of diameter and was stumped at how low these other
numbers were. As you say, this seems a much more sensible measure.


druidh

 

[Peter Clinch]

druidh wrote:

> That's the bit that confused me. When I first worked it out, I was using
> circumference instead of diameter and was stumped at how low these other
> numbers were. As you say, this seems a much more sensible measure.

It is more sensible, yes, but OTOH I know what a 20" gear feels like,
and I have no innate conception of how any given distance/crank rev
feels when I'm actually on the bike, so even though gear inches are daft
it's what I use...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/