Gears for city cycliing - Recommendations? Ratios?

Hi,
Newbie query; I recently aquired a full suspension, small wheeled
(16") folding bike for use around Manchester, UK. - a flat to
undulating city terrain. The bike looks to be designed for campsite /
caravaning use, with knobbly tyres (which I'm swapping for city
tyres).The trouble is the gear ratios are all wrong, such that the
bike goes way too slow for the pedalling rate. I figure I have to
increase the size of the chainset (single). Its 36 with five speed 14
to 28 gears at the wheel.
My question is - what would be the ideal size for the chainnset?
bearing in mind that the wheels are only 16".
How is this worked out?

Thanks,
Steve

Try http://sheldonbrown.com/gears

You can use it to calculate your min/max speed at a given RPM.

Since you've got a single chainring, you may be able to simply swap the
ring for a larger one, without replacing the crankset. If this was the
case, you would also need a new chain. Realize that this would also
limit your ability to spin up tough hills.

Of course, replacing these components and leaving the (worn?) cassette
could cause you problems when shifting/pedalling. I can't offer any
advice there, I'm afraid.

Cheers,
Dave



Steve wrote:
Hi,
Newbie query; I recently aquired a full suspension, small wheeled
(16") folding bike for use around Manchester, UK. - a flat to
undulating city terrain. The bike looks to be designed for campsite /
caravaning use, with knobbly tyres (which I'm swapping for city
tyres).The trouble is the gear ratios are all wrong, such that the
bike goes way too slow for the pedalling rate. I figure I have to
increase the size of the chainset (single). Its 36 with five speed 14
to 28 gears at the wheel.
My question is - what would be the ideal size for the chainnset?
bearing in mind that the wheels are only 16".
How is this worked out?

Thanks,
Steve

On Thu, 28 Jul 2005 09:16:16 GMT, Steve wrote:

Newbie query; I recently aquired a full suspension, small wheeled
(16") folding bike for use around Manchester, UK. - a flat to
undulating city terrain. The bike looks to be designed for campsite /
caravaning use, with knobbly tyres (which I'm swapping for city
tyres).The trouble is the gear ratios are all wrong, such that the
bike goes way too slow for the pedalling rate. I figure I have to
increase the size of the chainset (single). Its 36 with five speed 14
to 28 gears at the wheel.
My question is - what would be the ideal size for the chainnset?
bearing in mind that the wheels are only 16".
How is this worked out?

Try http://sheldonbrown.com/gears/ . Start by putting in another bike's
gearing details, including wheel size, that does work for you (you might
want to use the 'meters development' measure, as that's the european
standard), or the current gears of this bike, and then see what you need
to do to get it better. For road use, you'll probably want to make the
chainring the biggest you can get, say a 52 at least, just to start with.
You can replace the 5 speed freewheel with for example a Suntour 13-17
($40 at Harris), which gives you a slightly higher high gear and much
closer spacing (with a much higher low gear), or an Ultra-6 6 speed
freewheel 13-14-15-16-17-18 for $50 (although if you have index shifting,
that won't work properly any more).

Depending on what kind of crank you have on, you might have to switch out
the right crank for one that can handle replaceable chainrings.
First determine if you *have* a replaceable chainring (it might be riveted
on), then see http://sheldonbrown.com/gloss_bo-z.html#bcd to determine
what kind you'll want.

All in all, though, it's going to be hard going to get really high gears
out of the thing.

Jasper

Steve wrote: (clip) My question is - what would be the ideal size for the
chainnset? bearing in mind that the wheels are only 16". How is this worked
out?
^^^^^^^^^^^^^^^
My Dahon folder had a single chainring firmly attached to the right crank.
I ended up changing the cranks to the type which allow interchanging the
chainring. I ended up with two chainrings, so I now have twelve speeds
instead of the original six. It's not easy to add a front deraileur to a
folding bike, so I stop and shift the front by hand. Someone here posted
that he uses a salad fork to shift. Sounds neat, but I haven't tried it
yet.

As far as chainring size is concerned--for a given cadence, you will
increase your speed in the same ratio as you increase your chainring size.
Or, for a given speed, you will decrease your cadence in the same ratio as
you increase your chainring size.

Watch out that you don't get a chainring so large that it wants to
high-center you on bumps.

Agreed. A chainset with larger rings is what you need. This will
probably entail a new chainset as yours is unlikely to have replaceable
rings.

I doubt that bottoming out on bumps is a real issue. I have a 52 T
chainring on my Brompton folder and have never had any problems with
it. That will give you a satisfactory top gear for city cycling,
though still nothing like as high as on a conventional bike.

I like the Stronglight escapade chainset on my bike as it lets me use a
52/28 double - allowing very low gears as well, just in case so fancy a
jaunt in the peaks.

There are, of course, more exotic solutions, such as the Schlumpf speed
drive, but these are very expensive (250 pounds or so) - these are
epicyclic gears built into the chainset increasing the top gear by
1:1.6 or so.

Andrew Webster

"Andrew W" wrote: (clip) I doubt that bottoming out on bumps is a real
issue. I have a 52 T chainring on my Brompton folder and have never had any
problems with it. (clip)
^^^^^^^^^^^^^^^^^
You're probably right, Andrew, but what size wheels does your Brompton have?
16" wheels put the bottom bracket pretty low, so I thought it was worth
mentioning.

16" wheels put the bottom bracket pretty low, so I thought it was worth
mentioning.

Small-wheeled adult bikes generally have the bottom bracket at about
the same height as regular bikes since otherwise the pedals would be
too close to the ground.

To the original poster; good luck on finding a replacement large
chainring that fits your cranks. Given the small wheels I'd go for the
largest ring you can find. On my Bike Friday with 20" wheels I use
60/42 chainrings and an 11/28 cassette. The 60 & 11 combination gives
me a high gear that's about the same as the 52 & 13 high on my other
bike.

One way of considering the gearing on bikes with smaller wheels is to
multiply the number of teeth on the chainrings by the wheel size ratio.
So the 60 tooth chainring on my Friday gives me about the same gears
as a 44 tooth ring would on a bike with 700c/27" wheels. Your current
36 tooth ring is like having a 21 tooth ring on a regular bike - no
wonder the gears are way too low.

Many thanks for the great links and advice - basically I have to get
the biggest that will fit (50+)
Steve