Cycling UK Forum

I'm totally confused about gears. I have a Marin Kentfield, it has 21 gears.
I use 1 - 1 going up very steep hills which is great and 3 - 7 going down hills but not fast enough.
I would like to get a road bike, possibly an audax bike which I can use for work but also for cycling long distances as I'm contemplating doing JOGLE next year. I was looking at a Dawes Audax Galaxy Sport but it only seems to have 16 gears. Does that mean that it won't go down as low as my Marin or not as high as my Marin. I keep hearing talk of ratios, but don't really understand. Could someone please explain in plain english preferably.

thank you

Sarah

I've not checked the actual gear ratios of either bike, but the Audax Galaxay will have a double chainwheel which means almost inevitably that the lowest gear will not be as low as on your current bike, and even if you were to start changing chainwheels, triple chainsets always have the potential for much lower gears than doubles. (We do get a lot of queries on here from people who bought a bike with a double chainset, asking how they can achieve lower gears or how to fit a triple to get the same result.)

The number of gears does not actually decide how big the individual gears are - that is a ratio between the teeth at the front and those at the back. There is a formula for calculating this: size of gear in inches is wheel diameter in inches x number of teeth on chainwheel divided by teeth on rear sprocket. This is a pretty meaningless number (giving the theoretical size of a penny farthing wheel for that gear) but it does give you a set of comaprative figures to answer questions like yours. Rather than do the caluclation, you can use a gear table:

http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3521

Ratios are just how many times the rear wheel goes round for one turn of the pedal.
If it goes round twice then the ratio is 2:1.
Usually it doesn't go round a whole number, ie it might go round 2 and a half times, in this case you could say the ratio is 2.5:1 or 5:2 - they're just fractions.

A lot of people measure the distance the bike travels for one turn of the pedals usually in inches.
So if you see a gear quoted as say 100 inches, the bike moves 100 inches for one turn of the pedal.

The range is the difference between the highest and lowest gears, MTB's, hybrids etc tend to have the widest range, road bikes the lowest.

The number of gears is simply obtained by multiplying the number of rings on the chainwheel by the number of gears on the rear wheel, in your case 3 * 7 = 21.
However more gears doesn't imply more range, you'll find for the three chainwheels the gears overlap.

In terms of suitability of a particular bike that's a bit more difficult, depends on terrain and how fit you are. All I can say is manufacturers usually make some effort to give their bikes a sensible range for the purpose they designed them for...

You may find it easiest to start with what you know and work from there.

Your current bike has three chainrings at the front and seven sprockets at the back, making three "ranges" of seven gears each, or 21 gears. If you got rid of one chainring, you'd have 14 gears, and so on. (16 gears is two ranges of 8 gears; over time, the number of sprockets has tended to increase.)

The reason that you get different gears is (obviously) that the sprockets are different sizes. Hence, if you have a wide range of sprocket sizes, you get a wider gear range (but it can be a bit of a jump between gears - tourists tend to put up with that but racers prefer to manage with a narrower, closer-spaced range and stomp up the hills).

The same is true at the front, of course. As a result, it's quite normal to have considerable overlap, so that the next "range" of gears up actually starts half way through the present one. That's not necessarily a bad thing, because constant changing between chainrings can be a nuisance, so it's easier to ride for a while in one "range" of gears and then move to the next - but the change in terrain or wind may not be so large that you want a completely different range.

Thus, the total range of gears you need is determined by the highest and lowest gears you want. For a racer, that's likely to be from "medium" to "very high". For a laden tourist in the hills (or on a serious MTB), it's from "very low indeed" to "medium high", which is a bigger range.

The number of gears you want is determined by how closely spaced you would like that total range to be (racers tend to go for closer spacing whilst tourists accept wider to get more range), and how much overlap you want in your ranges.

Again, in practice, racers save weight by having only two chainrings with perhaps less overlap in ranges. Tourists need the third chainring anyway, because of the difference they want between top and bottom, so get slightly more overlap between ranges - good for finding a set of gears to plod along in

In practice, describing a gear as "medium high" is about as much use as a chocolate teapot, because it's so much a matter of opinion. Hence the quaint practice (in the UK) of measuring gears by stating the wheel diameter in inches of an Ordinary ("penny farthing") bike that would go the same distance for each revolution of the pedals as your bike will in that gear.

Thank you for your help everyone. It's a shame you can't go to a bike shop and test the bike for a day like you would a car. I would really like to get a faster bike but I do worry about the hills if I can't go low enough in gear. Maybe I just need to get fitter, build up the old leg muscles a tad. Has anyone tried the Dawes Galaxy?

Sarah

sarahm,

You talk of a Dawes Audax Galaxy Sport which is a confusion of different models. A Dawes Audax will only have relatively high gears. The front smallest ring is 34 and the biggest at the back is 23. Now that's quite a high gear relative to what your MTB will likely have (you will always get more turns of the back wheel than you turn the pedals ) which may be 26 at the front and 32 at the back (which gives you less turns of the back wheel than you turn the pedals). However a Dawes Galaxy is a different beast altogether and will have 27 gears with a low gear similar to and MTB.

Audax bikes and road bikes are geared IMHO for Lance Armstrong than Joe Bloggs! Tourers, Hybrids and MTBs tend to have lower gears.

I don't know ehere you are in the country, but a good bike shop should let you try a bike out before buying. The Galaxy is certainly a good bike, as are Roberts, Hewitt, Thorn and many, many others.

You should also be able to ask the shop to change the chainwheels or rear cassette to give you the range of gears you want

There are often very good secondhand bikes advertised on here - I've just sold one - so it's worth looking regularly.

Good luck in finding what you want.

N

kwackers wrote:So if you see a gear quoted as say 100 inches, the bike moves 100 inches for one turn of the pedal.

er shouldn't that be 100 x pie (as in 3.142 rather that who ate them). see Thirdcranks erudite explanation above.

Or are you referring to an imperial version of the system used in mainland Europe?

sarahm wrote:Maybe I just need to get fitter, build up the old leg muscles a tad.

This is the heart of the matter.
Understand how the gears work on your current bike.
Keep cycling until you are jolly fit.
Only then decide if you need a different gear range and/or a different bike.

Jack wrote:

kwackers wrote:So if you see a gear quoted as say 100 inches, the bike moves 100 inches for one turn of the pedal.

er shouldn't that be 100 x pie (as in 3.142 rather that who ate them). see Thirdcranks erudite explanation above.

Or are you referring to an imperial version of the system used in mainland Europe?

Personally I think the European version makes more sense, distance travelled per revolution.
Why anyone would torture themselves using an archaic system intended for penny farthings I've no idea...

But (sadly) your right, my description is of European origin, we English prefer to think of it as distance travelled / Pi...

sarahm

As I recover from my crimson blushing (one of my grandsons is called Jack and I'm proud that his vocabulary seems to include 'erudite' even though he is only three ) can I suggest that you can do a bit of research, simply by calculating your existing gear range i.e. what you describe in your OP as 1-1 and 3-7.

Once you have calculated those two numbers (and it does not matter if you use inches*, metres travelled or whatever takes your fancy) you have an idea what you are looking for. You can then see if bikes that take your fancy have the gears you need. I think if you are planning something like the End to End you should pay most attention to your lower gears rather than the high ones. There's a lot to be said for freewheeling down big hills.

* Inches is the one that might maximise your cred in a bike shop or similar.

kwackers wrote:Why anyone would torture themselves using an archaic system intended for penny farthings I've no idea...

The answer to that dawned on me when I visited the Transport Museum in Coventry. They have old posters and so on from around the time of the change from Ordinaries to Safeties, and it's clear that the manufacturers are trying to find ways to allow customers to compare the two.

On a more practical modern level, it's easier to compare inches than to decide whether 2.3:1 is a higher gear than 5:2.

drossall wrote:On a more practical modern level, it's easier to compare inches than to decide whether 2.3:1 is a higher gear than 5:2.

Some ratios are easier than others. When I bought my Birdy - 18" wheels 56 x 28 bottom gear, the man in the bikeshop had his calculator out to compute 56/28 x 18 = 36.

drossall wrote:On a more practical modern level, it's easier to compare inches

Yup. On some forums pretty much every single thread devolves into a comparison of inches

Er, that wasn't terribly constructive. Let me attempt to mke up for it by offering a link to Sheldon Brown's Bicycle Gear Calculator

Sarah your bike has 3 chain rings on the front with 48 38 28 teeth. 48 being the top gear (3) 28 being the low(1). This is usualy worked by the left changer.
The rear has 7 different ones on the back the smallest being 14 teeth (top gear) the largest with 28 teeth (bottom gear).
The front ring pulls the rear around so in 1 and 1 the front pulls the rear around once 28 to 28.
In 3 and 7 if the front has turned once the back will turn approx 3.5 times 48 to 14.
If you are happy with the low gears it is possible to change the rear gears to get higher gears with the low gear (1) having 28 teeth.
The high gear (7) having 11 teeth.
The only thing the steps in the gears is a little larger.
If it was me I would try getting the rear cassette changed to either a 12-28 or an 11-28. This will make the top pedaling speed higher.
A lot of bike shops now understand using the number of teeth. As inches stoped being taught in the early 1980s