Gearing and recommended selections

Kieran_Burns

A guy over on a car forum I frequent has commented on the huge number of gears on every bike you buy nowadays.

One of the knowledgeable lot has commented on the correct selection of gears, and I must admit it's something I've never thought about.

The comment made was that you should not use the lowest gears on the rear cassette while on the big ring (for 3 ring chain wheels) as the angle is too steep and will cause excess wear.

Now I just sit on the biggest chain ring all the time, and use one of the middle 3 gears (4-6 on the 9 speed casette) occasionally using 7-9 when on a good hill. I very rarely drop below 4th as there are no real hills around here for me to require it.

So could someone explain the correct gears that you should use? When you should you step down to the middle ring for example?

Am I right in how I am using the gears or committing a cardinal sin?

alfablue

The general idea is to keep a steady cadence (maybe 90 rpm) so change gears to achieve this (like you change gears in a car so the engine is neither labouring or revving too high, both of which are inefficient).

The other general idea is that you don't use small sprocket to small ring or large sprocket to large ring, as you suggest.

27 (or 30) gears are useful in that there is a gear for every eventuality that lets you use the optimum cadence, that's not to say bikes with fewer gears are no good, just you have fewer choices to achieve the optimum so either effort changes for a given cadence, or cadence changes for a given speed.

don_don

You are right insofar as running the chain from big chainring to big sprocket puts it under a lot of unnecessary sideways stress. However, I don't think the way you are using your gears will cause any problems at all.

If you were minded to upgrade, you could consider a compact double chain-set and lose the inner ring. Otherwise I'd say carry on and don't worry about it

sarajoy

I tend to sit on the middle ring for the most part, if the hill becomes very steep and my pedalling is likely to die miserably, I'll work all the way down to 2/3 or 2/2 then switch the ring down to 1/2 for a burst of easy-pedalling to get me up to the crest of the hill.

Similarly if I'm gaining speed or heading downhill fast, I switch up to 2/6 or 2/7 then switch chain ring to 3/7 and then 3/8 for my highest gear.

Also I like to use the chain rings to dump a load of gears at once, say when coming up to a stop at lights, or having crested the hill.

Bassjunkieuk

As alfablue has said it's all about matching your power output to the terrain your on.
More gears enables you to select the one that feels just right - neither too spinny or too tough to push :-)

There are a few occasions on my bike that I wish I had a few more cogs at the rear (8 at present) as I often wonder what the gear that would sit between the ones that feature more then a single tooth difference feel like :-)

I think most popular road cassettes run 12-25 (like my 8 speed) but you can get this all the way upto 10 or 11 cogs so the jumps become increasingly less each time. You can then get ones that go down to 11 or up to 27 (or more, feel free to correct me) depending on if you need to climb or descend a big, steep hill!

Personally I haven't yet managed to spin-out on my 52x12, but have been grateful of the 30x25 granny gear on some hills I've found during long rides!

Kieran_Burns

My gears go from 30/32 to 50/11 so I reckon I can climb near vertical hills and not spin out on the way back down with them!

Interesting answers here folks - with thanks. Use of the chain ring at lights never occurred to me.

I think really as my commute is so damn flat and the only hills are very short, i just stand up and use what little power I have available to get up them.

biondino

I have 20 gears but I don't have 50/18 and that's the one I would use most

My front derailleur is bent and I'm not a bit nervous about using the highest gears as there's a lot of noisy chain rub. But that's only a problem on downhills and, let's be honest, it's not like I need to race...

sarajoy

Kieran_Burns wrote:

I think really as my commute is so damn flat and the only hills are very short, i just stand up and use what little power I have available to get up them.

Sadly I don't have that choice in my Brizzle commute!

Tell me if I'm being thick, how do I figure out the gear numbers you lot keep using? Is it just number of teeth on the cogs?

alfablue

sarajoy wrote:

Kieran_Burns wrote:

I think really as my commute is so damn flat and the only hills are very short, i just stand up and use what little power I have available to get up them.

Sadly I don't have that choice in my Brizzle commute!

Tell me if I'm being thick, how do I figure out the gear numbers you lot keep using? Is it just number of teeth on the cogs?

Sprocket teeth - smallest is likely to be 11 or 12, largest might be 21, 25, 26, 27, 28, 29, 30, 32, 34

Typically road bikes come with 11-25 as standard

Chain ring sizes, road bikes typically 52 or 53 big, 42 or 39 small (double)

or

50 big, 36 or 34 small (compact)

or 52/39/30 (triple).

MTB typically have 11-32 or 34 cassette, 44, 30, 24 or 22 chainrings.

I have a 50/36 compact chainset on my road bike with a 12-27 cassette. On my Audax bike I have a 52/39/30 triple with a crazy 11-32 9 speed cassette (I do some mega hills! Though last week I managed a 1 mile hill at 16% on my compact - just!)

CiB

Use the gears to keep within a comfortable and efficient cadence - 70 to 90 is the norm. Remember that having 10 gears on the cassette and 3 rings on the front doesn't give you 30 ratios. It gives you a lot fewer but with a lot of overlap. Easier to think of having 3 overlapping stepped ranges (or just 2 on a double clanger) that you can work your way up & down to fit the terrain, wind, apathy & elapsed mileage. The lowest and highest gears in these ranges are only achievable by changing on the front rings.

It's your bike - ride it as you feel best on it. I've never come across a policeman, or a roadside Judge of Fact, or even a fellow-cyclist who's pulled me over to point out that my gear selection is invalid.

There was a similar thread on the Road -> Beginners forum last week about this, started by a chap who hadn't been able to work out what the front derailleur was for.

wgwarburton

sarajoy wrote:

Tell me if I'm being thick, how do I figure out the gear numbers you lot keep using? Is it just number of teeth on the cogs?

Yes. The ratio front to rear dictates the leverage between pedal and road, so if you have a 48 tooth front chainring, a 12 tooth rear sprocket gives you a 4:1 multiplier, an 18 gives you 3:1 and a 24 gives you 2:1. There's usually a fair bit of overlap, so you could have a 48 combined with a 36, for example, where the 48:24 and 36:18 would give you exactly the same ratio. To avoid duplications, and hence give you a wider choice, the front and rear are often set up so that this doesn't happen and the ratios that are close offer you the "middle" gears that bassjunkie wonders about.

Back in the day, the number of available gears was limited by the equipment in use- more than five sprockets on the freewheel and the back axle strength would be compromised- so you might pick and choose your chainring/sprocket sizes to suit the style of riding, strength, load, terrain etc.
These days, the freehub at the rear, ultra-narrow chains and a general acceptance that parts will need replacing every few years means you can have many more ratios, so the selection isn't as critical. Manufacturers can cut down on the variation they offer and optimise their kit to get easy-clicky shifts when it's nice & new. This is progress, apparantly...

If you want to explore the ratios available, you need an easier way to compare ratios than the tooth-count. Traditionally, gears are quoted in "inches", by multiplying the actual wheel diameter by the ratio. This gives a number which is equivalent size of a "penny-farthing" front wheel, incidentally.
Typical numbers would be 30" or so for a steep climb, 50"-60" for an uphill gradient, mid 70s/early 80s for cruising on the flat and 90+ for descents. Depends on fitness, cadence preference etc- a sprinter would be looking for a top gear of well over 100".

You can also compare by "development"- the distance in metres the bike travels for one pedal revolution, or using Sheldon Brown(RIP)'s Gain Ratios, which factor in the crank-length, too (long cranks provide more leverage, but higher pedal speed, just like lower gears).

Hope this helps.

Cheers,
W.

Bassjunkieuk

+1 for Sheldons Gear Calc, once you know what sizes your chain ring and rear cassette sprockets are your pretty much set and can get a nice table that shows just how each gear stacks up! It also shows the glaring duplications that occur when you run a triple!

roger_merriman

Bassjunkieuk wrote:

+1 for Sheldons Gear Calc, once you know what sizes your chain ring and rear cassette sprockets are your pretty much set and can get a nice table that shows just how each gear stacks up! It also shows the glaring duplications that occur when you run a triple!

and a double to be fair!

does show that most of the gearing is in the cassette,

CiB

Running a 39/53 on an 11-25 cassette, and allowing for rounding & v near hits, there's a nice progression on the 39 from gears 1 to 7, then swap to the 53 and run from 4 to 10 on there, 39/7 being effectively the same ratio as 53/4.

The reality is that we don't use gears like that but the chart shows that moving from the 39 to the 53 should mean a drop of 3 - 4 gears on the rear to move smoothly through the range. Or just push harder on the pedals. That works.

Quick edit - it does show that on this set up at least, 2 x 10 = about 13 usable ratios, not 20 gears.