# Understanding (my) gearing

onedayer
Posts:

**41**
Something that has always baffled me is what the numbers on the cassettes and chainsets actually mean to your riding.

My bike has the following (from manufacturer):

Chainset: MicroTech, compact 50x34

Cassette: Campagnolo Xenon 12-26 (although actually counting my biggest gear has 13t and a #13 etched onto it)

Front and rear 10 speed (Campag)

I think this is a very hill-friendly bike, at least I've never had many problems and the ones I've had come on very steep inclines when I'm not fit. What makes it good on the hills?

I've heard an 11-25 is very common, how would that change my riding? Do smaller numbers equal less gears for those tough climbs? Can anybody explain this to me like they were talking to a child? :P

My bike has the following (from manufacturer):

Chainset: MicroTech, compact 50x34

Cassette: Campagnolo Xenon 12-26 (although actually counting my biggest gear has 13t and a #13 etched onto it)

Front and rear 10 speed (Campag)

I think this is a very hill-friendly bike, at least I've never had many problems and the ones I've had come on very steep inclines when I'm not fit. What makes it good on the hills?

I've heard an 11-25 is very common, how would that change my riding? Do smaller numbers equal less gears for those tough climbs? Can anybody explain this to me like they were talking to a child? :P

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## Posts

32,601There is no secret ingredient - Kung Fu Panda

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4111,373Small number at the back = hard gear

Big number at the front = hard gear

Small number at the front = easy gear

That's about as simple as it gets. Stick to those maxims and you won't go far wrong.

2,526Have a look at the link below. You can customise it to suit the gear set up you have although to be honest I cant see a 12 - 26 rear cassette - nearest is a 12-27.

http://www.gear-calculator.com/#KB=24,3 ... 130&SL=2.5

You can then set your cadence level for the chainset spinning - say 80rpm and it will tell you what speed you will do in different gear combinations

1,197I feel I am putting my grumpy old man hat on,again. I have started this post several times and deleted it but I am going to grumble.Please do not take this too personally Onedayer. I do not know how old you are, but I am assuming you have spent at least 11 years in full time education and you can make a legible post on this forum.

However I can not see how you can not apply a bit of common sense and work this out yourself or this is a wind up.

If it is the former it is no wonder the Germans censored on us at engineering.

4,351At the other end your 50-13 setup (if that’s what it is) is your hardest gear. This may mean you spin out when motoring down inclines, an 11 tooth cog will mean you can pedal a good bit slower at the same speed, or keep pedalling to a higher speed. This may or may not be a good thing for you. For a lot of (quite able) people 50x12 is high enough.

The difference in speed at the same cadence by going from 13 to 11 will be 100x13/11= 18% but this will take a lot more effort to achieve.

41Hmm. Yes I'd say fairly fit (and light!). Recently took the bike to the North York Moors and coped with ~20% but >25% cracked me, they're not small hills. I'd been putting a lot of miles in and was fairly surprised I'd been forced to stop tbh. I do find myself in the biggest gear a lot but I don't find it too easy.

So if I wanted to make hills easier I'd make the 26 more like a 28 and if I wanted the downhills to be quicker I'd lower the 13 to a 12 or 11? What would be the difference between a 13-26 and an 11-26? If I'm getting this I'd say no change on hills and more downhill gears?

Is the chainset that important when talking about gearing or is it mainly the size spread on the cassette?

Not taking it personally, and not on the wind up. Just not at all mechanically minded! At least I'm trying to understand these things. Remember, you had to be taught to use a spoon!

4,825Pretty much.

Consider two things:

- the small chainring/big sprocket combo gives you your lowest heat (for up hill). I have 34Fx29R or 34Fx32R...great for steep hills

- the big chainring/small sprocket gives you your highest gear for going downhill, the higher the gear, the faster you can go before having to freewheel.

So if you change your cassette from say 13-26 to 11-28, three things happen:

- you have a lower low gear (26 -> 28)

- you have a higher high gear (13 -> 11)

- but you also have a bigger spread of gears on the cassette, which means the ratios between gears on the cassette will be larger.

A 13-26 on 11sp might be say 13-14-15-16-17-18-19-20-22-24-26

A 11-28 on 11sp might be 11-12-13-14-15-17-19-21-23-25-28

So where as before you had a nice smooth transition in the mid cassette 16-17-18-19-20, you now have larger jumps where you ride most of the time 15-17-19-21

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4,351Correct

Correct. The former has the advantage of closer spacing though, so there are smaller gaps between each gear change. This is the main reason that an 11-32 isn't that good unless you regularly need the range to ride up walls and need to pedal downhill.

It's both, the ratio is what is important, so a 11-44 is exactly the same gear as 12-48 and 13-52. There are tiny differences in efficiency due to drag with small cogs, and you are carrying more metal around with the bigger cogs.

The other point is that a big difference in the front chainset rings means that you have a big jump when you change, which can interrupt cadence. Historically front derailleurs struggled with the mechanics of big differences, but this is much less of an issue now.

4,3516,865The easiest i. E spinner gear up a high is 34 inner ring and 26t on the cassette. Your gear ratio is 34/26 = 17/13= 1.307. Your tallest gear ratio is 50/13= 3.846

If you fit an 11 to 24T cassette your gear ratios change too

Tallest 50/11 = 4.54

Shortest 34/25= 1.36

So the new cassette has a gear ratio that will require you to push out 4% more torque to maintain a specific cadance.

Your tallest gear will require you to push out 18% mire torque to maintain a given cadance. So the new cassette is a harder fear but if you can sustain that effort you will be travelling faster at thaT cadance.

That does not mean you will be faster though.

Think of gear ratios as circular levers. The bigger the bigger the cog at the back the bigger the lever and the smaller the cog at the front the bigger the ever.

Also there is no such thing as a xenon cassette. You have a campagnolo veloce cassette not that matters much.

4,351Sorry to be a pain, but your typos are not helping clarify.

1,197OK Onedayer I am sure you have got your head around it now.

99Just USE the above calculator - it is the best... and also NOTE you can arrange it with two setups for easy comparison.

If the actual cassette ratios aren't quite correct, they can be manually adjusted also.

2,605I understand gearing and that explanation confused the censored out of me

41Thankfully Mad_Malx had already picked the right words to help me get a basic understanding otherwise I'd have gotten a headache!

Cheers guys, Malx and drlodge especially and Mr Firth for keeping it real!

4,6472020 Voodoo Marasa

2017 Cube Attain GTC Pro Disc 2016

2016 Voodoo Wazoo

6,098So. A toddler on his trike, pedals fixed to a front wheel that's 12" diameter. One turn of the pedals = about 3' forward motion. You want to go further on one full turn of the pedals? Make the wheel that the pedals act on bigger; voila, the Penny Farthing. A 40" wheel will go about 10 feet for one turn of the pedals. The downside is that you can't keep making the connected wheel bigger to go further for each turn, and you can't change the size once you set off, so the answer is to have a system that allows the number of turns that the driven wheel makes to be independent [variable] of the pedal revolutions. That's what your gears do.

Ignore all the numbers as it just complicates matters. If the front cog [the pedals end of the gears] is the same size as the driven cog on the wheel, the ratio of pedal turns to wheel turns is 1:1. It doesn't matter how big the cogs are if they're the same size, it's going to be 1 turn of the wheel for each turn of the pedal. A 700c wheel will go forward about 6 feet for one turn. So what you want to do with your gears is change how many times the wheel goes round for each pedal turn.

Again, ignore the tooth count. Teeth and diameter are a fixed relationship anyway so more teeth = bigger cog, fewer teeth = smaller cog.

We've established that if the driving and driven cogs are the same size, it's 1 to 1. Make the front cog twice as big as the driven cog and it becomes 2:1 - the wheel goes round twice for each pedal turn. The same happens if you leave the front cog as big as it was at the 1:1 ratio and then make the rear cog half the size, it becomes a 2:1 ratio again. With bike gears we don't want massive jumps of 1:1, 2:1, 3:1 etc, we require finer adjustment so we do it with rear cogs that are just a little bit bigger or smaller than their neighbour. That change in diameter (diameter goes with tooth count remember) gives us the small incremental changes in pedal turns to wheel revolutions that we require. The changes on the cassette are a nice sequential set of small steps. The two cogs at the front give one bigger step that's analogous to the Hi & Lo ratio on a Land Rover gearbox.

You asked about how a 13-28 would differ from an 11-25. 13-28 starts of with a bigger cog (13) than the 11 tooth, so it's bigger so turns fewer times per pedal rev. The 11 tooth is smaller, more turns per pedal turn = further. But physics means that it takes more effort or longer [time] to go further for the same physical action of 1 pedal turn. Equally 28 is bigger than 25 so that's fewer turns per pedal turn, so it's less distance but easier. The gaps across each gear change are different to go from 28 to 13 in 10 steps, compared to the 11-25. In short, 11-25 is for a decent level of fitness road rider, 13-28 is more relaxed and easier range of gears more suited to the the varying roads that most of us use.

The closer the front & rear cogs are in size (up to matching sizes), the easier it is easier to pedal but you go slower. Reducing the size of the rear cog relative to the front means you can go faster but it takes more effort. Each step up in rear cog size = easier but slower. Each step down = faster but harder. But we know that instinctively.

If you plug numbers in, it becomes clear. Lets use a 53/39 front and 11-25, then 13-28. All you're doing here is dividing the teeth on the front cog by the teeth on the rear cog.

Biggest front, smallest rear = 53/11 = a ratio of 4.81:1 - the wheel goes round 4.81 times for each pedal turn, so about 30 feet.

Biggest front, middle gear = 53/15 = 3.53:1 - the wheel goes round 3.53 times per pedal. That's about 8 feet shorter distance for the same action.

53/25 = 2.12:1 - much easier, much slower. About 13 feet per pedal turn.

Small front for the same is 39/11 = 3.54:1, 39/15 = 2.60:1 and 39/25 = 1.56:1. All these ratios are lower, than the 53 cog so it's easier but slower.

53/39 fronts on a 13-28?

53/13 (this is now your fastest gear) = 4.07:1 down from 4.81:1 for the 11 tooth cog. 53/15 = the same in the middle but the 53/28 = 1.89:1, which is lower than the 53/25 that gives 2.12:1. A lower ratio is always easier but slower

39/13 = 3.00:1 and 39/28 = 1.39:1.

4,825The cassette teeth are along the x axis (left-right) and the gear ratio (in inches) is up the y axis. You can see the lowest gear I have is 33.1 gear inches (on 34-27) and the highest gear is 109.5 gear inches (on 52-13). Gear inches is just the ratio of the two gears * wheel diameter in inches (26.28" in this case)

The two lines represent the two chain rings and I marked where the useful gears are since there is a lot of overlap. So the useful gears are the 8 smallest cassette sprockets using the 52 chainring, then the 8 largest cassette sprockets using the small chainring. So 16 useful ratios.

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