Cross ratios, wide ratios, and the deep world of gear ratios

Modified at: Mar. 17, 2021

Posted at: Mar. 16, 2021

Cross ratios, wide ratios, the world of gear ratios is a deep one. We will take a look at the advantages and disadvantages of changing the number of teeth on the sprocket, and the combination with the chainring.

Table of contents

What is the cross ratio?

A sprocket configuration with a small difference in the number of teeth on the rear sprocket is called a cross ratio. In the case of recent Shimano sprockets, 11t-25t sprockets are used in 11 stages.

The first eight steps only change the number of teeth by one.

Advantages of cross-ratios

A small difference in the number of teeth means that there is little change in weight when you shift gears, so shifting gears can be done smoothly. The cross ratio is also useful in situations where you want to change gear ratios finely depending on the gradient of a hill or other slope to reduce the burden.

Another advantage of the cross ratio sprocket is that it weighs a little less because it has fewer teeth.

Disadvantages of cross ratio

On the other hand, because of the small difference in the number of teeth, you will inevitably have to shift gears more when driving on roads that are not flat or have many gradient differences. Also, when you want to accelerate all at once, you will need to shift up continuously.

However, with Shimano’s STI levers, when the lever is inserted deeply, the system is designed to go up two or three gears at once, so once you get used to it, you can shift gears with large gear ratios like wide ratios.

What is the wide ratio?

The opposite of the cross ratio, a sprocket configuration with a large difference in the number of teeth on the rear sprocket is called a wide ratio.

In the case of the 11t-32t sprocket, the number of teeth is completely different from that of the cross ratio sprocket even though they have the same 11 steps.

Advantages of Wide Ratios

The advantage of a wide ratio is that it has gears with more teeth.

More teeth on the sprocket means less difference in the number of teeth from the front, which naturally means a smaller gear ratio and lighter pedal. However, a light gear ratio of one gear is not useful unless you are riding up a very steep hill, so you may not have many opportunities to use it unless there is a very steep hill on the road you usually ride on.

One of the reasons why wide ratios are being adopted in many cases these days is that wide ratios have a “wide range of protection” and can be used to some extent without having to use different front inner/outer ratios. Without using the front, you can avoid shifting problems such as chain drop.

However, depending on the combination with the front, the chain will be tucked in, so be careful.

Summary of gear combinations to avoid "chain tucking" on road bikes

I've put together a list of gears that cause chain slippage on road bikes and gear combinations that avoid chain slippage. Also, what to look out for when shifting gears and how to practice.

Disadvantages of Wide Ratio

Since the wide ratio has a larger gear ratio to the next gear, the weight of the pedal when shifting can vary greatly.

However, the difference in the number of teeth on the current wide ratio 11-speed sprockets is about the same as the difference in the number of teeth on the old 8-speed and 9-speed sprockets, so there is not an extreme difference.

Pay attention to the number of gearshifts

It is said that the recent increase in demand for wide ratios is largely due to the fact that the latest Shimano components, 105 and above, are now 11-speed. This is because the number of sprockets can be increased to cover a wider range of gear ratios with wider ratios.

On the other hand, Shimano’s components for road bikes, such as SORA and CLARIS, have 8 and 9 speeds, so be careful not to use too many cross ratios, because you may not be able to handle hills, or on the other hand, too many wide ratios may result in gears you don’t use.

The number of teeth on the chainring is also important.

Sprockets are used to make minor gear ratio adjustments, but if you want to make your bike lighter or faster, it is more effective to change the overall gear ratio by changing the number of teeth on the chainring rather than changing the sprocket.

For example, if you change the front outer chainring from 50T to 53T, the gear ratio will be as follows for the same sprocket.

Speed	50T	53T
11	4.5	4.8
12	4.2	4.4
13	3.8	4.1
14	3.6	3.8
15	3.3	3.5
16	3.1	3.3
17	2.9	3.1
19	2.6	2.8
21	2.4	2.5
23	2.2	2.3
25	2.0	2.1

The image is that the chainring is generally about one step higher.

It is said that even professional riders change their chainring depending on the course they are riding, so one way is to use a cross ratio sprocket and change the gear ratio with the chainring, such as “50t for climbing” or “53t for flatland cycling” depending on the course you are riding.

Chainrings can be easily replaced with a wrench without removing the crank, so you can easily change the overall gear ratio.

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Speed	50T	53T
11	4.5	4.8
12	4.2	4.4
13	3.8	4.1
14	3.6	3.8
15	3.3	3.5
16	3.1	3.3
17	2.9	3.1
19	2.6	2.8
21	2.4	2.5
23	2.2	2.3
25	2.0	2.1

Speed	50T	53T
11	4.5	4.8
12	4.2	4.4
13	3.8	4.1
14	3.6	3.8
15	3.3	3.5
16	3.1	3.3
17	2.9	3.1
19	2.6	2.8
21	2.4	2.5
23	2.2	2.3
25	2.0	2.1