This post compares the advantages and disadvantages of 50/34 and 52/36 cranks.
Note: The numbers indicate the teeth on the large and smaller chainring. 50 = 50 teeth on the large ring; 34 = 34 teeth on the smaller ring.
The Advantages of 50/34 Cranks
50/34 cranks are known as compact as they are smaller than the standard 53/39.
They have the following advantages:
- Lower Joint Stress
The larger the chainring, the more speed it can generate. However, the extra size requires extra power output coming from the rider. The extra force that’s needed stresses the joints.
A compact crank softens the strain on the joints and is therefore more suitable for people with tender knees and hips.
Theoretically, when all parameters are equal (material, design…etc.), 50/34 cranks are lighter because the chainrings are smaller. The chain is shorter too as it has to go over a smaller diameter and contributes to the weight savings.
However, a high-end 52/36 crankset will be a lot lighter than a low-end 50/34 unit.
The table below compares the weight of 50/34 and 52/36 cranks:
|Shimano Sora FC-R3000-CG||960g||FSA Powerbox Carbon||733g|
|FSA Omega Modular 2X MegaExo||979g||Praxis Works Zayante Carbon M30||684g|
|Shimano FC-R345||770g||Campagnolo Chorus Carbon||728g|
|SRAM Rival 22 Crankset||857g||Campagnolo Record Carbon||710g|
|Shimano 105 FC-R7000||714g||Shimano 105 FC-R7000||742g|
|FSA Gossamer Pro BB386EVO||751g|
Conclusion: When all parameters are equal a 50/34 crankset offers about 30 grams of weight savings which is an un insignificant number. Ultimately, the weight depends on the model and the material used for the cranks (aluminum or carbon).
If your goal is to build the lightest possible bicycle, then it makes sense to use the lightest 50/34 crankset available. For practical purposes, however, the weight savings that 50/34 could potentially offer are inconsequential.
The Disadvantages of 50/34 Cranks
- Lower Top Speed
The main disadvantage of 50/34 cranks is the lower top speed. Or in other words, when the cassettes are identical, the cranks with the larger chainring produce more speed if the rider can pedal effectively in the highest gear.
To understand the relation between chainring and size, one has to become familiar with a concept known as gear ratio.
The gear ratio depends on the number of teeth on the chainring and the rear cog in use. It describes how many rotations are made by the rear cog and respectively the rear wheel per 1 spin of the cranks.
For example, if the large ring has 50 teeth and the chain is on a cog with 25 teeth, the gear ratio is 50:25 or 2:1.
Or in other words, 1 spin of the chainring equals 2 spins of the rear cog and respectively the rear wheel.
If the large ring has 52 teeth, then the gear ratio would be 2.08:1. Or in other words, the rear wheel will rotate slightly more.
If two bikes have the same wheels and the rider is spinning the cranks at the same RPM (rotations per minute), the bike with higher gearing will travel a greater distance for the same time and thus will be faster.
Larger chainrings allow you to reach/maintain a higher top speed and make it less likely to “spin out” when descending.
Spinning out happens when the rear wheel is rotating faster than the speed that the rider can generate via the pedals. In that case, pedaling becomes pointless as it doesn’t contribute to more speed. Another downside of spinning out is that you are giving up some control over the bike.
The table below shows the speed difference between 50/34 and 52/36 cranks when using an 11-32 cassette and pedaling at 90 RPM.
(The wheels used for the speed calculation are 700c with 25mm tires)
- The columns from 11 to 32 indicate the number of teeth on the cogs.
- The left column shows the number of teeth on the chainrings.
- The speed is in km/h.
50T chainrings offer up to 4.5% lower top speed than 52T chainrings.
The 34T chainrings offer up to 6.5% lower gearing than the 36T model.
А 5% difference on average isn’t substantial in the world of recreational cycling, but it matters when the riders are after the greatest performance and thus need gears that fit maximally well with the terrain and the competition strategy.
The Advantages of 52/36 Cranks
The pros of 52/36 cranks are essentially the negatives of 50/34 models, namely:
- Up to 5% higher top speeds when using the same cassette.
- Lower chances of spinning out
- An option to produce more power
- Encouragement to become stronger
(When you have a higher gearing, you have no option but to pedal harder. It’s known that cyclists often resort to a lower gear if it’s available even when it’s technically possible to pedal through in a higher one.)
The Disadvantages of 52/36 Cranks
- Higher joint stress due to the larger chainrings
- Extra weight (when all parameters are equal)
- Not significantly faster than 50/34 when the bike is used for recreational purposes.
What to choose?
The most important aspect is the quality of the crankset rather than the number of teeth on the chainrings. If you’re torn between two models, choose the higher-end one.
Then, you can increase or decrease the gearing by purchasing an appropriate cassette. (Cassettes are cheaper than cranksets.)
Chainrings and cassettes are part of one system and should not be analyzed separately.
Recreational Use or Racing
If you use your bike for commuting and an occasional group ride, then a 50/34 is a perfectly adequate setup. However, if you are after more serious racing then you might consider increasing the difficulty by getting larger chainrings.