This post compares the advantages and disadvantages of 31.8mm and 25.4mm handlebars.
The Advantages of 31.8mm Handlebars
31.8mm handlebars and stems have been the industry standard for more than a decade. Consequently, the vast majority of manufacturers focus on that size. If you want the highest number of options, then 31.8mm handlebars are the logical choice.
Since 31.8mm stems and handlebars have become the default standard, producers of higher-end models focus on that particular size to satisfy the market and maximize their sales. Meanwhile, 25.4mm handlebars are found primarily on entry-level bikes. Of course, there are higher-end 25.4mm bars too, but the choice is more limited.
More Clamping Real Estate
31.8mm handlebars offer approximately 25% more clamping area than 25.4mm handlebars. As a result, the stem needs less torque to hold the handlebars. The reduced compression is important when using carbon handlebars because carbon has poor resistance to clamping/compression force.
When all parameters such as wall thickness, material, and build quality are equal, a pipe with a larger diameter is much stronger than a pipe with a smaller diameter. Consequently, 31.8mm handlebars have the potential to be much stronger.
In practice, however, this doesn’t happen because 31.8mm handlebars are usually made thinner to save weight. (The goal is to offer the strength of 25.4mm handlebars in a lighter package thanks to the larger tube diameter.)
The Disadvantages of 31.8mm Handlebars
- Extra stiff
It depends on the model, but in general, handlebars with larger diameters tend to be stiffer. (Hence why 35mm bars are notably stiffer than 31.8mm units.) The same applies when comparing 31.8mm to 25.4mm or 26mm models.
The extra stiffness increases joint stress and makes the ride less comfortable.
- Anti-retro appearance
31.8mm handlebars are and look modern. Consequently, they aren’t as aesthetic when installed on retro machines. Furthermore, they can’t be coupled with a standard quill stem designed for 25.4mm handlebars.
Or in other words, if you want to put 31.8mm handlebars on a retro bike, you will have to convert from a threaded to a threadless stem. If that’s not an option, you can use a quill adapter that starts as a quill stem and then transitions into a 1 1/8″ tube that can operate with modern threadless stems.
This conversion is functional, but it further hurts the aesthetics of a retro machine while adding extra weight too.
The Advantages of 25.4mm Handlebars
- Less stiff (potentially)
25.4mm handlebars have the potential to be more compliant and joint-friendly. However, whether this property will manifest to a high degree depends on the particular model. Truth be told, most people will not feel a tremendous difference.
25.4mm handlebars look right on a retro bicycle and are compatible with quill stems.
25.4mm bars tend to have a lower price tag.
The Disadvantages of 25.4mm Handlebars
- Dead standard
In practice, 25.4mm handlebars are a dead standard that’s losing “support”. As a result, it’s difficult to find a lot of options.
- Not as strong (potentially)
As explained above, when all parameters are equal, a tube with a smaller diameter is weaker than one with a larger diameter. Thus, when maximal strength is needed, 31.8mm bars have the potential to offer it.
The next table compares the weight of 25.4mm and 31.8mm handlebars:
|Dartmoor MTB Handlebar Swing High v.2||750mm||395g||Levelnine Race||720mm||280g|
|XLC HB-M04||630mm||345g||Newmen Evolution SL||760mm||280g|
|Reverse Components – E-Element||770mm||340g||Chromag Fubars FU40||800mm||330g|
|XLC HB-M04||630mm||345g||Truvativ Hussefelt Comp||700mm||347g|
|NS Bikes Lick||740mm||415g||SQlab 3OX MTB 31.8||780mm||325g|
|NS Bikes Proof||760mm||376g||PRO FRS 31.8||800mm||345g|
|Ritchey SC Low Rizer||670mm||470g||Spank Spike 800||800mm||330g|
|Reverse Components Base||760mm||305g||Spank Oozy Trail 780 Vibrocore||780mm||270g|
Conclusions: As expected, 31.8mm handlebars are slightly lighter on average (24%). That said, the final weight depends on the model and its length (longer handlebars such as 800mm are cut in most cases).
The weight savings offered by 31.8mm handlebars are not substantial enough but present.
Summary: What You Need To Know
|Variety (more handlebar and stem models)||Too modern for retro bicycles|
|Potentially stronger||Stiffer (extra joint stress)|
|Looks complimenting modern MTBs||Non-compatible with standard quill stems|
|Larger clamping area resulting in reduced compression force (carbon-friendly)|
|Potentially lighter thanks to the larger diameter|
|Retro look||Low availability (close to abandoned standard)|
|More compliant (potentially)||Non-carbon friendly due to the smaller clamping area|
|Compatible with quill stems||Potentially weaker|
|Some models are too short by modern standards|
What to choose?
If you want to have the maximum number of choices when it comes to handlebars and stems 31.8mm is the logical choice. That said, 25.4mm handlebars are perfectly fine as long as the model corresponds to the function of the bike (e.g., MTB, urban…etc.) and is made by a reputable brand.