Let’s Talk About BMX Spindle Thickness

from Rookie’s keyboard,

Hello, friends

It’s time for another BBT (Basic BMX Theory) post. And Sunday is a great day to write one of those.

Today, the focus will be on bottom bracket spindles/axles.

The spindle provides attachment points for the crank arms and rotates inside the bottom bracket. As a result….your pedals spin.

BMX bikes have two types of spindles from the perspective of their diameters – 19mm and 22mm.

19mm models have the following pros:

1. Availability

This is the most popular size and consequently allows you to choose between more crank arms. (This is key and the main reason why most people go for 19mm).

And, of course, it’s also a lot easier to find replacement parts for the bottom bracket.

2. Larger bearings = Stronger + Smoother

The thinner the spindle, the larger the BB bearings can be.

In this case, we have an approx. 3mm difference. Larger bearings are stronger, more durable and smoother.


At this point, you may be asking yourself why do 22mm spindles even exist. A good question.

There are two official incentives for their production – lighter weight and extra strength (potentially).

Most of a pipe/tube’s strength comes from its outer layers.

For that reason, a pipe is stronger than a solid rod of equal mass when both are made of the same material.

Bicycle engineers have been relying on this phenomenon to produce components with excellent strength to weight ratio.

The most obvious example would be bike frames – they’re all composed of tubes.


The larger the tube, the hollower it can be while preserving most of its strength.

To match the strength of a 22mm spindle, a 19mm model needs to be thicker or forged out of a stronger material.

Hence 22mm spindles are often slightly lighter.


22mm axles can be made exceptionally strong thanks to the extra material.

But it would be wrong to conclude that they are always stronger than 19mm versions because the final strength level depends on the engineering and the production material.


22mm cranks are considered stiffer thanks to their larger diameter (a thin tube is easier to flex than a thicker one).

Truth be told, most people can’t even feel the difference.

If a rider is given a bike with a 19mm spindle but told that it’s 22mm, he may say that the axle is stiffer because “it has to be”.

It’s also worth noting that the crank arms flex a lot more than the spindle itself. As a result, a cyclist may conclude that their 19mm spindle is flexing due to crank flex even though the axle itself is solid.

Pro Status?

22mm and 24mm BMX cranks are the strongest out there and therefore present on the bikes of elite riders performing huge drops.

Most people will never be on that level, but many BMX enthusiasts take pride in riding indestructible components engineered for professionals.

For that reason, one can sometimes face a bit of illogical elitism coming from “22mm spindle snobs”.

Table Summary

The table below summarizes the pros and cons:

19mm Spindles

ProsCons
Widely availableCannot be as strong as the toughest 22mm spindles
Support bottom brackets with larger bearingsMore flex (debatable)
Easy to find bottom bracket spare parts
A larger selection of crank arms
Cheaper (potentially)

22mm Spindles

ProsCons
StrongLower availability
LighterSmaller bottom bracket bearings
StifferA smaller selection of crank arms
“Pro status”More expensive (potentially)

Don’t Obsess Over Components and Just Ride

Just like computer nerds, many riders spend an unreal amount of time obsessing over their bike components.

Quite often the discussions are injected with a healthy dose of “paralysis by analysis” a.k.a. too much thinking and not enough doing.

If your bike is “healthy” and strong enough for your skill level, it’s best to skip the overthinking part and just ride regardless of the spindle size.

Until next time,

Rookie


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