Basic BMX Theory: Female Axles and Pegs (2 graphs included)

from Rookie’s keyboard,

Hello, friends

It’s Friday evening where I live – a.k.a. a good time to type another article before we enter the weekend.

Yesterday, I saw a couple of BMX riders mess around in my neighborhood. Later one of them came to the shop where I work for the time being and asked me a couple of question that I think most rookie BMX-ers may be interested in.

So, today, I’ll talk about female axles (explanation coming in a second) and their relationship/engineering connection with pegs.

As always, I will start with the basics.

Axles are a support element for rotating parts (in this case wheels). In the case of bicycles, the wheel is rotating around the axle with the help of ball bearings inside the hub.

There are two main types of BMX axles – male and female.

Female axles are short and have internal threading. The wheel is secured to the axle with bolts screwed into the axle.

Meanwhile, male axles are long rods with external threading. The wheel is tightened to the axle via nuts screwed onto the axle’s threads.

Attachment Methods

A BMX peg is mounted directly to the axle.

For a male hub and axle, the installation is as follows:

1. Unscrew and remove the axle nut. Remove the washer too as the peg itself acts like one. You could also put the washer on the inside of the peg.

2. Slide the peg onto the axle.

3. Place the axle nut into a socket wrench with a long extension and carefully screw it on the axle. Move slowly to avoid cross-threading.

You will need a long socket extension as you have to screw the axle nut through the peg.

The image below shows the order:

Peg installation On a Male Axle

If you have a female axle and hub, the procedure is quite similar. The only difference is that instead of a nut screwing onto a threaded rod, there’s a bolt screwing into a threaded pipe/cylinder.

Here are the steps:

1. Remove the female axle bolts and the washer.

2. Put the head of the bolt into a socket and then slide the socket and the washer through the peg until the thread of the bolt is sticking out of the peg’s end.

3. Screw the female axle bolts into the axle.

The image below illustrates the order of the elements.

Peg Installation on a Female Hub (graph 2)

Voila! That’s all there is to it.

A Note On Strength

Theoretically, a female axle is stronger than a male one of the same thickness because it doesn’t extend as much.

The narrowness makes the hub less vulnerable because the mechanical advantage (leverage) is lower when exerting force on it.

Or in simpler terms – it’s easier to break a longer stick than a short one.

That said, male axles are stronger when they’re thicker than the female ones.

For example, a 14mm male axle is tougher than a 3/8″ female when all other parameters are equal.

In terms of strength, axles rank as follows:

1. 14mm female axle

2. 14mm male axle

3. 3/8″ female axle

4. 3/8″ male axle

This ranking is based on the strength of the center axle itself. In practice, the axle bolts of a female hub are very likely to give up first because they’re weaker than a male axle.

The weakness of the bolts is somewhat beneficial because you rarely have to replace the axle itself – just the bolts.

Conversely, when a male axle breaks, you have no option but to replace it.

Protected Threading

Female axles do not have exposed threading and neither do the bolts.

You can’t damage the threads of either component during riding or when doing some sort of peg-less grinding.

Meanwhile, the threading of male axles is exposed and can be stripped fairly easily.

Weight Comparison

In general, female axles are lighter than male axles because they require less material. Often the difference is too small to matter.

The tables below contain the weight of various female and male hubs:

Table 1: Front Hubs (3/8″/10mm Axles)

Female HubsWeightMale hubsWeight
Supreme Female Front Hub286 gramsEclat Kolibri243 grams
Fiend Process Front Hub289 gramsKHE ACME234 grams
Fly Classic Front Hub246 gramsProper Microlite237 grams
Halo MXR185 gramsVwp BMX Front Hub 36G265 grams
Odyssey Antigram255 gramsKHE U50235 grams
Profile Elite230 gramsKHE V81244 grams
Proper Select203 gramsFirma Front Hub250 grams
Shadow Symbol258 gramsTrebol Front Hub246 grams
Stranger Ballast 295 gramsJOYTECH Front280 grams
TotalBMX Tech V2 250 gramsPROPER Microlite V2232 grams
Average:249.7 gramsAverage:246 grams

Result: Even though there are some very light female hubs, the weight discrepancies between the male and female front hubs are slim.

The male axles ended up being a few grams lighter on average. That said, I couldn’t find a male axle under 200 grams.

Table 2: Rear Hubs (14mm axles)

Female HubsWeightMale HubsWeight
Colony BMX Wasp Cassette Hub445 gramsProfile Racing Profile Elite510 grams
BSD Back Street Pro Cassette Hub487 gramsProfile Racing Profile SS Mini Cassette Hub470 grams
United Supreme460 gramsPrimo Remix441 grams
CULT Match V2499 gramsFiend Process SDS466 grams
Total BMX Tech 2467gramsTotal BMX Tech 2457 grams
BSD SWERVE495 gramsStolen Magnum559 grams
Profile Mini372 gramsProfile Mini501 grams
Eclat Pulse477 gramsStranger Ballast 587g
Average:465.72 gramsAverage:498 grams

Result: Rear female hubs show a slight weight advantage over the male models. The difference is 6.5% percent in favor of female hubs.


Different Axles At The Front And Back Are A Common Combo

Many bikes come with a 3/8″ female front axle combined with a 14mm rear male axle.

The reasons for this combo are:

Strength. A quality, solid 14mm male axle is close to unbreakable. And since the rear axle receives most of the “punishment” during grinding, it makes sense to reinforce this area.

Weight savings. 3/8″ axles are weaker than 14mm ones but also lighter. Over the years, the BMX community decided that a 14mm axle is overkill for the front because the area isn’t as stressed. As a result, 3/8″ axles started getting more traction. A 3/8″ female is chosen over a 3/8″ male because it’s stronger.


By the way here are also she-male axles.

To a large extent, the she-male axle is the same as a regular female axle. The only main difference is that the center part is longer and thus sits into the dropouts.

Some she-male axles combine a male axle on one side and a female axle on the other.


Until next time,

Rookie


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