The Beauty of Bolt Through Axles

bike tech Mar 16, 2021

I am lucky enough to be in a 2-cyclists relationship. And even luckier to be in a “dating the mechanic” relationship. What does this mean? Well, often it means I get lots of new shiny things on my bike – not only without asking for them, but often without noticing them.

The latest on my Scott Scale MTB is a front wheel with a bolt through axle. Last week, the boy looks at me like an expectant puppy as I come to collect Scotty for a ride with the girls after having it serviced (by him, of course). He looks at me, then down at the bike. Then back at me, then back at the bike. Then back at me… you get the picture.

“Notice anything different??” he asks with wide, excited eyes.

“Ummmm…” is the normal response mumbled as I frantically search the bike for something glaringly obvious. Like a whole new bright pink bike. I reckon I could spot that.

“I’ve given you a new front wheel and now you have a bolt through axle!”

“Brilliant! What does that do?”

The axle, as we know, is the central shaft in the wheel. Currently, the most widely used axle on bicycles is the Quick Release – or QR Axle. You may recognise it from such activities as taking your front wheel off to put your bike in your car, or locking the back wheel into a mag or fluid trainer.

As with anything else, for every pro there is a con. And in the case of the QR Axle, the pro is that it’s quick to release (clue was in the title there), but the cons are:

  • Malfunction/misalignment due to incorrect (read: hasty) installation
  • Smaller diameter so not as stiff
  • Can loosen with rattling
  • A number of little parts to lose under the cupboard or trailside

In mountain bikes with disc brakes, it has been identified that the forces generated by the disc brake can cause the skewer to loosen up during use. If you have ever ridden a mountain bike downhill at any speed, you will understand that this could constitute much more than an “uh oh” moment.

In comparison to the QR Axle, a Bolt-Through Axle is a shaft that is inserted through one side of the fork/frame, slides through the hub and screws into the other side of the fork/frame. This undoubtedly leads to a stronger and more secure-fitting connection with no worries about the skewer loosening during your ride.

Other pros include:

  • It’s all one piece so you can only lose the axle (but don’t)
  • It’s wider and thicker diameter makes for a stiff wheel and steering ‘tracking’ with means better deflection of bumps and better cornering
  • It has a natural ‘lock’ so you know when it’s tight, which means less fussing and more riding

Also, because it slides straight through the hub and frame of the bike before locking, there is little room for error in “doing it up wrong”.

Cons include cost associated with purchase and upgrade in addition to a slightly heavier axle - perhaps up to 100g of extra weight… but this may just be weight you are happy to carry if you are a particularly gnar-core rider.