You might have heard about bike dropouts in conversation. If so, you might be mistaken for thinking that these are twenty-somethings who’ve abandoned their college courses for an alternative life of cruising around Europe on a bicycle.

An appealing way to spend a few ‘gap years’? Sure. But is this what ‘bike dropouts’ really are?

Unfortunately not (although there’s actually a well-hidden clue as to what they are in the name).

So, bike dropouts? What are they? Why do you need them? Let’s take a look.

What are dropouts and why do you need them?

In simple terms, dropouts are the parts of your bike frame where the rear wheel attaches.

They are a pair of notches in the bike frame and, on most modern bikes (hybrids / mountain bike / e-bikes / etc), these allow the rear wheel to be fitted and removed without having to dismantle the chain and derailleur (we’ll cover off the exception in a moment).

The wheel’s axle sits in the dropouts and the quick-release skewer then tightens and locks it into place.

Undo and loosen the quick-release and the rear wheel is then able to, literally, drop out.

That’s useful because it allows for easier and quicker maintenance – tires can be replaced and inner tubes can be patched, without having to faff about with the chain and derailleur.

Dropouts aren’t a component as such but an integral part of the frame, that means you won’t have to worry about replacing them or paying for expensive upgrades at any point.

At this point, it’s worth a quick digression to mention ‘derailleur hangers’.

These attach to the right-hand side dropout notch (on the side where the cogs are). They are an ‘S’ shaped piece of metal and the rear derailleur is bolted onto the bottom of the hanger.

Whereas the dropouts can’t be replaced, the derailleur hangers can. That’s useful because it’s easy to knock the rear derailleur and this can often bend the hanger. If the hanger wasn’t there, it might be the dropout that took the strain and got bent. That would be expensive and potentially impossible to repair (you might have to get a new bike frame).

However, the derailleur hanger is cheap as chips to replace and, in fact, it’s sometimes possible to bend the hanger back into alignment – which can be useful as an emergency trailside fix to get you back to base.

The two most common types of bike dropout (and a less common third)

Over the years there have been many variations on the dropout, but these have now been slimmed down to three – vertical (the most common), semi-vertical (a somewhat distant second), and horizontal (only found on some very specialist bikes).

Let’s take a look at these now.

Vertical dropout

The vertical dropout is the type that, nowadays, you’ll see most often on bikes.

This is really the only TRUE type of dropout, because if you undo the quick-release skewer and lift the bike up by the saddle, the rear wheel will actually drop out.

You’ll see from the photo above that the notches on the frame are pointing straight downwards – hence ‘vertical dropout’.

One big benefit to a vertical dropout is that it’s easy to get the rear wheel settled correctly in the dropouts:

• Slide the rear wheel axle into the dropouts on both sides
• Press down on the saddle and the axle will fully slot home into the vertical notches
• Tighten the QR skewer…et voila!

Semi-vertical dropout (Forward-facing)

The semi-vertical dropout is far less common these days than the vertical dropout.

The likely reason for this is that it’s easier to get the rear wheel axle (and therefore the rear wheel itself) set at an incorrect skewed angle – if the axle is fully in the dropout slot on one side, but only partway into the dropout on the other, then the wheel will be wonky.

If the rear wheel is skewed then this will give problems for brakes (which won’t connect with the wheel rims or disc rotors correctly) causing brakes not to work properly and/or pads to wear unevenly.

It could also cause drivetrain issues, so if you have semi-vertical dropouts on your bike, it’s worth double-checking that you’ve got the axles set fully home in the dropouts.

Horizontal dropout

It’s unlikely that you’ll see horizontal dropouts, but if you do, you’ll probably be looking at a track racing bike, single-speed bike or a fixie bike. Either way, it will be a bike that doesn’t have gears as horizontal dropouts don’t mix nicely with derailleurs.

‘Horizontal dropout’ is a bit of a misnomer really – take a look at the image above and you’ll see that the horizontal slot faces towards the rear of the bike. Undo the bolts holding the wheel axle annnnd the wheel isn’t going to dropout at all.

In order to remove the rear wheel on this style of dropout you need to undo the axle, then slide the wheel towards the pedals so that you can loosen and remove the chain, before taking the wheel out.

Conclusion

So, ‘bike dropouts’ aren’t the name for people on a cycling sabbatical after all.

Instead, they’re the notched parts at the back of the bike frame where the rear wheel is secured.

They come in three distinct flavors – vertical, semi-vertical, and horizontal – with the first of these, vertical dropouts being the type that you’re most likely to encounter.