This post compares the advantages and disadvantages of horizontal and vertical dropouts in relation to one another.
The Advantages of Horizontal Dropouts
- Single-speed and Fixed-gear Compatible
Horizontal dropouts allow the rider to slide the rear wheel forward and back.
As a consequence, it’s possible to increase or decrease the chain tension by changing the wheel’s position.
This makes horizontal dropouts a necessity for bicycles with one gear because those do not have a derailleur to tension the chain. The only exceptions are one-speed bicycles that use a dedicated chain tensioner.
- Rear Wheel Position Adjustment
Horizontal wheels permit the user to change the position of the rear wheel. This property could be used to increase or decrease the distance between the rear tire and the seat tube.
This option is beneficial for frames that have a tight rear wheel clearance and/or a cutout in the seat tube for the rear wheel.
If you change the rear tire model, the new one may inflate to a greater volume than the previous one and get too close to the seat tube. In that case, the user can slide the wheel backward to increase the clearance.
Conversely, if you switch from wide to narrow tires, there may be a needlessly large gap between the tire and the seat tube.
People who want optimal performance can increase the bike’s aerodynamic qualities and the power transfer from the chain to the rear wheel by sliding the wheel closer to the wheel cutout.
This is one of the reasons for the presence of horizontal dropouts on frames with a wheel cutout.
- Potential For Shorter Chainstays
There are two versions of horizontal dropouts – rear and forward facing.
At the moment, rear-facing dropouts are the more popular version because they allow the user to remove the wheel by pulling it back and away from the frame. As a result, the frame can have shorter chainstays.
In contrast, forward-facing dropouts were the norm back in the days of steel road bikes. At the time, the frames had longer chainstays and it was still possible to remove the rear wheel by sliding it forward and down. Today, this isn’t the case. Hence why rear-facing dropouts are more popular.
It’s also worth mentioning that the position of the wheel affects chainstay length too. By pushing the wheel closer to the seat tube, one is effectively shortening the chainstays because the axle which is the pivot point that matters is getting closer to the bottom bracket.
Having said that, vertical dropouts allow the use of very short chainstays too because the wheel moves vertically when removing and installing it.
What vertical dropouts don’t offer, however, is the precise adjustment. Vertical dropouts have a preset setting for the axle’s position which cannot be changed.
- Good For Single-speed Conversion
Frames with horizontal dropouts are superior for single-speed conversions because the rider can use the available axle room to tension the chain and avoid the use of a chain tensioner.
The Disadvantages of Horizontal Dropouts
- Problems when Paired With Quick-release Skewers
Horizontal dropouts receive a lot of criticism when paired with a quick-release skewer.
The main problem is that the skewer fails to squeeze the dropouts sufficiently and the rear wheel slides forward, becomes uneven and decreases the chain tension.
The issue is more likely to occur when riding up a very steep hill and generating lots of torque.
The recommended solution is to increase the grip between the quick-release and the dropouts. Normally, the sides of the quick-release ends that come in contact with the dropouts are serrated, but this isn’t the case for every model out there.
The outer part of the hub’s locknut should also be serrated. If the areа is clean (no grease, dirt…etc.) the grip is often sufficient as long as the serrations are present.
Some people go a bit more extreme and even remove the paint on the dropout contact area to maximize friction even further. This procedure has a downside – the area can corrode due to the absence of paint. Truth be told, however, if the ends and the locknut are serrated, they will chew up the paint anyway.
Note: The slippage problem is a lot more common for aluminum frames because the material is softer. When the rider pedals hard, the chain may pull the rear wheel forward with a lot of torque causing the quick-release ends to cut material from the dropouts, lose grip and slide towards the fork.
Another solution to this problem is to switch to solid-axle hubs secured to the wheel via nuts. Nutted axles offer a superior clamping power to quick-release skewers. Hence why track bikes continue to use solid-axles with nuts to this day.
- Removing The Rear Wheel Is More Tricky
Horizontal Dropouts make the removal of the rear wheel trickier.
If the dropouts are forward-facing, the chainstay bridge may prevent the user from removing the wheel without deflating the tire. This is a common scenario for retro road bikes. The problem is more pronounced when running the maximum tire size that the frame can accommodate.
If the dropouts are rear-facing, the problem mentioned above is not present, but the removal of the rear wheel is still trickier than it is with vertical dropouts.
When the dropouts are vertical, the rear wheel will drop out as soon as you undo the quick-release and press the derailleur forward to create chain slack.
With rear-facing dropouts, you have to pull the wheel back and out, and if you’re not familiar with the proper technique, the process can be a bit annoying.
And if the bike has disc brakes, you may also have to loosen the caliper bolts to get the wheel out. This is a common problem for bikes that have the caliper mounted on the seat stay. If the caliper is on the chainstay, the wheel should slide out without having to untighten the caliper bolts.
The Advantages of Vertical Dropouts
- Solid Wheel Position
Vertical dropouts do not give the axle room to move and subsequently, the wheel does not get crooked either during installation or riding.
- Stable Quick Release Skewers
In this case, the quick-release skewers do not have to fight a wheel that wants to go forward. As a result, it takes less clamping force to keep the wheel in place.
- Easier Rear Wheel Removal
To remove the rear wheel, the rider has to shift to the smallest sprocket at the back as well as to the smallest chainring, undo the quick release, and push the derailleur forward. Then, the wheel will drop out right away.
The Disadvantages of Vertical Dropouts
- Single-speed Mode Requires Chain Tensioners
If you want to run a single-speed set-up on a bike with vertical dropouts, you will need a chain tensioner because the dropouts do not allow you to move the wheel to adjust the tension.
Another option would be to keep the rear derailleur which also serves as a chain tensioner.
- Less Control
Vertical dropouts do not allow the rider to increase or decrease the space between the rear wheel and the seat tube. In some situations, this could result in poor clearance.
- Less Aero
Since the rear wheel is going down when removing it, the frame has to offer additional clearance in comparison to rear-facing horizontal dropouts, or else the user won’t be able to remove the wheel.
As a result, the wheel is further away and the chainstays are longer. Time trial bikes have rear-facing horizontal dropouts to avoid this situation.
Who Would Benefit From Horizontal Dropouts?
Horizontal dropouts shine the most on single-speed bikes E.g., BMXs, dirt jumpers, track bikes, fixies…etc.
They are also needed for bikes with a cutout wheel.
Who Would Benefit From Vertical Dropouts?
Vertical dropouts work best on geared bicycles for the following reasons:
- The wheel cannot slide forward and the quick-release clamping force is adequate.
- The derailleur tensions the chain, and the user does not have to move the wheel to increase the tension.
Removable Dropouts – The Best of Both Worlds
Some frames allow the rider to remove the dropouts and switch from vertical to horizontal or vise versa.
FAQ: Why Are Dropouts Called Dropouts?
Dropouts are called dropouts because the wheel will drop out/escape if there isn’t a quick-release or nuts holding it tight to the bike.
Technically, the rear facing horizontal dropouts found on track bikes and fixies are not dropouts because the wheel won’t drop out if the bolts get looser. The proper term is fork-end.