This post discusses the differences between quick-release skewers using an internal and an external cam mechanism to mount the wheel to the bike’s dropouts.
What is a cam?
A cam is a rotating or sliding mechanical part transforming rotary motion into linear motion.
Quick-release skewers have an internal or an external cam that pushes one end of the quick-release and pulls the other into the dropouts of the bike.
As a result, the hollow axle through which the quick-release skewer passes is securely attached to the frame or fork.
The hollow axle remains stationary while the wheel’s hub rotates around it with the help of bearings.
(Most hubs have a cup and cone structure.)
Internal Cam Quick-Release
As the name suggests, those models have a cam mechanism hidden inside the skewer cap with a lever.
This is the quick-release skewer invented by Tullio Campagnolo in 1927 after he experienced extreme frustration when flipping his wheel to switch gears during a brutal winter race.
The lever controlling the movement of the cam and subsequently, the tightening and untightening of the quick-release skewer passes through the end cap too. (image below).
The cam is surrounded by a full-metal body. When the cam is rotated via the lever, it pulls (closing) or pushes (opening) the end of the quick-release without a lever.
External Cam Quick-release
In this case, the cam is outside and independent of the quick-release end cap as shown in the image below.
The Advantages of Internal Cam Skewers
Internal cam skewers are considered of better quality because the mechanism is hidden from the elements and entirely made of metal. For that reason, they are harder to find and tend to cost more.
- Superior Clamping Power
An internal cam skewer offers superior clamping strength and can therefore be used even on horizontal dropouts.
The clamping force comes from the metal construction of the cam lever which eliminates power transfer losses.
- Protection From The Elements
The cam is protected from the elements and thus retains its structure and performance. It’s recommended to put a drop of oil on it maybe once a year depending on the conditions that the bike faces daily.
The Disadvantages of Internal Cam Skewers
- Harder to Find
Quick-release skewers with internal cam require superior materials and a more complex production process even though the overall mechanism is simple.
Consequently, manufacturers have a lower incentive to make them given that even cheap quick-release skewers with external cams are good enough for vertical dropouts (the most common type these days.)
Both the retro and the modern internal cam skewers of Shimano are considered the best in the business.
I have a Centurian road bike from 1987 and it has a Shimano internal cam skewer at the back plus forward-facing dropouts. The quick-release skewer is still as solid as it gets.
However, if you go into an average bike shop, you will more than likely be offered a set of cheap quick-release skewers with external cams.
The cheapest way to acquire a good internal cam skewer is to search on the second-hand market for a Shimano model. It may be necessary to apply some WD-40 to remove the rust and a drop of lubricant to get it in proper shape.
That said, Shimano still makes modern quick-release skewers with internal cams. The table below contains popular models and their lengths.
|Shimano 105 HB-5800
The Advantages Of Quick-release Skewers With External Cams
- Price and Availability
External cam QR skewers are not fabulous, but they certainly get the job done when the bike has vertical dropouts.
The low demand for something better in conjunction with the cheaper technological process results in a big market share and large availability.
The Disadvantages of QR Skewers With External Cams
- Inferior Clamping Power
Quick-release skewers with external cams have the lowest clamping strength.
For that reason, they are not seen on the rear of bicycles with horizontal dropouts.
The table below contains the clamping pressure of different wheel fastening systems.
|Quick-release skewer with external cam
|approx. 550 kgf
|Quick-release skewer with internal cam
|approx. 550-800 kgf**
|Axle with Track nuts
|approx. 2450 kgf.
**The number depends on the quality of the skewer
The main reason for the inferior clamping power is the concave plastic/rubber washer between the cam lever and the cam.
When the lever is closed, the plastic/rubber washer compresses. The result is a loss of power transfer from the lever to the cam.
Subsequently, the skewer doesn’t clamp the dropouts as securely as possible. Of course, the clamping pressure can be increased by pre-tightening one or both ends of the skewer even more.
Another negative of plastic washers is that they create a mushy feeling when closing the skewer.
Higher-end QR skewers with external cams have concave washers made of brass. The brass washer reduces the power transfer loss because it doesn’t compress. As a result, the user can achieve decent clamping force with less effort. Also, the closing feels smoother and more “direct”.
The photo above shows a high-quality quick-release skewer with an external cam from Hope. Notice the yellow brass concave washer next to the lever.
FAQ: What about weight?
In general, more expensive QR skewers weigh less.
For instance, a quality quick-release skewer with a titanium axle, aluminum lever, and a brass washer weighs approximately 35 grams less than a basic model.
Of course, the final weight also depends on the length of the quick-release skewer too.
That said, the weight savings are inconsequential as they amount to 70-80 grams at best. Unless one is trying to build the lightest possible bicycle, a light QR skewer is not needed.
Below is a list of extremely light QR skewers for those interested in setting weight records:
|Zipp Ti Aero (external cam, brass washers, titanium axle, aluminum lever)
|Tune DC 100 / DC 130 (external cam, titanium axle, carbon lever)
|Enve TI ROAD Skewers
|DT Swiss RWS (bolted connection + ratchet lever)
What About Seat Post Clamps?
The same properties apply to seat post clamps securing the seat post to the seat tube.
Seat post clamps are less of an issue for the following reasons:
- If the seat post clamp does not provide enough clamping power, the outcome will be a sinking seat post. It’s annoying, but it’s unlikely to cause an accident.
- Seat posts do not require frequent adjustment once their height is set.
Summary: What You Need To Know
- QR skewers with internal cams are on the top of the food chain as they provide more clamping pressure and last longer because their mechanism is protected from the elements.
- QR skewers with internal cams can be used on all sorts of bicycles including models with horizontal dropouts.
- QR skewers with external cams are cheaper but do not offer enough retaining strength unless one is using vertical dropouts.
- The cheapest QR skewers with external cams have plastic washers that cause power transfer losses and a mushy feeling when using the lever.
- High-quality QR skewers with external cams have brash washers preventing power loss.