This post analyzes the installation of a cargo rack on a bicycle with a rear shock.
The Problems With Installing a Rear Rack On a Full Suspension Bike
- Movement Of the Rear Triangle
The rear triangle of the frame is formed by the chainstays, seat stays, and the seat tube. In the case of full-suspension bikes, the rear triangle has to move so that the shock can compress and decompress.
Normally, the legs of a rear rack attach to а set of eyelets near the rear axle whereas the stabilization stays are mounted to the seat stays. If the bike doesn’t have eyelets on the seat stays, the user can also attach the stabilization seat stays to а seat post collar with rack mounts.
If rear a rack is installed on a full-suspension bike with the help of a seat post collar, the rear shock will not be able to compress freely.
Since the stabilization stays are usually made of soft metal, they will most likely bend when the rear tire meets a bump, and the shock tries to close.
The solution to this problem is to install a rack that mounts only to the rear triangle of the frame. When that condition is met, the shock will be free to operate as intended.
This leaves the user with three options:
- Buy a rack specifically made for full-suspension bikes
- Install a seat post rack
- Modify an existing rack to fit a full-suspension bike.
Racks Designed For Full Suspension Frames
Below is a list of rear racks compatible with a full-suspension frame by default:
- Thule Pack ‘N Pedal Tour Rack
The Thule Pack ‘N Pedal Tour Rack has 2 pairs of connection points that wrap around the seat stays. The rack does not require rack eyelets and does not intervene with the operation of the rear shock.
The capacity of the rack is 25lbs/11.36kg when installed on the rear (22lbs when installed on the fork).
- Old Man Mountain Rack
The Old Man Mountain Divide rack is another model that can be installed on a full-suspension bike without rack eyelets. The rack attaches to the rear axle (it comes with a quick-release skewer) and the seat stays. For the seat stay attachment, the unit uses adapters connected to the bike via zip ties.
The weight limit of the rack is 70lbs/31.81kg when using axle support and 55lbs/25kg when relying on the rack eyelets of the bike.
The video below demonstrates the installation process.
- Topeak TetraRack
Topeak’s TetraRack is another rack model that can be mounted on a bike with a suspended rear end. Similarly to the other products, it attaches to the seat stays via a loop tensioning system. The weight limit of the rack is 19.8lbs/9kg.
The video below shows the installation process in greater detail:
Seat Post Mounted Rear Racks
Racks that mount directly to the seat post of the bicycle have no effect on the rear triangle’s movement and are therefore another option for full-suspension racks.
The advantages of seat post racks are:
- Compatible with almost any bike
- Cheaper than dedicated full-suspension rear racks
- Greater number of choices
That said, seat post racks have massive downsides too:
- High center of gravity resulting in instability
- Low weight limit
- Poor architecture (the joint/weld near the connection point is under great stress due to the long moment arm. Thus, the chances of the rack failing at that location are significant.)
- Insufficient stabilization (seat post racks often get out of position)
The downsides of seat post racks make them suitable only for transporting light cargo (e.g., repair kit, some clothing, food…etc.)
Truth be told, seat post racks are often inferior to saddlebags.
A large saddle bag will fit about as much as a seat post rack could support while also protecting the cargo from the elements and making it close to impossible to lose an item.
Modifying an Existing Rear Rack
Another option is to make a standard rear rack work on a full-suspension bike. This method saves money because basic racks tend to be notably cheaper than the models created specifically for full suspension bicycles.
There are two problems that prevent a rear rack from being installed on a full-suspension frame right away:
- No rack eyelets
- No connection points for the stabilization rack stays
The absence of mounting points for the support struts can be overcome via a set of clamps that go onto the seat stays or by using a rack that connects to the quick-release skewer.
Standard P-clamps are the most affordable and the easiest to find clamps. To choose the right size P-clamp, measure the diameter of the seat stay area where the clamp would go. It’s also recommended to wrap isolation around the location that the P-clamps will grab for extra frame protection.
The downside of the P-clamp approach is that they aren’t as maximally strong. Nonetheless, if the rack isn’t going to be overloaded, they should be sufficient.
If you want maximum strength, you can fabricate (or pay someone to do it) a P-clamp made of stronger steel.
Alternatively, you can buy a rear rack that comes with a set of seat stay clamps by default. (image below).
Note: Another option is to use a set of pipe clamps that have a soldered/welded nut onto them. (image below). The pipe clamp grabs onto the seat stay. Then the legs of the rack are connected to the side nut.
Advice: When choosing a rack, it’s better to stay away from models that come with stabilization stays that have to be bent. Those stays are too soft to offer maximum support. When installing the rack on a standard bike, this isn’t a big deal, but when mounting the unit on a full-suspension bike every percentage of extra support is appreciated.
It’s better to go for a rear rack with stays that accommodate the bike by pivoting instead of via bending.
The second issue (stabilization stays connection) can also be solved by using P-clamps to attach the rack’s stays to the seat stays so that the rear shock can compress as intended.
The stays of the rack do not support the bulk of the weight and serve primarily as stabilizers. Thus, the P-clamps are even more adequate as adapters.
That said, stronger clamps can still be used. It may also be necessary to extend the stabilization stays with a set of brackets.
(Note: In some cases, the stabilization stays are cut once the rack is installed. If the rack is old or bought second-hand, it’s possible that the previous user has cut the stays, and they are now insufficiently long to reach the seat stays of a suspension bike.)
The Advantages of Installing a Rear Rack On a Full Suspension Bike
A rear rack increases the utility of a full-suspension bike by allowing you to transport cargo. Thus, if you’re using your bicycle primarily for commuting, a rack would greatly facilitate that task. A pair of panniers or even a single one will allow you to carry a surprising volume of items.
- Less Joint Stress and More Comfort
Beginner commuters often choose to carry a backpack. Initially, this seems like a great choice because the bike weight and handling do not change. However, the backpack suffocates your back even when it’s extremely cold outside. Also, the backpack is harmful to the kidneys since every irregularity/bump results in vibrations causing a micro-punch to your waist when the bag is loaded.
A rear rack takes the weight off your back and puts it on the bike.
The Disadvantages of Installing a Rear Rack On a Full Suspension Bike
- Extra Weight
A rear rack as well as the mounting hardware that it comes with could easily add 2kg/4.4lbs to а bike.
In the world of cycling, this is a lot of weight. Full-suspension bikes amplify this issue because they tend to weigh notably more than hardtails and fully rigid bikes.
The additional weight makes it more difficult to carry the bike, perform tricks and climb. Therefore, a rear rack has no business on a suspension bike that is actually used for competing in an MTB race.