What is a hookless rim?
Normally, there is a hook on the rim of a wheel to fit a tire.
Rim hooks are designed to hook the bead of the tire to prevent the tire from coming off the rim. In the past, clincher and tubeless wheels usually had rim hooks.
With the spread of tubeless tires in the past few years, hookless rims have appeared. As the name implies, these rims have no hooks, and the tire contact surface of the rim is vertical.
Standards for hookless rims (TSS)
Hookless rims have a common standard to hold tires securely without hooks. The hookless standard is specified in ETRTO, the European standard for tires and rims.
The ETRTO standard for wheel rims consists of the following three elements
- rim diameter size
- tubeless or tubeless
- whether it is hookless
The rim diameter size is the ETRTO size, which is 622mm for a 700C wheel and 584mm for a 650B wheel, and the inner width of the rim is added to this size. For example, “622x23” means a 700C wheel with a rim inner width of 23mm.
Next, for tubeless rims, a normal rim with hooks is denoted by TC (Tubeless Crochet) and a hookless rim is denoted by TSS (Tubeless Straight Side). For example, 622-23-TSS means that the rim is tubeless and hookless.
In most cases, hookless wheels have the TSS designation on the wheel rim or on the manufacturer’s specifications, so you can tell if the wheel is based on the ETRTO hookless standard by the presence or absence of TSS.
Not all manufacturers indicate the tubeless rim standard, and some older tubeless wheels may not have TC on the rim, but if there is no clear indication of TSS, you can basically assume that it is a hook rim.
Advantages of hookless rims
There are two main types of merits of hookless rims: “merits of the wheel itself” and “merits of the tire to be mounted.
Advantages on the wheel side
- lower price
- weight reduction
First, since hooks are not inserted into the rim, the manufacturing process of the rim is simplified and the price is reduced. Especially in the case of carbon wheels, the manufacturing process seems to be much simpler than that of carbon wheels with rim brakes, if they are hook-less with disc brakes.
Also, of course, the weight is reduced by the amount of hooks. However, this is only for disc wheels. For rim wheels, the price is higher because the rim surface needs to be processed for thermal protection.
Advantages on the side of the tire to be mounted
Next, there are also advantages on the tire side.
- Increased adhesion between the tubeless tire and rim
- Increased air volume
- Increased inner width of the rim reduces tire deformation and increases rigidity
In the case of tubeless tires, the degree of adhesion between the tire and the rim determines how well the tire can hold air. If there is a hook, the contact point for trapping air is the narrow hook, which reduces the degree of adhesion.
Therefore, tubeless tires sometimes “leak air even when sealant is injected,” but the hookless design reduces air leakage because the tire is in close contact with the rim wall.
The hooks also increase the inner width of the rim, which reduces the amount of deformation of the tire and increases its rigidity. And since a wider tire means more volume inside the tire, the air volume can also be increased.
For the same tire size, a larger air volume allows for lower pressure operation and a more comfortable ride.
Disadvantages of hookless rims
Although hookless rims seem to have only advantages, they also have disadvantages.
- basically, they are for tubeless tires only
- may not be compatible with narrower tires
- lower pressure compared to clincher rims
- hookless compatible tires are required
First of all, the basics are all tubeless-only; it is rare to find a manufacturer like Mavic that says “hookless but clincher is OK,” and most manufacturers basically say “do not run with a tube in except in an emergency such as a flat tire.
Also, because of the increased inner width of the rim, the compatible tire size will be larger. In many cases, 28C or larger tires are recommended for hookless rim wheels.
Finally, compatible tires and air pressure.
Since hookless rims are constructed differently from conventional rims, both the rim side and the tire side must be manufactured exactly to the new ETRTO standard.
For example, for Panaracer’s Agilest TLR, the manufacturer has published detailed specifications for the rim side and compatible tire sizes.
Hookless rims are less safe if they do not conform to ETRTO because of the lack of hooks, so check to make sure they conform properly.
Also, with hookless rims, the maximum air pressure specified by the wheel side is lower than that of clinchers. However, this may not be a major issue, since it is often rather low if you consider using tubeless tires.
How to choose hookless rim wheels
Be sure to check if the wheel is clincher compatible!
Even if you operate tubeless, if you get a flat tire or an air leak while on the road, there is no zero chance that you will be able to ride back home as a clincher with a tube in as a last resort.
With this in mind, it is a major point to consider whether a hookless rim can be used as a clincher. Most manufacturers state that it is OK as long as it is not used regularly, but check carefully before purchasing.
Check to see if the wheel’s compatible tire size fits your bike.
When buying wheels, most people check to see if they can fit the tires of their choice. In many cases, hookless rims have wide rims and the minimum tire size is larger.
Most modern disc brake road bikes and gravel road bikes have a tire clearance of 32-38C, so this may not be a problem for many bikes, but check to be sure because you don’t want to be unable to use them after you buy them.
Choose a wheel from a well-known manufacturer!
Since hookless rims are still a new product on the market, it is recommended that you first choose a product from a well-known manufacturer. The manufacturers of hookless rim wheels include
ZIPP is a good choice.