Wheels, tires and axles
What Fits on a Hookless Rim, and the Pressure Ceiling Once It Is Mounted
Whether a tire is allowed on a hookless rim depends on that tire's own manufacturer clearing it, not just on the tire being tubeless-ready - and once it's mounted, the maximum pressure your rim's maker publishes for that exact model is a hard stop, not a target. Here are the real published numbers from three current hookless lines, and how to find the number for your own rim.
The short answer
A tire being tubeless-ready does not by itself mean it is approved for your hookless rim - those are two separate claims, and either company can decline to back a combination even when both parts are otherwise solid tubeless components. Before you mount anything: first, confirm your rim's own spec sheet actually says hookless, straight-side, or TSS, not hooked. Second, go to that rim maker's own current tire-compatibility page for your exact model - not a retailer listing or a general chart - and read off the minimum tire width and the maximum pressure published for it. Third, check the tire's own sidewall or box for its printed maximum pressure and for a hookless or TSS mark. Fourth, run whichever of the two maximum-pressure numbers is lower, on every fill-up, not just the first one.
Real numbers, by rim, not a generic chart
The number that actually governs your setup is the one your rim's own manufacturer publishes for that exact model, not a number read off a generic width-based chart. Three current hookless lines below show how much that published number can vary from one rim to the next:
| Rim (maker and model) | Internal width | Minimum tire width | Maximum pressure |
|---|---|---|---|
| ENVE Foundation | 21mm | 25mm or wider | 90 psi / 6.2 bar with a 25mm tire; 80 psi / 5.5 bar with tires wider than 28mm |
| ENVE G23 | 23mm | 28mm or wider | 60 psi / 4.1 bar with a 32mm tire |
| ENVE AG25 | 25mm | 36mm or wider | 55 psi / 3.79 bar for 32-40mm tires; 50 psi / 3.44 bar for 41-50mm tires |
| Zipp TSS road (303, 404, 808 Firecrest; 353, 454, 858 NSW; 303 S) | varies by model | set by the tire's own manufacturer, not a fixed figure | 72 psi / 5 bar - one flat ceiling for every current TSS road wheel |
ENVE's own Foundation ceiling - 90 psi with a 25mm tire - is higher than the 5 bar figure that shows up repeatedly as 'the' hookless road number (Zipp states this as 72 psi; CADEX states it as 72.5 psi - both are rounding the same 5 bar figure slightly differently). Both are correctly sourced from the company that makes the rim. The 5 bar figure is what those specific companies set for their own rims; it is not a ceiling every hookless rim shares. Use the number your rim's own maker publishes, not the number that is easiest to find elsewhere.
Tubeless-ready and hookless-approved are not the same claim
A tubeless-ready tire, marked TLR or TLE, is built to hold air without a tube on a tubeless rim bed. Being hookless-approved is a separate, further claim: the tire's own manufacturer has confirmed the bead stays seated on a rim with no mechanical hook holding it in place. Rim makers check for that second claim in different ways:
| Rim maker | How a tire qualifies | Where to check |
|---|---|---|
| ENVE | For its Foundation and SES AR road wheelsets, ENVE tests and publishes its own approved/recommended tire list; an off-list tire is mounted at the rider's own risk. For its G Series and Foundation AG gravel wheels - which include the G23 and AG25 featured above - ENVE instead states only two requirements: the tire must be Straight Side Wall (TSS) Hookless compatible, and pressure must stay under the rim's stated max rating. No approved list applies to that gravel line. | ENVE's Tire Compatibility page |
| Zipp (SRAM) | Any tire its own manufacturer labels TSS-compatible qualifies; a smaller set is also dual-tested by Zipp together with that tire's manufacturer | Zipp's Hookless Tire Compatibility guide |
| CADEX | The tire must be declared hookless-compatible by its own manufacturer; CADEX then publishes a joint chart of the tires that clear that bar | CADEX's Hookless Compatibility page |
In every version, the tire's own manufacturer has to sign off, not just the rim's. If your tire is not named on either company's page, that does not automatically mean it will fail - it means the two companies have not published an agreement that the combination is safe, and contacting the tire's manufacturer directly is the only way to close that gap before you mount it.
Why the ceiling is a hard stop, not a suggestion
On a hooked rim, a small lip curls inward over the tire bead and physically blocks it from climbing off the rim under pressure - WTB, which builds only hooked rims, describes this lip as the point on the rim wall that grips the bead. A hookless rim has no such lip. The tire stays seated for two reasons only: the bead's diameter is made to match the rim closely enough to hold an airtight seal, and the bead material itself is stiff enough to resist stretching outward under pressure, according to CADEX's own description of its hookless rims. Push the pressure past the number the rim's maker published and you are testing both of those margins at once, with nothing mechanical backing them up. That is a different failure than a pinch flat, where a tube gets caught between the tire and the rim on an impact - here, the tire itself can come off the bead seat, which is why the number on the rim is a ceiling and not a target to ride up against. ENVE adds one more point worth knowing: if a hookless rim's bead seat is deformed by an impact or a crash, the tire is then less likely to stay seated even below the normal maximum pressure - a reason to check the rim itself, not just the tire, after a hard hit.
How to tell if your rim is actually hookless
The reliable way is to read your rim's own spec sheet, box, or manual, where the maker states hookless, straight-side, or TSS outright, or gives the ISO code SS or TSS - see the full list of ISO/ETRTO rim and tire codes for how those are marked. If you only have the wheel in hand: look at the inner wall the tire bead rests against, just below the rim's outer edge. On a hooked rim there is a small lip or ridge curling inward that the bead tucks under; a hookless rim's wall runs straight or gently curved with no such lip. Treat that as a starting point, not a final answer - some rims built for low-pressure gravel or all-road use are semi-hooked, a separate category the maker treats differently from either a fully hooked or a fully hookless design. Reserve, for instance, states that its own road rims are semi-hooked rather than hookless, specifically to avoid the width and pressure restrictions a hookless design carries. When your spec sheet uses the word semi-hooked, follow that maker's own number for that word, not the hookless figures on this page.
Where the numbers come from
The requirement that a hookless rim and its approved tires be tested and published together comes from ETRTO, the European Tire and Rim Technical Organization, working with ISO. The standard itself is sold as a paid document and its tables are not reproduced here; what is on this page is what ENVE, Zipp, CADEX, Schwalbe, and Continental each state on their own site about how they apply it to their own products. One specific, citable change: in 2023, ISO and ETRTO tightened the rule so a mounted tire cannot measure more than 2mm wider than its marked width. Zipp's own explanation of that change is that many tires long labeled 28mm, shaped for an older generation of narrower rims, now measure oversize on today's wider hookless rims and fall outside the current recommendation on rims like its 303 Firecrest.
Before you mount that tire
- Get your exact rim model's page from the rim's own manufacturer - not a retailer listing or a forum thread - and read off the minimum tire width and maximum pressure it states.
- Read the tire's sidewall or box for its own maximum pressure and any hookless or TSS marking. No marking and no statement from that tire's manufacturer means the combination is not confirmed yet.
- Compare the two maximum-pressure figures and commit to the lower one on every fill-up, not just the first.
- Recheck the maximum pressure when you change tire width. ENVE's own Foundation figures above show why: the same rim allows 90 psi at 25mm but drops to 80 psi once the tire is wider than 28mm.
- After any hard impact or crash, check the rim again before your next ride - a deformed bead seat is what more than one manufacturer points to as the actual point of failure.
- If you want to run a tube: ENVE marks Foundation, G23, and AG25 each 'Inner-Tube Compatible: Yes, Only with Tubeless/Tubeless Ready Tire,' and Zipp allows a tube inside a TSS-compatible tire on its hookless rims. Hookless does not by itself rule out a tube - it rules out a tire that is not tubeless/tubeless-ready or not declared compatible. For the tube itself, see how to size a tube from your tire's ISO marking.
None of this replaces reading your own rim's current page. Approved-tire lists are updated as brands test new tires, so treat any list - including the examples above - as a snapshot, and check the current version on the rim maker's own site before you buy. If you are setting the tire up tubeless rather than with a tube, getting the sealant dose and topping-up interval right is the next thing to settle once the tire and pressure are decided.
Check it on your own equipment
These take you to the manufacturers and standards bodies the page draws on, so you can look up your exact model.
- Manufacturer specification
ENVE's Tire Compatibility chart (opens in a new tab)The approved/recommended tire list and the exact minimum tire width and maximum pressure ENVE publishes for each hookless rim model, including Foundation, G23, and AG25. — enve.com - Manufacturer specification
Zipp's Hookless Tire Compatibility guide (opens in a new tab)Zipp's flat 5 bar (72 psi) ceiling for every TSS road wheel, plus the list of tires each tire brand has declared TSS-compatible. — www.sram.com - Manufacturer specification
CADEX's Hookless Compatibility page (opens in a new tab)CADEX's joint compatibility table of tire models each tire manufacturer has declared hookless-compatible for CADEX rims. — www.cadex-cycling.com - Official support page
Schwalbe's Hookless Rims technology FAQ (opens in a new tab)Schwalbe's own statement of the ETRTO hookless pressure rule and which of its own tires are TLE/TLR rated for hookless rims. — www.schwalbe.com
What this page does not tell you
- Approved-tire lists change as brands test new tires. Check the rim maker's current page before you buy, not a saved copy of it.
- The figures on this page are what ENVE, Zipp/SRAM, and CADEX each publish for their own current hookless rims. Other rim makers set their own separate numbers for their own models and are not covered by the table above.
- The ETRTO/ISO standard itself is a paid publication. The numbers on this page are each manufacturer's own stated figures, not a reproduction of the standard's tables.
Sources
12 documents, each with the facts on this page it supports. Manufacturers revise specifications, so every source is dated — open it before you buy.
- ENVE's Foundation hookless road rim has a 21mm internal width, requires a tire 25mm or wider, and carries a maximum pressure of 90 psi (6.2 bar) with a 25mm tire, dropping to 80 psi (5.5 bar) with any tire wider than 28mm.
- ENVE's G23 hookless gravel rim has a 23mm internal width, requires a tire 28mm or wider, and carries a maximum pressure of 60 psi (4.1 bar) with a 32mm tire.
- ENVE's AG25 hookless all-road/gravel rim has a 25mm internal width, requires a tire 36mm or wider, and carries a maximum pressure of 55 psi (3.79 bar) for 32-40mm tires and 50 psi (3.44 bar) for 41-50mm tires.
- ENVE states that when a tire's own maximum pressure and the rim's published maximum differ, the lower of the two becomes the actual maximum for the wheel-and-tire system.
- ENVE's Foundation, G23, and AG25 hookless rims each carry the spec line 'Inner-Tube Compatible: Yes, Only with Tubeless/Tubeless Ready Tire' - a tube is permitted, but only inside a tire that is itself tubeless or tubeless-ready, not any standard clincher tire.
- ENVE maintains a published approved/recommended tire list, with an off-list tire mounted 'at your own risk,' specifically for its Foundation and SES-AR road hookless wheelsets. For its G Series and Foundation AG gravel wheels - which include the G23 and AG25 featured on this page - ENVE instead states only two requirements: the tire must be Straight Side Wall (TSS) Hookless compatible, and pressure must stay under the rim's max rating. No approved list applies to the gravel line.
- Zipp states that its TSS (hookless) road wheel and tire systems should never be inflated above 5 bar, which Zipp's own page states as 72 psi.
- Zipp states its TSS rims are not compatible with any tire whose own minimum required pressure is already above 5 bar (72 psi).
- Zipp qualifies a tire for its hookless rims when that tire's own manufacturer labels it TSS-compatible; Zipp does not require the tire to appear on a Zipp-only closed list, though it separately dual-tests a smaller set of tires jointly with the tire's manufacturer outside the standard size range.
- Zipp limits its 303 XPLR gravel hookless rim to tires between 40mm and 60mm wide.
- Zipp's current TSS (hookless) road wheels are organized into three named lines, each with its own Zipp support page confirming a hookless rim design: the 303, 404, and 808 Firecrest Collection; the 353, 454, and 858 NSW Collection; and the 303 S.
- Zipp permits an inner tube inside a tire mounted on its hookless rims, as long as the tire itself is still TSS-compatible.
- In 2023, ISO and ETRTO jointly updated their hookless standard so a mounted tire's measured width cannot exceed its marked width by more than 2mm; Zipp states this is why many tires labeled 28mm, shaped for older, narrower rims, now measure oversize on newer, wider hookless rims such as its 303 Firecrest and fall outside the current recommendation.
- Zipp states that minimum tire width for its hookless wheels depends on the wheel model and the tire brand rather than one fixed number, and that maximum tire size is limited separately by frame clearance, which it says to confirm with the frame's manufacturer.
- CADEX states that the maximum pressure printed on its hookless-compatible tires is 72.5 psi (5 bar), and that this figure is not to be exceeded.
- CADEX requires a tire mounted on its hookless rims to be tubeless and specifically declared hookless-compatible by that tire's own manufacturer, and publishes its own joint compatibility table built from those declarations.
- CADEX explains that a tire stays seated on its hookless rim because the tire bead's diameter matches the rim closely enough to form an airtight seal, and because the bead material is stiff enough to resist stretching under pressure.
- Schwalbe states that under the ETRTO standard, road hookless rims carry a maximum pressure of 5 bar, and that its hookless/straight-side-compatible tires are limited to its own TLE/TLR (tubeless-ready) models.
- Continental states that on a hookless rim, both the tire's own maximum inflation pressure and the rim's must be checked, and that whichever figure is lower is the one to follow.
- WTB defines a rim's bead hook as the point on the inner wall that grips and holds the tire bead, and states that all of WTB's own rims include this hook, while noting that some other manufacturers' rims do not.
- Reserve states that its own road rims are semi-hooked rather than hookless, a design choice it makes specifically to avoid the tire-width and pressure restrictions that come with a fully hookless rim.
- ENVE states that if a hookless rim's bead-seat dimension is altered by impact or crash damage, the tire is then unlikely to stay seated on the rim.