Gravel Tire Specs Explained: Width, TPI, Compound, and Casing
The Short Answer
Width determines fit and comfort. TPI determines ride feel and durability. Compound determines grip and longevity. Casing determines puncture resistance. Tubeless markings determine whether the tire will work without a tube. Once you understand these five things, you can read any tire sidewall and know exactly what you're getting.
Tire labels are written for engineers. Width in millimetres, ETRTO codes, TPI ratings, compound names that vary between manufacturers — none of it is designed to help a rider make a decision. This article translates all of it into terms that actually inform a purchase.
If you're new to gravel tires, read this before anything else. If you already know the basics, use it as a reference when a spec doesn't make sense.
What does gravel tire width mean?
Gravel tire width is measured in millimetres and refers to the inflated external width of the tire at a reference pressure on a standard test rim. The number on the sidewall is a target; your actual mounted width will vary by 2–4mm depending on your rim's internal width.
Wider rims make tires mount wider. Narrower rims make tires mount narrower. A 40mm tire on a 21mm internal-width rim might measure 38.5mm. The same tire on a 25mm internal-width rim might measure 42mm.
What each width range is good for:
| Width | Best for | Trade-off |
|---|---|---|
| 35mm | Road-heavy mixed routes, speed-focused gravel events | Less comfort on rough terrain; less grip at low pressure |
| 38–40mm | The versatile sweet spot — mixed terrain, most bikepacking | No significant trade-offs; this is the default for a reason |
| 42–45mm | Technical terrain, loaded touring, rough or unpredictable surfaces | Marginally slower on tarmac; may not clear all frames |
| 47–50mm | Remote bikepacking, expedition touring, very rough routes | Requires frame clearance check; significant tarmac drag |
Before choosing a width: measure your frame's actual tire clearance with a calliper at the narrowest points — the chainstay gap and fork crown. Manufacturer-stated clearances are frequently optimistic. Add at least 3mm of clearance beyond the tire width to account for mud, rim width variation, and sidewall flex under load.
What does TPI mean on a gravel tire?
TPI stands for Threads Per Inch — a measure of the density of the fabric threads in the tire casing. Higher TPI means more, finer threads packed into the same space, producing a more supple and lighter casing.
What TPI actually affects:
- Ride quality: A higher-TPI casing conforms more readily to the surface beneath it, absorbing vibration rather than transmitting it. On rough gravel over long distances, this is a meaningful comfort difference.
- Rolling resistance: A supple, high-TPI casing deforms more easily over obstacles, spending less energy bouncing off them. Premium high-TPI tires have measurably lower rolling resistance than lower-TPI alternatives of the same width.
- Weight: Higher TPI generally means lighter — finer threads add up to less rubber per casing.
- Durability: This is the trade-off. Finer threads are more vulnerable to cuts and abrasion. A 60 TPI casing absorbs punishment that would cut through a 320 TPI racing casing.
| TPI | Characteristics | Best for |
|---|---|---|
| 60 TPI | Durable, stiffer, heavier, cut-resistant | Training, commuting, rough terrain, value touring |
| 120 TPI | Balanced — the most common for general gravel use | Mixed-terrain riding, general bikepacking |
| 180–240 TPI | Supple, lightweight, efficient | Performance-oriented riding, lighter loads |
| 320+ TPI | Maximum suppleness, highest cost, most fragile | Racing, fast touring on quality surfaces |
The practical decision: For bikepacking and loaded touring, 120 TPI with a protection layer is the right balance. For day rides or performance-focused riding on quality surfaces, 180–240 TPI unlocks meaningfully better ride feel and rolling speed.
What does gravel tire compound mean?
The rubber compound is the material of the tread itself — the part that contacts the surface. It determines three things simultaneously: rolling resistance, grip, and longevity. These three things pull in different directions, and every compound is a negotiated position between them.
The core tension:
- Harder compound → lower rolling resistance + longer wear life + less grip (especially in cold and wet)
- Softer compound → higher rolling resistance + shorter wear life + more grip
How manufacturers name their compounds (using Schwalbe's Addix system as a common reference):
| Name | Hardness | Best conditions |
|---|---|---|
| Addix Speed | Hardest | Dry, warm, tarmac and hardpack |
| Addix SpeedGrip | Medium-hard | Mixed terrain, most conditions |
| Addix Soft | Softer | Wet, cold, technical |
Other brands use different names — Vittoria's G+ Graphene, Continental's BlackChili, WTB's DNA — but the hierarchy is the same: softer grips more, wears faster; harder rolls faster, loses grip first when conditions deteriorate.
Dual compound construction appears on premium tires: a harder centre tread for rolling efficiency, softer shoulder rubber for cornering grip. This is the most practical engineering solution to the compound trade-off, and worth the price premium if you regularly ride in variable conditions.
The practical implication most riders miss: compound hardness matters most in two conditions — cold temperatures and wet surfaces. A hard compound that performs well in warm, dry conditions can feel like a different tire at 5°C or in rain. If you ride year-round or in variable European weather, prioritise a mid-hardness or dual compound over pure rolling-speed optimisation.
What is a gravel tire casing?
The casing is the structural fabric of the tire — the layers of threads that give it shape, absorb impacts, and determine how much puncture resistance sits between you and the surface.
Two components of the casing matter for buying decisions: thread construction (see TPI above) and protection layers.
Most gravel tires add a secondary protective layer beneath the tread and sometimes the sidewalls. This layer intercepts sharp objects before they reach the tube or sealant. Common examples:
- Schwalbe MicroSkin: A full-coverage protection layer over the entire casing, including sidewalls. One of the most effective systems in the category. Adds approximately 30–50g.
- Teravail Durable: A thicker overall build rather than a distinct layer. Adds significant weight but genuinely resists sidewall cuts better than lighter alternatives.
- WTB TCS Tough / SG2: Similar logic — a puncture protection layer beneath the tread. Effective on the tread; variable sidewall coverage depending on model.
- Continental ShieldWall: A beaded protection system focused on tread puncture resistance. Less sidewall protection than MicroSkin.
For touring and bikepacking, a protection layer is not optional — it's the difference between a tire that completes a long route and one that doesn't. For short rides on known terrain, a lighter unprotected casing is an acceptable trade.
What do tubeless markings mean?
Gravel tires come in three configurations:
- Tubeless Ready (TLR or TLE): The tire bead is engineered to seat airtight on a tubeless rim and the casing has low enough porosity to hold air with latex sealant. No conversion kit required. This is the correct configuration for most gravel riding.
- Tubeless Compatible: A looser designation that means the tire may work tubeless, but this is not guaranteed by engineering. Some tires marked "compatible" set up reliably; others don't. Always verify with the manufacturer before assuming.
- Standard / clincher (folding or wire bead): Requires an inner tube. Can sometimes be converted to tubeless with a conversion kit and heavy sealant application, but this is unreliable and not recommended for routes where a failure is inconvenient.
Why tubeless matters for gravel: running tubeless allows you to use 5–10 psi lower pressure than with a tube, because there's no pinch flat risk. Lower pressure means the tire conforms more to the surface, which improves grip and reduces rolling resistance on rough terrain — often more than any tire or compound upgrade. It also means small punctures seal automatically.
How to read a gravel tire sidewall
A typical sidewall label contains everything you need to know about a tire. Using the Schwalbe G-One Allround as an example:
SCHWALBE G-ONE ALLROUND — 40-622 — TLR — MicroSkin — Addix SpeedGrip — Max 5.0 Bar / 73 PSI
- G-ONE ALLROUND — model name and intended category
- 40-622 — ETRTO sizing: 40mm width, 622mm bead seat diameter (= standard 700c wheel)
- TLR — Tubeless Ready
- MicroSkin — casing protection layer
- Addix SpeedGrip — rubber compound
- Max 5.0 Bar / 73 PSI — structural maximum pressure (not a recommendation — see the pressure guide)
Use the ETRTO code (40-622) rather than the informal designation (700 × 40c) when verifying compatibility — the ETRTO code is standardised, while informal sizes vary between manufacturers.
FAQ: Gravel Tubeless Setup
What width gravel tire should I use?
For most riders on mixed terrain, 40mm is the right starting point — it balances rolling efficiency with comfort and grip on varied surfaces. Go narrower (35–38mm) if your routes are road-heavy or speed-focused; wider (42–45mm) if you're carrying load or riding technical terrain. Always check your frame's actual clearance before buying a wider tire.
Is higher TPI always better on a gravel tire?
No. Higher TPI means a more supple, lighter casing — better ride feel and lower rolling resistance — but also more vulnerability to cuts and abrasion. For bikepacking and touring on rough terrain, a 120 TPI casing with a protection layer is more practical than a 240 TPI racing casing. For smooth surfaces and lighter use, higher TPI is worth it.
Does compound matter as much as tread pattern?
Yes, and in some conditions more. Tread pattern determines how the tire engages loose surfaces; compound determines how the rubber behaves on any surface, especially when cold or wet. A soft compound with a modest tread pattern will outgrip a hard compound with aggressive knobs in cold, wet corners. Both matter — but compound is the variable most riders underweight.
What does TLR mean on a gravel tire?
TLR stands for Tubeless Ready. It means the tire bead and casing are engineered to work without an inner tube, holding air with latex sealant. It is the correct tubeless configuration for gravel riding. "Tubeless Compatible" is a looser designation that may or may not deliver reliable results — verify before assuming.
Can I use a tubeless tire with a tube?
Yes. A tubeless-ready tire runs perfectly well with an inner tube. Many riders set up tubeless but carry a tube as a backup — if sealant and plugs can't fix a puncture, they mount the tube and ride home. The tube goes in exactly the same way as in a non-tubeless tire.
What is the ETRTO code on a gravel tire?
ETRTO (European Tyre and Rim Technical Organisation) is the standardised sizing system for bicycle tires. The code appears as two numbers separated by a hyphen — for example, 40-622. The first number is the tire width in millimetres; the second is the bead seat diameter of the rim it fits. 622mm is standard 700c. This code is more reliable than informal designations like "700 × 40c," which vary between manufacturers.