SILCA Tire Pressure Calculator
Find your exact aerodynamic and rolling resistance impedance breakpoint using the pro-tour methodology developed by SILCA. Covers road, gravel, MTB, and cyclocross — clincher, tubeless, and tubular. Also see the road bike PSI guide for full width tables.
Real-World Example
65 kg Rider · 47mm Gravel Tire — SILCA Calculator Output
Inputs: 65 kg total system weight (rider + bike + gear) · 47mm measured tire width · high-performance tubeless · gravel weight distribution · moderate group ride pace
| Wheel · Surface | Front (PSI / Bar) | Rear (PSI / Bar) |
|---|---|---|
| 650B (27.5") · Cat 1 Gravel — hardpack / light gravel | 31.7 PSI (2.19 bar) | 33.2 PSI (2.29 bar) |
| 650B (27.5") · Cat 2 Gravel — moderate gravel | 28.7 PSI (1.98 bar) | 30.0 PSI (2.07 bar) |
| 700C (29") · Cat 1 Gravel — hardpack / light gravel | 30.0 PSI (2.07 bar) | 31.4 PSI (2.17 bar) |
| 700C (29") · Cat 2 Gravel — moderate gravel | 27.2 PSI (1.88 bar) | 28.4 PSI (1.96 bar) |
Values computed with the SILCA impedance algorithm (1 Bar = 14.504 PSI). Cat 1 = hardpack dirt / light gravel. Cat 2 = moderate mixed gravel. Enter your exact inputs below for a personalised result.
Typical Scenarios
SILCA Tire Pressure: Common Examples
Smooth tarmac vs rough pavement
A 175 lb (79 kg) total system weight running high-performance tubeless tires with a measured width of 30mm on new smooth tarmac should run 73.5 PSI (5.07 bar) rear / 71.7 PSI (4.94 bar) front. Transitioning to rough, worn pavement, the algorithm drops to 69.6 PSI (4.80 bar) rear / 67.9 PSI (4.68 bar) front — a 3.9 PSI reduction that prevents vibration absorption from wasting watts at speed.
Stated vs measured width error
A rider inputs their tire's stated width of 28mm and the calculator returns 82 PSI rear. But their tire, mounted on a modern 25mm internal-width rim, actually measures 31mm. The correct input gives 70 PSI (4.83 bar) rear — a 12 PSI difference that completely changes rolling resistance and comfort. Always measure; never guess.
Gravel event scenario
A 175 lb (79 kg) system on a 40mm measured gravel tire (650B wheel) targeting hardpack dirt should run 44.9 PSI (3.10 bar) rear / 42.9 PSI (2.96 bar) front (cat1-gravel, high-performance tubeless). Moving to moderate mixed gravel drops both by 4.1 PSI to 40.8 PSI (2.81 bar) rear / 39.0 PSI (2.69 bar) front. Switching to a mid-range tubeless casing on hardpack reduces output by a further 1.3 PSI to 43.6 PSI (3.01 bar) rear / 41.7 PSI (2.88 bar) front.
Quick Reference
SILCA PSI & Bar by Surface Category
175 lb (79.4 kg) total system weight · 30mm measured width · 700C · road weight distribution · high-performance tubeless · moderate group ride pace
| Surface Condition | SILCA Category | Front (PSI / Bar) | Rear (PSI / Bar) |
|---|---|---|---|
| New, Smooth Tarmac | Cat 1 | 71.7 PSI (4.94 bar) | 73.5 PSI (5.07 bar) |
| Rough / Worn Pavement | Cat 2 | 67.9 PSI (4.68 bar) | 69.6 PSI (4.80 bar) |
| Hardpack Dirt / Light Gravel | Cat 3 | 65.0 PSI (4.48 bar) | 66.7 PSI (4.60 bar) |
| Moderate Gravel | Cat 4 | 59.1 PSI (4.07 bar) | 60.6 PSI (4.18 bar) |
| Deep / Chunky Gravel | Cat 5 | 48.0 PSI (3.31 bar) | 49.2 PSI (3.39 bar) |
Use the calculator above for your exact weight and measured tire width. When in doubt between two surface categories, choose the rougher one.
Bike Tire Pressure Quick Reference Guide (PSI & Bar)
Universal baseline pressure charts for road, gravel, mountain, and commuter bikes. All values are listed in dual units (PSI and Bar) across exact rider weight brackets (kg & lbs).
Tire Pressure by Rider Weight (kg & lbs) & Discipline
Tubeless baseline (Dry / Mixed terrain)| Rider Weight | Road 700×28c (Front / Rear) | Gravel 700×40c (Front / Rear) | MTB Trail 29×2.4" (Front / Rear) |
|---|---|---|---|
| 55 kg (121 lbs) | 58 / 62 PSI 4.0 / 4.3 bar | 31 / 33 PSI 2.1 / 2.3 bar | 17 / 19 PSI 1.2 / 1.3 bar |
| 65–66 kg (143–146 lbs) | 65 / 70 PSI 4.5 / 4.8 bar | 35 / 37 PSI 2.4 / 2.6 bar | 19 / 22 PSI 1.3 / 1.5 bar |
| 72–75 kg (159–165 lbs) | 71 / 76 PSI 4.9 / 5.2 bar | 38 / 41 PSI 2.6 / 2.8 bar | 21 / 24 PSI 1.4 / 1.7 bar |
| 85 kg (187 lbs) | 78 / 83 PSI 5.4 / 5.7 bar | 42 / 45 PSI 2.9 / 3.1 bar | 23 / 26 PSI 1.6 / 1.8 bar |
| 93–95 kg (205–209 lbs) | 84 / 89 PSI 5.8 / 6.1 bar | 45 / 48 PSI 3.1 / 3.3 bar | 25 / 28 PSI 1.7 / 1.9 bar |
| 105 kg (231 lbs) | 89 / 94 PSI* 6.1 / 6.5 bar | 49 / 52 PSI 3.4 / 3.6 bar | 27 / 30 PSI 1.9 / 2.1 bar |
*Note: For hookless road rims, the ETRTO maximum pressure is 72.5 PSI (5.0 bar). Riders over 80 kg on hookless rims should use 30mm or 32mm tires to stay safely below the pressure ceiling.
Road Bike Pressure by Tire Width (75 kg / 165 lb Rider)
| Tire Width | Tubeless (PSI / Bar) | Inner Tube (PSI / Bar) |
|---|---|---|
| 23mm | 80–85 PSI (5.5–5.9 bar) | 90–95 PSI (6.2–6.6 bar) |
| 25mm | 72–78 PSI (5.0–5.4 bar) | 80–85 PSI (5.5–5.9 bar) |
| 28mm | 65–72 PSI (4.5–5.0 bar) | 72–78 PSI (5.0–5.4 bar) |
| 30mm | 58–65 PSI (4.0–4.5 bar) | 64–70 PSI (4.4–4.8 bar) |
| 32mm | 52–58 PSI (3.6–4.0 bar) | 58–64 PSI (4.0–4.4 bar) |
MTB Pressure by Tire Width (Tubeless, 75 kg / 165 lb Rider)
| Tire Width | Front (PSI / Bar) | Rear (PSI / Bar) |
|---|---|---|
| 2.1"–2.25" | 23–25 PSI (1.6–1.7 bar) | 26–28 PSI (1.8–1.9 bar) |
| 2.3"–2.4" | 20–22 PSI (1.4–1.5 bar) | 23–25 PSI (1.6–1.7 bar) |
| 2.5"–2.6" | 18–20 PSI (1.2–1.4 bar) | 21–23 PSI (1.4–1.6 bar) |
| 2.8" (Plus) | 15–17 PSI (1.0–1.2 bar) | 17–19 PSI (1.2–1.3 bar) |
🌍 International Cycling Pressure Standards: PSI, Bar & kPa
Conversion formulas: 1 Bar = 14.5038 PSI = 100 kPa | 1 PSI = 0.0689 Bar.
In European and international cycling, tire pressure is routinely measured in Bar rather than PSI. Across search engines and forums:
- German (Reifendruck): Fahrrad Reifendruck Tabelle or E-Bike Reifendruck Rechner refer to Bar settings.
- French (Pression des pneus): Pression pneu vélo de route / VTT uses Bar increments (e.g., 2.0 bar MTB, 5.0 bar road).
- Dutch (Bandenspanning): Bandenspanning racefiets / mountainbike calculator typically targets 2.5–6.0 bar.
- Italian (Pressione gomme): Calcolatore pressione gomme bici da corsa aligns with European ETRTO standards.
All BikePSI calculators support both imperial and metric systems natively to give exact decimal recommendations.
Step-by-Step
How to Use This Calculator
- 1
Calculate total system weight
Weigh yourself fully kitted — helmet, shoes, hydration pack — and add the exact weight of your bicycle. SILCA uses total system weight, not body weight alone. A 155 lb rider on a 17 lb bike = 172 lb system weight.
- 2
Determine measured tire width
Do not use the number printed on the tire sidewall. Use digital calipers to measure the actual inflated width. A '28c' tire on a modern 25mm internal-width rim balloons to 30–31mm. Inputting stated width instead of measured width is the single most common source of SILCA miscalculation.
- 3
Select surface condition
Choose the SILCA surface category that best matches your ride. Smooth tarmac (Cat 1) runs the highest PSI; chunky gravel (Cat 5) the lowest. When in doubt between two categories, choose the rougher one — erring toward lower pressure protects against suspension losses.
- 4
Select tire casing type
High-performance casings (supple 320 TPI cotton) deform more easily and need slightly higher pressure to prevent collapse. Stiff puncture-resistant casings require slightly less pressure to achieve the same contact patch shape.
- 5
Select wheel diameter
700c is standard road; 650b is common on gravel and smaller riders; 26" covers older MTB and some touring bikes. Smaller diameter wheels need marginally higher pressure to achieve the same air volume and casing drop.
- 6
Calculate and note your front/rear split
The SILCA algorithm automatically applies a front/rear weight distribution bias — typically 2–4 PSI lower front. Note both numbers and inflate your tires separately. Never inflate both to the rear PSI figure.
Methodology
How the SILCA Algorithm Works
Core formula
Optimal PSI = (System Weight × Width/Volume Constant)
− Surface Impedance Penalty
− Casing Stiffness Modifier
Front PSI = Rear PSI × Front/Rear Weight Distribution Ratio
Variable definitions
- Surface Impedance Penalty: As the road gets rougher, the algorithm lowers PSI to let the tire absorb bumps rather than transferring vibration energy into the rider. Deep/chunky gravel (Cat 5) output is approximately 33% lower than smooth new tarmac (Cat 1) at the same system weight and tire width.
- Width/Volume Constant: Air volume increases with the square of tire width, so a 30mm tire requires drastically less pressure than a 28mm tire to achieve the same casing tension. This is why using measured width — not stated width — is critical.
- Casing Stiffness Modifier: Supple, high-TPI tires (cotton or 320+ TPI) use coefficient 1.0 as the baseline. Mid-range tubeless reduces output by ~3%, mid-range butyl tube by ~6%, and puncture-resistant casings by ~9% — a practical range of 2–7 PSI between the most and least supple options at typical road pressures.
Worked example
180 lb (81.6 kg) system weight · 28mm measured tire · 700C · road weight distribution · high-performance tubeless · moderate group ride pace
New smooth tarmac (baseline) = 82.3 PSI rear / 80.3 PSI front
Worn pavement surface factor = 78.0 PSI rear / 76.1 PSI front (−5.2%)
Worn pave + mid-range butyl tube = 73.3 PSI rear / 71.5 PSI front (casing −6%)
Road distribution (48/52 split) → front is 97.5% of rear in all rows above
Tool Comparison
SILCA vs. SRAM AXS Calculator: Which Should You Trust?
Comparing outputs between SILCA and SRAM often shows a 5–15 PSI difference on road tires. Here is why the numbers diverge and when to use each tool:
SILCA Pro Methodology (Pure Speed)
- • Target: Pro-Tour rolling efficiency impedance breakpoint (minimum watt loss).
- • Tire Width: Measured inflated width with digital calipers (not sidewall print).
- • Speed: Accounts for vibration frequency resonance (5–8 Hz) and dynamic impact forces.
- • Best for: Crits, time trials, fast road racing, and hooked rim setups.
SRAM AXS Methodology (Comfort & Safety)
- • Target: Handling stability, compliance, and rim protection with a built-in safety margin.
- • Tire Width: Labeled tire width paired with internal rim width (ETRTO tables).
- • Safety Cap: Enforces the mandatory 72.5 PSI / 5.0 bar hookless rim ceiling.
- • Best for: Hookless carbon wheels (Zipp, Cadex, ENVE), endurance riding, and rough pavement.
Read our full in-depth engineering breakdown: SILCA vs. SRAM Methodology Guide & Comparison Table or test your setup in our SRAM AXS Calculator.
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