What is SAG in MTB suspension?

SAG is the static compression of the suspension spring under the rider's weight in a neutral riding position. Expressed as a percentage of the total stroke: SAG% = (sag mm / total stroke mm) × 100. Typical ranges: XC 15-20%, Trail 20-23%, Enduro 23-26%, DH 25-28% (fork). SAG defines the spring's operating point — all other adjustments (rebound, compression) work relative to it.

How much air pressure do I need for my Fox or RockShox fork?

Pressure depends on your weight, your fork's specific stroke, chamber volume, and installed tokens. The relationship is non-linear (polytropic law). Use the BikeLab Studio SAG Calculator — 132 models calibrated against official Fox, RockShox, Öhlins and SR Suntour data — to get the correct pressure in seconds.

Does the calculator work for my full suspension frame?

For front forks: yes, with no frame data needed. For rear shocks: select your linkage type (Horst Link, VPP, DW-Link, Single Pivot, Switch Infinity, High Pivot). 33 specific frames are catalogued. If yours isn't listed, the linkage type covers 99% of full suspension frames on the market.

What are tokens or volume spacers in MTB forks?

Tokens (volume spacers) are inserts that reduce the positive chamber volume, increasing progressivity without changing initial pressure. More tokens = stiffer ramp-up at end of travel. The calculator recommends the optimal token count for your discipline: XC (low progressivity), Trail (moderate), Enduro/DH (high).

How do I measure SAG on my MTB suspension?

1) Slide the rubber O-ring to the fork seal with suspension fully extended. 2) Mount the bike with full gear in neutral riding position. 3) Dismount carefully — the O-ring marks the SAG position. 4) Measure the distance from O-ring to seal in mm. SAG% = measured mm / total stroke × 100. Repeat 3 times and average for accuracy.

Which suspension brands does the calculator cover?

Fox Racing Shox (29 models), RockShox (45 models), SR Suntour (12 models), Öhlins (6 models), Manitou (8 models), Marzocchi (4 models), DVO (4 models), Cane Creek (5 models), X-Fusion (4 models), MRP (3 models), Formula (6 models), RST, Wintek, Zoom, Sturdy and Push Industries. Total: 132 suspensions across 10 brands.

MTB SAG Calculator — BikeLab Studio | Fox, RockShox, Öhlins, SR Suntour

// TRANSPARENCY — CALIBRATION STATUS

An honest note about some models in the list.

Brands like Fox, RockShox, and Öhlins publish official technical specs — pressure-volume tables that let us calibrate their models with high confidence. The following models appear on this list for two distinct reasons: (1) entry-level models without public documentation — their parameters were estimated from our own measurements and indirect references; (2) Solo Air design (single-chamber) — forks like the Judy or Epixon use a single air-chamber spring, while the polytropic engine is calibrated for the standard dual-chamber design. In both cases the result is a useful starting point, but with a wider uncertainty band than premium models.

The data isn't wrong. It's data with less technical backing than the premium models.

Models with estimated parameters (under review):

RST · Aerial Air 34mm [XC/Trail] RST · Blaze Air 30mm [XC] SR Suntour · NCX Air [Trekking/E-bike] SR Suntour · NCX-D Air [Trekking/E-bike] SR Suntour · XCR 32mm Air [XC] SR Suntour · XCR 34 Air [XC/Trail] SR Suntour · Epixon 32mm Air [XC/Trail] ¹ SR Suntour · Epixon LO-R 32mm Air [XC/Trail] ¹ SR Suntour · Raidon 34mm Air [Trail] ¹ SR Suntour · Raidon LO-R 34mm Air [Trail] ¹ RockShox · Judy Gold/Silver Air [XC/Trail] ¹ RockShox · Judy Gold Air B+ Boost [XC/Trail] ¹ Zoom · C30 Air [XC] Sturdy · EM100 Air E-MTB [E-MTB] Wintek · Air 32mm [XC/Trail]

¹ Solo Air — single-chamber design. The polytropic model is an approximation for this type of air spring.

If you ride one of these models and want to help improve the calibration, your real-world data would be very valuable to us: the pressure you normally run, your total riding weight, your fork stroke, and the SAG you measure with the O-ring. With enough community data we'll update the parameters and announce it here.

SHARE MY DATA →

// ORIGIN — WHY THIS EXISTS

"We didn't start with 132 models.
We started with a question no pressure table could answer well."

Months reading applied thermodynamics papers.
Sending emails to Fox and SRAM engineers who never replied.
Working through technical documentation not meant to be read by an independent workshop.

One Python model. Another model. Then another.
Each broken in a different way.

Differential evolution optimization. Parameters calibrated against official manufacturer tables.
10,000 Monte Carlo iterations per model to understand exactly how much to trust each number.
Until the physics stopped lying.

The result: a dual-chamber polytropic air spring engine.
132 suspensions. 10 brands. One number you can use today.

For front forks, the frame doesn't matter — the fork is independent of the linkage.
For rear shocks, we work with the real leverage ratio: 33 frames catalogued.
If yours isn't listed, select your linkage type — it covers 99% of full suspension frames on the market.

It's not a lookup table.
It's the model we wanted to exist.
So we built it.

BikeLab Studio — Industrial & Scientific Noir

// HOW TO USE THE CALCULATOR

Under 60 seconds

STEP_01

Select your suspension

Search by name or filter by segment. Fox, RockShox, Öhlins, SR Suntour, Manitou and 5 more brands. Legacy models (2013–2022) are included.

STEP_02

Enter your weight

Your total weight with full gear: helmet, clothes, pack, water. The model uses it to calculate the real force on the piston.

STEP_03

Discipline and style

Select XC, Trail, Enduro, DH or E-MTB. Then your riding style and typical terrain. This fine-tunes the SAG target within the correct range for your use.

STEP_04

Installed tokens

If you have tokens in your fork, enter how many. If unsure, leave at zero. The calculator also recommends how many to use for your discipline.

STEP_05

Rear shocks: linkage type

Select your frame's suspension type: Horst Link (Specialized, Canyon), VPP (Santa Cruz), DW-Link (Pivot, Ibis), Single Pivot, Switch Infinity (Yeti) or High Pivot.

RESULT

Your starting pressure

You get the recommended pressure with its confidence band by segment, real wheel SAG, rebound and compression starting clicks, and token recommendation. Set it, ride, fine-tune on trail.

// NOTE

The result is your documented starting point, not the final adjustment. Inflate to recommended pressure, measure SAG physically with the O-ring, adjust within the indicated band, and fine-tune by feel on trail. Rebound and compression are touched after confirming SAG.

// FREQUENTLY ASKED QUESTIONS

MTB Suspension FAQ

What is MTB suspension SAG and why does it matter?

SAG is the static compression of your air spring under your body weight in a neutral riding position. It defines the spring's operating point — rebound, compression and progressivity all work relative to it. Wrong SAG means all other settings are optimized on a broken foundation.

How much pressure for my Fox 36 / Fox 38 / Fox 34?

It depends on your total weight, the specific stroke of your fork, chamber volume and installed tokens. The relationship is non-linear. Select your Fox model in the calculator above and enter your weight — the physics model gives you the correct pressure in seconds, calibrated against Fox's official tables.

How much air pressure for RockShox Pike / Lyrik / ZEB / SID?

All RockShox Pike, Lyrik, ZEB, SID, BoXXer, Super Deluxe and Deluxe variants are in the calculator — including Select, Select+, Ultimate and legacy models back to 2015. Select your model, enter your weight, get your pressure.

What is the difference between shock SAG and wheel SAG?

Shock SAG is measured directly on the damper body. Wheel SAG is the actual rear wheel travel as a percentage of the frame's total travel. A leverage ratio of 2.5–3.5 means wheel travel is 2.5–3.5× the shock travel. Frame manufacturers specify SAG in wheel travel. This calculator computes both — a technical differentiator absent from all other calculators.

Does it work for Öhlins RXF36, RXF38 or TTX shocks?

Yes. Öhlins RXF32, RXF36 and RXF38 m.2 (all three-chamber air forks), plus TTX Air, TTX22 and TTX2L shocks are in the database. Parameters are inferred from the three-chamber air system physics — Öhlins does not publish official pressure tables.

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Under 60 seconds

MTB Suspension FAQ

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