The most important fork-setup question is not “what do riders my weight run?” It is “which exact fork and source am I using?”
Fork chassis, generation, travel, air spring and damper can all change the pressure and damping guidance. Roadman's MTB suspension calculator now gives a direct chart value only for the four listed 2026 FOX 38 variants. For RockShox it follows SRAM's instruction to use the pressure decal or Trailhead.
For fork and rear shock as a system, use the complete MTB suspension setup guide.
1. Identify the fork before choosing PSI
Record these fields:
| Field | Why it matters |
|---|---|
| Chassis and generation | Air-spring and limit changes can sit under the same family name |
| Variant | FLOAT, Rhythm and e-bike versions can have separate charts |
| Travel | Pressure, sag distance and spacer limits can change with travel |
| Damper | Rebound and compression recommendations depend on the installed damper |
| Maximum pressure | It is a limit, never a target |
| Serial or ID | It resolves the exact manual and service information |
The 2026 FOX 38 manual has separate pressure columns for standard FLOAT, FLOAT E-Bike+, Rhythm and Rhythm E-Optimized. It states 140 PSI maximum for FLOAT/E-Bike+ and 120 PSI for Rhythm. Never copy those limits to another fork.
RockShox's current suspension manual directs air-fork riders to the fork decal or Trailhead for starting pressure and rebound. That is more defensible than Roadman's old generic tables because it resolves the actual product.
2. Get a source-backed starting pressure
Use this hierarchy:
- exact bicycle guidance where the fork is OEM-tuned;
- exact fork manual or serial/product lookup;
- the pressure decal on the identified fork;
- a calculator only when it names the same product, generation and source.
Avoid shortcuts such as “PSI equals rider weight in kilograms” or “fork PSI is 60% of body weight in pounds”. Different columns in one FOX 38 manual already disprove the idea that one weight formula spans even a single chassis family.
Worked example: 2026 FOX 38 FLOAT
An 80 kg rider including kit is about 176 lb. The published 170–180 lb band for the standard 2026 FOX 38 FLOAT lists 93 PSI. At 170 mm travel, 20% sag is 34 mm.
Those two numbers have different jobs:
- 93 PSI is the sourced starting input;
- 34 mm is the measurement used to calibrate the final setup.
FOX notes that actual pressure can differ from its chart with variables such as riding style, terrain and bike geometry. That is a reason to measure sag—not a reason for a hidden calculator multiplier.
3. Calculate fork sag in millimetres
Use:
fork travel × target sag percentage = sag distance
| Travel | 15% | 20% | 25% |
|---|---|---|---|
| 100 mm | 15 mm | 20 mm | 25 mm |
| 130 mm | 19.5 mm | 26 mm | 32.5 mm |
| 150 mm | 22.5 mm | 30 mm | 37.5 mm |
| 170 mm | 25.5 mm | 34 mm | 42.5 mm |
| 180 mm | 27 mm | 36 mm | 45 mm |
The table does arithmetic; it does not choose the correct percentage. FOX specifies 15–20% for the selected 2026 38. Other forks and bikes can differ, so confirm the exact manual before selecting a column.
4. Inflate and equalise as the product requires
Use a high-pressure suspension pump. Set compression controls to the manual's open position before measuring sag. Add air without exceeding the lowest applicable limit, then follow the fork's exact equalisation process.
Do not use one generic instruction such as “cycle every fork 15 times”. RockShox publishes staged instructions for current DebonAir+ products, while a FOX model can specify its own procedure. The air chambers and pump gauge can settle differently as pressures equalise.
Likewise, do not deliberately overinflate to account for assumed hose loss. The air that changes the gauge on reconnection can be the air required to pressurise the pump hose rather than proof that the fork leaked. Use the manufacturer's procedure and confirm the result with sag.
5. Measure sag consistently
- Slide the O-ring to the dust wiper.
- Wear normal helmet, shoes, pads, pack, water and tools.
- Use a wall or helper and settle into the instructed riding position.
- Hold still without bouncing.
- Move the O-ring if the exact procedure requires it while weighted.
- Dismount carefully.
- Measure from the wiper to the O-ring.
- Add or release a small amount of air, equalise again and repeat.
A fixed 5 PSI step is a much bigger relative change in a 55 PSI fork than a 120 PSI fork. “Small amount” should follow the product guidance and pump resolution, not one site-wide number.
6. Set rebound after pressure and sag
Rebound controls how quickly the fork extends. Too little rebound damping can make the return abrupt; too much can stop recovery between repeated impacts.
Start at the exact pressure-linked setting for the installed damper. The same FOX 38 manual provides different rebound columns for GRIP, GRIP X and GRIP X2. Count clicks from the direction named by the manual, record the setting, then change one click at a time on a repeatable section.
The car-park push test can reveal an extreme setting. It cannot reproduce a sequence of trail impacts, braking loads and rider inputs, so it is not the final test.
7. Add compression only from a known baseline
Low-speed and high-speed compression describe damper shaft-speed regimes, not simply slow and fast bicycle speed. Available controls differ by damper.
Begin at the product's published start. Test one change at a time. If a fork is harsh, first verify product identity, pressure, sag, equalisation and service condition instead of assuming that opening one control must solve it.
8. Treat spacers as progression tuning
FOX says approved volume spacers change mid-stroke and bottom-out resistance. RockShox says tokens reduce air volume and increase progression. Neither supports an automatic PSI uplift for each spacer.
Only consider a permitted change after sag is correct and representative riding shows an end-stroke problem. Check the exact travel-dependent maximum, follow the official installation procedure or use a technician, then repeat sag and damping setup.
9. Keep a fork setup log
| Date | Fork and travel | PSI | Sag mm / % | Rebound | Compression | Temperature | Trail note |
|---|---|---|---|---|---|---|---|
| Example | 2026 38 FLOAT, 170 mm | 93 | 34 / 20% | exact clicks from closed | exact damper start | 15°C | baseline |
Always record the rebound/compression reference direction. “Seven clicks” is ambiguous unless it says seven out from fully closed or another defined start.
When to stop adjusting
Stop riding and seek qualified inspection for visible damage, oil leakage, unexpected pressure loss, harsh top-out, abnormal noise, a control that has no effect or an inability to reach correct sag inside the permitted pressure range. Never use another rider's setting to tune around a mechanical fault.
Once the fork is traceable and repeatable, set the rear through the full suspension guide, then handle the other contact system separately with the MTB tyre-pressure guide and tyre-pressure calculator.