How a reformer spring creates resistance
Within its elastic range, a coil spring pulls back with a force proportional to how far it is stretched. Britannica gives this as F = kx, where k is the spring constant: a higher k means a stiffer spring. Engineering references define spring rate as force change divided by deflection.
For a round-wire helical spring, the usual formula is k ≈ G·d⁴ / (8·D³·n), where d is wire diameter, D is mean coil diameter and n is the number of active coils. In plain terms, thicker wire makes a stiffer spring; a wider coil or more coils makes it softer.
A reformer carriage is attached to one or more springs on a spring bar, so the springs you hook on set how hard the user pushes.
What a buyer should specify
| Item | What to write down | Why it matters |
|---|---|---|
| Spring source | Wagner, German piano wire, Korean Sangbo steel or domestic carbon steel | Sets feel, consistency and your positioning |
| Resistance per spring | Measured value in your unit, per colour | Colours are not standard across brands |
| Springs per machine | Count and which colours | Defines the resistance range of the machine |
| Spring bar | 3-position spring bar (our standard hardware) | Changes how the springs engage |
| Spare set | Whether spare springs ship with the order | Studios replace springs over time |
| Sample check | Compare sample springs to your spec sheet | Catches colour or resistance mismatch before bulk |
Why colours do not travel between brands
There is no shared standard that says red equals one resistance and blue another. A studio that mixes springs from two makers can end up with a machine whose colours no longer mean what the instructors expect. For an OEM or private-label order, define your own colour set and write the resistance for each colour into the spec sheet.
The four spring sources we build with
Our 2026 catalogue lists German Wagner springs, German piano-wire springs, Korean Sangbo steel and domestic carbon steel. The source is set per model and resistance profile, so you choose it with the model. We do not rank them here; the right pick depends on your brand position and the sample feel.
Replacement and care
- Springs are consumable parts: plan spares in the order.
- Replace a spring that is rusted, damaged, stretched out of shape or no longer feels like the rest of the set.
- Replace in matched sets so both sides of the carriage feel the same.
- Do not mix springs of unknown resistance on one machine.
We do not state a lifespan in cycles, because it depends on use and we have no confirmed figure to publish.
Key facts
- A reformer spring is a helical steel spring; stiffer spring rate means more resistance.
- There is no industry-wide colour code for reformer springs.
- SANFAN reformers use Wagner, German piano-wire, Korean Sangbo steel or domestic carbon steel springs, set per model.
- SANFAN reformers use a 3-position spring bar and stainless-steel rails.
- Spring set, upholstery colour and packaging can all be customised for OEM and ODM orders.
- SANFAN has made fitness equipment since 2013 and its factory is ISO 9001:2015 certified; ISO has since published the 2026 edition.
FAQ
Are reformer spring colours standard across brands?
No. There is no industry-wide colour code for reformer springs. Each maker sets its own colours and resistance values, so always specify springs by measured resistance, not by colour name.
What makes one reformer spring heavier than another?
Spring rate: the force needed per unit of stretch. For a helical spring it rises with thicker wire and fewer or smaller coils, so a heavier spring is stiffer. Engineering references describe this with Hooke's law, F = kx.
Which spring materials does SANFAN use on reformers?
Per the 2026 catalogue, springs are German Wagner springs, German piano-wire springs, Korean Sangbo steel or domestic carbon steel, set per model and resistance profile. Tell us which source your brand needs.
How do I specify reformer springs in an OEM order?
Write down the spring source, the number of springs per machine, the resistance of each colour in the unit you use, and the bar position settings. Then check the sample against that sheet.
When should reformer springs be replaced?
Replace a spring that has lost its original feel, stretched out of shape, shows rust or damage, or no longer matches its set. Springs are consumable parts; we do not publish a fixed lifespan, because it depends on use.
Can SANFAN supply a custom spring set for my brand?
Yes. Springs are one of the items customised per model and resistance profile on our reformers. Send the model and the resistance profile you want to sales@fjsanfan.com and we quote it.
Related pages
- SANFAN Pilates equipment range
- Pilates reformer models: aluminium, foldable and timber
- Pilates reformer buyer's guide: frame types compared
- OEM Pilates equipment from China
Sources
External references checked on 2026-11-10. None of these organisations is affiliated with SANFAN.
- Britannica — Spring constant: Hooke's law, F = kx, and what a higher spring constant means.
- RoyMech — Helical compression and extension spring design: spring rate definition and the round-wire rate formula.
- ISO — ISO 9001:2015: quality management systems standard and its 2026 revision.
Need a spring spec for your reformer? Send the model and resistance profile to sales@fjsanfan.com. We give a first reply within 2 hours on working days (Mon–Sat, 9:00–22:00 China time). Request a quote