What is a monotube shock?
A monotube shock does all its work inside a single tube. This guide explains what is inside, how it differs from a twin-tube shock, and what to know before you choose one.
What a shock does
The springs carry the car’s weight. The shocks control how fast the springs compress and extend.
Inside a shock there is oil and a piston. When the wheel moves, the piston pushes oil through small valve openings. The resistance this creates is called damping, and it stops the car bouncing on after a bump.
Inside a monotube shock
A monotube shock has one tube wall, divided into 2 chambers.
- Oil chamber — the piston and shaft move in this chamber
- Gas chamber — filled with high-pressure nitrogen gas
- Floating piston — sits between the oil and the gas and keeps them apart
When the shaft slides into the tube, the floating piston moves and compresses the gas chamber, making room for the volume of the shaft.
How it differs from a twin-tube shock
A twin-tube shock has 2 tubes, one inside the other. The piston works in the inner tube, and the outer tube is a reserve for the oil.
| Topic | Monotube | Twin-tube |
|---|---|---|
| Tube walls | 1 | 2, one inside the other |
| Oil and gas | Kept apart by a floating piston | Oil shares the outer tube with gas or air |
| Gas pressure | Generally higher | Generally lower |
| Heat | The tube wall is in direct contact with the air | Heat has to pass through 2 tube walls |
| Mounting direction | Can be mounted upside down | Generally has to stay in its designed orientation |
This table describes the general principle of each design. It does not compare any brand’s products.
Strengths of the monotube design
- Oil and gas do not mix — less chance of air bubbles in the oil when the shock works hard for a long time, which helps keep damping consistent
- Direct cooling — the single tube wall is in direct contact with the air
- Room for a larger piston — for the same outside diameter, a monotube piston generally has more area
- Flexible mounting — because the oil and the gas are kept apart
Limits to know about
- The tube wall is the wall the piston runs on — a dent from an impact can affect how the piston moves, so watch for stones and scraping
- High gas pressure — generally gives a firmer feel over small movements
- It needs length for the gas chamber — the manufacturer has to design the stroke to suit each car
- Comfort does not depend on construction alone — it also depends on spring rates, the damping setting, ride height and tyres
Which DGR Suspension series are monotube?
Per the manufacturer:
- DGR ST — monotube, 30 damping settings
- DGR RC — monotube, 30 damping settings
- DGR DCS-2 — Monotube with a separate external reservoir, 30 Rebound and 15 Compression settings
Looking after a monotube shock
- Check the shock body for dents and for oil running down it, especially after a scrape or a hard impact
- Wash mud and dust off the shock body and the threads regularly
- If the car bounces more than before, or you hear unusual noises, have an installer check it