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This Raychem DR25 size guide explains how to choose DR25 heatshrink tubing for motorsport wiring harnesses, EFI looms, ECU wiring, engine bay wiring and custom automotive harness builds.
Raychem DR25 is commonly used in motorsport wiring because it is flexible, abrasion resistant, fluid resistant and suitable for protecting wire bundles in harsh automotive and engine bay environments.
To choose DR25 size, measure the outside diameter of the wire bundle first. Pick a DR25 size with a supplied inside diameter large enough to slide over the bundle, and a recovered inside diameter small enough to grip the bundle after shrinking. DR25 has an approximate 2:1 shrink ratio, so 1/4" DR25 starts around 6.4 mm ID and recovers to around 3.2 mm ID.
The table below gives a practical guide to common DR25 sizes used in motorsport harness work. Exact fit depends on the wire bundle diameter, branch layout, connector size, boots, transitions and how much movement or strain relief is required.
| DR25 Size | Supplied ID Approx. | Recovered ID Approx. | Common Motorsport Use |
|---|---|---|---|
| 1/8" | 3.2 mm | 1.6 mm | Small sensor branches, single wires, small signal wire groups |
| 3/16" | 4.8 mm | 2.4 mm | Small branch sections, 2 to 4 wire sensor branches, CAN branches |
| 1/4" | 6.4 mm | 3.2 mm | Sensor branches, injector branches, small loom sections |
| 3/8" | 9.5 mm | 4.8 mm | Medium harness branches, ECU branch groups, engine sensor groups |
| 1/2" | 12.7 mm | 6.4 mm | Main branch sections, medium engine harness sections, chassis loom branches |
| 3/4" | 19.1 mm | 9.5 mm | Main trunk sections, larger engine loom sections, grouped harness branches |
| 1" | 25.4 mm | 12.7 mm | Large main trunk sections, large chassis harness sections, bulk wire groups |
The easiest way to choose DR25 is to measure the finished wire bundle diameter, not just count the number of wires. Wire size, insulation thickness, twisting, shielding, labels, splices and branch points all change the final bundle size.
Lay the wires together in the same layout they will use in the harness. Measure the outside diameter of the bundle with verniers or calipers. For twisted pairs, shielded cable or bundled branches, measure the actual finished diameter.
The supplied ID of the DR25 must be large enough to slide over the wire bundle without damaging the wires. If the harness has labels, splices, joins or larger transition points, allow extra clearance.
The recovered ID should be small enough to grip the bundle after shrinking. If the recovered size is still too large, the DR25 may sit loose on the harness and move around.
For professional motorsport harness work, DR25 is often used with moulded boots, SCL, ATUM or adhesive-lined heatshrink at branch points and transitions. The DR25 size should work with the boot or transition part being used.
DR25 is used as outer harness sleeving. It protects wire bundles from abrasion, heat, fluids and general engine bay conditions. It is commonly used in motorsport, race car, military, heavy vehicle and harsh-environment wiring applications.
DR25 is not the same as basic electrical heatshrink. Standard heatshrink is useful for insulation, small repairs and simple protection, but it is usually not the best choice for outer sleeving on a motorsport wiring harness.
DR25 is designed for harsh-environment harness protection. It is more suitable for engine bay and motorsport use where heat, abrasion, fuel, oil, fluids and movement are part of the job.
DR25 is normally used as the outer harness sleeve. SCL and ATUM are adhesive-lined heatshrink products used for sealing, strain relief and transitions.
In many motorsport harnesses, Tefzel wire is bundled, covered with DR25, then sealed or finished using SCL, ATUM or moulded boots depending on the harness design.
12Volt Motorsports supplies Raychem DR25 heatshrink tubing for motorsport wiring harnesses, engine bay looms, ECU wiring and custom automotive harness builds.
Shop Raychem DR25Measure the outside diameter of the finished wire bundle, then choose a DR25 size with a supplied ID large enough to slide over the bundle and a recovered ID small enough to grip it after shrinking.
Yes, DR25 is generally treated as a 2:1 heatshrink tubing. For example, 1/4" DR25 is approximately 6.4 mm supplied ID and approximately 3.2 mm recovered ID.
Yes, DR25 is commonly used for engine bay and motorsport wiring because it is flexible, abrasion resistant and suited to harsh automotive environments.
Normal heatshrink can be used for simple insulation and small repairs, but DR25 is a better choice for outer harness sleeving in motorsport and engine bay applications.
DR25 protects the wire bundle, while SCL or ATUM can be used to seal ends, transitions and branch points. They are often used together in motorsport harness builds.
DR25 used in motorsport harness work is commonly black, which gives a clean professional finish and suits engine bay and chassis wiring applications.
Last updated: June 2026
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