Hardness Selection

Polyurethane products can come in varying degrees of hardness — exactly the same as rubber parts, stiffer than the original, or, on the contrary, softer. In most cases, polyurethane spare parts are exact copies of rubber ones. However, adjustments can be made. Choose standard hardness polyurethane silent blocks or custom hardness for special tasks.

Do rubber silent blocks and bushings differ in hardness from polyurethane ones?

The hardness of elastic materials, both rubber and polyurethane, depends on the polymerization conditions. It is possible to produce soft polyurethane as well as hard rubber. Depending on the proportions of the raw material components, polyurethane can be produced with a Shore A hardness of 45 units (comparable in softness to silicone) or extremely hard, with a hardness of 90 A and above.

If the task is to make an exact copy of an original spare part, Poly Pro manufactures polyurethane parts with the exact same hardness as standard rubber ones — 65 Shore A. This reproduces the performance characteristics intended by the vehicle manufacturer.

We inspect every silent block to ensure its hardness matches the requested specifications. Therefore, we are confident that you won't be able to tell while driving whether your vehicle's suspension relies on rubber silent blocks or polyurethane ones from PolyPro. Telling two cars apart based on suspension handling — where one runs on rubber and the other on our polyurethane — is a 50:50 guess at best.

At the same time, we offer an important custom service: manufacturing polyurethane silent blocks of custom hardness — either firmer than standard or, conversely, softer.

When is a different silent block hardness needed?

There are many cases where custom hardness silent blocks are used. When is it worth using parts stiffer than 65A?

Motorsport. Stiffer suspension silent blocks are used for sports cars to reduce suspension travel. The goal is to minimize silent block movement at high speeds, avoiding bouncing and body roll while still allowing proper suspension articulation and twisting under load. For such scenarios, PolyPro offers durable, high-performance polyurethane silent blocks in 85 Shore A, 90 Shore A, and 65 Shore A.
Off-Road. If an SUV owner decides to install a heavy-duty suspension with stiffer springs and shock absorbers, this will only restrict vertical suspension travel. However, for a comfortable ride, lateral (left-to-right) suspension movement must also be considered.
Armored Vehicles. Armoring a vehicle increases its weight by approximately two tons. To preserve driving dynamics after such modifications, all load-bearing structures must be reinforced. Naturally, the suspension of such a vehicle needs to be stiffer as well.

Thus, to balance a reinforced suspension, higher hardness silent blocks are required — around 90 Shore A units. Poly Pro offers these polyurethane bushings and silent blocks in our Hardness product line. What sets PolyPro's Hardness silent blocks apart?

When comparing PolyPro stiff silent blocks with similar products from other manufacturers, ours feature a solid, fully bonded construction, whereas others resemble a multi-piece DIY assembly.

Stiff silent blocks from other market manufacturers are essentially a piece of polyurethane simply wrapped around a metal sleeve. This setup fails to function properly as a silent block because the metal and elastic sections delaminate, allowing moisture, sand, and dirt to get inside, resulting in squeaking and premature failure.

PolyPro uses a different manufacturing technology: the polyurethane is chemically bonded (vulcanized) into the outer shell and inner sleeve, allowing it to work seamlessly in torsion and oscillation just like an original OEM silent block.

Softer polyurethane products are typically used for restoring engine mounts and other similar applications.

Need silent blocks with a specific hardness? Consult with our manager