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  1. How does ATRO differ from rubber bushings?
  2. Aren’t all polyurethanes the same?
  3. What is the difference between the words “urethane”, “poly” and “polyurethane”?
  4. Why do ATRO bushings feel so hard?
  5. Can I mix ATRO bushings with rubber or metal bushings?
  6. Where did the word "ATRO" come from?

How do ATRO bushings differ from rubber bushings?

ATRO makes two major changes from standard rubber bushings: a Material change and a Design change.

Material Change

ATRO used polyurethane when originally designing its bushings for two reasons. The first advantage is that polyurethane is a chemically resistant material. This means that diesel fuel, road salt, caustic cleaning solvents, hydraulic fluid, etc. do not affect the polyurethane. It does not crack, become harder or softer, or age quicker with exposure to these elements.

Rubber absorbs these elements and this causes deterioration of the material. Road salt, dry air and ozone, for example, all cause the material to dry out and crack over time. Certain oils can cause the rubber to become very soft and jelly-like.

Polyurethane also does not break down when under constant stress (load). Rubber, under constant stress, deteriorates.

The second advantage to polyurethane is that ATRO’s proprietary material is more durable than standard rubber bushings. In the areas of abrasion resistance, tensile strength and tear resistance, ATRO’s bushings are more than twice as strong as rubber.

Design Change

Regarding design, ATRO chemically bonds the polyurethane to the outer sleeve of steel but allows the inner sleeve to rotate. Because the material is not bonded to both surfaces, the effects of shear/torsional stresses are eliminated. This means the outer sleeve and the polyurethane rotate around the inner sleeve rather than have the material twisted and contorted by movement in the bushing.

The benefit of the rotating inner sleeve design becomes very obvious when installing torque rod bushings. First, you can rotate the inner pin so the bolt holes line up with the bracket. Secondly, this design allows the bushing to automatically zero out to ride height. Per manufacturer requirements, rods are to be installed at ride height but that can become virtually impossible with a wheel supported lift because the lowered vehicle can be difficult to get under in order to install rods. So it is common for the jacks to be placed against the frame thus allowing the axles to drop to make the torque rods accessible. When rods with bonded rubber bushings are installed in this fashion, the bushings are in a relaxed state while the vehicle is jacked up, but one it is lowered to the ground and the axles are returned under the load of the vehicle, the bonded bushing “winds up” and is continually stressed as the material tries to return to its relaxed position.

ATRO bushings with the free-rotation design, coupled with the use of polyurethane, have been show to last 3-5 times longer than rubber.

Aren’t all polyurethanes the same?

Not even close! Polyurethane manufacturers in different industries will promote that idea but nothing could be further from the truth. Currently ATRO uses 11 different polyurethanes depending on the demands of the application. We have different materials for vibration dampening, quick rebound, high temperature under-hood applications, extreme load bearing and others. Some may have the same hardness, but varying physical properties.

That is to say, by changing the formulation of the polyurethane, we can dramatically change the characteristics. To say all polyurethanes are the same, or all polyurethane with the same hardness are the same, is like saying all suspensions are the same. But obviously there are leaf spring suspensions, walking beam suspensions, air-ride suspensions, etc. and all are designed, just like polyurethane, for different applications.

And, similarly, color of polyurethane makes absolutely no difference. The color is just a pigment mixed into the formula. Is a red ballpoint pen functionally different from a blue ballpoint pen? Of course not, its just cosmetics.

That is why we are ATRO Engineered Systems, we engineer the part based on what the application calls for.

What is the difference between the words “urethane”, “poly” and “polyurethane”?

No difference. They each refer to the same material.

Why do ATRO bushings feel so hard?

The hardness of ATRO’s bushings is comparable to that of a rubber bushing. Most of the rubber used in OEM bushings is a 70-75-A durometer material. In assembling a rubber bushing, the material is compressed then pressed between the inner and outer sleeves about 20%. The effective hardness of the compressed rubber, therefore, is 90-A durometer (75 x 20% = 15, 15 + 75 = 90). Rubber bushings feel much softer because the exposed rubber you can touch is uncompressed and remains 70-75-A durometer. A reading under the outer sleeve without releasing any compression would relate to 90-A.

Some ATRO’s bushings are 10-15% stiffer than rubber because they are 92-A durometer from end to end, instead of being softer on the ends and compressed harder in the middle. This increase in hardness does not negatively affect the suspension or bushing life because of the elimination of the shearing stresses with the freely rotating inner sleeve.

Can I mix ATRO bushings with rubber or metal bushings?

For walking beam applications, it is acceptable to mix ATRO ends and metal center bushings but we do not recommend mixing ATRO with rubber bushings.

ATRO end bushings are designed to withstand the added stress that a rigid metal center bushing puts on the end bushings. In fact, ATRO end bushings will perform better than rubber bushings used in conjunction with metal centers because the free rotation of the inner sleeves and the use of durable polyurethane will handle the stress better.

Because ATRO bushings feature a freely rotating inner sleeve and rubber bushings do not, a mix of ATRO and rubber (end/ center applications) could put additional stress on the rubber bushings and cause the rubber bushings to wear out faster than normal.

Mixing ATRO with rubber and / or metal bushings does not affect warranty except in the case of Mack pads. Mack pads must be installed as an 8-pad kit or warranty is void.

Where did the word "ATRO" come from?

ATRO comes from "American Torque Rod of Ohio", the original name of the company when we only rebuilt torque rods using the patented freely rotating pin feature. As we expanded our product line — and moved to Missouri — the name of the company was changed to ATRO, LLC