Polyurethane vs. UHMW: What's the Difference?

If you have been around BMWs long enough, you know that they are considered one of the best cars on the market. For decades they have offered a blend of comfort and handling that few of their competitors can match, and this is proven on highways and race tracks around the world on a regular basis. This also means that they have become a popular car to modify by enthusiasts, tuners, and racers to extract the most performance possible out of these machines, and while this may mean sacrificing some comfort, it also means improving performance. These modifications and upgrades often involve replacing rubber bushings and mounts with ones made of materials such as polyurethane and UHMW, but what is the difference between these products and which will work best for you?

1. Rubber

BMWs come from the factory with many rubber-based components. These parts, which include various bushings and mounts, are engineered at the factory to provide the most comfort possible, and by using rubber, it allows them to absorb vibrations from the engine and the road surface and also allows for some movement between components which creates a smoother ride. This dampening effect provides a smooth ride, but the use of rubber means that these parts will deteriorate over time due to movement and the intense heat cycles that they’re exposed to. When it comes time to replace these parts, many enthusiasts upgrade the mounts and bushings to BMW performance parts made of polyurethane or UHMW. While both these materials are a definite upgrade over rubber, they both provide a different experience that will affect how your car performs on the road or track. 

2. Polyurethane

Polyurethane is a material that many would just refer to as plastic, but it’s a polymer (a substance composed of large molecules) made up of organic components joined together by carbamate links. It can be made from a large variety of starting materials with different properties that allows for it to take many forms for various applications. BMW parts such as engine mounts come from the factory with rubber components but can be upgraded with a Condor Speed Shop engine mount made from polyurethane that is 30% stiffer than OEM rubber mounts. This makes polyurethane mounts a popular performance upgrade for BMWs because not only do they last longer, but they also improve throttle response and cutting down on engine movement during cornering and acceleration. 

Installing a polyurethane mount is a straightforward process that can be completed by most knowledgeable and competent BMW enthusiasts, which is another reason why replacing rubber parts with polyurethane is such a popular upgrade. Many manufacturers produce polyurethane bushings and mounts in various degrees of hardness, and they usually come in three degrees of stiffness -- hard, medium and soft. There isn’t really a global standard for the manufacturing of these parts, so you need to be careful when purchasing. Buy them from a reputable manufacturer that sells track-tested BMW racing parts. For the best polyurethane, engine mounts available, check out the selection at Condor Speed Shop.

3. UHMW

UHMW (ultra-high-molecular-weight polyethylene) is a type of thermoplastic polyethylene and is basically an extremely tough plastic. The chemical links that hold it together are much stronger than polyurethane. It is lightweight but still very strong and resistant to wear and heat, making it the ideal material for use in BMW performance parts. UHMW is used in parts that move, such as suspension bushings, and in parts that hold a component in place like the engine or subframe mounts. It is a self-lubricating material which makes it easy to install for a competent BMW enthusiast, and it does not squeak like polyurethane can. 

To get the most out of your BMW on track, you want the suspension to be as stiff as possible and the distortion between components to be as minimal as possible. Some purpose-built race cars, like F1 cars, do away with engine mounts altogether. On these cars, the engine is attached directly to the frame and becomes a stressed member of the chassis. Some GT-based racers replicated this level of stiffness by utilizing solid metal engine mounts. These limit movement between components but offer no vibration dampening at all and might have unwanted side effects on street cars.  

Rubber and polyurethane mounts can’t offer anywhere near this amount of stiffness, and bushings made of these materials can deflect and slide, which can lead to alignment issues and uneven component wear. Solid UHMW components offer almost the same level of stiffness as a metal component, but they provide some vibration absorption which significantly aids in driver comfort. This is a huge plus because it means UHMW components are acceptable for street use, where solid metal components are uncomfortable when used this way.

Performance is the most significant factor to consider for driving on the street. BMW goes to great lengths to ensure that their road and race cars are as fast as possible. So any time you replace a component like a bushing or a mount, you want to use the highest quality performance parts available, and this is where UHMW and polyurethane components really stand out. Condor Speed Shop, produces high-quality, made-in-the-USA components that have been track tested for thousands of miles on the street and at the most challenging and most demanding racing tracks. Rubber and low quality polyurethane mounts have been known to fail under the large amount of stress that racing conditions create, but UHMW components have been proven to be reliable and more robust.

Polyurethane vs. UHMW, which is best for you?

Whether you are replacing bushings or mounts on your daily driver or dedicated track car, it really doesn’t make sense to replace the parts with stock rubber-based components. Polyurethane parts, especially engine mounts, can be considered a performance upgrade for your street car and make spirited driving on back roads an overall better experience. If you plan on spending any time on the track, from a few track days a year to full-on endurance races, UHMW is the way to go. The beauty of solid UHMW components is that they offer an extraordinary amount of stiffness while still giving you the ability to use the car on the street (the bushings are stiff but not noisy). Polyurethane components like engine mounts are a good street car upgrade and is a must for any true BMW enthusiast. No one buys a BMW, the Ultimate Driving Machine, to sit on the sidelines, so replace those mounts and bushings with the best parts available from Condor Speed Shop and hit the track!