Rubber vs Polyurethane Bushings
Rubber or Polyurethane? Each has their pros, and each has their cons. In the suspension bushing world, the majority of decisions comes down to these two materials and the inevitable question: which one is better?
In this article, we’ll discuss the pros and cons of each material. Specifically we’ll look at the differences between rubber and polyurethane in:
It’s all Relative
When asking the question, “which is better for bushings: polyurethane or rubber?”, you must first acknowledge that this is a relative question. Imagine a guy from Texas and a guy from Alaska meet at a July conference in Seattle, Washington. The guy from Texas, who is used to the average temperature of about 96 degrees Fahrenheit, would sense the relief in the 72 degree weather. While the guy from Alaska would gladly welcome the warm weather instead of the mid 60s he would usually get in July. So to these guys, cold or hot is relative. In comparing rubber bushings against polyurethane, its much the same. Noise, vibration and harshness (aka NVH – important later) are relative to the driver. Here are the facts regarding rubber and polyurethane so you can make an informed decision.
Opposite ends of the spectrum?
It is important to clarify that rubber and polyurethane are not polar opposites. They are not on opposite ends of the spectrum. There are softer things than rubber, like jello, and harder things than polyurethane, like aluminum or metal joints. While there probably isn’t a car out there that utilizes the innovative jello bushing, there are a lot of race car drivers who run aluminum joints on their vehicles. Rubber and polyurethane, while differing in a lot of ways, fall more in the middle of the spectrum.
Trade off: Smooth and Quiet ride vs a Bit more NVH
Rubber is a much softer material than polyurethane, so it dampens a lot of the road noise and vibrations from entering the cab of the vehicle. In other words, it softens the blow from the road.
Polyurethane on the other hand is made to be a firmer bushing than rubber. This means more noise and vibration will be transferred to the cab as the suspension travels. Some may feel the ride is harsh, while others welcome the enhanced feel of the road. Again, recall our sojourners from Texas and Alaska. How you answer the question of ride quality is a relative question. Would you like a more tactile feel of the road or pillows for tires?
Trade off: Repeat offender vs Longevity
Think about it for a minute. What are you replacing? A rubber O.E. bushing right? So it’s pretty safe to assume that replacing a worn and torn rubber bushing with the same material will put you right back in this same spot one day. Entropy will eventually run its course and the bushing will wear out. Rubber is soft, and more importantly, takes damage from heat, road chemicals, oil and UV rays. So these bushing are already going to take a beating, and that’s before you put the weight of the vehicle and the stresses of the suspension on them.
As the suspension travels the bushings stretch and compress to comply with the suspension movement. Over time, rubber begins to wear and distort causing your suspension to work less efficiently due to the failing part. Loose suspension parts, constant mis-alignment, and annoying noises are common symptoms of a failed rubber bushing. If you use rubber to replace failed rubber, don’t be surprised to find yourself in a similar situation several years down the road. For some people that’s okay. A rubber suspension bushing is like a tire, in that eventually the bushing will wear out and need to be replaced. Some would rather keep the soft bushing and its characteristics even if they have to replace it again in the future.
Others, however, want a part that lasts the lifetime of their vehicle. That’s where polyurethane comes in. Polyurethane bushings are a firmer material and far better suited to handle the grind of being a suspension bushing. This material is resistant to heat, road chemicals, other oils and UV rays. Not only is polyurethane weather proof, it’s also wear resistant. Rubber is damaged after repeated flexing and stretching. Polyurethane doesn’t have that problem. Since there is very little flexing and stretching, a polyurethane bushing doesn’t warp or distort the way rubber does. Many poly bushing manufacturers offer a lifetime warranty on their polyurethane bushings to show their confidence in the material standing the test of time.
Trade off: Standard Feel vs Enhanced Feel
Another relative term, so again it’s all about user preference here. Rubber is what comes standard when your car is brand new. Vehicle manufacturers have used rubber for suspension bushings for decades. Now whether this was because they thought it was the “best” or just the “cheapest” is a topic for further debate. Regardless, rubber is what came stock on your vehicle. Using a rubber bushing as a replacement will give you the same feel your vehicle had before the rubber failed.
Polyurethane on the other hand will give the driver an enhanced feel of the road. This may be a turn off to some, but there are drivers that desire to feel every bit of the road to maximize their ability to drive. With the feel of polyurethane, the vehicle seems to be an extension of the driver himself, far more than rubber would allow.
With the feel of polyurethane, the vehicle seems to be an extension of the driver himself…
Trade off: Standard Steering and Handling vs Enhanced Steering and Handling
Using a softer material such as rubber for a suspension bushing means foregoing a lot of performance benefits in order to achieve a smoother ride. Rubber is much more compliant, meaning it has a lot of give when the suspension moves. The effect of this is a smoother ride in the car. However this can lead to a lot of excess suspension movement and a slower response time in your handling. This is usually okay when you’re going 40 mph down the road in a straight line. But what happens when you’re driving fast and want to turn quickly?
Polyurethane bushings are firmer than rubber, so it doesn’t flex or deflect as much as rubber. By reducing the excess suspension movement, polyurethane makes the suspension more efficient and more responsive to the driver. Polyurethane bushing engineers design the hardness bushings specifically for each vehicle. By utilizing the best durometer for each bushing in a suspension, the result is a careful balance between NVH and performance.
Polyurethane is not just for race car drivers, but any driving enthusiast who wants more performance and handling from their vehicle. On the other hand, rubber isn’t just for the old Cadillac driven by your grandmother. Some people desire the smooth ride and care little about the performance they miss out on with rubber. Others like to drive their vehicle aggressively and don’t mind the added NVH polyurethane brings with the performance boost. The choice is yours.
Trade off: No opportunity for squeaking vs Opportunity for squeaking
This is a fun topic because there are a lot of misconceptions out there regarding polyurethane and squeaking. But before we address those, here are the facts about a rubber bushing regarding the issue. Rubber is chemically bonded with the outer shell. So from the moment you take it out of the box and install the rubber replacement bushing, you don’t have to worry about squeaking. Squeaking occurs when the bushing rubs against metal. Because the rubber is affixed to the metal and can’t move in relation to the metal, there isn’t an opportunity for squeaking.
Polyurethane on the other hand is a different story. Polyurethane bushings have this stigma that they WILL 100 percent absolutely squeak. This is FALSE. Polyurethane absolutely CAN squeak, IF you don’t use grease. Polyurethane bushings do not have a chemical bond with the housing they’re installed into, but rather a mechanical bond. A mechanical bond occurs when the larger polyurethane bushing is installed into the slightly smaller hole. The pressure between the bushing and the metal keeps the bushing centered. With this mechanical bond, the opportunity for the polyurethane to squeak is opened up. If the bushing rotates and rubs the outer metal shell as the suspension travels, squeaking can occur. This is where the grease is VITAL. If you install the bushing properly, and lubricate the bushing well, there will not be any squeaking. See the Servicing section below for more on this.
Trade off: Install and Replace vs Install and Maintain
Rubber bushings are an “install it and forget it” type operation. There is no need to re-grease any bushing. In fact you never grease them at all because the rubber is chemically bonded with metal. The only maintenance required with rubber bushings is the need to replace them once they eventually wear out.
With polyurethane you are getting a much longer lifespan out of the bushing. Consequently you won’t need to replace anything for a long time, if ever. The problem is if the polyurethane part is poorly designed, the grease could be squeezed out and you are left with no lubrication between the polyurethane and metal. This has led polyurethane bushing engineers to incorporate a design that retains grease on the bushing. Some manufactures leave little grooves on the inside of the bushing, while others have developed a knurling. These grooves or knurling help prevent grease from squeezing out. Over time, unfortunately, gunk can get in the tacky grease or the grease could rub off. Without the grease, the opportunity for squeaking presents itself. While these grooves and knurls are designed to avoid that for as long as possible, polyurethane manufacturers will tell you (if you ask) that you may want to re-grease the polyurethane bushings within 5 years. This is especially true with high stress parts like the control arm bushings or sway bar bushings. At around 4 to 5 years, the lubricant may have rubbed off enough that you’ll begin to hear squeaking. As soon as you hear any squeaking, just hit it with some grease and you should be good for another half decade.
Trade off: Advanced Mechanic vs DIY
Rubber bushings have to be created with a new outer bushing shell. This is great for eliminating any opportunity for squeaking, but not so great for ease of DIY installation. Installing a rubber bushing can be much harder than a polyurethane bushing. Usually you will have to take the arm or spring off the vehicle and use a hydraulic press to both remove the O.E. bushing and to install the new rubber bushing. Most people don’t have a hydraulic press, so they have to take their vehicle to a mechanic in order to get their bushings replaced. There are still those extreme DIY’ers that will attempt to install a bushing themselves. If that’s you take a look at our article showing you How to Install a Bushing Without a Press.
A polyurethane bushing is much easier to install because a hydraulic press is typically not required. The two piece design of a polyurethane bushing utilizes the original outer metal bushing shell. Once you’ve learned How to Burn Out Bushings the Right Way by reading our article on the subject, you can easily install the two piece design polyurethane bushing yourself.
Engineers design polyurethane bushings with the DIY’er in mind. There are a few polyurethane bushings on various applications that have an outer shell, but the majority use a two piece design. The two piece design bushings install by hand. You install one piece on either side of the housing and the center sleeve slides in the middle.
This should give you enough general information to determine whether rubber or polyurethane is the best choice for your vehicle. Just remember the differences in:
Rubber and polyurethane, while different in performance and feel, are actually more on the middle ground in the scale of bushing material. If you’re a race car driver that wants maximum performance and cares little about ride quality, an aluminum mount or metal joint is for you. I don’t know of any bushing softer than rubber but if you are crazy and innovative, attempt jello. For the majority of us, when it comes to suspension bushings, it comes down to rubber or polyurethane. Each has its own benefits and drawbacks. When it comes down to it, the only person that can tell you what’s better for your ride, is you.
Are you a polyurethane die-hard who would rather feel like you’re riding on rails? Or do you swear by rubber? Put your thoughts and experiences in the comments and let’s have some discussion.
The acronym NVH applies to the noise, vibration and harshness from the suspension of a vehicle.