Solid Bushing Explained:
Polyurethane vs Delrin vs Aluminum Bushings
If you own a BMW, chances are it will need to have some or more likely all of its' chassis and suspension bushings replaced. A few common questions we see here at Garagistic are, "which hardness polyurethane bushings should I choose for my vehicle" and "should I choose polyurethane or solid bushings" This article will cover the different types of polyurethanes, and the differences between polyurethane, Delrin, and solid aluminum. Hopefully, this understanding will help you determine which hardness bushings are right for your build.
Before you make the decision on which bushings to purchase you'll need to determine what your vehicle will be used for. Whether it be exclusively daily driven, daily driven with some track use, or strictly track use. These will give you a good indication of which material bushings you'll want to purchase.
Polyurethane is a type of elastomer in the plastic family of materials. This means that it has excellent vibration absorption and has the ability to deform slightly and return to its' original shape. Polyurethane is an excellent material as it can be made into different hardness levels. Keep in mind the harder a polyurethane the more noise and vibration it will transfer into your chassis.
80a: This is our softest available polyurethane. It is ideal for those looking to maintain comfort levels in a daily driven vehicle. This is a great option for someone who is looking for a setup that will be comfortable on the street but can also perform well at the occasional autocross or HPDE.
95a: This hardness polyurethane is more suited to those who have vehicles that are track-oriented and will see less street time than your usual daily driver. This hardness polyurethane is rigid enough to make a huge difference in a vehicle's overall feel and handling characteristics while allowing a moderate amount of vibration and noise absorption.
Delrin is actually very hard plastic. It is much stiffer than 95a polyurethane with much less NVH transferred vs aluminum. This makes it an excellent alternative to solid aluminum or polyurethane. This material is excellent for track-oriented or dedicated track vehicles as it does still offer some vibration absorption over solid aluminum while still being extremely rigid. Unlike polyurethane, Delrin does not have the ability to deform slightly and return to its' original shape. If your vehicle is likely to see impacts frequently (drifters) this material may not be the best for you. Additionally, if your vehicle is equipped with Delrin bushings and it is in a collision it is highly recommended to check tolerances on any bushings you have installed that may have been impacted. As Delrin does not return to its' original shape after compression it can create play within the bushing and chassis which may lead to premature wear or failure of other components.
Solid Aluminum is the stiffest and strongest material used for bushings. It offers almost no vibration absorption and is not recommended for daily driving. Unlike both polyurethane and Delrin, aluminum offers no deformation. This means that it is best suited for vehicles that are exclusively used on track as any impacts to the vehicle can cause unwanted energy to be sent into places it shouldn't (internal drivetrain components.) This is something you should take into consideration if you know your vehicle may be at risk for contact. However, if you are looking for the most feedback from your chassis and the most rigid feel, these may be ideal for you.
Which bushings should I choose?
Hopefully, this article has helped point you in the right direction when it comes to selecting new bushings for your vehicle. At the end of the day, the choice is yours to make. We recommend our 80a soft polyurethane bushings to those looking for a comfortable ride on the street with a small amount of autocross, HPDE, or drifting on the side. We Recommend 95a polyurethane bushings for those of you who are looking to get out on track more often but still occasionally street drive your vehicle. As for our Delrin and solid aluminum bushings we strongly recommend that these only be used on track-oriented vehicles with little to no street driving as they will provide an extremely firm and responsive feedback from the road.