What is durometer and what does it mean? If you know what it is, when does it actually matter? Every day at CorkSport we are asked this question. Many times, we are told that many of you assume that the higher the durometer or something attached to a car, the more noise and vibration will be transmitted into the passenger compartment. This however, is not always the case.
Durometer is the measure of the hardness of a material. The higher the number, the harder the material is. When talking about rubber or polyurethane, you will often hear durometer numbers between 60a and 90a. There are several scales for the measurement of durometer, in the case of bushings, you will almost always hear about the Shore A scale. The letter at the end of the rating will tell you which scale you are rating.
When designing engine mounts or suspension pieces, the durometer can be very important, but the shape and how the piece is used can be even more important. The overall durometer number will give you the first idea of how much vibration the mount or bushing might transmit, but this can easily feel different depending on the surface area used.
If you have an engine mount that has to fit a certain area and you decide to design it with a very small bushing, or a bushing that has to do more than just isolate the two parts, you can end up transmitting a lot more vibration. If you compare a 1” diameter bushing and a 2” diameter bushing you don’t end up with double the amount of surface area, you actually increase the surface area by 4 times! That isn’t the only way bushings work though. Depending on the direction of the force, you could use a bushing much smaller and obtain a much better isolation than one with a bigger available surface area subjected to more force. In many cases, only the durometer of the bushing is taken into consideration when many mounts are designed; not how the bushing is used, its size or the forces applied to it.
Recently I was asked by Kevin Pugh (the owner of MazdaSpeed Forum) the durometer of a mount we released. I replied to him; “it doesn’t really matter, but I will tell you anyway”. We had a good laugh and talked about many of these points; and because of that conversation this blog post was born. Much like many of the topics on the CorkSport blog, we recognize the market and what is important to you. This information is as important to you as it is to us, and whether you buy our entire catalog or just read our blog and stay stock, we always want to be of service to the Mazda community that we have been dedicated to since 1998.