Re: Polyurethane question (MAx)
Well, I have no experience with Groton, but I can tell you that the words Urethane and Polyurethane can be and often are used interchangeably. They are almost the same type of thing just a different ratio of polyester, isocyanates and alcohols. Some are soft and stretchy like the seating foam in your car and others are hard as a rock. Some are thermoplastics and others are heat activated thermosets. Think of a thermoplastic like ice. You can melt it and reform it into another shape. But a thermoset is like an egg. Once you crack it open and fry it, you cannot return it to its former state. I believe that the Polyurethane in question in our car's suspensions is a thermoplastic. Thermosets tend to decay with heat and time and are not too useful in industrial applications. But most of my experience in thermosets are the polyester resin types like fast cast or insta-cast resins. I have used a material in casting that we simply call urethane. It is a two part resin compound that cures over a couple of days to a rock hard clear. The stuff that our bushings are made from is something like skateboard wheels but softer. I know that I have not supplied a clear answer to your question but I hope I have shed some light on it. I would not worry as to which supplier is selling what type of bushings. Chances are that they are the same material regardless of manufacturer, and that is suspension grade polyurethane. All that aside....I am an IPD customer and so I say, go with IPD.
As to the difference in price, I can only say that final product cost is wrapped up in mold cost, materials cost, and of course retail markup. If a lot of work and money went into developing the molds for the bushings then the end user can expect to see that cost reflected in the final cost of the product and also may see a better quality product as a result. Conversely, if little money was put into the mold making process, then the part will be cheaper, profit margin higher and the quality may be significantly lower. There are exceptions to the rule however. Product run plays an important role in final cost. Two companies spend the same money on molds and materials but one runs a production of half that of the other (considering both break even when all is said and done) the first company has to sell at a higher price. In short, a good many factors can affect the prices of the two offerings you see advertized. I have the IPD bushings in my car and I have had no problems with them. Wait for a sale or something to buy them and the hit won't be so bad, but once you have them in, you'll love them. Sorry for the long explanation(s) but it's like studying for me. The more I use the information, the more I remember for classes and work.