Monday, 18 June 2007

Urethane Parts for Beetles

Progress with the Beetle is slow but everybody warned me that I'd discover more problems than I could see initially and that it'd take longer than I'd anticipated to do the work; so while the nature of the extra problems and work is a surprise, the discover of it isn't. I'll say more about that in another post (it's about time I posted a progress report) because in this post I wanted to say something about urethane parts.

I'd seen them on sale in a number of places and was tempted by their pretty red colour. Of course I wasn't about go changing everything just because of the colour but when one of the rear bump stops broke off in my hand, such that new brackets and 'rubbers' were added to my shopping list, I thought I might give them a try.

Before diving in however I did a search on the VZi forum and was surprised to see that hardly anybody had a good word for urethane. I started a new thread to try to get to the bottom of it (click here) and based on this, plus a little reading elsewhere, I came to the following conclusions:

Most of the urethane parts for Beetles are for use in places where they will be flexed and/or squashed (as opposed to having mechanical movement against them). These inclide bump stops, suspension bushings and gearbox mounts. My research indicates that urethane parts are harder than their rubber equivalents so while they will hold a gearbox more firmly, they will also transmit more vibration into the car. This seems even more counter productive in the case of bump stops and suspension components where they will transmit more vibration, and shocks in the case of bump stops, to the metal components they are supposed to be cushioning. I've been lead to understand that this has benefits in off-road vehicles like dune buggies (where you're expecting a rough ride anyway) because they will last longer. It would appear however that the additional life of the component is little compensation for the loss of ride comfort and protention of other parts in a road car.

There is one major deviation from the flex/squash use of urethane parts in a Beetle and that is in the form of urethane bushings for the front beam where they are used as replacements for the original metal roller bearings and rubber seals. It seems however that they have only one advantage over the original parts: they're cheaper. They will (apparently) wear out much faster and the only argument that I've seen that held any water was that if you're using them in an off road car where you might anticipate knackering and having to replace bearings on a regular basis because of the way you are using the car as opposed to through normal wear and tear...

Thus I will be replacing my bump stops, and any other relevant bits, with rubber as I've concluded that while urethane parts might be of use on an off road vehicle or one whose primary purpose is to look pretty, they have no place on a road car intended for daily use.

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