springs?!, WTF Options

[sk8kat1]

I wanted to get some 140# springs .. I bought some used ones and they seemed short and not 140#... but I wasn't sure because they were not marked

so I broke down and bought some that I knew were 140# they were marked

well I got the new ones and they are huge!

so what are the ones I got used they seem to measure out almost ident the yellow are about 1/16 th tighter coil

[ChrisFoley]

QUOTE (McMark @ Mar 18 2006, 10:19 PM)

I think it's the standard issue of engineers looking at math and not realizing the assumption they are making. Using a spring compressor to measure spring rate IS NOT THE SAME FORCES as a spring experiences in a car. So you can't compare the two. But I have no data or experience, so I'll shut up after this post unless some asks me a question. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

The rate of a coil spring is dependent on wire length and diameter in addition to metal composition, nothing else. When the close coils of a "progressive" spring go into coil bind the wire is effectively shortened causing a higher apparent rate. Therefore calling them "progressive" is a misnomer. They have only two distinct spring rates and there is nothing progressive about them.
What Andy experienced and what Erik described have nothing to do with the compression rate of the spring coils, only inertia. The coils at the suspension arm end of the spring are being accelerated when the arm moves. Putting the closely spaced coils at the bottom means they will slow the movement of the suspension more than the other way around due to the greater mass of coils. On a lightweight motorcycle driven over bumps and jumps this will give a similar feeling as a higher rate spring.
Andy's experience with motorcycles has no application here - it's apples and oranges. Whatever he experienced at autocrossing had nothing to do with inverting the springs in spite of his belief that it was the only thing that changed. (just my opinion!) The same feeling won't be experienced on a car since other factors play a much bigger role. If you want to reduce the unsprung weight you will have to live with a higher center of gravity and vice versa. Put them either way and you won't notice any difference unless you are a very talented driver and your car is a well built race car. But race cars typically don't use progressive springs because drivers don't want to experience a sudden change in spring rate when entering a corner. The comfort value of progressive springs is only for bumps on public roads.
BTW, I got a good laugh while reading the old discussion. Talk about people taking themselves too seriously. It's just like creationism vs. evolution. Both sides think in order for them to be right the other side has to be wrong. (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/bootyshake.gif)