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Originally Posted by xBlueStreakx
You're right on alot of points.
Also, after I mentioned that the E46 had similar motion ratios, I went to verify and realized "oh shit", they're not as similar as I thought. Foot in mouth on that one.At any rate, I understand theory says X and I was all about targeting a wheel frequency, springing it accordingly and calling it a day. But then after searching around, the theory isn't applied verbatim which leaves me scratching my head. I'm versed enough in suspensions to not try something willy nilly (hence the move to go with an incremental approach with a stiffer rear spring) but
not well versed enough to discount 'common knowledge' (whether right or wrong) and just do my own thing. Definitely want to get to the latter where I can comfortably do my own thing regardless of what others say.
One thing the wheel frequency calculations do not account for (or just assume) is chassis flex, give in the subframe etc (which fe1rx touches on). The calculations assume the suspension is acting on a fully rigid chassis... which is not the case in any street car and to be honest may not be the case in my caged racecar either. For instance, my cage doesn't tie in to any part of the front suspension (or near it).
Yeah. Will definitely scour the FRS/BRZ forums to see what's up. Thanks for the other links btw!
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Yeah, I was heated when I wrote all that after I had just installed my YCW coilovers. They tout delivering even F:R ratios, but I installed them only to find out I received 6k/12k springs that they were using for "stage 2" testing. It doesn't feel right with the 27mm bar up front. Car understeers if I turn in too hard. It also feels like it runs a wider line on exit. They will be sending me shorter 4k springs when the coilovers are in production stage.
The basic natural frequency approach is only taking a static 2d picture of the suspension into account. The suspension changes dynamically as it goes through it's motions which effects the springs effectiveness. Making alignment changes, changing bushings, and lowering the ride height also changes the motion ratio so you need to account for that as well. The typical changes we make to the rear, like spherical bushings and solid subframe mounts, serves to further reduce the effective rear spring rate, as fel1x points out in his testing. So no, spring frequency alone is not 100% accurate and shouldn't be relied on solely. It's a good place to start though rather than dialing in massive understeer right off the bat.
I jumped on the bandwagon modding my 135i suspension as everyone else does. The result so far is a car that handles worse in comparison to my 128i lol. I hope lowering the spring rate up front helps. Maybe simply removing the 27mm whiteline front bar will help get the car back to a more neutral balance. I'll try both.
Your car looks amazing btw!