Quote:
Originally Posted by cvc 22349a
Are you keeping your BMW PS springs in the front?
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Originally, I was thinking of doing just that. But, I am using front springs from the 335d. The estimated spring rate of this spring is 156#, and that estimate is based on the known nominal 335i spring rate of 145# (to the best of my knowledge, Orb got this number from BMW). Vorshlag has measured a bunch of springs, and found the actual rate of the 335i sport spring to be a little lower, about 138#.
An alternative front spring to the one I chose is the performance spring for the 135i, which Jah29 measured at 160#. Exactly the right rate. The 135i is just a little heavier than the 328i, which means used on the 328i it would ride 0.3" higher. That means a ride height of about 14.3", not bad!
This may be a great choice of spring for someone looking to do a similar "M3 tune" on a 328i. There's a risk that the 1er coupe fender height is slightly different, though. I wanted to avoid that risk so I stuck with spring choices that came from sedans (e90), to match my car's body style. That way I could match equipment exactly and predict the ride height. (We'll see how well
that turns out.)
Here are some front corner weights to give an idea of what's available. There are sport springs and performance springs for each car!
328i sedan manual. (3362 * .505 / 2) - 105 = 744 lbs
135i coupe manual. (3373 * 0.516 / 2) - 105 = 765
135i coupe auto. (3439 * 0.519 / 2) - 105 = 787
335i sedan manual. (3593 * 0.509 / 2) - 105 = 809
335i sedan auto. (3605 * 0.511 / 2) - 105 = 816
135i convertible auto. (3704 * 0.497 / 2) - 105 = 815
335d sedan auto. (3825 * .51 / 2) - 105 = 870
335i convertible. (4001 * .47 / 2) - 105 = 835
As you can see, the convertible is the heaviest car; but its rearward weight distribution makes its front corner lighter than the 335d's.
These car weights come from BMWUSA, straight off their web site. My understanding is that these are wet weights, and include some gas and a 165 pound driver. The estimate for unsprung weight comes originally from JAJ, I think. It came with the spreadsheet I've been using to model steady-state corner behavior.