Ideal spring rates for a light 128i

[squidge]

I keep telling myself I'm happy with the stock M-Sport suspension. Naturally, after doing an HPDE at Thunderhill, I became more aware of deficiencies in the stock setup. Especially transitioning from T5 to T6 -- the balance of the car shifts heavily from left to right and you can't do much until it's settled, and it just seems to take forever.

I've got my eye on the TCK SA setup with their camber plates. In TCK's article on the 128i, they suggest 350/500. The ratio between these rates seems too small given the factory ratio, or that of most lowering springs. I also have a pretty light 128i -- 6MT, no sunroof, halogens, no additional options or equipment besides M-Sport. Would 300/500 be better? Or 300/600 to get that 1:2 ratio? I have RSFB inserts, an E92 M3 FSB, and M3 front control arms and tension struts. I anticipate adding the M3 rear guide rods and controls arms too, so I think a little extra spring rate is needed to compensate, right?

I feel like I'm nitpicking but don't want to go through all the work of installing and then have to change it out later.

(I know, I know, call the vendor. I'd like some more data points before I get on the phone and get talked into buying something.)

[ShocknAwe]

I'd give TC a call and talk it through with him.

[John_01]

500# on the rear is still quite soft in the context of a dual duty track and road car. I suggest to go for at least 600# on the rear. Especially if you keep the stock rear sway bar that is very soft. I think there are comments from TCK on the forum somewhere where he wrote that 600# was later found to be preferable to 500# for the 128i in the magazine article. Again it depends on the context of usage, tires, sway bar etc, so I don't think there is any single correct answer.

[Dackelone]

The Ultimate Handling Machine...
TC Kline’s suspension tuning transforms the entry-level 128i Coupe into a car that can rival the 1 Series M Coupe for pure driving fun.

http://www.bimmer-mag.com/issues/101...e#.V3oXNLh97IU

http://www.1addicts.com/forums/showt...ndling+Machine

[John_01]

Here is some info about the TCK rear spring rate used on the car in question.

http://www.1addicts.com/forums/showp...21&postcount=6

[squidge]

Dack, the whole point of this post is questioning the rates suggested by those articles... so I've definitely already read them.

Thanks for the input, John. I'm on stock RSFBs with Whiteline inserts right now, and intend to eventually change them to M3 bushings, but probably not for a year or two (waiting until I get moved back into my house in Raleigh with more working room.) I'll likely bundle that upgrade in with an LSD and rear sway.

Sounds like maybe 350/600 is the way to go. I'll talk it over more with HPA or TCK before I pull the trigger on anything.

[HP Autosport]

If you are not tracking the car and comfort is what you are after, 300 front and 500 rear is perfect. If you are taking it to the track, 350 front and 600 rear will keep the dive, squat and body roll to a minimum, but still not beat you up on the streets.

With the upgraded rear subframe bushings, you can up the spring rates a bit in the rear without having extra deflection in the bushings that can't be controlled by the rear shocks.

[squidge]

Thanks for the helpful input! I'm doing HPDEs with it, so that confirms that 350/600 should be a good choice for me.

[HP Autosport]

Originally Posted by squidge

Thanks for the helpful input! I'm doing HPDEs with it, so that confirms that 350/600 should be a good choice for me.

It is a lighter car than 135i and you will be doing mostly street driving. I would go with 350 and 600 for the best street ride possible. It will be a night and day difference vs your OEM suspension regardless of the rates you run.

Let us know if you need a price quote of have further questions.

[Ginger_Extract]

Try 300/600 for a car that still sees street miles. I have 400/700 on my 135i and even with the dampers turned down and the car at a reasonable ride height, it's too much for LA's shitty roads.

[HP Autosport]

Originally Posted by Ginger_Extract

Try 300/600 for a car that still sees street miles. I have 400/700 on my 135i and even with the dampers turned down and the car at a reasonable ride height, it's too much for LA's shitty roads.

What dampers?