Rear coilover spring rate

[CrookedCommie]

Hello, those running rear coilover conversion, what is your spring rate front to rear? I am aiming for equivalent 900/1000 but that is for a divorced rear. Maybe even 800/950, have a set of Moton 3-way remotes going in. Experience appreciated,
-Rudy

[S54330Ci]

Hello, those running rear coilover conversion, what is your spring rate front to rear? I am aiming for equivalent 900/1000 but that is for a divorced rear. Maybe even 800/950, have a set of Moton 3-way remotes going in. Experience appreciated,
-Rudy

I assume this is for a track oriented car?

My track car (no aero) is running MCS 2WNR with a C/O rear and Eibach springs. Also running Hotchkis sway bars front and rear (30mm/25mm). On tires that are less grippy such as the Hankook RS4 or Toyo RR the spring rates I am using work very well with these types of tires. If you are running a true slick or a Hoosier R7 I'd bump the rates up. Same if you are running front and rear aero.

So lots of variables to consider. This is my configuration.

Front
Length: 5"
Dia: 2.25"
Rate: 650lbs

Rear
Length: 7"
Dia: 2.25"
Rate: 500lbs

The shop that setup my car has 1000's of hours of race experience with the E46 chassis and likes this combination as it allows the front bar to be a bit stiffer to combat roll without having to take away from the compliance of the car. I find my car to be extremely well balanced and easy to drive fast.

[CrookedCommie]

This would be a fully built race car on Pirelli or Michelin slicks. Not sure the multiplier between shock at coil over and divorced would be. I personally prefer handling all the body roll on the springs and leaving sway bars soft which is why I'd be aiming for 900 fronts and whatever the corresponding rear rate would be. The remote Motons should be able to handle that nicely without having to go lower on the spring rate.

[elbert]

Hello, those running rear coilover conversion, what is your spring rate front to rear? I am aiming for equivalent 900/1000 but that is for a divorced rear.

Wheel rate for divorced set up is roughly half of a coilover. So 500# springs would be a good starting point.

[cobra]

The ratio to convert from divorced to true coilover is 0.55 so 900*.55 = 500lb/in

That's very stiff for what I'm guessing is a lightened track car so I assume you're running aero too?

[CrookedCommie]

Yep, sub 3k with driver, Artisan clubsport splitter with the Klaus BW wing. Sounds like 900/~550 might be the base line and see if we need to move it down. I still need to check what spring rate it has, the race car we pulled it from might have been setup too stiff. 800/500 might be a good trade off between WRL tires, slicks, and rain setup.

[fourmula1]

Seems like the 800/900, 900/1000 range is pretty conventional and is what bimmerworld will recommend and can be found all over forums etc. My observation is some really fast builders/racers in the north east usa have been using way less spring.

Tacking on with another question - are people using oem hardware for the rear lower shock mount? Now that it sees more weight does it require stronger hardware? Or just more frequent replacement?

[bigjae46]

According to the flat ride calculator, I should be running about the same spring rate at all 4 corners with a rear coilover - its +/- 25 lbs to be spot on at some corners but hard to find springs in the 25lb increments I need.

[Sergmann]

moton 2 way clubsports here. Nine lives rear wing, home made front splitter setup. car is 3100 with me in it. strictly HPDE with NT01's of Toyo RR's depending on what I can get at the time. 900 front 450 rear

[Projecte46m3]

JRZ Motorsport Series 11 2W remotes here. I'm running a very soft setup with 6" 450lb front spring and 8" 350lb rear springs. No aero and street tires.