We’ve gotten most of the reliability issues taken care of so now it’s time to start the performance modifications. As I said in the previous post, the focus of the performance upgrades for the BMW E36 will be in the handling category. Basically, the car needs to change from comfortable to more like a go-kart.
It’s best to go with a complete suspension package that is proven to work well together. This mean springs with well balanced front and rear rates coupled with shocks valved for the springs and intended driving (autocross racing in this instance). Being that the BMW E36 platform is over 20 years old and has been raced successfully for many years, there are several different options that should work well. One that seemed to receive great reviews no matter where I looked was Ground Control Suspension Systems complete coilover kits. Ground Control is a California headquartered company that’s been in business since 1980 supporting the racing community with quality suspension systems. I scored a sweet deal on a slightly used setup from someone who was upgrading to an upper tier suspension system.
The stock springs in the E36 325is are a compromise between a nice cushy ride and still “sporty” for cornering. The stock spring rates for the front are around 100 lbs/in. This means that it takes 100 lbs of force to compress the spring 1 inch. The front spring rates on the Street / School Hybrid kit that I’m using from Ground Control are 450 lbs/in. Quite the increase! However, this is most likely a little on the low end of what I may eventually be running (possibly move up to 525 lbs/in) as many people run slightly higher for similar racing. You can see the difference in the picture above between the stock front strut (bottom) and the GC front strut (top). Front struts also include a shock inside the spring. However, the stock shock is non-adjustable and pretty soft while the GC assembly uses an adjustable Koni shock that can be set from less stiff to very stiff by simply turning a knob allowing suspension adjustments to actually be made in between runs at the track. The ride height is also adjustable using the yellow adjuster ring on the red threaded strut housing.
Another key item in the Ground Control front strut assembly is the camber/caster plate. This can be seen in the picture above as well as the picture showing the full GC strut assembly (shiny bronze looking piece on the far right side of the assembly). Racing cars need to be aligned such that the greatest amount of the tire is in contact with the road when going around corners. This optimal setting is more than can be attained in a stock car. In normal cars the top of the strut mounts to a fixed assembly that allows for only limited adjustability in the alignment of the tires. In most all race cars the top of the strut mounts into a “camber plate” which actually allows for a fairly large adjustment of camber and caster. I’ll cover alignment settings in a future post.
Stiffer rear springs and shocks are also included in the GC kit. The stock spring rates for the rear are around 300 lbs/in. The rear spring rates on the GC kit are 550 lbs/in. As you see, not nearly the same drastic increase in the front but still a good bit higher (all about the right balance). Same adjustable Koni shocks are also used in the rear. Heavy duty shock mounts are included as BMW E36 cars are known to crack and/or tear out the rear shock mounting location in the chassis when subjected to the greater strain the comes from racing.
Luckily, installation of the suspension system is actually pretty straight forward. There aren’t even any spring compression tools required. Also, I was lucky that the previous owner recently replaced the shocks/struts with other OEM shocks/struts and thus all the bolts were easy to loosen and not corroded over from 20 years being on the road. Anyone need OEM BMW 325is shocks and struts in great condition??? Ha ha!
Once everything was installed I was pretty excited to get it back out on the road and experience the transformation that I was pretty sure had occurred. Sure enough, the car responded to steering inputs like never before! Definitely a very firm ride but feels like it would do well on the track. There’s just honestly way too much handling potential to even think about testing it to any real extent on a normal road. Plus the alignment hasn’t been fully dialed in yet either…
I really won’t know how awesome this setup is until I get it out in the first autocross event and put it through it’s paces. Stay tuned!