Go-fast Improvements

(c) 2002 J. Sage Schreiner

 

After 6 or 7 track events in the car, I started looking for ways to incrementally improve its  performance. As things stood, there were several significant problems with the way the car drove. The first was really high gearing, done to meet strict US MPG requirements. The second problem was very soft suspension. Both significantly hampered the speed and "fun-ness" of the 318i on the track. I decided to address the suspension first and save the gearing for a later date.

 

The softer suspension had several results. First, it made the car feel more "vague". The car simply took longer to respond to my inputs. This meant that I had to turn-in a little earlier, simply because of the time the car took to respond. Additionally, it was difficult to feel exactly what was going on with the car at any given time. The softer suspension also lead to the car feeling unsettled in really firm braking. I believe that, in part, this is because the front suspension compressed ("dived"), resulting in the rear suspension decompressing and lifting. With an already light rear-end, this change in suspension geometry caused the car's rear-end to dart around, especially where the surface was rough. One benefit of the softer suspension was that things happened slower to the car, giving the novice driver (me) more time to react and fix the problem. This was a good way to start with the car, but after 6 or 700 miles on the track, I was ready to bump it up a notch.

 

Super quick lesson in shocks and springs (this wasn't completely obvious to me at first): springs are what actually "support" the body of the car. Without springs, the car would sag slowly to the ground as the shocks were compressed. But as you can imagine, if there were just springs, the ride would be very bouncy – every time you went over a bump, the spring would undergo a series of oscillations that would very, very slowly disappear. Shock absorbers (known as "dampers" in Europe) on each corner of the car help damp these oscillations. Without shocks, the car would be really uncomfortable (because it would bounce for a long time for every little bump) and impossible to drive. Shocks and springs are a system and work together. Therefore, you shouldn't just replace or modify one component (such as the springs) with out modifying the other. If you have ever seen a car with stiffened springs and stock shocks, you'll know what I mean: when the car goes over a bump, it bounces three or four times because the cut spring is stiffer (requires more force to compress)  but the shocks don't sufficiently "dampen" the now stiffened spring. On the track, this is really bad.

 

The first issue to address was the tall, soft stock springs. To solve this issue, I bought a set of Suspension Technique springs from a club member. They were a "sport" spring, a little lower and a little harder than stock, but nowhere near a "race" spring. My rational for using a taller softer spring was that, in my quest for incremental improvements to the car, the driver (me) would be better served by a small improvements over time vs. a more radical (albeit faster) modification. Plus they were cheap.

 

For shock absorbers, aka dampeners, I chose the Bilstein Sports. They are designed for lowered cars, having less overall travel. They are much stiffer than the stock shock absorber. I was able to find a set of fronts new on Ebay for a very good price, and ordered the rears online. My total investment in suspension components was about $400. The Bilstein Sports are probably a hair too stiff for the spring, but I'm not trying to build a fast car – just make moderate improvements cheaply.

 

The first work I did was the rear suspension. The rear shocks and springs on an E30 are really easy. The shock and shock mount comes out as a single unit. It takes about 20 minutes to get both of them out. Once they're out, you pull them apart, stick the new shock in the mount and bolt the whole contraption back in the car. If you're slow and kind of dim, like me, it'll take about three hours. Nifty trick: the top of the shock is "flat" and can be squeezed with a big pair of pliers as you undo the large nut the holds the shock and the mount together. I didn't discover this until I had done this twice.

 

Rear springs are a matter of jacking the car up and working the springs out by hand. I used my "human spring compressor" housemate, a big guy, to help with this, although I could probably do it myself. The new springs, because they're shorter, are easy to remount.

 

All told, I spent about 5 or 6 hours doing the rear suspension. This would have been a great time to replace the rear shock mounts, except I had already done that a few months previously.

 

Time for the front suspension. BMWs use a "McPherson" strut-type design. The strut is the bit that connects the wheel and the chassis. The strut is made of four main pieces. The bottom piece has steering components, brake rotor, wheel hub and so forth attached. The "back bone" of the strut is the shock absorber that is surrounded by a spring. Capping both the shock absorber and spring is the strut-top bearing which bolts into the chassis of the car. The first step is to get the strut off the car. I could tell this would be pretty easy.

 

I was totally wrong. The first step is to disconnect the tie-rod ends and control arms from the bottom of the strut. These two pieces control the suspension geometry of the front wheels. The nut that hold each mounting point came off pretty easily. Then I had to actually knock the "pin" that holds them in the strut. I banged them out with a hammer and a little bit of lubricant. The key to banging on them with a hammer is to not squash the threads. Some people bang on the actual tie rod end or control arm to jar them out. I used a metal "spike" on the top of the threaded pin to avoid mashing the threads. That worked fine, although it took quite awhile of progressively firmer banging before the pin suddenly gave.

 

The next step was undoing the three nuts that hold the top of the strut to the car. On the right side this was very easy, and the strut came right out. On the left side… I had a problem. Some @$%^#(*!& kindergarten dropout (square peg, round hole – failed) with compressed air tools had zapped on a too-small nut. I spent close to 8 hours trying to get the nut off without destroying the threaded rivet, but once I had it off I discovered the threads had been completely stripped and was useless anyway. I wasn't really happy about the idea of buying a new strut top bearing for close to $100, so I ended up whacking out the ruined rivet and epoxy-welding a bolt with the same thread onto the bearing. It held fine since the nut is what grips the bearing to the chassis – at least until I need to undo the nut at sometime in the future! The strut bearing didn't turn smoothly, so while I was at it I dribbled a little TriFlo into it and worked it back and forth until it was smooth again.

 

With the left strut out of the car, and my weekend work schedule completely blown (it was late Sunday night), I took the old struts, new springs and shocks down to Strictly BMW. They charged me a nominal fee to disassemble and reassemble the strut. I would do this again in the future – compressing the spring with a cheapo rented spring compressor while wrenching at the big nut that holds the strut bearing to the shock can be quite dangerous (and a lot of work).

 

I put the new struts back into the car the following Saturday, just in time for track days on both Sunday and Monday. I finished the job around 11.30 pm and took the car out for a drive. It felt very, very different and I was excited about the chance to wring it out the next day on the track. Except for one small detail: pulling back into my driveway, steam came pouring out of my engine. I popped the hood and found that a three-inch, oddly shaped hose running to the heater core had cracked wide open. That was a set of hoses I hadn't replaced. I ended up missing the Sunday track day because I couldn't find this oddly shaped piece of hose, or even something that was remotely close. Monday morning I had no problem finding an OEM replacement hose and was out on the track first thing.

 

The new suspension made the car feel very different. It was a whole new beast and I had to learn to drive it all over again. It was much faster and more responsive. Things tended to happen more quickly as well, as the car had less "give". Best of all, the car was better balanced and more confident. I found that as I went through the long sweeping turn 2, a tiny, gentle lift off the throttle would cause the car to turn in and line up on the apex, and I would squeeze the throttle back to the floor as I approached the apex. It was great feeling – you really can steer a car with the gas!

 

Monday was also the day the car rolled over 200,000 miles – somewhere on the back straight of SIR during my second session. I felt proud for my little car!