Wheel, Tire and Suspension Upgrades
Now that the 320i has passed inspection and is drivable it is time to customize the car a bit. The first thing I did was buy 15" Alpina knock-off wheels. They are 15"x7" spoke rims and look very similar to the original wheels on the car. The knock-off meant that they cost less than $200 a wheel. Real Alpina wheels cost $1000 a wheel! The 13" wheels that came on the 320i really limited the number and type of tires available today because of the diameter and width. The new 15" wheels make many more tires available. I got tires for the 15" wheels that were the exact same circumference as the 13" wheels and tires. That was done so the speedometer would still be accurate. I found a website that calculates things like offset and circumference called Rims and Tires. I also got the 15" wheels to help the clearance issue with the rear disk brakes. When I did the upgrade to disk brakes in the rear the upgrade kit warned that the calipers might interfere with 13" wheels. I had ground down the contact points on the calipers but they still dragged a little bit. Now with 15" wheels there is plenty of room. Of course getting the new wheels on the car would not be so easy. The issue is the offset of the wheel. That determines how far in or out of the wheel well the wheel will sit once it is mounted on the hub. It is important that the offset is correct so the wheel does not interfere with the fender or the shock mounts. The offset for the 320i rear wheels is 13mm. Unfortunately the wheels I got came with 18mm offset. That meant I had to get 5mm wheel spacers to make up the difference. Many wheel spacers are available for the 320i from many manufactures, in the correct diameter, thickness and bolt pattern. However, installing the wheel spacers was not that easy. I found that the rear hubs on the 320i had a 2mm area that was not machined down to the 57.1mm hub diameter. That meant the spacer would interfere on that edge and not make flush contact with the rotor. I had to take the spacers to my local machine shop High Tech Machine and have them cut clearance for that larger diameter offset. I found after installing the wheels a few times that I needed to install threaded studs into the rear hubs. That made alighment of the spacer disk and mounting the wheel much easier.
The next upgrade was to get a new suspension setup with coil-over shocks. A company called Ground Control makes a set of coil-overs for the 320i. I wanted to change the suspension so I could adjust the ride height and make it even in all the corners. With the added weight of the batteries over the rear axel, the rear of the car squat a bit with the old springs and shocks. Unfortunately installing the coil-over system was not that simple. For the front wheels the Ground Control system uses a larger diameter strut tube than what came standard on the 320i. That meant the old strut tube had to be cut off the wheel spindles and a new one welded on. I could not do that work, but I found a company near me that specializes in restoring old BMWs and does that kind of shock work all the time. The company Vintage Sport and Restoration (VSR) has quite an operation going. Not only do they have a multiple bay area with car lifts, they also have a full machine shop, weld shop, a body shop and paint room. They took the wheel struts off, cut the strut tubes off and sent the wheel spindles to Ground Control. For some reason it took Ground Control a long time to turn the struts around. I thought the whole process would take a couple of weeks but the 320i was there for over a month. Even though VSR measured the weight of the car (same weight I measured) and measured the corner to ground heights, Ground Control sent the wrong springs for the rear setup. Too short and too low of spring rate. VSR had to order longer and stiffer springs to get the right ride height. The ride height is adjustable with the Ground Control system and I had them set the height lowered to about 1".
When I was driving the 320i to VSR I noticed that I had a vibration in the front end at 40 -50 mph. Even from the beginning first drives there never has been any vibration of any kind while driving at any speed. The only difference was the new wheels and tires. I doubted it was the wheels and thought maybe the car needed a wheel alignment. When I told the guys at VSR about that, they noticed the new Dunlop Direzza tires I got were mounted backwards on the wheels. High performance tires like that have a rotation direction, so the vibration was caused by the improper mounting. Of course the tires had to be remounted and spun balanced. The new tires really make the ride feel great, very positive tracking. But they do have a downside. Because they stick much better to the payment they really cut the battery mileage down - nearly 20% compared to the old wheels and tires. Even with that mileage reduction I will have plenty of range to use the car as a daily driver. While the 320i was at VSR they also corrected a problem with the driveshaft alignment and an issue with the calipers on the rear brakes. The driveshft issue required the front engine mounts to be lowered more than an inch. That mean the left side mount spacer block was removed and the right side replaced with a bushing. While at VSRt they thought I should refer to the car as the 320e for electric drive. The "I" at the end of the model number for BMW always meant fuel injection. No gas being injected in this car, although you could say electrons are being injected into the electric motor, but that might be a little too much for some people to understand. So I think from now on I will refer to the car as the 320e. Thank you VSR!
The last upgrade was not really and upgrade as much as a reconfiguration. I took the rear seat to an upholstery shop and had them take the leather seating material off and mount it on a piece of plywood, with a 1-inch dense foam pad underneath. The plywood I cut from a cardboard template I made of the rear seat area with the battery box tops. It did not cost much for the upholstery work and the rear seat now fits much better over the battery boxes in the rear seat area. It still will not be possible for someone to sit there, but it looks much better and should support small weight like groceries. Related to the rear seat area I installed sound damping material in the side cavities, behind the lateral trim panels, in the back seat. The new tires make a lot more sound on the road so the sound damping is necessary. In fact the first time I drove the car with the new tires I though there was problem with the tires because with the electric drive, the car is very quite. Of course a lot of the noise was from the tires being mounting the wrong way. After VSR remounted the tires the noise was reduced, but still louder on the highway than the other tires. The Direzza tire formulation is only for summer driving. They are not recommended for winter driving - probably get too hard in the cold. I might get a set of Michelin Energy Saver tires like I have on my Chevy Volt for winter use. I might also have to get another set of cheap wheels. Not that I am going to drive in the snow much, but when there is a nice clear day I would like to drive the car. In the winter around here they put a lot of salt on the roads and I don't want to ruin my new Alpina knock-offs.
The way the 320e drives with the new stiff suspension and new tires is very different than the way it drove before. Because of the heavy weight on the rear suspension the car would pitch a lot in turns and understeer. It also took bumps hard because most of the suspension was compressed with the heavy weight of the batteries. With the new setup the ride is a little bumpy on side streets but on the highway very smooth and very positive control. The car also corners really well now. Very happy with the upgrades!
A video will be coming shortly.