So much progress has been made on the coupe in so many areas. Things like rust/metal restoration, suspension upgrades, brakes, steering, software and more. In this blog I prefer to write about a story, or sub-project, from start to finish. That being the case, our steering system fits the bill for this post.
The original steering setup of the coupe, like the inline six motor is an important part of the E9 racing heritage. It was a conflict to rip it out, but for our particular goals, it needed to happen. We need to fit a lot of Tesla battery modules under the hood, and the large steering box takes up a lot of space. The steering column, box and all that iron linkage is also incredibly heavy. We opted to convert to a modern hydraulic power steering rack which is lightweight, efficient, and tucks in tight and low under the battery modules.
Why Not Electric Power Steering?
A lot of folks have asked me why we are not going with an electric power steering system. We deliberated a lot about this, as it is the future of power steering, and completely in line with our EV ethos. There are two reasons we opted against:
1- Electric racks have traditionally been terrible for driving experience in terms of their feel and input from the road. Only in very recent years have manufacturers made vast improvements in that area. The best systems also require constant communication with the computer which is receiving a lot of data about car speed, accelerometer, turn degree, steering wheel rotation and more in order to give proper assistance while retaining a desirable amount of road feedback. I went pretty far down this road before deciding that it was not going to be worth the effort - not when a good hydraulic steering rack feels great right out of the box.
2- We plan to use a hydro-boost brake system. Remember, we have no engine to produce vacuum. More importantly, vacuum systems are very large under the hood). Since hydro-boost systems run on a power steering pump, it made perfect sense to install a 12 volt power steering pump (from a Mini or Volvo) which will nicely power our brake and steering systems in a clean loop.
I can see a time in the near future when there will be good options for electric steering and brake boost systems for conversions like this. Maybe my next car…
Let’s Build It
We started with a goal to use nothing but BMW or Tesla parts for this project. However, when it came to the steering rack we had to deviate. BMW’s modern racks are front-steer (the rack sits in front of the wheels) and our coupe is rear-steer. We prefer the car to follow the most widely-recognized standard of turn the steering wheel to the left and the car goes left. Since we did not want to completely modify our car to front-steer, we opted for another German-engineered rack from a car of similar weight and size. The Volkswagen MK3 GTI VR6 rack fit the bill. Even then we had to shorten the tie-rods quite a bit. It’s crazy how small BMW’s original “big coupe" is compared to modern "compact” cars.
The “Everything You Touch” Motto
A few months ago I was chatting with a friend about what should be original what should be modern on the car. Clearly our Tesla unit is modern, but that doesn’t affect how the car looks inside or out. He made a comment that stuck with me: “Everything you touch should be modern”. While I would love to take credit for the motto, we have really continued down that path. The steering column falls into that category.
We decided to fit a BMW E46 (1997-2006 3 Series) steering column for a few reasons. It weighs half of our original column, but it also gives us a host of features without going over the top with complexities (no electric memory tilt, etc) We get a modern turn signal lever with lane-change soft touch, a wiper lever with modern variable intermittent control. The computer button on the end of the turn signal lever can be useful to us as well. Most of all, we get telescoping and tilt steering. These items directly fall into our “Everything You Touch” motto.
Finally, we have a working steering system that should feel great on the road, weighs about half of the original setup, and leaves more room for batteries. That there is a win-win-win.