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BMW 135i Track Car Build

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My 2008 BMW 135i is a work in progress. I bought it new as a summer daily driver with the intention that it would eventually take over as my track car. I had previously developed a 1989 FC RX-7 Turbo II as a time attack car for a local racing series. That car worked well, but after replacing the engine 3 times, I decided to sell it before a 4thone was required.

I have learned that suspension improvements provide much more bang than engine power increases, so most of my efforts have been focused on suspension. Serious suspension upgrades on the BMW began in 2014. I have been documenting most aspects of the BMW development on the 1Addicts forum. I find that writing for an audience forces me to think more deeply and document more thoroughly.

My background is in the design, approval, manufacture and installation of special purpose aircraft modifications. That has given me access to the space, tools and materials needed to dive pretty deeply into the subject of suspension design. Canada’s long winters have helped provide the time to do so. As Tim has noted elsewhere in this Forum, thousands of hours have gone into this car. The attached link provides a glimpse into how it started.


Thanks for posting this here James. Your comment about finding gains in concentrating on the suspension resonates with me! I know there will be a lot of value in you sharing more of this development process and your lessons learned with Racecraft members.

What you say about writing for an audience forcing you into refining the way you work is interesting too.


Once this car became a dedicated track machine, some roll-over protection started to sound like a really good idea. As the car still gets itself to the track, but is not involved in wheel-to-wheel racing, a roll bar seemed a better idea than a full cage. Here is the storry of how I built a roll bar.


Nice Build!

One of the first (and more important) lessons I've learn in the track world, was... "don't spend any dollar ("pesos" in my country :D) in upgrades, before you have spent all you have in tyres... then, go for a good suspenssion setup, and then, repeat." XD

Wise words there Luis!

While the 135i comes with some pretty good looking 6-piston front brakes, even with good race pads they are a weak point on the car. To solve this, I designed and built an AP Radi-Cal 5000 installation for the front. The original 2-piston rear brakes have proven to be completely adequate, and the AP front brakes have been bullet-proof. While generally an off-the-shelf big brake solution is a much more sensible approach, I had access to a set of calipers intended for an STi for the initial design, which took some up-front sting out of the process. Here are the details:


Essex Parts (AP's US dealer) has some interesing thoughts on brake ducting:


That last was a good read - and with more consistent disc temperatures the pads can also be better optimised for that working range, as many will vary their CoF across their nominal operating range - and there is the wear problem, as mentioned, from pads becoming abrasive at excessively high, or low, temperatures.

Essex has added an article on carbon-ceramic vs. cast iron discs that is worth a read.


Nice one, thanks James. Will give it a read

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