Project BMW 135i STU at Kansas City SCCA MiDiv

Car Set Up

Project: BMW 135i STU

7 Apr , 2010   David  

Since my first autocross event of the season, at least driving event, is fastly approaching (this Sunday!), I thought I would give an update on what I’ve done to the 135i during the autocross offseason. Last year I ran in STU with my only modifications being a larger front sway bar and larger width front wheels. The larger front sway bar and less staggered wheel/tire combo helped a lot over the stock set up (with run flat tires), but to get the car to be anywhere near competitive some more upgrades were required.

BMW 135i HDR

The first improvement I decided to make to the car was swap out the stock E-Diff and put in a Quaife LSD. This by far and away the best mod you can make to the car. It is not a cheap or easy to install modification by any means, but the return on investment is very high. It’s just too bad that BMW didn’t supply a proper LSD in the car to begin with!

APEX ARC-8 Wheels

APEX ARC-8 Wheels for BMW 135i (Satin Black)

Next, I ordered new wheels and tires from APEX, ARC-8 Racing wheels in custom 135i offsets, well at least for the rears. I decided to try and minimize the stagger as much as I could and opted for the 18×9 designed for the E46. So I ended up with 18×9 for the front and 18×9.5 for the rear. I have opted to go with Dunlop Direzza Star Spec tires, mainly because it was the only option in the sizes I need; 255x35x18 (front) and 275x35x18 (rear).

AST 5200 Suspension

AST 5200 Suspension Bits

Suspension was next and I placed an order with Tarsust for AST 5200s with custom spring rates, which Tarsust advised me on. Taking into account supporting modifications (sway bars, LSD, wheel/tire setup, etc.), my current autocross skill level and desired dual duty use of car (autocross and daily drive) we decided on spring rates of 700/850. The ride comfort has been amazing, even better then it was before on stock, which is pretty amazing considering the spring rates the car is running! Tarsust went above and beyond when it came to customer service and making sure everything went well and got installed properly.

The final piece for my offseason upgrades was a new exhaust, to save some weight and add some much needed noise. The car in stock form was much too quiet and I hoped to add a bit of noise to better hear the car. I decided on an Agency Power cat back system (midpipes and muffler). It is much lighter and adds the sound I was looking for, but I have had a lot of fitment issues causing some rather annoying rattles. Hopefully I can get those worked out sometime in the near future.

2008 BMW 135i HDR

2008 BMW 135i with AST 5200 & APEX ARC-8 Satin Black Wheels

I am very excited to see what the car can do with the new upgrades this weekend. Hope to see a bunch of you out at Lincoln Air Park this weekend for the event!

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