Quote:
Originally Posted by ovekvam
I don't have an M135i, but I have driven the F20 on quite a few track days. My current 118i has the same brakes as the M135i.
The brake feel is good, and the balance of the car going deeply into corners with trail braking is excellent. Very consistent. With my engine, it is impossible to overheat the brakes, but I suspect I could do it with 300+ hp. There are optional Performance brakes from BMW. They are probably slightly better.
The stock non adaptive suspension is very compliant. It can feel a bit sluggish, but if works well for experienced drivers. In my opinion, the balance is best with a square tyre setup. With the narrower front wheels, you get a bit too much understeer. There is an optional Performance suspension from BMW, but I have never come across any F20 that has it, so I don't know how it performs.
The fake LSD works well for the smaller engines, but I would have gone for a Quaife unit on the M135i.
Another thing to consider, is M4 front control arms for more negative camber. Otherwise you will experience excessive outer tyre wear up front during track days.
The steering feel is a bit vague in the F20 until you push the car to the limit, but when you take it to the limit, you get plenty of feedback, even on ice tracks.
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I had an m135i and over time fettled it to fix foibles I felt needed addressing.
Brakes - agreed they're not bad out of the box and I chose to upgrade hoses and changed to DOT5.1 fluid. Pads were OK and eventually switched to OE m4 sport pads however OE f8x standard pads are useful upgrade for m sport brakes. I also chose to upgrade to mpbbk spec by adding 370mm discs and calipers to the front axle of the car. Not essential TBH as you can buy 340mm slotted/dimpled discs to fit standard calipers but I tend to late and trial brake and this setup worked well for me.
Suspension - wallowy and vague on track - upgraded springs with OE existing adaptive will help - I went further with mine upgrading ARBs, adding F8x front arms and fitting f22 underfloor v brace to help locate rear subframe.
Diff - yes traction is an issue esp with 245 rear tyres and I had a Quaife LSD - superb.
Tyres - I think the car is under-tyred from the factory and so would work better with 8"/8.5" wheels with 245/255 tyres.
BP
PS - read this m135i owners thread on BabyBMW forum about his car and use on track
http://www.babybmw.net/viewtopic.php?f=19&t=100021