oldschoolZ
Well-known member
I just started the 2014 lapping season April 23 at ICAR. Was eager to test my new endurance brake pads (Carbotech XP10), Quaife LSD, and new alignment. Temperature was cold (8 degrees Celcius/46 degrees Fahrenheit). I am quite happy with the braking performance, with no or very little fade towards the end of my session. After four 20 minute sessions, the front pads already are thinner than the rear pads. Im a bit surprised by that. I now understand why people get a more robust pad in the front than in the rear (XP12f and XP10r).
I have the M3 front control arms, and Camber plates set to max, and my alignment is -3.2. I have RE-11 tires (225/40R18f and 255/35R18r), maintain my hot pressure below 40PSI, but still get outside edge wear and some understeer. My RE-11 front tire outside edge tread is almost gone (looks like slicks). Maybe the sidewalls of this tire is too soft, even with correct pressure in them.
I need advice on next modification on my 135i to increase my cornering turn-in speeds. Turn out speed is much better with my LSD, but still overwhelming my rear tires (could use a little more traction). I consider myself an intermediate/advanced driver.
To those who track their 135i on stock suspension, how much does the E92/M3 and E93/M3 Front Sway Bar help with reduction of understeer?
I wonder what the next logical and affordable modification I should invest in to reduce understeer even more, without sacrificing rear traction. Budget is $1000-$1500.
Scenario #1: Try different alignment in the front , more toe out for better turn-in.
Scenario #2 : Get E93/M3 or thicker Front Sway Bar. Evaluate results on the track, and move on to the next logical upgrade if required (Swift springs and Koni sport struts).
Scenario #3 - On my stock style 261 RIMs (18x7.5f and 18x8.5r), get wider/stickier Extreme Performance tires in the front (235/40R18), or narrower in back (245/35R18, to approach square setup. I would hate to do that because I want best traction possible to have my Quaife LSD (with 3.46 final drive ratio) put the power down. This is already a challenge in second gear with RE-11 tires.
Scenario #4 - On my stock style 261 RIMs, get R-compound/streetable tires (front = 225/40R18, and rear=245/35R18, or 255/35R18). I wonder if stickier tires and stiffer sidewalls would help my situation.
Scenario #5 - Get a dedicated set of 17" style 68 M RIMS (7.5x17 and 8.5x17) shod with R-compound 225/45R17f and 255/40R17r. Keep my my stock style 261 RIMs for street use, or sell them altogether as I use the car mainly for lapping events (70%) and street (30%). Besides the major advantage of lighter RIMS and reduced unsprung weight, I wonder if this choice would result in better or worse traction than scenario #4.
Open to your suggestions. Thanks for your help!
The tire pressures (40+ psi) seem very high. Tire pressures vary with tires, car, suspension geometry, suspension stiffness, car weight, downforce, etc. But still, 40 PSI seems a bit high. Perhaps someone who has run the same tires on the same car could give you an indication of a ballpark figure that works ?
1.
The alignment in the front is a good idea, 0 toe or even toe-out will improve your turn in. If you still use the car on the street, toe-out is not recommended as it will make the car twitchy and somewhat scary to drive in the rain and on rough roads (Montreal has plenty of those )
Toe-in will increase stability, but turn-in will be worse. Also, since (almost) ALL modern car suspensions toe-in under compression, running toe-in in the front will result in even more toe-in after the weight transfer has occured under braking.
2.
A stiffer front swaybar will actually increase understeer. What you could try for 1 session only is to disconnect the swaybar you currently have. It'll take you 10 minutes and if you don't like it you can always connect it back. You can do this by disconnecting just 1 endlink (left or right). This will allow you to know if a softer setup is better (no swaybar) or if a stiffer setup would be the way to go.
I would really start with tire pressures, honestly pressures and temperatures can do such a big difference. On the cars I work on, we adjust pressures within 0.1 psi, at some tracks a 1 psi difference is worth seconds, not tenths, SECONDS.
When we go testing with the race team, we have dedicated days to try different pressures and see the effect on tire temps / lap times & tire wear. We we work with engineers from the tire manufacturer and change NOTHING else on the car except tire pressures for a whole day (300+ laps) to find the right setup and compromise between tire temperature/wear/laptimes.