Need help on next track modification

[dcaron9999]

The 235/40 is a taller tire than 255/40 and even the 255/35, so rubbing may occur. Also wonder if it would hurt the steering feal, and rake ...


I run -3.2 camber in the front all summer long on street/track, and -2.1 in the rear.

Did an experiment last week, and switched my 255/35 and 225/40 from front to rear, with 10mm spacers in the front. No rubbing at all on the street.

This resulted in very good turn in at moderate speeds, but terrible tramlining/twitchiness on the highway. Cannot isolate if it was the stronger grip up front, smaller/stiffer sidewalls in the front, skimpy tires in the rear, or current bizarre alignment specs. I did not like it at all though. I went back to standard setup this week 225/40 fronts 255/35 rear with same alignment for now, and this got rid of the tramlining.

[timbo_3101]

Thanks for updating us on your progress, dcaron. Great effort!

I shall humbly answer your queries here, because you have an excellent and informative thread

Link to 1addicts/Australia since someone else was at a similar decision point recently:
http://www.1addicts.com/forums/showt...=941183&page=4
(Melbourne/Victorian temperatures are 10-40oC or 50-105oF, but we prefer 15-25oC or 60-80oF on circuit.)

Personally, if I did not currently have understeer issues on slow corners, then I would probably remain staggered (stock 1M specs 245/265). When I order parts for 2015-2016, it will possibly include a square setup (slicks).

Otherwise, I would have remained staggered. Many 1M and M3 drivers are 255/275, 265/285, and even wider on rears; some are 275 or 285 square to optimise balance. I think the dimensions are not as important as overall handling/dynamics - once one is cornering at lateral 1.0g, everything becomes secondary (ie be safe, we are not professional drivers).

One concern that John kindly raised was rubbing. If in doubt, be conservative on sizing to avoid headaches/disappointment or incompatibility. For example, I might consider upgrading to 255/275 because I cannot afford to risk rubbing with 265/285 (each track day costs US$1000 and over 20 hours of preparation/evaluation ie we cannot afford to misjudge). Even Advevo (1M+1M, Nurburgring 8:00) elected to remain stock specs 245/265.

The 135i driver amongst our group uses a square setup (245) on 17" slicks; I generally regard him as a reference ("gold standard") for E82 driving due to his consistency and technique over the last few years. In fact, we are effectively driving the same vehicle anyway

Sorry, I cannot provide a simple answer to a simple question. I hope you can understand

[dcaron9999]

I noticed from feedback of forum members that some of you bought a second set of staggered wheels, and used your four 18x7.5 RIMS for a street setup with 225/40R18 tires, and four 18x8.5 RIMS with 235/40R18 tires for your track setup. Other interesting fact is that its almost impossible to find R-comp tires larger than 235/40 that fit on 18x8.5" RIMS.

I got my hands on used 255/35R18 Michelin Pilot Sport PS2 ZP ("Zero Pressure"/RunFlats) for $100, that I put in the front for now. I still have my rear 255/35R18 RE-11's. Both front and rear are close to the wear bars. My intention is to test this size on the street and on the track, and decide if I like it. So far, they feel great on the street, and the car stance looks mean (like a baby NASCAR vehicle). The stiffer sidewalls and the soft compound of the Michelin runflats feels good, and in fact much better than the worn out 225/40 RE11's in the front. Noise and harshness is reduced, there is almost no tramlining, and turn-in is sharper.

I will also try switching from front PS to rear RE-11s (both 255/35R18), as the MAX performance Michelin's in the front may get destroyed at the 1st track event versus the Extreme Performace RE-11's.

I must say I love the look and fell of the square 255/35R18, and leaning towards running this setup full time, on EHP tires (ZII's, RE-11's, R-S3's, or AD08R's) versus skinnier R-comps.

I may end up running the 255/35R18 square setup for another year on stock suspension. I would run a few more events, get more experience on different tracks, upgrade the driver before moving on to R-comps, and upgraded suspension.

[dcaron9999]

I finally got a squared set of 255/35R18 Dunlop Direzza ZII installed on four BMW OE style 261 RIMS. Feels good to be running on fresh rubber. My worn out and mismatched tires were getting nasty, tramlined badly, were loud, and harsh. Loving the ZII's so far, even on the street. Getting a faint howl over the general road noise at highway speeds. Its really not that bad, and I expected it to be much worse. Ive only used Extreme High Perf tires on this car, so must be used to the "white noise" at highway speeds.

Must be the thicker layer of fresh rubber but I noticed more isolation from road harshness, and tramlining is gone.

Going from 225/40R18 to 255/35R18 in the front, provides a shorter and stiffer sidewall. I turned down the front camber by half a degree (sitting at about -2.5* now).

Will be driving them on the track soon, and monitoring tire temps across the tread to figure out optimal camber settings.

[fe1rx]

Originally Posted by dcaron9999

Must be the thicker layer of fresh rubber but I noticed more isolation from road harshness, and tramlining is gone.

Going from 225/40R18 to 255/35R18 in the front, provides a shorter and stiffer sidewall. I turned down the front camber by half a degree (sitting at about -2.5* now).

Will be driving them on the track soon, and monitoring tire temps across the tread to figure out optimal camber settings.

Very nice. I am sure you will enjoy these. I am not surprised you fixed the tramlining. I think it is often made worse by tire wear. Same with road noise. I find the ZIIs are noticeably noisier after a track day (and I notice the noise more whenever I have a passenger).

I doubt the reduced camber will benefit you at the track, but obviously it is fine for the street. If you didn't adjust the toe when you changed the camber, you will also have added a bit of toe in at the front. This isn't a problem because the toe moves in the correct direction for the camber change, but you probably shouldn't go more than about 1 degree camber change from where you had the car aligned.

225/40 and 255/35 actually have the same sidewall height in absolute terms. 255/35 is just lower profile as a percentage of width, but not as an actual dimension. What I am saying is the two tires have the same rolling radius.