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10-10-2014, 07:51 AM | #45 | |
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10-10-2014, 09:55 PM | #46 |
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Some things...
Many around here go from the 215-40/245-35 setup to 225-40/255-35. That does nothing to either increase front grip or decrease rear grip. It is possible on the later model 135i cars to get 1.5 degree negative camber up front via alignment adjustment. All sorts of mods get discussed around here, but I can't ever remember seeing before and after lap times. At least with engine mods there are dyno runs and time slips. Lacking good data, it is hard to believe just about anything. The guys who say learn how to drive fast, are the smartest guys in the room.
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10-11-2014, 10:33 AM | #47 | |
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With AutoX, it's harder to put a concrete number on it since the course changes every event. However, comparing deltas between myself and the hot shoes in my class, the difference from tire grip alone was substantial. However, the car needs a lot more tire to really turn the way I want it to.
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10-13-2014, 09:32 AM | #48 |
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10-13-2014, 01:25 PM | #49 |
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I don't have an instrument for an accurate measurement, but I would say -1.5 is what I have on a stock 2012 that was aligned at the dealer. I did not ask them to max it out, but that is what they did.
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10-13-2014, 02:18 PM | #50 |
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It's well documented that stock 1ers of all years can only achieve a max camber of around -0.5 per side. That's all multiple shops in my area could get out of my stock 2012. You need camber plates and M3 LCAs to get anywhere near -1.5. No way a dealer could or would get you there, particularly if you didn't ask for max camber. Even if they could get you that much, the alignment machine would flag that as being out of the accepted range and the tech would adjust it back down.
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10-13-2014, 04:23 PM | #51 | |
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Now perhaps I am doing that completely wrong, so enlighten me. What I don't understand around here is a lot of forum members keep the three size differential between front and rear when the first thing I always thought was a cure for under steer was larger front tires. Some of the AC guys go square which should help things a lot. I get the impression that over steer might help a lot more on and AC course than a road course. Meanwhile, even if I see one report of a track time comparison, which is nice, I rarely see them, and driver skills play a greater role at the track or AC than at the drag strip. It may be the same driver before and after, but an occasional track user is not going to be as consistent as a pro, and will probably improve more noticeably between sessions. Unfortunately we don't have the kind of twisty mountain roads where I live that will reveal a car's flaws at reasonable speeds. I am set up now with 225/40 front and 245/35 rear Michelin PSS. The car seems well planted. I am not saying that all of this is BS, but solid data is hard to come by.
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10-14-2014, 08:35 AM | #52 | |
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10-14-2014, 02:28 PM | #53 |
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Diver, you are spot on that the best way to alleviate understeer on this car would be increasing front tire size and leaving the rear alone. The main reason you don't see that often here is in the extreme performance category there are little to no options with a 245 rear. Going square is an option, but at that point you are choosing handling balance over total grip, which in theory should make you slower, not faster (all things being equal).
As for the camber measure, put it on a Hunter alignment and see what it spits out if you want to be sure. DIYing it typically has a margin of error of +/- 0.5 degrees, which is probably not the level of confidence you want when measuring something that should fall within a 1 degree range. And yes, as much as I wish people would be more diligent about posting lap times, etc... the reality is there are way too many variables in play to make any of that statistically reliable. Bottom line: come to forums for ideas and lots of anecdotal evidence, but only rely on your own testing for the truth.
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10-14-2014, 05:10 PM | #54 | |
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10-14-2014, 05:13 PM | #55 | |
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This thread has been very good in pinpointing how to reduce our car's understeering nature.
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10-14-2014, 07:43 PM | #56 | |
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Don't tell me you are running anything short of -2.8 of camber. EDIT -- looks like it is somewhere between -3 and -3.5 so IMHO while bushings, sway bars and spring rates may help, adding some negative camber will have a profound impact on reducing BMW engineered understeer.
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10-14-2014, 11:11 PM | #57 |
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Dack, I saved one of my run flat front tires for that reason. One thing I have learned, if TPM goes on, stop and diagnose the problem.
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10-16-2014, 04:15 PM | #58 | |
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10-16-2014, 05:00 PM | #59 | |
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10-16-2014, 05:43 PM | #60 | |
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Been running the ZII's very hard on the track last season (May 2014 to October 2014), and concur. They can take the abuse at the track (pavement or concrete), and do fairly good in the wet. They are noisy (they hum) on the street, more so when cold, or after abuse at the track. They stick like glue when hot. Not sure what to do next season as Im close to the wear bars already. Might give the newer Dunlop ZII's Starspec's a try, or move on to entry level "DOT approved" R-compound tires (Nitto NT01, or Toyo R888) ... I wish I could afford a dedicated set of Street and Track tires and have the patience of swapping back and forth, but I visit the track as often as every week, so must settle for a dual duty set.
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10-16-2014, 08:51 PM | #61 |
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Sorry I can't agree with using Michelin PSS on the track. They get very slippery when hot and you will see very high wear rates. Save them for the street as they don't work on the track.
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10-17-2014, 10:53 AM | #62 | |
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Sorry for the confusion.
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10-17-2014, 12:11 PM | #63 |
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I have occasionally driven my 135i fast enough to where under steer just barely becomes noticeable in the form of a bit of noise from the front tires. With the new tires that has gone away and noise is is from the rear tires, at a higher speed. This is not the limit of adhesion, but it is close enough that the change was evident.
Some FWD rental cars I have driven on twisty European roads experienced extreme under steer at relatively low speeds. The worst was a VW mini van. The diesel Golf I had last month was a lot better. People buy cars because of what they are capable of on the track and never track their cars. 45% of 2014 Stingrays were delivered with Z51, and I doubt that more than a quarter of those will ever see the track. A good many of those Z51 Stingrays had the slow shifting 6-Speed auto. Cars get lowered and have large diameter wheels installed for looks most of the time. These mods may or may not improve track performance. One of my motivations for going up a tire size in the front is the 215's just felt too damn small.
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10-17-2014, 02:56 PM | #65 | |
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Pay attention to the pitch of the tire noise and the sudden change from squeal to "groan".
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10-17-2014, 03:24 PM | #66 | |
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Video from when my tires were kind of noisy...but well within their levels of grip |
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