Limiting understeering and tire wear on BMW 135i

I tried my mis-matched 255/35R18 squared setup on the track for three 20-minute sessions yesterday evening. The local ICAR track (cement pavement) was wet - it was raining for the first session.

I took pressure readings on my front tires before and after each session.

I started out with 32PSI cold front and rear. First session was on a wet track, I hardly got any heat into my tires. 2nd and 3rd sessions were on an almost dry track. With more speed and heat into the tires, this is where things got interesting, and Id like your educated feedback on.

Front tires (Michelin Pilot Sport RunFlats) only went up by 2PSI, and rears (Bridgestone RE-11) by 6PSI. This is the opposite of what I was getting with my previous staggered setup (255/40R18 & 255/35R18 RE-11's). During previous track days, the fronts were obviously getting overworked. The fronts use to go up by 6-10PSI after a 20 minute session on the dry. Now, the emphasis seems to have shifted to the back. Maybe the sidewalls in the Run Flats, and the lower 35 profile are keeping the front tires from rolling over and working harder. The rears are now working & sliding a little more.

For the first time at this track, I experienced no understeer, but the rear end was a little more twitchy. There was no rolling over onto the edges of the front tires or top of their sidewalls.

Do you guys think I should reduce the front camber (-3.2* and 0 toe) now that the meatier 255/35R18 tires seem to be staying more flat, and building up less heat?

Ideally, I know I should be doing pyrometer temperature readings across the tread to determine ideal camber setting, but what would you start off with?

Ive made a decision: No R-comps for now. Ill be sticking to a nice 255/35R18 extreme performance square street tire setup, until I "upgrade the driver" (more lapping and driving events).
 
C'est pas juste «idéal» de mesurer les températures; c'est la seule vraie façons de prendre une décision d'ajustement.

J'ai comparé un pyro et un thermomètre IR de poche (mesure directement collé sur le pneu), et c'est exactement les mêmes écarts relatifs. Il vient à 15$ assez souvent au CT. Pourquoi s'en passer.

Je n'ai pas d'auto en ce moment, mais je vais a icar avec mon frère de temps en temps (Honda Civic Si 4 portes noir, mags noirs). J'amenerai un pyro la prochaine fois si tu veux prendre des mesures. Quelle couleur est ton BMW pour que je te reconnaisse ?
 
STN_Pat said:
C'est pas juste «idéal» de mesurer les températures; c'est la seule vraie façons de prendre une décision d'ajustement.

J'ai comparé un pyro et un thermomètre IR de poche (mesure directement collé sur le pneu), et c'est exactement les mêmes écarts relatifs. Il vient à 15$ assez souvent au CT. Pourquoi s'en passer.

Je n'ai pas d'auto en ce moment, mais je vais a icar avec mon frère de temps en temps (Honda Civic Si 4 portes noir, mags noirs). J'amenerai un pyro la prochaine fois si tu veux prendre des mesures. Quelle couleur est ton BMW pour que je te reconnaisse ?
Click to expand...

Est-ce que ca ressemble a ceci?
http://www.ebay.ca/itm/Non-Contact-...238?pt=LH_DefaultDomain_2&hash=item54086b050e

Link pour le Ca-CanTire?
Ma 135i est noire.
 
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dcaron999 said:
Yes. I ran the AISA with my staggered setup, and at ICAR with the squared setup.
Why?
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Don't underestimate the changes in your driving style. I'm not saying it's the only factor, but it can contribute greatly.

At ASE, you were on a less familiar track (presumably), with the all-seeing eye of the instructor pushing you to be smooth and consistent. It's entirely possible that this modified your driving style (in a good way) for smoother inputs, hence putting less pressure on those front tires and generating a more neutral balance. You may also (on purpose or not) have started trail-braking more, putting more weight and therefore more grip on the fronts and changing the balance on corner entry. It's possible that, with more and more laps accumulating at ICAR before, you were overloading the front tires too much by turning it too abruptly or by adding more steering lock instead of transferring weight or reducing entry speed. You wouldn't be the first one.

Definitely do the pyrometer thing, but I still wouldn't draw any firm conclusiongs and make alignment changes until you're running the same tires front/back, ideally in a square setup as discussed previously. What you have now is a Franken-setup, which hopefully is temporary, so why change alignment settings when they will most likely have to be changed again once you change tires (which will happen quickly if you run at ICAR)?

To give you an idea of the influence of driving technique on car behavior, I was able to make a 100% stock WRX wagon (understeery car if there ever was one) oversteer on corner entry at ASE a few years back, by playing with weight transfer.
 
Sebdavid said:
Don't underestimate the changes in your driving style. I'm not saying it's the only factor, but it can contribute greatly.

At ASE, you were on a less familiar track (presumably), with the all-seeing eye of the instructor pushing you to be smooth and consistent. It's entirely possible that this modified your driving style (in a good way) for smoother inputs, hence putting less pressure on those front tires and generating a more neutral balance. You may also (on purpose or not) have started trail-braking more, putting more weight and therefore more grip on the fronts and changing the balance on corner entry. It's possible that, with more and more laps accumulating at ICAR before, you were overloading the front tires too much by turning it too abruptly or by adding more steering lock instead of transferring weight or reducing entry speed. You wouldn't be the first one.

Definitely do the pyrometer thing, but I still wouldn't draw any firm conclusiongs and make alignment changes until you're running the same tires front/back, ideally in a square setup as discussed previously. What you have now is a Franken-setup, which hopefully is temporary, so why change alignment settings when they will most likely have to be changed again once you change tires (which will happen quickly if you run at ICAR)?

To give you an idea of the influence of driving technique on car behavior, I was able to make a 100% stock WRX wagon (understeery car if there ever was one) oversteer on corner entry at ASE a few years back, by playing with weight transfer.
Click to expand...

You are correct about smoothing out my driving inputs at the AISA academy, but the asphalt pavement grip had a lot to do with it as well.

Did a few sessions at ICAR this week (first session was raining and I was the only fool on the track). Fast forward four days, I did the St Eustache lapping day today, with nine 20-minutes sessions with my 255/35R18 square setup. I switched my stiffer Pilot Sports RUNFlats in the back and RE-11's in the front.

I had a blast and got comfortable with the 255/35R18 and adjusted hot pressure until tires stabilized at 32 PSI front and 34 PSI rear. I removed one level of traction control on my 135i, and was gaining momentum, and better control of the car.

Got some brake fade with my Carbotech XP10 pads towards the end of my 20 minute sessions. May try XP12 front pads or Endless ME20 soon.


Will try to stretch my mismatched RE-11 (front) and Michelin Pilot Sports (rear) until Mid June, as my Yokohams AD08R's are backorder.

I may consider the RS-3 or RE-11's come mid June if Yokohama Quebec Tire distributor bails on Talon Tire ...
 
Personally, I would just buy the RS-3s anyway. I'm sure you researched more than I did, but fast guys in the know seem to swear by them. And you'll finally have matched tires, and THEN you can start to really experiment usefully.
 
Sebdavid said:
Personally, I would just buy the RS-3s anyway. I'm sure you researched more than I did, but fast guys in the know seem to swear by them. And you'll finally have matched tires, and THEN you can start to really experiment usefully.
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Thanks Seb. The RS3's are definitely on my short list. Ive seen them on a lot of street cars at the ASE track.

From a post on a popular M3 forum: "Seems that the ad08R lasts much longer than the Rs3 and maybe be a bit quicker on the track. .2-.4 seconds faster on a 1:30-2min road course. The ad08R is more expensive but lasts much longer. From my experience the rs3 is best it's first day. Close the second day and 3rd day really falls off by 1-2 seconds maybe. Although they are useable still. He says the ad08r falls off a bit after the first day but holds steady and lasts 6-8 days. Which actually makes it a cheaper buy in the long run..."

RS3's were ranked fourth from a Car and Driver comparison test. They seem average on wet pavement. http://www.caranddriver.com/comparisons/hankook-ventus-r-s3-page-7

Decent but old thread comparing RS-3 vs Z1SS vs 595 RS-R vs RE-11 vs Z2 vs Rivals: http://www.s2ki.com/s2000/topic/839...1ss-vs-federal-595-rs-r-vs-bridgestone-re-11/

Another one from GrassRoots: http://grassrootsmotorsports.com/articles/top-tires/
 
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