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      04-14-2008, 11:00 AM   #1
mikeo
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My First 135i Autocross Events and Analysis

I should start by saying this is not my first autocross, I'm a three-time regional class champ in a E36 M3. After a two day autocross in my new car I have some opinions about the capabilities of our beloved 135i as to its potential in this sport. The events were held on the largest venue we have available in New Mexico (Farmington) and therefore the course designs tend to be more open, faster layouts and a LOT of fun. top speeds by the faster cars were near the SCCA recommended limits of 65mph.

First the bad news. There is throttle lag with the turbos. It's my opinion that while there is hardly any lag in street use, the constant on-off-on-off throttle work of autocross simply overcomes the ability of the boost management system to react quickly enough to avoid noticable lag. This can be compensated for to some degree by earlier throttle application, and perhaps left-foot-braking (which is beyond my current level of expertise) while keeping just enough throttle applied to maintain boost. For those running in non-stock classes maybe aftermarket or modified diverter valves will yield siginificantly reduced lag--experiementation in this area may be beneficial.

The good news. Running stock wheels and OE runflat 'Stones at 41lbs front and 38 rear the understeer was limited and turn in was very good (once the stock springs and shocks got settled). I was VERY surprised at how good the car handled as I was expecting massive understeer similar to my unmodified E36 M3. The relatively short wheelbase is a big help in handling. I'm thinking a staggered wheel setup may be fine for the car and would like to see how 8.0-8.5" wide front and 9" (or even 9.5") rear with 235-245 and 255-265 tires would work in non-stock class autocross. This would require some fender 'massaging' I'm sure.

The eDiff. Not too bad, actually. Would it be better with a true LSD? Of course. 1st gear on-boost throttle while turning even slightly totally overcomes the braking of the inside rear wheel. In 2nd gear it works pretty well with less inside wheel spin. Larger and sticker tires in the rear would help a lot, I think.

The results. Well, I ran in D-Stock Street Tire and did well enough be make the top-ten PAX both days, not bad for street tires. In fact, other members are whining about my class and want to see it raised siginificantly before the next event in three weeks. Oh well, I may wind up in B-Stock or even STU if I decide to do any mods. Over time, and as the car progresses in modification development, I think the 135i will prove to be a fierce competitor, especially in the modified classes, and even will do better in stock classes than previous 'MacStrut' BMWs. However, I was beaten handily by a well-driven A-Stock E46 M3 on street tires as the Class Results show (scroll down to the bottom and note Raw times).

Here is a video by a very fast Z06 Corvette that shows the relatively open and fast course.
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      04-14-2008, 11:22 AM   #2
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Great review/experience. I can't wait to test it out myself.
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      04-14-2008, 11:29 AM   #3
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Thanks for your impressions! As you run more events, please continue posting other things you notice.

In particular, if you switch to stickier tires, whether high performance street type (Yoko Neova, Bridgestone RE-01R's, etc) or R-compounds, it would be interesting to hear if the handling balance seems to change.
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      04-14-2008, 12:44 PM   #4
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please elaborate about the lag. is it throttle lag or turbo lag? also, there was another post around here about a trick to reset the throttle response that has helped the issue on 3ers and 5ers. I'm gonna try to find it.
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      04-14-2008, 01:00 PM   #5
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Good info .. for those of us that have never autocrossed, can you explain: Raw ----- Pax -- Corr -- Ratio

thanks,
Crowley
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      04-14-2008, 02:38 PM   #6
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Thank you for this review.
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      04-14-2008, 03:34 PM   #7
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Quote:
Originally Posted by Crowley View Post
Good info .. for those of us that have never autocrossed, can you explain: Raw ----- Pax -- Corr -- Ratio

thanks,
Crowley
Sure.

Raw = Actual elapsed time of your best run.

PAX = A formula, set annually by SCCA, that attempts to remove the class differences between cars (SuperSport vs. H-Stock say) by assigning a % factor to each class. This % factor is applied to Raw times (Raw X Pax%) which yields the Corrected time (Corr). This Corrected Time suposedly is a better indication of driver vs. driver skills without the actual car.

Ratio = Your relative position time-wise compared to the fastest PAX driver (who is always 100.00)
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      04-14-2008, 03:39 PM   #8
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Quote:
Originally Posted by mistermojorizin View Post
please elaborate about the lag. is it throttle lag or turbo lag? also, there was another post around here about a trick to reset the throttle response that has helped the issue on 3ers and 5ers. I'm gonna try to find it.
The lag I expierenced was xTime from full throttle application until I noticed any significant increase in power/torque occurring. I don't know what caused that lag, the drive-by-wire system or the turbos taking time to build boost.
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      04-14-2008, 03:41 PM   #9
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Small nit; the PAX index values are not set by the SCCA, they are set informally and traditionally by Rick Ruth, an autocross competitor but not an official of any sort.

"This Index was developed by Rick Ruth and reflects results from over 30 large events including, the Tire Rack® Solo II National Championships, National Tour, Subaru CenDiv, Chicago Region SCCA, Tri-State Sports Car Council and Wisconsin Autocrossers Inc events. This index is designed to incorporate some of the previous PAX substance with the RTP Index of the past"
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      04-14-2008, 03:47 PM   #10
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how much did the e-diff help? Whenever I hear of a new car technology doing the braking for me (i.e. DSC) then I picture a car going around the autox course slower than without it.

I am also afraid of wearing out the rear brakes with the e-diff thing going off all the time at the autox. My buddy wore out his rear brakes before his fronts just by having his DSC on when driving winding roads on the weekend.
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      04-14-2008, 03:53 PM   #11
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Quote:
Originally Posted by BimmerMeUp View Post
Small nit; the PAX index values are not set by the SCCA, they are set informally and traditionally by Rick Ruth, an autocross competitor but not an official of any sort.

"This Index was developed by Rick Ruth and reflects results from over 30 large events including, the Tire Rack® Solo II National Championships, National Tour, Subaru CenDiv, Chicago Region SCCA, Tri-State Sports Car Council and Wisconsin Autocrossers Inc events. This index is designed to incorporate some of the previous PAX substance with the RTP Index of the past"
I stand corrected. Thanks. :smile:
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      04-14-2008, 03:57 PM   #12
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Quote:
Originally Posted by nordique14 View Post
how much did the e-diff help? Whenever I hear of a new car technology doing the braking for me (i.e. DSC) then I picture a car going around the autox course slower than without it.

I am also afraid of wearing out the rear brakes with the e-diff thing going off all the time at the autox. My buddy wore out his rear brakes before his fronts just by having his DSC on when driving winding roads on the weekend.
Pretty hard to say how much it helped without driving the car without it, and that is not easily possible. I can only offer the opinion that it is somewhat better with the eDiff braking than it would be without it.
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      04-14-2008, 05:20 PM   #13
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How was it decided that the car was put in D-Stock. Has the stock classing "officially" been set?

Do you think that with more practice the "lag" issue can be at least somewhat addressed? For example, down shifting, left foot braking (with practice as you said already). 2 to 1 downshifts can be a real pain.

You described this course as being open in nature, I am assuming then that a twistier course would be even worse with the lag issue, your opinion please.

How was it on sweepers-

Slaloms-

Chicago boxes-


Thanks in advance for your input.
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      04-14-2008, 05:31 PM   #14
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D-Stock is not yet 'official', but the SCCA Solo SAC (Stock Advisory Committee) is suposedly recommending to the SEB that both the 128i and 135i be classed in D-Stock for 2008. The SEB will publish its Official classing in the SCCA Fastrack monthly.

As far as 'lag' is concerned I can't venture a guess yet how this will play out--I need more time in the car on course.

Keeping in mind it takes the OE springs and shocks (the car is definitly under-damped, IMO) a fraction of a second to take a 'set' when corning, I was impressed by the cars ability to go where I pointed it. It felt nimble in a very long 8-cone slalom, got good grip in sweepers and felt fairly neutral on entry and mid-corner, and allowed rolling into the throttle on corner exit without excessively upsetting balance.
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      04-14-2008, 06:03 PM   #15
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More questions if you don't mind?

I looked at the video and I was wondering how the car did braking in to those couple corners where you had a relatively high speed entry.

Did it dive much? How quickly did it rebound and settle?

You mentioned it being underdamped already, but not directly in regard to braking.

Thanks again great post.
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      04-14-2008, 06:12 PM   #16
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Does your car have the active steering option? I did a BMW drive event that had a small autoX and slalom course set up. You could see an advantage for the active steering ratio in a autoX course. I don't know if it would be a big advantage in the real world but it might be sweet in autoX.
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      04-14-2008, 07:30 PM   #17
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JB135,
Braking initial bite was very good, but ultimately limited by the 215 front tires. Ride-alongs commented on the good brakes. There was certainly front dive on braking but it didn't seem to upset braking effectiveness.

vanbmw,
I avoided the active steering option. Just didn't want to be the beta-tester for autocross.

I really want to underline how responsive and FUN the dead stock 135i was in this event! Was it perfect? No. Does it have a lot of potential? Absolutely.
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      04-14-2008, 08:08 PM   #18
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Quote:
Originally Posted by mikeo View Post
The lag I expierenced was xTime from full throttle application until I noticed any significant increase in power/torque occurring. I don't know what caused that lag, the drive-by-wire system or the turbos taking time to build boost.

Great post Mike! I can't wait to get my car out there...

Btw, I posted about this lag months ago here, from when I was doing instructor runs in student's 335's. I was able to overcome it (for the most part), by early throttle application. The problem is I like to finesse the throttle thru slaloms, and that was nearly impossible to do with the delay. Sweepers, offsets, and clamshells were not a problem.
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      04-14-2008, 09:12 PM   #19
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The 135i is a real hoot at an autocross. You'll have a blast, Larry! Next weekend for you, isn't it?
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      04-15-2008, 08:03 AM   #20
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Quote:
Originally Posted by mikeo View Post
Sure.

Raw = Actual elapsed time of your best run.

PAX = A formula, set annually by SCCA, that attempts to remove the class differences between cars (SuperSport vs. H-Stock say) by assigning a % factor to each class. This % factor is applied to Raw times (Raw X Pax%) which yields the Corrected time (Corr). This Corrected Time suposedly is a better indication of driver vs. driver skills without the actual car.

Ratio = Your relative position time-wise compared to the fastest PAX driver (who is always 100.00)

Thanks !

Good info!

Crowley
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      04-15-2008, 08:14 AM   #21
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Quote:
Originally Posted by mikeo View Post
The 135i is a real hoot at an autocross. You'll have a blast, Larry! Next weekend for you, isn't it?
No.. unfortunately the weekend after. I also don't know how much fun I'll be having.. the schedule that week is:

Sun night.. Drive to Yale for 2 days of meetings
Tues night.. take Acela to to NYC for 2 more days of meetings
Thurs night, wife and kid drive down to meet in NYC for Fri college tour
Fri night drive to Philly for college tour on Sat
Sat night drive back home - get home at midnight, and prep for autox
Sun - be at autox at 6:30am (2 hrs away from home)

I probably will not get any sleep at all, and I have to get all the worker assignments done for the event, while on the road. I'll have to guage if I will even run the car, if I'm too tired.
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      04-15-2008, 11:29 AM   #22
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Good review, Mike.

Hmm... too bad about the turbo/throttle lag, but this is becoming a common theme in the latest electronic throttle and/or turbo cars. You really need to left foot brake all cars in an autocross environment (its worth a lot of time), and with the turbo cars it helps to get into the throttle as early as possible.

I had some similar problems even in a non-turbo 2005 Corvette - the electronic throttle didn't exactly do what you wanted all the time (especially at the drag strip, even with the traction control "off" - some new cars never really turn it all the way off). We also fought with a 2007 Subaru STi turbo in STU last year and left foot braking/early throttle application was the only way to get this thing to exit a corner under boost. We couldn't legally "fix" the problems inherent with the lag, even with the programming and exhaust work allowed for in STU (our tuner tried, but the issues were deeper than they could fix). It was painful - exiting corners was a "Two count" before it would boost, so we were driving the car with the throttle applied about 2 seconds before corner exit... Hopping into a similarly prepped '05 STi was night and day, and violently better in the '05.

The LFB "boost trick" worked OK for exiting stead state corners but the power application still sucked HARD for slaloms and transitions, where you can be on/off the gas a lot. With a naturally aspirated car (like our E36 M3) I am dancing on the gas a brake pedals constantly and in/out of the gas a lot - nothing compares to the crispness of a Naturally Aspirated engine in these instances, but some turbo cars can come close if they boost quickly.

The eDiff is a marketing trick, of course - it cannot work anywhere nearly as well as a "real" LSD in an autocross environment. BMW is lazy and/or cheap by doing this to the non-M cars. The M cars all have a real limited slip diff. Wouldn't their top M cars get the eDiff if it worked? Of course. At least this can be fixed if you go to STU. :biggrin:

So even though left foot braking and early throttle application will help, it might not cure what ails a laggy turbo car... it may take some "programming" and it may take "more". Do you have a driver in your region that can LFB and is familiar with driving a turbo car? Maybe have them do a "fun run" after your next event and see what they think... just a thought.
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