My First 135i Autocross Events and Analysis

[gan08]

Nice review! Thanks Mikeo

[Conemasher]

Looking at the results....you were probably a set of A6's or 710's away from contending for top 2 pax in your first event. What are your thoughts now about it's chances in DS? I am 99.5% sure that is where it is going to end up. It will not go to BS.

[mikeo]

Good suggestions, Terry. I'll have a couple more experienced people to drive the car and see what they think.

[TazioNYC]

Based on my street driving, I think it's throttle lag. I recall driving a Cayman S and that had one of the best "right there" throttles of any car I've ever driven. Would a lighter flywheel help or is it really in the electronics?

[mikeo]

Originally Posted by TazioNYC

Based on my street driving, I think it's throttle lag. I recall driving a Cayman S and that had one of the best "right there" throttles of any car I've ever driven. Would a lighter flywheel help or is it really in the electronics?

I think the boost control system, both electronic and the physical plumbing and diverter valves, just can't keep up with the on-off-on-off-on autocross throttle requirements which results in more noticeable lag than on the street.

[BerkTechnology]

Originally Posted by TazioNYC

Based on my street driving, I think it's throttle lag. I recall driving a Cayman S and that had one of the best "right there" throttles of any car I've ever driven. Would a lighter flywheel help or is it really in the electronics?

Flywheel won't help much with turbo spool. It's more to do with the physical limitations of having to accellerate the turbine wheels. The drive by wire throttle probably has some to do with it as well.

On most DBW applications, the throttle plate won't always do exactly what you tell it to. So when you go WOT in 0.1 sec, the throttle plate may gradually to go WOT in 0.2 sec. At redline, the throttle plate will also close slightly from 100% open, to 80% near redline. Hopefully the reflashes will address the ramp rate and opening/closing of the throttle.

As far as the turbos go, I don't think you can go any smaller (quicker spooling) than what BMW already has in there.

[petertruong]

What's your opinion re E46 M3 vs 135i for autocross? I am pondering my next vehicle.

[gap]

Mikeo I did my first autocross Saturday with the Mississippi SCCA and really enjoyed it. I used your air pressure recommendations and they were spot on. I have the sports suspension so was classed as BSP. My times were not great since I was cruising the course rather than attacking it. It is all new to me and I am not a natural at it.
It is very evident how hard autocrossing is on the tires but what about the car?
I like to keep my cars forever and am concerned about the long term effects of 4-5 autocross event per year. I'm still on my honeymoon with my new 135i and came away for the event feeling like I had abused my bride.

[larryn]

Originally Posted by gap

I have the sports suspension so was classed as BSP.

This is wrong. You do not have any added suspension package.. all 135i's come with the sport suspension, so you should not have been penalized. You should have run in the DS class.

You are a D Stock car, unless you're made mods, which it doesn't sound like you have.

Congrats on going though, and hope you had fun.

[gap]

My mistake, I had the performance suspension, perf. exhaust, and perf. front rotors installed, tires are OME. A couple of the experienced guys rode with me and were impressed with the car. I let one of them drive it and I was impressed with the capabilities of the car when driven by a experienced driver.

[mikeo]

It's my opinion that autocrossing is the least stressful on the car of about any other type of motorsport, tires notwithstanding. A few 60 second runs in second gear with off and on throttle do not exceed the design limits of the drivetrain (if you are not doing drag launches). Tires are brutalized however, and perhaps suspension bushings and struts/shocks are worked a little harder than normal. If you enjoyed the experience and want to continue develop a tire strategy, keep the car properly maintained, and have fun with it.

I have given up on race tires (which can overstress suspension components) and only run on street tires now, simplyfing prep before an event. I'll move out of DS next year probably into Street Tire Ultra (STU).

[gap]

Thanks Mikeo. For a tire strategy would you suggest just running the OME until they are gone or getting a less expensive wheel and street tire combination
to use at events.

[mikeo]

Originally Posted by gap

Thanks Mikeo. For a tire strategy would you suggest just running the OME until they are gone or getting a less expensive wheel and street tire combination
to use at events.

I'm running the OE tires until they are used up this season and plan on going with slightly larger Dunlop Direzza Z-1 Star Specs (no plans to drive my car in snow). I've been doing about 12-15 events a year and that about does it for a set of tires. If you need to have winter capability you would want to consider an additional set of wheels. If it were me, I'd used the OE wheels for winter and buy something wider and lighter for summer/auto-x use. Of course, you don't get much snow in Mississippi. :biggrin:

[redwood]

Will the 135 be allowed in STU?

[mikeo]

Originally Posted by Redwood

Will the 135 be allowed in STU?

Not offical yet, but that is what's going around for 2009. Not much else could give the STEvo boost buggies any RWD competition. And that will require some pretty serious mods, first being a LSD.

Me, I just get the car the way I like it for street then run the regional SCCA Solo class that configuration happens to land me in. I don't compete nationally.

[sybarite]

Originally Posted by petertruong

What's your opinion re E46 M3 vs 135i for autocross? I am pondering my next vehicle.

I haven't driven the 135i yet, but based on the OP's observations I'd have to say the M3 is probably a better bet for autox. I'm grappling with the same decision, but may end up going 135i. I have yet to see one at a local autox; I'm dying to ride in one to gauge its abilities.

[weathergrl]

I just drove the 135i last sunday and was able to compare times on the same course with the times I put down in an AS 06 STI (both on street tires). I pax'd 0.6 of a second faster in the 135i than I did in the STI, and that was my first time driving it. I see a lot of potential for this car, just as it is!

[Decent local driver, who competes nationally. Wish me luck in DSPL this year.]

mikeo, have you tried playing with the camber settings on the 135i yet?

[3RotorRX7]

Originally Posted by petertruong

What's your opinion re E46 M3 vs 135i for autocross? I am pondering my next vehicle.

I would say the 135i would be your choice, as the E46 M3 runs in AS and the 135i runs in DS. In a straight line, they are about equal, but the 135i has better low end, so would feel better in an autocross environment. The E46 doesn't stand a chance in AS.

The problem with the 135i, as most stock BMW's, is no front camber. Therefore, you have to do everything in stock form to make it turn better. Here is a small suggestion list to run the car in SCCA DS competition.

- Max front camber adjustment by removing alignment pin on top of camber plate and sliding plates within slotted factory holes.

- Take out as much rear camber as possible. Stock is around 1.6 degrees, and probably can get it down to 0.9 degrees negative.

- Toe the rear out just a bit 1/8", as well as the front.

- Actually put a larger front bar on, as the car is so soft it tends to lean so much you lose front contact patch.

- Autocross tire suggestion: 275/35/18 Hoosier A6 front and rear will fit. You have to put on 1/4" spacer on the front and it still rubs just a minimal amount, but won't hurt anything. Hoosier is coming out with a 265/30/18 tire probably around October. This will be the best tire for the car when it is available.

- Pressure suggestions using these tires Front 45-50 / Rear 40-50.

Erik Strelnieks

[mikeo]

Originally Posted by weathergrl

... mikeo, have you tried playing with the camber settings on the 135i yet?

I'm only getting -0.6 deg front camber with the adjustment pins removed, at stock height. Rear is at the stock -1.6 and I prefer not reduce to negative camber for this street car--I like the corner exit grip at this setting. Over the off season I'll be going to Koni Sports on H&R OE Sport springs, so I may get another 1/2 degree, or I may add a set of Vorshlag camber plates.

[mikeo]

Originally Posted by 3RotorRX7

...
- Max front camber adjustment by removing alignment pin on top of camber plate and sliding plates within slotted factory holes.

- Take out as much rear camber as possible. Stock is around 1.6 degrees, and probably can get it down to 0.9 degrees negative.

- Toe the rear out just a bit 1/8", as well as the front.

- Actually put a larger front bar on, as the car is so soft it tends to lean so much you lose front contact patch.

- Autocross tire suggestion: 275/35/18 Hoosier A6 front and rear will fit. You have to put on 1/4" spacer on the front and it still rubs just a minimal amount, but won't hurt anything. Hoosier is coming out with a 265/30/18 tire probably around October. This will be the best tire for the car when it is available.

- Pressure suggestions using these tires Front 45-50 / Rear 40-50.

Erik Strelnieks

Erik,
Have you tried rear toe-out on a 135i? Most BMWs don't react well, especially on the street, with rear toe-out (severe oversteer), but maybe the 135i 5-link rear suspension can handle it. Anyone trying it should be very careful at first if on the street.

I'd love 275x35-18 tires up front but how in the world would you get them 7.5" wide wheels?

[larryn]

Erik, are you running the 135i in Topeka this year?

[Fair]

A couple more things to add to Erik's excellent suggestions for DStock prep on an 135i...

• Custom monotube double adjustable shocks with high nitrogen pressures (this increases spring rate slightly, which the car desperately needs, and improved damping is better for course tuning and lowering time as well).
• After-cat exhaust (mostly for WEIGHT, but also for added power. BMW factory exhausts are extremely heavy)
• MUCH lighter wheels than stock (the stock wheels are boat anchors)
• Better brake pads (the stock pads are proven to fade with only moderate track use; a much more aggressive but cold tolerant compound pad is usually beneficial for autocross use).
• Lots of front Toe out (up to 1/4" total) and 1/4" rear toe-in (this works on the E36/E46, which are slightly different in the rear; haven't tried it on the E82 yet)

Factory 7.5" width front wheel and non-run-flat tire = 48.3 pounds! That gives you lots of room to improve. I'm not a fan of the 275mm tire on a 7.5" wheel, but some of the Stock class guys do this stuff all the time (and yet others continually win some Stock classes with properly sized tires for their wheel widths, too - there's no hard and fast rule either way).

As previously stated, the lack of front negative camber is going to be the biggest handicap in Stock class for this and any modern BMW. Align it within an inch of its life. Adding a lot more negative camber up front transforms the car - we had a customer that added our camber plates to an otherwise 100% stock 135i and he told me he dropped 2 seconds per lap on a local road course (-3°).