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      06-06-2019, 10:23 PM   #1
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My 2018 M2 for B-Street Autocross

Took my totally stock '18 M2 to it's first autocross last weekend, had a blast! It handled better than I expected. A fair amount of roll, but the rear Diff worked great, and the MPSS tires stock did fairly well. It was a hot day, and with 2 drivers the tires got pretty cooked. Slight understeer turned into more significant understeer! It is definitely a fun car for the autocross hobby, and still very comfortable on the street. Really a very easy car to autocross. I did my first run in Sport+ mode, just to feel it. Rest of my runs with DSC off. It was the way to go. Really felt the rear diff activate, lock, put power down.

For this coming weekend, I just added Apex SM-10 wheels, 18x9 30mm offset in front, 18x10 33 mm offset in rear, with RE71 tires square in 275/35-18. Stock wheels/tires should be good for 68 mph top of 2nd gear, so this setup might top out at about 66 mph since the 275mm tires is a bit shorter than stock. For big courses, I might consider the 285/35-19 on stock rear wheels, just to get a bit more top speed in 2nd, probably about 70 mph.

Got the Hotchkiss sway bar kit from Summit. Awesome price at under $500 the pair, and I will only use the front. Similar specs to the Dinan bars, but quite a bit less costly. Weighed the Hotchkiss front bar, it was 10 lbs. The stock bar with the brackets and bushing still attached weighed 9 lbs total. Pretty impressive weight on the Hotchkiss bar, considering its 32mm size, and nice it is hollow, with 4 hole adjustment. Very impressed with the finish, quality, and completeness of the kit. Fit was easy. Will start with endlinks at one hole from the stiffest setting. Anxious to see how it feels on course. Won't have a chance to get an alignment done before the weekend, so whatever the car came stock it is for now.

Decided to stay with TPMS sensors in the Apex wheels, so got some from Amazon for about $110 a set. Pre-programed and just required a standard tire pressure reset on the IDrive. Works fine with pressure and temp showing.

https://www.amazon.com/ITM-Pressure-...gateway&sr=8-6

Some pics of the Apex wheels, 275mm tires front and rear. Lots of clearance.

Really enjoying this car. Everything just fits me. Fun and practical.
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      06-07-2019, 07:19 AM   #2
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Nice! Get ready for a huge difference on course with the 275 RE71Rs and the front bar this weekend compared to the stock setup.
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      06-07-2019, 11:22 AM   #3
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This weekend will be a smaller, tighter course than my first event. Doubt I would be exceeding 65 mph anywhere so the 275mm square should be good. Expecting exceptional turn in, much faster sweepers, and less of the "rocking boat" feeling in slaloms. That said, the first event was pretty darn good, so yes, really looking forward to this weekend!

Not sure about tire pressures though. I ran 34 psi front, 31 psi rear, last weekend stock on the MPSS. I tend to lean toward the lower pressures, but then I have been running Z06 corvettes .
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      06-09-2019, 12:02 PM   #4
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Quote:
Originally Posted by toy4speed View Post
This weekend will be a smaller, tighter course than my first event. Doubt I would be exceeding 65 mph anywhere so the 275mm square should be good. Expecting exceptional turn in, much faster sweepers, and less of the "rocking boat" feeling in slaloms. That said, the first event was pretty darn good, so yes, really looking forward to this weekend!

Not sure about tire pressures though. I ran 34 psi front, 31 psi rear, last weekend stock on the MPSS. I tend to lean toward the lower pressures, but then I have been running Z06 corvettes .
In my experience, the RE-71Rs have a fairly wide range of pressures at which they are effective. On a stock suspension, Ive run anywhere from 32-36. At low end of that range, the front tire edges get destroyed quickly. You may be able to get away with 32, since the sway bar will limit the amount of camber change in corners. With my OG on stock suspension and square 265s, I found running a couple psi higher in back gave a nice amount of rotation.
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      06-09-2019, 05:22 PM   #5
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Quote:
Originally Posted by toy4speed View Post
Took my totally stock '18 M2 to it's first autocross last weekend, had a blast! It handled better than I expected. A fair amount of roll, but the rear Diff worked great, and the MPSS tires stock did fairly well. It was a hot day, and with 2 drivers the tires got pretty cooked. Slight understeer turned into more significant understeer! It is definitely a fun car for the autocross hobby, and still very comfortable on the street. Really a very easy car to autocross. I did my first run in Sport+ mode, just to feel it. Rest of my runs with DSC off. It was the way to go. Really felt the rear diff activate, lock, put power down.

For this coming weekend, I just added Apex SM-10 wheels, 18x9 30mm offset in front, 18x10 33 mm offset in rear, with RE71 tires square in 275/35-18. Stock wheels/tires should be good for 68 mph top of 2nd gear, so this setup might top out at about 66 mph since the 275mm tires is a bit shorter than stock. For big courses, I might consider the 285/35-19 on stock rear wheels, just to get a bit more top speed in 2nd, probably about 70 mph.

Got the Hotchkiss sway bar kit from Summit. Awesome price at under $500 the pair, and I will only use the front. Similar specs to the Dinan bars, but quite a bit less costly. Weighed the Hotchkiss front bar, it was 10 lbs. The stock bar with the brackets and bushing still attached weighed 9 lbs total. Pretty impressive weight on the Hotchkiss bar, considering its 32mm size, and nice it is hollow, with 4 hole adjustment. Very impressed with the finish, quality, and completeness of the kit. Fit was easy. Will start with endlinks at one hole from the stiffest setting. Anxious to see how it feels on course. Won't have a chance to get an alignment done before the weekend, so whatever the car came stock it is for now.

Decided to stay with TPMS sensors in the Apex wheels, so got some from Amazon for about $110 a set. Pre-programed and just required a standard tire pressure reset on the IDrive. Works fine with pressure and temp showing.

https://www.amazon.com/ITM-Pressure-...way&sr=8-6

Some pics of the Apex wheels, 275mm tires front and rear. Lots of clearance.

Really enjoying this car. Everything just fits me. Fun and practical.
Nice

275/35/18 on 9" wide et30mm and no rubbing ?
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      06-09-2019, 08:07 PM   #6
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Just got back from my first autocross in the M2 with the RE71R tires, 275mm square, Hotchkis front bar, wheels as mentioned in above posting.

Warm day, about 85-86 degrees, 2 drivers, smallish concrete surface. Last week I autocrossed the M2 totally stock, on a large concrete surface with impression of some understeer, good turn-in generally, put power down fine.

Today, with the front bar on hole #2 (calling #1 stiffest, #4 softest), the car pushed in a big way. It was frustrating. Couldn't adjust it on grid, no time. Inclined to try on #4 hole next time. Car was much flatter on course, but grip was disappointing.

Now I wonder about the relative stiffness of the Hotchkis bar vs. the Dinan and H&R bars. Externally the dimensions of the Hotchkis and Dinan seem similar, but I have no info on the wall thickness or other factors. All I can say is the front was not a little bit pushy, it was a lotta bit pushy. I guess that's why they call it test and tune

All the tires/wheels had plenty of clearance, especially the 18x9, et 30mm, with 275/35-18 tires. I ran the front tires at 34 psi to 31 psi range. No alignment info, not done yet.

Good thing the sway bar endlinks are pretty easy to adjust (at home).
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      06-10-2019, 08:13 PM   #7
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Maybe it's the extra tire and square set up giving you the understeer?

I run my tire pressures at 38-40psi cold, I find if it's not higher my sidewalls on the outer edge of my front tires will get scuffed.
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      06-11-2019, 01:08 AM   #8
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Quote:
Originally Posted by OldDirtyCoaks View Post
Maybe it's the extra tire and square set up giving you the understeer?

I run my tire pressures at 38-40psi cold, I find if it's not higher my sidewalls on the outer edge of my front tires will get scuffed.
I'm inclined to think the front sway bar was set too stiff, causing the understeer effects. Will need to adjust and test to confirm though.

Going to a square tire setup, especially increasing the front tire width by 30mm, and the rears by only 10mm, would have expected less understeer from just the tire changes alone. Not to mention going from stock MPSS to the RE71R tires. Last thing I expected was lots of understeer.

Very little information I could find on relative stiffness of the Hotchkis bar compared to the Dinan bar. Have read some owners were favoring the 2nd holes (from stiff) on the Dinan bar, so that is how I set my Hotchkis bar.

Some indication I found on line that the Hotchkis bar I weighed at 10 lbs, might be a bit heavier than the Dinan bar. Although both claim a 32mm hollow design, that doesn't specify wall thickness of the bar, the arm relative lengths or angles.

Planning to go FULL soft on the Hotchkis bar for next event.

Front RE71R tires did not have unusually large wearing toward the sidewalls, eg. doesn't appear the tires needed more pressure since they didn't appear to roll over much. They just didn't stick.

I also realize the forward rake of the car decreased slightly going to the square tire setup, vs. stock sizes. Very slight change, but in theory that could cause a small likelihood of understeer.

Can't wait till the next event.
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      06-30-2019, 12:21 PM   #9
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Back from my autocross event, nice fairly flowing course, rather short, about 30+ secs, concrete surface. Moved the Hotchkis front bar to #4 hole (#1 being stiffest), after last event with significant understeer. Today the car turned much better, well balanced, with tire pressures at 34 psi frt/ 32 psi rear. Had a bit of rear tire spin on power exiting turns, not bad, but with the front turning so well, might try to stiffen the front bar very slightly to try to help plant the rear better on power exit. My thought is to try one bar end at #4, the other bar end at #3. Really don't expect to be changing the bar much more, although I wouldn't mind a little less leaning in transitions.

The other issue that occurred at the autox was I got a warning just before my 2nd run that tire pressure may be low, the TPMS sensor system doing its job. I was already in line to run, so took the lap, and it was an awful feeling! I usually run with DSC totally off (no nannies!), and this lap was like all the nannies and gremlins came back into the car. Couldn't power around turns, braking was modulated, thought I was going to miss a turn. I had to drive around the paddock a bit to reset the tire pressue system, took some time, annoying, then all was fine. I thought I had reset my system at home for about 31 psi before the event, thinking that was good for a range of tire pressure adjustments, but guess I messed that up. I like having tire pressure info available, otherwise I would pull the TPMS sensors out. I heard the car would run ok, and default to comfort mode with DSC totally off. Not a bad thing either.

My autox run:

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      06-30-2019, 11:40 PM   #10
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Still need to get an alignment done. I've been told that BMWs come with a fair amount of front toe-in stock, so a more autox friendly setting should help my front turning some more. Hope so!
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      07-01-2019, 09:22 AM   #11
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You can probably run more tire. I ran 285 square on a 18x10 ET25 Apex EC7 on my M2 at stock ride height.
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      07-01-2019, 10:10 AM   #12
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Quote:
Originally Posted by CosmosMpower View Post
You can probably run more tire. I ran 285 square on a 18x10 ET25 Apex EC7 on my M2 at stock ride height.
The wheel width change up front would move it out of stock (street) class. Has to maintain stock wheel widths, offset +/-7mm from stock, diameter +/- 1" from stock.
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      07-01-2019, 11:20 AM   #13
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Yup, the SCCA ruleset for B-Street limits me to stock 9" wide front, 10" wide rear wheels. Car would be awesome with wider wheels in front (and tires), but coilovers and adjustable shocks would also transform the car too. The the money pit deepens

Depending on how the rears continue to put down power, I may consider trying 285/35-19 tires in rear on stock wheels. Would effectively increase top speed in 2nd gear a bit too.

For now, I will continue to work with the 275mm square tire size, improve my driving!
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      07-01-2019, 01:36 PM   #14
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Quote:
Originally Posted by toy4speed View Post
I like having tire pressure info available, otherwise I would pull the TPMS sensors out. I heard the car would run ok, and default to comfort mode with DSC totally off. Not a bad thing either.
I've got an M2C, but what has worked for me is to reset the TPMS before each run. So far, no pressure issues.
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      07-01-2019, 05:30 PM   #15
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Quote:
Originally Posted by McSmash View Post
I've got an M2C, but what has worked for me is to reset the TPMS before each run. So far, no pressure issues.
Not sure how the M2C differs from my M2 in tpms resetting, but I needed to drive about 4 laps around the parking area to get my tpms system to reset, slowly going from 0% to 100%. Trying to get it done between my runs, it seemed like an eternity! I believe the car must be moving for the system to reset too. One of the very few things about my car I don't much care for.
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      07-02-2019, 01:43 PM   #16
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Originally Posted by toy4speed View Post
Not sure how the M2C differs from my M2 in tpms resetting, but I needed to drive about 4 laps around the parking area to get my tpms system to reset, slowly going from 0% to 100%. Trying to get it done between my runs, it seemed like an eternity! I believe the car must be moving for the system to reset too. One of the very few things about my car I don't much care for.
Exactly! It's the same on the M2C but that means that your TPMS won't have completed their reset before you're done with your autox run. It's not ideal if you want to see your pressures from inside the car, but I'd rather check them manually than ruin a run.
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      07-02-2019, 02:40 PM   #17
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Ok, I think I understand better now. So when I get the tpms warning, my DSC can't be totally off, and the car defaults to comfort mode (as I gather info on this). However, if I initiate the tpms reset command, and as the car slowly resets the sensors from 0% to 100%, during this interim period the DSC can again be turned off and my autox lap will be happy. So, I only need to start the tpms reset procedure, not wait for it to complete, before going for the autox lap. That's why you can initiate the tpms reset before each run? Interesting! I don't depend on the display for tire pressures, as I set pressures with my manual gauge, but I do look at them occasionally on the road.

Thanks for helping clarify these details. Lots of stuff not well explained in the owners manual!
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      07-02-2019, 02:54 PM   #18
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Quote:
Originally Posted by toy4speed View Post
Ok, I think I understand better now. So when I get the tpms warning, my DSC can't be totally off, and the car defaults to comfort mode (as I gather info on this). However, if I initiate the tpms reset command, and as the car slowly resets the sensors from 0% to 100%, during this interim period the DSC can again be turned off and my autox lap will be happy. So, I only need to start the tpms reset procedure, not wait for it to complete, before going for the autox lap. That's why you can initiate the tpms reset before each run? Interesting! I don't depend on the display for tire pressures, as I set pressures with my manual gauge, but I do look at them occasionally on the road.

Thanks for helping clarify these details. Lots of stuff not well explained in the owners manual!
Yup! Happy to help. I just made it a habit of resetting the TPMS every time I go up to the line. It's easier on the M2C, since you can program the numbered buttons on the top of the dash, so one of them brings me right to the reset page.
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      07-04-2019, 12:31 AM   #19
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So, my 2018 M2 also suffers from wicked push issues. 275 square helped, and an alignment helped even more (3rd PAX overall at a Chicago region event recently). The car had some weird stock alignment settings including some toe out in the rear. That’s fixed now.

My Apex EC-7’s are, unfortunately, already ET33 in the rear, so I can’t narrow that track any. I’m going to push the fronts out to the max and see if that helps. The Dinan sway is on full soft already.

Should the push still be un-bearable, I’ve contemplated going up to 19’s in the rear and making the track as narrow as possible using the natural stagger help promote weight transfer. All of this is to avoid spending $$$$ on MCS shocks.

If nothing fixes it I’ll go down that silly rabbit hole for a car that gets 3000 miles a year of driving if that. I thought “street” was supposed to be cheap?

Also - the easy button for the TPMS issues is to just not use them. My car lets me know that there’s a malfunction in the TPMS system and then lets me do whatever the heck I want without interfering.
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      07-04-2019, 01:31 AM   #20
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My autox run:

Interesting course design. Marina is nice but Crows Landing is a lot more fun. Once I pick up an M2, I will definitely be trying to do a lot of autox events.
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      07-04-2019, 01:44 AM   #21
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@Wisco M3: great to share thoughts and ideas with you and others! There are a number of M2 and M2C cars doing pretty well in SCCA autox at a national level. So I am thinking the understeer can be managed. The M2 may not turn as well as a Cayman S, but looking at some autox results, both cars have been fairyly equallly competitive.

I understand your thought on going to 19" in the rear. A 285/35-19 on a stock rear wheel would not only give me another 2 mph top speed in 2nd gear, but also give a bit more forward rake. As long as the forward rake is not excessive, it could possibly decrease understeer. I'm holding off on that option until I fully explore the square 275mm setup.

What tire pressures are you running? Sometimes lowering the front tire pressures will help grip. Yes, the outer tire edges get some crazy wear, but with virtually no negative camber in front, the tire edges are toast soon anyway. After running 275/335 tires on a Corvette, these M2 tires (RE71) seem pretty cheap.

Another thought is to make sure the front bar is not binding at the center mounts, and at rest there is no preload on the bar.

I wouldn't normally run any toe-out in the rear, for a RWD car, but all options will be considered if needed. Normally I like close to zero toe in rear if I am trying to get more rotation in the car otherwise its 1/8" toe -in or so, total.

Sounds like you do pretty well in your M2 as is. I get it, that it needs to "feel" better.

No doubt you run the car with the DSC fully off?
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      07-04-2019, 01:49 AM   #22
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Quote:
Originally Posted by Gusman1 View Post
Interesting course design. Marina is nice but Crows Landing is a lot more fun. Once I pick up an M2, I will definitely be trying to do a lot of autox events.
For sure Crows is a whole different venue. The speeds and shifting are so different than anything else we can play on. Fortunately, the M2 is a nice shifting car so getting into 3rd gear at Crows is not a bad thing. Sometimes at the Annual Larry Park Memorial event at Crows, the speeds get really high. One year we hit 110 toward the finish. It was a bit scary.

Hard to beat Marina weather in the summer though!
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