[M1500Z]

June 2024 update

NASA TX | Round 4 Hallett Motor Racing Circuit

NASA TX round 4 was the annual event at —a small club track in Oklahoma. This marks 1 year of me driving with NASA TX since it was last year's event that my friend convinced me to tag along for their DE. The Hallett event is a really great example of how fun this sport can be at the grassroots level. Hallett is somewhat remote, so quite a few people camp out at the track, and in addition to the usual Saturday evening banquet, there's a competition called the Slip and Flip that involves a long plastic sheet slicked down with soap and water, some beer, and a rather unique relay race. There are some other traditions and good times as well.

The track, in my opinion, is fun, flowing, and challenging. It's 10 turns over 1.8 miles with 80 feet of elevation change. At first glance, it's pretty simple and the line is not hard to pickup. Where it gets tricky is many of the turns are blind and require commitment, and the surface is a constant barrage of bumps and cracks which makes grip less predictable. To complete the difficulty—this is a track where I'd rather not put a wheel off with many deep ruts outside the curbs just waiting to damage a wheel or worse. In my limited driving experience, it's the most challenging track for me to actually execute a complete lap.

Last year, I'd traveled with 2 sets of wheels/tires but would end up only using a set of questionable 265 RS4 takeoffs. The plan was to learn the track on the RS4s and then swap to my faster set but some weather and just general coming to grips with the track meant I only ran the RS4s and ended with a best time of 1:26.492.

At the track
I didn’t make any changes to the car from the last time out at COTA aside from taking damping out to account for the bumps and lower speeds—ok I replaced my passenger seat with a Cool Shirt system. I again brought 2 sets of wheels—both RE-71RS— one set with ~20 heat cycles and the other a sticker set. My frugality making sure I got the most out of the old set and running them on Saturday. 2 car field again, so the only person I was competing with was myself.

Saturday would be on the old tire set and the car was struggling with the front end. This was somewhat expected given the nature of the tires but nonetheless frustrating dealing with understeer and trying to work the car to rotate more mid-corner. One somewhat humorous mistake that I’d made was with the new Cool Shirt box—first hot lap of the firs session, coming out of the last corner something catches my eye. It was the Cool Shirt cooler flopping around! I’d set it all up and forgotten to strap it down ��. One thing that’s gotten more complicated is the little checklist of things to do when rolling out to grid… hopefully a lesson learned.

My fastest lap on Saturday was a 1:24.856, so about 2s quicker than I’d gone previously. Even though my tires were pretty much toast, I’ve improved much as a driver over the last year. I’ll go into data in another post, but this is a big improvement—it’s not small things. I put this down to 2 major improvements:

• Getting rid of my habit of getting to throttle early
• Continued improvements in braking

That’s very blunt, but those changes have led to better rotation and higher corner speeds.

I learned another lesson. I should have been testing damper adjustments all day Saturday but I chose not to thinking that it wouldn’t be very useful since I was on trash tires. This was a mistake. I should have adjusted compression to find an optimal setting prior to putting on the good tires. After swapping to the sticker tires Saturday evening, I would be very cautious to make any adjustments.



Sunday I had 3 sessions. It’s a long trek home from Hallett and the last session is always in the opposite direction anyway so we pack up to hit the road as quickly as possible. Because of the limited number of sessions and being on new tires, I added 2 clicks of rebound to settle the car in transitions and that was as experimental as I would get. My original thought of pulling a click or 2 of compression out might have been a good experiment but I went with what I know would work. So new tires (these were pre-heat cycled) and the car now does what I want! Within 2 sessions, I’d taken 2s off my previous time and would end the day with a fastest transponder time of 1:22.725. Oddly enough, AiM says I ran a 1:22.543 but the transponder data for that lap was about .3s off.

The whole weekend was another success and a really fun. Our team came up the bracket in the Slip and Flip competition but lost close to the final, I took 2nd place in TT3 both days (duh) and won the Time Trial Target on Saturday for most consistent driver. I’m left with some things to contemplate for the future.

[M1500Z]

Continuing a conversation about active M differential lockup from the top-times thread.

Originally Posted by E90convert

Cool data, thanks for sharing. Adding in the front wheel speeds might also give an indication of what the diff is doing. Of course, there is response time from when the ECU reads the wheel speed difference under load, to when the diff ball ramp actuator finishes it's position change and the clutch material brakes the spinning wheel.

What do you mean by the front wheels giving an indication of what the diff is doing? For that screenshot, I hid the front wheel speeds but they're usually displayed to see lockup during braking. I read that the diff is able to provide lockup faster than a clutch type diff, I went looking for where I'd seen that but couldn't find it. It's definitely quick though.

Here's an overhead view of the data from COTA. The slip % is the purple trace in the 3rd row—the higher the spike, the higher the slip %. Plotted in the same row is steering angle to see how they relate.



Digging in a little further, this is what I can glean:

• Under decel, diff slip* increases as steering angle increases
• Under accel, the diff locks* up by ~160lbft torque being delivered
• The time it takes to achieve diff lock* is achieved in .3 to .4s.

*All inferred from a math channel to calculate slip as a % using difference in rear wheel speed.



The other thing I looked at that I found interesting is using RS3's scatter plot to look at slip % vs. longitudinal Gs. This image compares 2 laps, my fastest lap from last December (left) to this year's fastest lap (right). In terms of time, there is less slip over the course of this year's lap, but there is more amplitude of slip. I haven't been able to figure out what the major difference is that would cause that.

[hjj2385131896]

hello, nice driving skill and great car build! i have quick question, how you fix the problem that M2CSR rear sway bar conflict the hose? is rear sway bar link fix that contact? i am plan to do the m2csr front and rear sway bar but the problem make me confuse.[IMG][/IMG]

[medphysdave]

Originally Posted by hjj2385131896

hello, nice driving skill and great car build! i have quick question, how you fix the problem that M2CSR rear sway bar conflict the hose? is rear sway bar link fix that contact? i am plan to do the m2csr front and rear sway bar but the problem make me confuse.[IMG][/IMG]

My understanding is that you need to use a different rear sway like the Hotchkis sport. That is my plan. I run the CSR front bar.

[hjj2385131896]

Originally Posted by medphysdave

My understanding is that you need to use a different rear sway like the Hotchkis sport. That is my plan. I run the CSR front bar.

Hello, thanks for the replay. just check Hotchkis sport sway bar on bimmerword and those seems been discontinued by the Manufacturer lol. It would be perfect if the m2csr rear sway bar could be installed directly on the car.

[M1500Z]

Originally Posted by hjj2385131896

hello, nice driving skill and great car build! i have quick question, how you fix the problem that M2CSR rear sway bar conflict the hose? is rear sway bar link fix that contact? i am plan to do the m2csr front and rear sway bar but the problem make me confuse.[IMG]

Hey, appreciate the comments on my driving and the car . In your photo, if you're referring to the fuel filler pipe and not the blue line (not sure what that blue line is), then no, I haven't fully resolved it.

What I did was remove the fender liner to gain access to where that pipe mounts to the chassis. It's a plastic bracket that I slotted with a drill bit to allow me to push the pipe further away from the sway bar. The next thing I'll do is take a piece of PTFE like a piece of a plastic oil container and zip tie it in place as a barrier. I think that'll resolve the issue for the foreseeable future. If the bar rubs through the PTFE, then I can replace it, but that's doubtful given how slick that stuff is.

Eventually, I'd like to figure out the rear bar stiffness and see if there is another aftermarket option that I could swap to that would mirror it, but until then, I just check it when I check the rest of the car between events.

[hjj2385131896]

Originally Posted by M1500Z

Hey, appreciate the comments on my driving and the car . In your photo, if you're referring to the fuel filler pipe and not the blue line (not sure what that blue line is), then no, I haven't fully resolved it.

What I did was remove the fender liner to gain access to where that pipe mounts to the chassis. It's a plastic bracket that I slotted with a drill bit to allow me to push the pipe further away from the sway bar. The next thing I'll do is take a piece of PTFE like a piece of a plastic oil container and zip tie it in place as a barrier. I think that'll resolve the issue for the foreseeable future. If the bar rubs through the PTFE, then I can replace it, but that's doubtful given how slick that stuff is.

Eventually, I'd like to figure out the rear bar stiffness and see if there is another aftermarket option that I could swap to that would mirror it, but until then, I just check it when I check the rest of the car between events.

Hi, yes, what I am confused about is the friction fuel filler pipe. The blue line should not affect anything. I appreciate the information/solution you give. Will purchase CSR front and rear sway bar and install.

After a lot of searching can not find the information about stiffness even in m2csr technical customer manual. And there are not many options we can choose on the market. (rear)

Dinan: 24mm
H&R: 25mm
BimmerWorld GTMore(Hotchkis): 25.5mm
m2csr: 26mmwith bushing set 26.5mm
m4gt4: 26.5mm

Judging from the thickness of the anti-roll bar, the stiffness of CSR/GT4 should be the highest. （Just a guess）

[M3SQRD]

Originally Posted by M1500Z

Continuing a conversation about active M differential lockup from the top-times thread.



What do you mean by the front wheels giving an indication of what the diff is doing? For that screenshot, I hid the front wheel speeds but they're usually displayed to see lockup during braking. I read that the diff is able to provide lockup faster than a clutch type diff, I went looking for where I'd seen that but couldn't find it. It's definitely quick though.

Here's an overhead view of the data from COTA. The slip % is the purple trace in the 3rd row—the higher the spike, the higher the slip %. Plotted in the same row is steering angle to see how they relate.


Digging in a little further, this is what I can glean:

• Under decel, diff slip* increases as steering angle increases
• Under accel, the diff locks* up by ~160lbft torque being delivered
• The time it takes to achieve diff lock* is achieved in .3 to .4s.

*All inferred from a math channel to calculate slip as a % using difference in rear wheel speed.

The other thing I looked at that I found interesting is using RS3's scatter plot to look at slip % vs. longitudinal Gs. This image compares 2 laps, my fastest lap from last December (left) to this year's fastest lap (right). In terms of time, there is less slip over the course of this year's lap, but there is more amplitude of slip. I haven't been able to figure out what the major difference is that would cause that.

I’d recommend you discuss diff options and diff performance parameters with driftflo. If you haven’t seen it, there’s a long thread by him discussing any and all things diff related. A multi-clutch diff is a better track option, helical diff is a better street option. I absolutely love my clutch-type diffs on my e92 M3 and e46 M3 on track. Driving my stock diff e92 M3 on track really shows the advantages of a clutch-type diff.

[Track/S]

Originally Posted by M1500Z

Continuing a conversation about active M differential lockup from the top-times thread.



What do you mean by the front wheels giving an indication of what the diff is doing? For that screenshot, I hid the front wheel speeds but they're usually displayed to see lockup during braking. I read that the diff is able to provide lockup faster than a clutch type diff, I went looking for where I'd seen that but couldn't find it. It's definitely quick though.

Here's an overhead view of the data from COTA. The slip % is the purple trace in the 3rd row—the higher the spike, the higher the slip %. Plotted in the same row is steering angle to see how they relate.

Digging in a little further, this is what I can glean:

• Under decel, diff slip* increases as steering angle increases
• Under accel, the diff locks* up by ~160lbft torque being delivered
• The time it takes to achieve diff lock* is achieved in .3 to .4s.

*All inferred from a math channel to calculate slip as a % using difference in rear wheel speed.

The other thing I looked at that I found interesting is using RS3's scatter plot to look at slip % vs. longitudinal Gs. This image compares 2 laps, my fastest lap from last December (left) to this year's fastest lap (right). In terms of time, there is less slip over the course of this year's lap, but there is more amplitude of slip. I haven't been able to figure out what the major difference is that would cause that.

When you try a Drexler diff, you will not want to go back to the OEM, the OEM does not have more lock in retention or acceleration, in any way.

[M1500Z]

Got a weekend review coming up shortly, but first some tire updates on the RE-71RS. In April, I tweaked my alignment, adding in a little more camber while retaining the same caster and toe settings.

These tires saw 5 days on track

• 2 days at Eagles Canyon in April
• 2 days at Circuit of the Americas in May
• 1 day at Hallett in June

All in all, I think the additional front camber looks to have been a nice change with the front providing some really strong grip. The rear also looks to be an improvement, and while tire temps were good when checked with a pyro, I'm still getting a little blueing/heat out the outside shoulder. I may push the rear camber to see if I can get -2.6º on the stock rear arms.

The front wear is still worse than the rear (because of my staggered wheel size, I can only flip side to side) and this is likely due partially to setup but also driving style. Although I'm a very smooth driver, I do lean on the front a lot.







In terms of setup changes I may make. I'd like to reduce front wear and then work the rear a little more. Mid corner speed is pretty good, but the rear on high-speed corner entry and lower-speed corner exit can require a little finesse to keep in-line.

Things I'll consider

• Move the front from 0 toe to slight toe-out and see if that reduces camber thrust. I'm not sure I have enough static camber to worry about this too much.
• Increase camber at the rear and see if that improves contact patch
• Reduce rear sway stiffness
• Reduce overall rear damping force

[M1500Z]

November 2024 update

NASA TX | Round 5 MSR Cresson

October brought me back to MSR Cresson for the fifth NASA TX round. The previous time I'd been here was a little less than ideal—forgetting my Solo 2 DL and being on some well abused tires. For this round, the TT3 field was much more stacked with 8 participants total. My main goal was get into the teens and then see how far I could push it.



NASA runs MSRC in the 1.7 mile CCW configuration and it’s a great club track. The lap is pretty short, and once you get out of the first section known as Rattlesnake, has some nice flow. Part of what makes it fun gears it toward high-grip cars that can roll corner speed—power helps, but a lot less so here. I’ve also been told the surface favors worn tires. I can't confirm that, but I arrived on tires with only 3 heat cycles from Hallett so pretty new.

Saturday
If you're not familiar, TT grids up by lap time, but that first warmup session is where everything gets established. I found a spot around people I'm usually similar to in speed, but with something like 30 cars across all of TT, the session was pretty crowded. I ended up with 2 cleanish laps and a best of 1:22.48—overall pretty slow. The next session out, with the grid properly established, I was able to lop off time and get a 1:20.37.

Saturday was spent working on getting the feel back since I hadn’t driven the car on track for 4 months. In between sessions, I spent more time chatting with people in the paddock than looking at data. As the feel started to come back, I chipped away time to end the day with a best of 1:20.14. Better than I'd gone before, but not my goal.

That 1:20.14 had come in the afternoon during the heat of the day. Looking in RS3, I wasn’t surprised to see a theoretical best of 1:19.4 and it was just a matter of stringing the lap together. From looking at my driving, I needed some small line adjustments, but mostly carry less brake pressure into the corner and then spend less time rolling on throttle. That should translate into higher entry/min-speed and, if the car is rotated enough at apex, less time at partial throttle.



Sunday
I can’t speak to other NASA regions, but the TX region will often split the TT field on Sunday ensure everyone has a chance to get some good laps in without traffic. This puts TTU, 1, 2, and 3 in one group and 4, 5, and 6 in another. The morning temps were spot on for getting some temp in the tires and some quick laps in. I laid down my best lap for the weekend that session—1:19.13. Goal achieved! Now what—how much better can we get?

Before the weekend started, the guy in the E92 who basically cleans up my class, reached out asking if he could drive the M2. Of course I said yes—I’d love to get a reference or just some setup feedback. So after the Sunday morning session, we caught up with each other and I figuratively tossed him the keys. The car hadn't been sitting long and was still above min-weight so it’s the perfect way to see how we compare.

He was able to get about 2.75 good laps in. First flying lap is a 1:19.47, follow up lap is an 1:18.64. At this point, he decides to let the car come back, build a gap, then go for another flyer thinking that a low 18 is possible. His last lap in the car, he was on track to an 18-flat or a high 17 but had a small mistake then hit hilariously slow traffic.



His takeaways

• The car is really impressive given the relatively small amount of modifications and the fact it’s on a 275 street tire
• Front end is really sharp—very darty to use his words
• Back-end can’t keep up with the front—his biggest complaint
• He felt there’s likely a bit of bump-steer

This made me feel pretty good. We’re not too far off in times in the same car and he has a lot more laps at this track than I do. Looking at the data, you can see our different driving styles and I feel pretty confident that with a bit more time at the track, I could get on par, if not pretty damn close. The feedback he provided is extremely helpful and I'm glad he enjoyed the car. I’ve always felt the car to be pretty neutral, but once he mentioned the rear end to be lacking, I began to recall areas where I feel having some more rear grip would be quite helpful.

I watched the video from his session before going out again and gleaned a couple things. One larger thing I noticed was my perception of my entry into T1 and the reality were in opposition. I reoriented my visual references to better align with reality and was able to brake later and not drag the brakes as much. It was in that second session that I ran the lap I put on YouTube—a 1:19.27 that, had I not blown a corner, would’ve been 1:18.7. While I wouldn’t pick up any more time that weekend I feel good overall. My whole goal has been to improve as a driver and I’m definitely doing that.

Comparisons
Looking at the data to make some comparisons, I think it’s pretty interesting because our driving styles are very different. This is his fastest lap, in pink, vs my almost fastest lap in green.

1. Just feel the need to point out that if the lap ended about here, we’d be neck and neck .
2. Most of the time between us is through this section of 3 lefts, largely due to small nuances in line choice and throttle application.
3. This is where I messed things up by braking pretty late while also getting caught out by the cars in front of me—leading me to over-brake and overflow the car by quite a bit (here at 45s) .
4. To me, I love looking at steering inputs because it's such an easy way to see differences in style—almost every time you compare my steering traces to someone else’ you’ll see how much less I work the wheel.
5. The throttle trace also shows differences in application.

This is always interesting and given that these happened in back to back sessions, I think the comparison is a good one. All of it has to be viewed through the lens of one driver having a lot more laps at the track but also lacking familiarity with the car, while the other driver (me) is the inverse.

All in all, a really nice weekend that’s a bit bitter-sweet because it’ll likely be some time before the I get back to this track in the M2...

[JobanM]

Nice driving progression! I owned a time attack built E92 and now I own a M2C. The E92 had a better front end for whatever reason it turned in better, but the rear would be unstable on entry. M2C brakes better and had the same AP caliper along with same pads and fluid. M2C trail brakes better as well.

M2C is heavier and eats tires faster especially the front tires. I drove the car prior to the KMP Diff brace and it was harder to manage on power. Now with the diff brace even with the car tuned it's a lot more manageable and predictable.

I don't think the F8X gen needs a diff as bad the previous gen M cars. I had a Diffsonline diff in my E92 which was so much better than the stock unit. Drexler would be much better than OEM, but for now I am content with the stock unit. The car is super stable on entry and puts the power equally well even with stage 2 tune on it.

Front tire wear looks pretty good. I run a little above -3 at the rear, but the tires don't last more than three time attack events.

[noahf]

Just read through your thread and wanted to say I really enjoyed it and thanks for the documentation. Reminds me of the early forum days.

What are the goals for 2025?

[M1500Z]

Originally Posted by JobanM

Nice driving progression! I owned a time attack built E92 and now I own a M2C. The E92 had a better front end for whatever reason it turned in better, but the rear would be unstable on entry. M2C brakes better and had the same AP caliper along with same pads and fluid. M2C trail brakes better as well.

M2C is heavier and eats tires faster especially the front tires. I drove the car prior to the KMP Diff brace and it was harder to manage on power. Now with the diff brace even with the car tuned it's a lot more manageable and predictable.

I don't think the F8X gen needs a diff as bad the previous gen M cars. I had a Diffsonline diff in my E92 which was so much better than the stock unit. Drexler would be much better than OEM, but for now I am content with the stock unit. The car is super stable on entry and puts the power equally well even with stage 2 tune on it.

Front tire wear looks pretty good. I run a little above -3 at the rear, but the tires don't last more than three time attack events.

Interesting notes on the diff brace—if I ever do that, it'll probably be when/if I switch to a mechanical diff. I can't see the need to run so much rear camber on my setup. I'll likely increase it closer to -2.7º and see, but I think I'm very much within the window of the rear.

Originally Posted by noahf

Just read through your thread and wanted to say I really enjoyed it and thanks for the documentation. Reminds me of the early forum days.

What are the goals for 2025?

I am moving toward racing (not in a BMW), so I won't be competing in Time Trials next year. Outside of race weekends, I plan to do some instructing and have a little more time to dial in the setup. Some things I'd like to focus on, and experiment with:

Fitting a 295 square setup on 10.5" wheels
Shock pots (this project has been on hold unfortunately)
Compare a super-200 to an R comp
Compare detune vs stock tune

Basically I want to explore how to further optimize the car for NASA's TT3/ST3 class. While my driving could improve for sure, I don't find the rules too favorable toward power—aero is basically free and I have next to none. Tire width/compound are more advantageous and I'm far from maximizing there as well.