Tim's Mystic Blue ZHP Coupe

[t.er]

Man I thought I was obsessed with suspension but I looked at that chart you posted and noped out in 5 seconds.

Also those spring rates sound bonkers. I think the Pro-Kit is in the 150/375-750 (progressive) range. Also I would love for my front to be higher again lol. Alpina B3 stance ftw.

If you needed beefier rear shocks after all, what would your options be? Also, I would highly recommend Eibach sway bars. Our cars benefit the most from soft springs + stiff sway bars.

I'm learning. Lucky to have one of my friends, who is a vehicle dynamics guru (used to work at OptimumG and Calspan tire testing) so I can bounce ideas off him. He actually made his own spreadsheet which is the same as the one from FCM and said, I quote "damn I've been made obsolete lol".

Beefier rear shocks, well I found the PN from the GC build sheet and it's about $330 per shock. Not ideal since I am trying to do this on the "cheap" and two new rear shocks would already be more than half of what the whole kit cost. And revalves for DA are expensive, at ~$3-400 per shock, so not cheaper than new either. Honestly I'm not too sure what my plan would be, but I'm really hoping to avoid big expenses like that.

Yeah, 440 lbs is about the lowest you can run on the front dampers, GC advised that since the DA is a race damper it can easily accommodate 2x that rate. My plan is to keep the front at 440 and re-spring the rear to get a ~5-10% higher ride frequency than the front. Then anti-roll bars hopefully next year, if I can find a good used set of bars that research shows would work well with my setup

[t.er]

So… I know I said I wasn’t going to put my coilovers in until next year, but I did it anyways. I was working on my Master’s until last Friday and we all decided to take a break until Sept. 8^th, so I had a bunch of free time on my hands. Additionally, I still plan on going to the track at least 1 more time before I store my car for winter, so that would at least give me time to shake down the car, and test the current setup as-is (ie. see if 440/550 lbs F/R is actually a pitchy POS).

So firstly I was worried about the alignment getting out of wack, and don’t really want to pay for another alignment since I just got one about a month ago. Since I was doing this at home with no equipment, I just prayed to god that my garage floor was flat enough, and drove in with the steering as straight as possible:



When you do a DIY alignment you really need a ruler like this, so I bought this one off Amazon and will be using it specifically for string alignments:



Given my previous DIY alignment woes I was a bit concerned about inconsistent measurements, but surprise surprise the string alignment revealed measurements that were similar to that of what the shop actually did. ~-3.0 deg camber, 0 toe in front. I forgot to measure the rear camber, but toe was 1 mm in on both sides.

I currently do not have access to scales to corner balance, but given that the last time I was on scales with stock suspension cross weights were within 0.2% of 50/50, as long as I get the spring perches symmetric it’ll be close enough for now:





Before removing the old strut, I measured how far off centre the strut shaft was. The OD of the flange on the strut tower is 75 mm, the strut shaft was at 20 mm so this would mean it’s offset from centre by 17.5 mm. I decided to dial out a bit less camber so when I installed it, I went to 25 mm or 12.5 mm offset. I also decided to increase caster for a bit more camber under cornering, for now I have it at ~35 mm or 2.5 mm offset backwards, for practicality sake with camber adjustment.



Front ride height is alright, might be a touch too low for what I want to run. But the spring perch is at the top and increasing it further means less thread engagement, not sure I want to do that.


Rear ride height is definitely too low (barely 2 fingers between the tire and the fender) but I had to make 3 adjustments (first two were higher than stock) and each one is a PITA. I don't have the wrenches so it involves removing the lower shock bolt, using the BMW jack to push the upper CA away from the body to remove the spring, then changing spring seat height.



I then re-stringed the car, and re-checked the alignment. Front camber is now at -2.5 and toe is 0 (well, the left side apparently has 1 mm toe-in, but ¯\_(ツ)_/¯ something something measurement error). Rear camber is at -2.5 (~-1.0 deg more than what the shop set it to before) as a result of the lowering, toe is 1 mm in on each side. So either I'll jack up rear ride height, or dial out a bit of camber in the rear, or both.

Left both adjusters at nearly full soft less 2 clicks or half a turn, as I read online that it's not recommended to run at the very limits of adjustment as the adjusters could get stuck. Did a quick 10 minute drive around the block and didn't really get a chance to push it aside from a few slaloms within my lane and a couple swift lane changes, so I don't have too many comments. But during those transients the car definitely feels less "laggy" in its response, and body roll is decreased, as expected.

But what was really surprising was no apparent deterioration in ride quality, or increase in NVH when I intentionally drove over some small potholes or cracks in the pavement. Front ride frequency has nearly doubled, and I have spherical bearings in the front camber plates (though the rubber/poly upper spring perch, being a hybrid camber plate may help), so this comes as a rather pleasant surprise.

One other unpleasant surprise: The 2 rear shocks are for the right, when they’re supposed to be left and right. Pictured below is the right side:



Unfortunately, this means that the left side has the compression adjuster facing forward, which kinda sucks. I wonder if I can just buy the lower bushing, so I can press the old one out, and the new one in the other way?

Next on the list is to cut the rear trunk lining to allow easy access to the rear rebound adjusters. And install my underseat first aid box, since that arrived yesterday.

[johnrando]

Good stuff

Sent from my SM-G988U using Tapatalk

[Will]

Nice!! Happy to hear you're liking the ride quality and the no additional NVH, sounds like the dampers are doing their job properly.

[t.er]

Good stuff

Sent from my SM-G988U using Tapatalk

Thanks JR!

Nice!! Happy to hear you're liking the ride quality and the no additional NVH, sounds like the dampers are doing their job properly.

Yeah, I'm really happy with it so far. I still haven't pushed it but I did take a highway on-ramp fairly spiritedly and it just took it with no issue, whereas if I were to do the same with the stock suspension, the DSC warning triangle might flash and you'd feel the car complaining a bit.

Raised the ride height in the rear a bit, now it's ever so slightly lower than stock. Re-checked camber, one side was at -1.5 and the other was at -2.0 deg. It's likely due to the fact that the garage floor might not be as level as I'd hoped. Given the adjustment should be symmetric since it was last adjusted at the shop, I decided to leave it, knowing both sides should be between those two values.








Then headed over to crappy tire to rent the spring compressor - brought my tools and just took off the GC street camber plates in the parking lot, rather than making 2 trips.





I also installed the underseat first aid box, I’ll use it to store my tire pressure gauge and both Koni rebound adjustment knobs.

[Galapolis]

Raised the ride height in the rear a bit, now it's ever so slightly lower than stock.

Bro if you aren't tucking in the rear like a 90s BTCC car, are you even REALLY lower than stock?

[t.er]

Bro if you aren't tucking in the rear like a 90s BTCC car, are you even REALLY lower than stock?

Geez that thing looks crazy, I wonder what the spring rates are, must be f stiff if they're running such low clearances. Pretty sure their pickup points are different than stock too, my front isn't that low and from what I can tell any lower and I'd lose significant camber under compression.

I'd also like to add that I'm starting to think that the car does feel ever so slightly "pitchy" under bumps, but that could just be confirmation bias, knowing what rates are on the car right now

[Will]

What are your ride heights (center of hub to fender lip)?

[t.er]

What are your ride heights (center of hub to fender lip)?

IIRC just a hair under 13" for both front and back. I'd been checking what that was as I made adjustments because that's the standard the NAM3 guys seem to like using

[ZHPizza]

I cannot believe you used those deathtrap spring compressors in public. You could have killed dozens of bystanders.