Suspension Success/Event Report (LONG!)

[Guest Anonymous]

Just got back from a 3 day PCA event at Mid Ohio. Here's the WHOLE story....

 

The bushings, and struts, pads, and tires that were supposed to be delivered or in stock by Friday (1 week) before the event, weren't. I was up until 12 or 1 every night Sun thru Tues trying to get as much done as possible pending arrival of the parts.

 

Wednesday, my buddy brought the sectioned struts over (beautiful work) and I put the new inserts in. In order to finish everything so that I could drive the car Thurs a.m. to get my tires mounted and alignment done, I was up until 5 a.m. I only had to do one thing twice (those of you who have pulled all-nighters to prep a car probably know what I mean) and also forgot to put the bump stops back in. I went to bed and got up at 6 (1 hour of sleep) to be at the tire store early - I was told that arriving early would shorten the wait. When I got there (8 a.m.), I was told that they were a man short and the alignment guy wouldn't be in until 10:00. Grrrrr.... After the tires were mounted, I talked and walked the alignment guy through what I wanted, i.e., checking the street and track settings to see if there was a significant change in toe with the camber adjustments. It worked out perfectly, with a tad of toe-out for the track, a tad of toe-in for the street.

 

After that mess, I hit the bank, ran some last minute errands, and got home at 2. Then, my son and I put the RF fender back on (it was his boo-boo to begin with). By the time I had the race seats in and the car cleaned out and packed, it was 6 p.m. I drove through the night, stopping once for about 1.5 hrs of sleep, and arrived at the motel in Mansfield at 4:30. Wake up call was for 6.

 

Friday was hot as Hell, though there was a slight breeze to keep it at a constant "unbearable" reading, not quite touching "terminal". To say I was a rolling chicane on Friday would be charitable. I was rough, sloppy, inconsistent, and rusty. I sucked. The car seemed to be doing OK, but I never finished a session. I had headaches, lapses in concentration, and was glad when the day was over. Food and sleep were the only post-event activities.

 

Saturday I felt great, and it showed right away. Instead of being 4 seconds a lap slower than last year, I was right back to were I had left it. By the end of the day, I was more than 2 seconds better than last year's best. Now, let's talk about the suspension.

 

It is obvious now that I was bottoming the struts before I shortened them. The immediate understeer was gone, replaced by a nice balanced feel that allowed be to truly throttle steer the car in small increments. I even got some oversteer (what's that?) when I was hard on the gas in some of the tight corners. The car seemed to roll a lot more, which might be expected since I wasn't making solid contact through the struts, bump stops, and towers. It felt very forgiving, which is good because the new-found energy and new-found handling had me trying things too soon without enough patience. I was going fast, but tossing the car around too much. Near the end of the day, I started to smooth some things out and probably pissed off more than a few Porsche drivers who had so much fun Friday beating up on the Jap. There were some big hammers out there, and it is a world of fun to signal a pass and then dog the guy through 6 turns until he can use the loud pedal again.

 

Friday was one of those red-letter "good" days that make the late nights worthwhile. We even had the time and energy for a leisurely meal and evening conversation.

 

I didn't get around to dropping the x-member and relocating the pivots. I think this will help a little more, mostly through camber gain and raising the roll center. Stiffer springs are on the horizon, for sure. And brakes. That brings us to Sunday.

 

We had checked my brother's pads Sat evening at the track and found that the RF was tapered down to about 3/32. It was obvious that 1 run Sun a.m. was going to be his last. I went out after him in my group and was having a great time for about 20 minutes. Then, at the end of the main straight, just as I was coming off the brakes, I felt a sudden softening. My first thought was that I had boiled the fluid. No problem, just ride it back around slowly, bleed the brakes and get ready for round 2. As I came into the pits, I noticed that I was being followed by a large cloud of white smoke. As it turns out, the RR brake cylinder blew out 3 seconds after I had slowed the car from 120 to 50. If it had happened at the beginning of the (downhill) braking zone, they'd still be looking for me.

 

We drove into town and got a new BC at the local Pep Boys and slapped that puppy on there. By then, it was after lunch and I didn't feel like testing the brakes on track, so I packed up my stiff and hit the road for home, getting in at 2 a.m.

 

Another highlight of the weekend was instructing my brother in his C5 Corvette. He knocked off 16 (!!!) seconds from last year's best effort in a Z-28 Camaro. He also says I'm the only instructor he's ever had that said "go faster". The Corvete, with "Active Handling" and a million other gizmos is a technological wonder, though I don't need my car to give me a choice of languages for read-outs and automatic, on-the-fly tire pressure readings. Still, it's a neat car with gobs of power and good handling even on street tires.

 

Since I'm still running a significant sleep deficit, I probably left some things out. I'll add anything relevant later if need be. What I don't want to forget is the tremendous help I have gotten from people on this BB. I won't name names but you know who you are. Thanks - you guys spent more time analysing and recommending than I really have a right to expect. Best of all, it worked.

[Drax240z]

Awesome stuff John. I'm impressed that you managed to accomplish as much as you did on so little sleep!

 

Nice to hear some before/after comparisons on the strut sectioning. Do you have any pictures from the weekend?

[randy 77zt]

john-what spring rates are you running-i run 225 in front and 250 in rear.are you running track tires -like kumho or hoosier?get some disc brakes in rear-less maintenance.

[pparaska]

John, sounds like it was a great week. Burning that midnight oil was worth it, it sounds like!

 

BTW, how much lowered from stock was your car before you sectioned the struts? Hearing another instance of someone finding that their stock length struts were bottoming and causing understeer is refreshing. Glad it helped!

[randy 77zt]

i run a design products kit in rear-it uses a 84 300 zx rear rotor.billit caliper brackit and willwood dynalite single caliper.no e brake in car.

[Guest Anonymous]

Pete:

 

I didn't lower the car any more with strut sectioning, just added suspension travel. I'm just over 6" at the bottom of the front fender bolt that holds the bottom of the fender.

 

Drax:

 

I accomplished very little on Friday, mostly went through the motions. Saturday was a blast, however. Sunday was good until my wheel cylinder blew out. Only pics are the "hero shots" we got of us by our cars.

 

Randy:

 

I run 175F 200R and Kuhmo V-700's. I would LOVE to install some rear discs, but have to watch my budget. Got any Maxima brackets laying around?

[johnc]

Now its time to up the spring rates. What size anti-roll bars are you running?

[Guest Anonymous]

I have 1" sway bars F & R, 175F 200R springs - I was thinking of bumping up to 250F 300R. Dan pointed out that raising the pivot will raise the roll center which will increase roll stiffness. The 50# bias shouldn't be too much, ya think? I just GOTTA get that '73 running - the '78 is obviously headed for "track only" use.

[johnc]

On a 280Z you might be able to run the 300 rear springs without a roll bar, but I doubt it. On a 240Z the rear of the car will start flexing with spring rates over 275 unless you have a welded in roll bar or cage. On the front you need a strut tower brace (and more if the rules allow it) to run spring rates over 225.

 

Also, if you go with the higher spring rates you might need to drop the anti-roll bar diameters a bit. There are generally two schools of thought on suspension tuning:

 

1. Big springs, little anti-roll bars.

2. Little springs, big anti-roll bars.

 

With the advances in shock technology today, #1 is where most everyone is going.

 

With the triple adjust Penskes on my 240Z, I currently run a 25mm front and a 23mm rear anti-roll bar with 275F and 300R spring rates. I'm actually thinking about dropping the anti-roll bar diameters a bit more, but I'll have to have them custom made.

 

fyi: My car weights 2200 lbs and has almost perfect cross weights. Your car is probably different, so adjust accordingly...

[Dan Baldwin]

Congrats on your understeer excorcism, John! I wonder if the 280Z is more prone to suspension bottoming-out than the 240, as I don't *think* I've run into this problem in my 240 (lowered ~1", 160 lb/in front 200 lb/in rear springs).

 

Scary about the wheel cylinder. Yikes! I've got most of my rear disk conversion hardware now, might get started on that this weekend. Woohoo!

 

Speaking of suspension setups, the hot ticket for racing these days (on a 240, anyway) seems to be stiffer springs in front than in back, and NO rear anti-roll bar! Seems odd to me, though, as my car's pretty neutral with the 160/200 lb/in springs and 1" front/3/4" rear adjustable bars. I guess things change when the car is lowered to the SCCA-legal limit and mucho stiffer springs are employed.

[Guest Anonymous]

John C wrote:

On a 280Z you might be able to run the 300 rear springs without a roll bar, but I doubt it.

 

** (Me, with asterisks) This seems counter-intuitive - stiffer springs with the existing roll bars ought to eliminate some of the body roll, hopefully without upsetting the balance I have worked so hard to achieve.

 

On a 240Z the rear of the car will start flexing with spring rates over 275 unless you have a welded in roll bar or cage.

 

** I have a bolted-in cage - not much help but it ought to keep the car from twisting more than 10 degrees.

 

On the front you need a strut tower brace (and more if the rules allow it) to run spring rates over 225.

 

** I plan to triangulate tower/tower/firewall. And lower the car to ~5.25" at the bottom fender bolt head. And relocate the pivot hole. No rules, just right.

 

Also, if you go with the higher spring rates you might need to drop the anti-roll bar diameters a bit. There are generally two schools of thought on suspension tuning:

1. Big springs, little anti-roll bars.

2. Little springs, big anti-roll bars.

 

** Since they are both springs, maybe there is a maximum combined value over which you get stiffness/harshness but no gain in lateral G's. My intention is to bump the springs up some and see how that works. Maybe 250/300 is too much - 225/250 sound better?

 

With the advances in shock technology today, #1 is where most everyone is going.

 

** I can't afford to test various shocks. I'm "stuck" with the Tokico Illumina's until Regis calls.

 

fyi: My car weights 2200 lbs and has almost perfect cross weights. Your car is probably

different, so adjust accordingly...

 

** My 280Z weighs 2820 with me and 2/3 tank of fuel, cross-corners within 5# when last checked (before struts sectioned).

 

Dan B wrote:

Congrats on your understeer excorcism, John!

 

** Thanks, Dan - it's been a well-documented adventure for way too long.

 

I wonder if the 280Z is more prone to suspension bottoming-out than the 240, as I don't *think* I've run into this problem in my 240 (lowered ~1", 160 lb/in front 200 lb/in rear springs).

 

** I suppose it's to be expected in a heavier car. When you start transferring loads on a car that is 150# heavier at each corner, things are gonna change.

 

Scary about the wheel cylinder. Yikes! I've got most of my rear disk conversion hardware now, might get started on that this weekend. Woohoo!

 

** We will all be waiting for a performance report from your next track event.

 

Speaking of suspension setups, the hot ticket for racing these days (on a 240, anyway) seems to be stiffer springs in front than in back, and NO rear anti-roll bar! Seems odd to me, though, as my car's pretty neutral with the 160/200 lb/in springs and 1" front/3/4" rear adjustable bars. I guess things change when the car is lowered to the SCCA-legal limit and mucho stiffer springs are employed.

 

** Yeah, and a LSD doesn't hurt either. It has occurred to me that if I get this car to corner REALLY well, I'm gonna encounter rear wheel spin at some point, which will have me hunting for a new pumpkin.

[jeromio]

Increasing rear sway bar will decrease roll in favor of skid, right? IE, more rear bar equals more oversteer?

 

I'm getting really comfortable with my current setup (although no track time yet), except for it's tendency to oversteer. I don't have a rear sway bar, was planning on installing one, but now I'm having second thoughts.

 

The front bar is stock (71 240). I have 150lb springs front, 175 rear. It's stiff. You guys talk about 250 or 300lbs per corner?! Yikes. My car is like a skateboard. Expansion joints on the highway are torture.

 

So I hesitate to consider a larger front anti-sway bar. It may balance out the oversteer, but it can only make the ride harsher.

 

My summer project is to stiffen the chassis (full DOM cage and "K" strut bar up front), so we'll see how that affects ride/handling.

[johnc]

>> On a 280Z you might be able to run the

>> 300 rear springs without a roll bar, but

>> I doubt it.

> ** (Me, with asterisks) This seems counter-

> intuitive - stiffer springs with the

> existing roll bars ought to eliminate some

> of the body roll, hopefully without

> upsetting the balance I have worked so

> hard to achieve.

 

When I used the term "roll bar" above I meant the kind that goes inside the car to protect yer noggin.

 

> ** I have a bolted-in cage - not much help

> but it ought to keep the car from twisting

> more than 10 degrees.

 

Bolted in cages can work well to help stiffent the chassis, but you have to fabricate some good mounting and backing plates for each spot the cage is bolted to the chassis. The ones I've seen "out of the box" from Autopower are good from a safety standpoint but need some more fabrication to help the Z chassis.

 

> Maybe 250/300 is too much - 225/250 sound

> better?

 

With your cage I would go to 250F/275R. The Tokico Illumina applications used in a 240Z have trouble controlling rebound with spring rates over 300. When I ran them on the back of my 240Z (with the 300 springs) I had to keep them at 4 or 5 to get close on the rebound, but that made compression WAY too stiff and the back of the car would hop over bumps. With 275s you can turn them down to 3 and with 250s you can, maybe, turn them down to 2.

 

> Speaking of suspension setups, the hot

> ticket for racing these days (on a 240,

> anyway) seems to be stiffer springs in

> front than in back, and NO rear anti-roll

> bar! Seems odd to me,

 

Seems odd to me too. I'm haven't had any lengthy discussion with any of those guys to figure out why they run that setup. Its run mostly by East coast ITS racers and there's no arguing how fast they go.

[johnc]

> Increasing rear sway bar will decrease

> roll in favor of skid, right? IE, more

> rear bar equals more oversteer?

 

As a VERY general rule of thumb that's true, but sometimes reducing overall vehicle roll (thus reducing positive camber gain) can improve the tire's grip, thus increasing traction.

 

> I'm getting really comfortable with my

> current setup (although no track time

> yet), except for it's tendency to

> oversteer.

 

All of the discussions in this thread are about running a 240Z on the track which is remarkably different that any street driving. You might be surprised how differently you car's balance is at speed.

 

> I don't have a rear sway bar, was planning

> on installing one, but now I'm having

> second thoughts.

 

At your first track event, run the car the way you have it setup now. Then decide what you might want to do to change the car's balance.

 

> The front bar is stock (71 240). I have

> 150lb springs front, 175 rear. It's stiff.

> You guys talk about 250 or 300lbs per

> corner?! Yikes. My car is like a

> skateboard. Expansion joints on the

> highway are torture.

 

But, on a track, its pure joy! The feeling you get when you're foot to the floor (or almost there) as you hit the apex of a corner and pass a Porsche 996 just after corner exit is a real ego booster! Those Porsche guys just give up trying to drag race you down to the next corner 'cuz you have such a nice head start.

[Guest Anonymous]

Jeromio wrote:

> I'm getting really comfortable with my

> current setup (although no track time

> yet), except for it's tendency to

> oversteer.

 

John C wrote:

All of the discussions in this thread are about running a 240Z on the track which is remarkably different that any street driving. You might be surprised how differently you car's balance is at speed.

 

** All I can add is Amen. It's a whole new world of driving.

 

> I don't have a rear sway bar, was planning

> on installing one, but now I'm having

> second thoughts.

 

At your first track event, run the car the way you have it setup now. Then decide what you might want to do to change the car's balance.

 

** If your car has rear sway bar mounts, bring the bar in case you decide to install it at the track. You oughta sign up for the Alfa event at VIR in September - no better place to start, 'cept maybe one of the TZC events. Check out www.trackschedule.com

 

** And as for stiffness, most tracks are smoother than public roads by a huge factor, and VIR is one of the smoothest, 'cept for the gators.

[Guest Anonymous]

mm_280Z wrote:

 

I'm wary of 1" or larger front bar in almost any case. It all depends on your setup of course but the stock rear bar is larger than the stock front bar. If you switch that around (by putting a larger bar in front) you'd better change something else to compensate or prepare for massive understeer.

 

MM --

 

That's exactly what I thought! I have a 1" Addco front bar and a custom 1" rear bar - my thinking is that I will balance whatever I can (springs, bars, tire pressures, etc.) to get the balance I want, or over-weight some value (same choices) to dial in the handling I want, and deserve.

 

Now that I have the understeer under control, I'm looking at a 50# bias toward the rear (225F/275R) as opposed to my current 25# bias (175F/200R). The re-setting/re-building is a pain, but testing sure is fun!

[Guest MM_280Z]

I just cured massive understeer on my Z by replacing the stock rear sway with a 7/8" one. I have Tokiko lowering spring (I estimate about 140 lb rate since they claim 40 % stiffer than stock).

 

I tried a 1" front in addition to the 7/8" also. The car rolled less but still understeered severely. Maybe if I had better tires and could load the outside front tire more this wouldn't be an issue.

 

I'm wary of 1" or larger front bard in almost any case. It all depends on your setuo of course but the stock rear bar is larger than the stock front bar. If you switch that around (by putting a larger bar in front) you'd better change something else to compensate of prepare for massive understeer.

 

With stock front, 7/8" rear and plain H-rated tires my car rolls quite a bit, but is quite balanced. I believe the the optimum for my case would be around 225 Front, 200 rear springs and 7/8" Front, 1" rear bars.

 

[ June 24, 2001: Message edited by: MM_280Z ]