Circle Track Sway Bar

[JMortensen]

Jacking down occurs due to too much rebound and I have way too little and super stiff springs, so no fears about that. By comparison, I had the stock Bilsteins in my 10th Anniversary MIata and it jacked down bad. Was VICIOUS on concrete freeway expansion slots. Would jack down to the bumpstops then the whole frickin car would bounce violently, kinda jackhammering your spine. Luckily the stretch of concrete freeway that runs through Seattle is only about 10 or 15 miles... LOL.  I put much stiffer springs in it and it got better, was later told that if I had gone 1/2 again stiffer I could have eliminated it entirely and it would have been better in just about every respect. IIRC that would have been like 5 or 6 times as stiff as the original spring rates. I guess the idea was to valve the shocks for the Spec Miata spring rates, and screw all the idiots that bought Miatas with Bilsteins for street use...

The theory the guy was using on my shocks was that it's better to ignore ride quality and focus on keeping the tire on the ground. Most valving schemes are centered around controlling the sprung weight with the rebound and the unsprung with the compression damping. If you have too much rebound and the car goes over a dip, the wheel will get light or possibly leave the ground altogether, see pics of cars pulling a front tire in a turn. This made sense to me at the time because I had a mountain bike with a really terribly valved fork with almost no rebound, and the thing tracked GREAT, but after a couple jumps your hands were beat to hell, so I let him talk me into it. I also found that BMW E30 racers back in the day were running 300/300 with a 3:1 motion ratio, so they were basically doing exactly what I was, and spring rates were pretty similar after compensating for motion ratio too. It still kinda sorta makes sense. The problem is that it's not just ride quality that you need to concern yourself with. Allowing the sprung mass to move too fast creates its own set of issues, like the porpoising that I'm getting. I do think these shocks might work pretty well on a smooth road course.

The P30 pistons are linear, and my shock dyno plot shows that. They're not perfectly linear, but they are a lot closer to that than digressive. I have thought about revalving to 300/100, but I think that's wasted effort as you can't get a digressive piston nor are they able to be modded for adjustability. Was looking at 3000GT Bilstein inserts, people have modded them with canisters and made rebound and compression independently adjustable. Shocks are such a bummer for Zs, especially when you look at the options available for more modern cars. You can get Ohlins, Penske, FatCat, all these high end shocks for a Miata. For a Z it's Koni or some one off custom thing.

[clarkspeed]

Yes, I got the jacking thing backwards.  Too much rebound causes it and that is not your problem.  I went back and looked at some of my shock tuning info and your setup with 100/100 was not a bad idea at all.  That should feel very responsive in transitions which would be beneficial for AutoX.  I think the devil is in the details for shocks though. The shock dyno shows what is happening, but without adjustments, how do you know more or less will help or hurt?  I did think the Bilsteins could be tuned anyway you want.  I just assumed they use the same valves as all their other race shocks which are interchangeable.   Linear valving is usually too harsh at higher shock speeds.  Obviously if you lower the force to be compliant on the high speed stuff, you will have very low forces in the 0-1in/sec  low speed range and that might be your problem?  Normally you are trying to get the shock to respond in the 0-1 in/sec range with pitch and roll characteristics that "feel" good to the driver and compliant at higher speeds as not to skip over bumps.   That usually equals a digressive shock but not always.

 

If you have the $$, take a look at Motion Control.  I talked to one of their reps last year and he thought he could hook me up.  And I notice they have a cartridge listed now for the 1st gen Rabbit, which is what the P30's were.  If I can gather the funds, they will go on my next car.

[JMortensen]

10 hours ago, clarkspeed said:

I think the devil is in the details for shocks though. The shock dyno shows what is happening, but without adjustments, how do you know more or less will help or hurt?  I did think the Bilsteins could be tuned anyway you want.  I just assumed they use the same valves as all their other race shocks which are interchangeable.   Linear valving is usually too harsh at higher shock speeds.  Obviously if you lower the force to be compliant on the high speed stuff, you will have very low forces in the 0-1in/sec  low speed range and that might be your problem?  Normally you are trying to get the shock to respond in the 0-1 in/sec range with pitch and roll characteristics that "feel" good to the driver and compliant at higher speeds as not to skip over bumps.   That usually equals a digressive shock but not always.

That is it in a nutshell. At the time I bought mine, I thought that the Bilsteins were superior to the Konis which wear out the upper strut bushing and that there is a "correct" valving, but I think having the adjustability trumps having better bushings and a monotube shock. I do think that there is "correct" damping for a spring rate with a dry track, but if it rains that's out the window, and if you change springs, the shocks are no longer correct. For that reason I'm not going to buy anything else that isn't adjustable, and I'm really going to try to stick to double adjustable.

The guy who did my shocks had a long career and could say that he set up shocks for so many race winners, etc, but I think that properly setting up shocks is very subjective and also feel that people can drive past the shocks too. I raced with an EXTREMELY fast 510 when I started autoxing in the 90s. Gian Bowles was the driver. Very very fast car. He had Rancho 9000 shocks from a Camaro IIRC in the back. Rancho. R A N C H O, FFS.  And he was dominating everyone, taking FTD by a mile. 

[clarkspeed]

I ended with the same full circle you did about 4 years ago. I was, and I guess still convinced a race shock that is rebuild able by the user would be the best low cost option. I'm sure with a few trials I could get real close to the optimum damping. But paying $450 a rebuild adds up quickly when you just want to experiment. 

That low speed damping is just so critical for driver feel and different drivers like different feels. For me it is most detectable under braking, I go to full brakes fast and hard. It is like a timer, as you provide input through steering wheel or brakes, the harder the shock is, the longer it takes for the car to absorb the input and reach a steady state. Too hard a shock and you never reach steady state before the next input is given. Too soft, and it overshoots the input bounces back. Luckily there is a lot of margin in between and close is probably good enough

 

My current car has a very old set of non-adjustable  Tokikos on front and Konis on back. No complaints. But I want something much more sophisticated on the tube car I am building. I will need to extract all the grip I can to meet my goals. I plan to go at least 2 way adjustable and have suspension position sensors ready to go for data collection.

Edited February 14, 2021 by clarkspeed

[JMortensen]

Started down the shocks rabbit hole again after this exchange. Went and looked at the old info I had bookmarked years ago, and the 3kgt Bilsteins are still about $600 for a set, come with 36mm digressive pistons. Looks like DA strut shafts from Bilsteinrun $750 each, so could add 4 of those and already be at $3600,  that's without valving or remote canisters and adjusters or figuring out how to mount in the strut housings, etc. Thinking about buying 1 shock and disassembling and screwing around with it.

I do remember why I let it go last time though: I figured if it was going to be that much of a PITA I'd be better off going to SLA, then you can find DA quality shocks for a hell of a lot cheaper. Stopped there because changing to SLA requires new everything from stub axles and brakes to uprights and caliper mounts. Almost just as well to build another car. Could get a set of DA Konis and just replace them every couple years when the top bushing wears out. As much as I've resisted Konis that probably makes the most sense from a practical perspective.

[tube80z]

In XP suspension is free.  That means you could use an old strut and stay that way and add a rocker and use real coil overs.  You won't get the advantage of an SLA but you wouldn't have to pay tons extra just because you have struts.  This would be more like your ARB project as far as work goes.

[tube80z]

On 2/14/2021 at 7:24 AM, JMortensen said:

That is it in a nutshell. At the time I bought mine, I thought that the Bilsteins were superior to the Konis which wear out the upper strut bushing and that there is a "correct" valving, but I think having the adjustability trumps having better bushings and a monotube shock. I do think that there is "correct" damping for a spring rate with a dry track, but if it rains that's out the window, and if you change springs, the shocks are no longer correct. For that reason I'm not going to buy anything else that isn't adjustable, and I'm really going to try to stick to double adjustable. 

 

I know this has been the prevailing wisdom but it makes no sense.  When it's wet the weight of your car and the suspension don't change.  That's primarily what the shocks work with.  While it's true the grip is lower it's the same as saying I need to valve my shocks for 50 MPH or I need valving for 100 MPH.  

 

I can anecdotally share I tried softening everything on the wet and ended up going back to my normal rebound and compression on the DA shocks I was using.  I did remove the rear ARB and soften the front ARB but that was it.  Left springs alone.  I also suggest running your normal hot pressures when it rains. 

[clarkspeed]

1 hour ago, tube80z said:

In XP suspension is free.  That means you could use an old strut and stay that way and add a rocker and use real coil overs.  You won't get the advantage of an SLA but you wouldn't have to pay tons extra just because you have struts.  This would be more like your ARB project as far as work goes.

I have thought about doing this also. Do you have any pictures of this type of setup?

[JMortensen]

I thought the idea was that you just want to slow down the weight transfer to reduce sudden pressure changes at the tire. To put it differently, you can hit the magic number on the WTW with different springs, but the softer springs will be more predictable at the limit because weight transfer happens more slowly. Entirely possible I have that wrong. 

As to the workarounds, I'm not seeing how a rocker would work in the front with hood clearance, but I do recall you suggesting something like gutting the strut and using it just to take the side loads, then welding brackets to the strut housing and the top hat (or maybe the upper part of the strut shaft) and running a coilover shock right next to the strut.

[clarkspeed]

1 hour ago, tube80z said:

 

I know this has been the prevailing wisdom but it makes no sense.  When it's wet the weight of your car and the suspension don't change.  That's primarily what the shocks work with.  While it's true the grip is lower it's the same as saying I need to valve my shocks for 50 MPH or I need valving for 100 MPH.  

This is also what I was told in a suspension setup class from a few years ago. The correct thing to do in the rain is change spring rates and roll bar rates to increase grip. But depending on the situation, that is usually not practical. So most go for a shock adjustment because it is better than nothing.

[JMortensen]

Oh, I get it now. You don't want to change the SHOCK settings. You want to change the springs/bars. Makes sense. 

[JMortensen]

But if you halved the spring rate, wouldn't that mean you're way over-rebounded?

[tube80z]

29 minutes ago, clarkspeed said:

I have thought about doing this also. Do you have any pictures of this type of setup?

 

Unfortunately when I saw it I wasn't smart enough to know what I was looking at.  A friend explained it later and they called it a Preston strut at the time.  When I asked what the hell that was I was told Don Preston (maybe faulty memory) got fed up at IMSA and used coilovers that were mounted to the lower control arm and then hooked to the strut tower but used an old strut as the normal top suspension element.  This was all to do with rules that said you couldn't do this or that.  I can't remember if this was a 200SX Datsun or an RX-7.  Both had a live rear axle.  I think I was around 15 at the time helping my dad's friend who raced a super vee.  I only noticed this because we were pitted across from each other.

 

I wish I had pictures.  I tried Google but I can't seem to find any.  It may be one of those things that are lost to time.  

[tube80z]

1 hour ago, JMortensen said:

But if you halved the spring rate, wouldn't that mean you're way over-rebounded?

 

You'd be in revalve territory or very close.  Just as an FYI try searching for "used race shocks" on ebay (https://www.ebay.com/sch/i.html?_odkw=penske+shock&_osacat=107057&_from=R40&_trksid=p2045573.m570.l1313&_nkw=used+racing+shock&_sacat=107057&LH_TitleDesc=1)

 

You can get a few that aren't in the best of shape for 30 to 40 dollars and you can decide if this will work for you.  I bought some Penske 7300 adjustable shocks with base valves, two extra sets of pistons, VDP pistons, and a s-load of valving shims for $1400.  I bought new coilover tubes from Allstar, scored on a used shock vice, and fill cup.  To do this on struts would be more than I have in the rest of the car.

[JMortensen]

Possibly dumb/brilliant idea. Why not attach a shock to the sway bar and to a fabbed mount on the chassis, like welded to the front or back of the strut tower? Could just weld a shock mount to the strut tower and hook it up. That would insulate it from twisting with the strut. Would just need a shock that had enough travel. Then I could strip out the bilstein guts and run the same strut housings with the same springs and all, and just have the shock next door hooked up to the sway bar arm. Only real concern would be wheel/brakes/ducts hitting the shock when turning. 

I'm already fabbing up the sway bar arm anyway. One problem would be that if I mounted in front of the LCA it wouldn't move as far. IIRC that makes the shock harder to tune correctly because it isn't using as much travel. Could make the sway bar arms long and give the shock more travel/better resolution. That would make the shock angle change as it went through the bump travel, but if I put it straight up and down at ride height, shouldn't be too bad I wouldn't think. Then the question is how stiff would I need the  sway bar arms to be? I know shocks put more force into the chassis than springs. Maybe I'd be better off working with the solid ones.

If I did this I really could use some of those cheapo used race shocks.

Edited February 17, 2021 by JMortensen

[JMortensen]

One issue would be putting all that force on the rod end mount for the sway bar. I think that's likely too much to ask. But could still do a shock mount to the LCA inside of where the sway bar bracket is. Again, this would reduce the throw as compared to the stock strut...

[clarkspeed]

After Cary brought this up, I was thinking about the same thing. Really the only problem is having enough room and solid mounting for the shock. I don't see any reason you could not hook it to the sway bar mount preferrably in line with the end link. Yes you would need a solid end link, but 1/2 would probably work, hopefully not a 5/8, but I would need to think about the forces involved. 

I don't think shock travel has any influence. When selecting shocks, you can see there are a lot of travel lengths available. The shorter shock usually has shorter travel so it kind of works out. So if you have a non-binding place to mount it, you can probably find a shock to for the application. The tricky part is the shock will have a different motion ratio than the struts had. So if it is at a greater angle than the struts, the travel will be less than the struts and the damping greater. Essentially, the valving will be higher than what you had with the struts.  The Z has a motion ratio of like .9 or something. If you mounted shocks at 60 or 70 degrees, you would need a much higher shock damping due to the motion ratio. If you use adjustable dampers, then you just adjust. Probably end up more in the middle range of the shock adjustments. So maybe your 100/100 ends up at 300/300. It all depends on the angle you mount and how far the lower mounting point is away from the struts centerline.

Springs and roll bars should not be affected by this at all. Springs control the weight, and shocks control the velocity.

The downside is weight. I am obsessed with it on the car I am building.  Can't avoid some extra sprung and unsprung weight. But if you could do it right, that could be minimized.

 

 

 

 

 

[JMortensen]

On another forum someone pointed out that the LCA isn't built to handle the loads from a shock. I was going to argue, but then I realized that the stock shock loads go through the tire, spindle, into the strut housing and to the strut tower, and the LCA doesn't see that at all, so I'd be putting significantly more load into the LCA than it was designed for. Hmm...

[260DET]

As far as coilovers go MCA have a well deserved superb reputation in my country, see https://mcasuspension.com/shop/catalog/302/240Z

They did me a three way custom setup years ago, low and high speed bump, rebound. On my favourite circuit there was a turn in problem with one corner so after doing some research I did two clicks on the low speed bump, problem solved, unreal. That corner was the straight entry corner, two clicks to go from 'turn in you bitch' to whoah, PB coming up.

 

My point is that the best dampers and knowing what the adjustments do is everything. Before you get to that though the black art of damper valving is paramount, anything less can lead to endless frustration for the end user.

[JMortensen]

What did that cost you, Richard? Their single adjustable setup is about $2300 US which is pretty reasonable.

BTW I was talking about this some more elsewhere and someone suggested DG's Far North Racing website to give shock valving suggestions. I've quoted that site here many times, didn't realize it had the shock valving suggestion page though. Bought the guy's book yesterday too, just out of appreciation. My rear shocks are surprisingly close to their suggested valving. Graphs are in different scales, but man, it's right there despite the lack of digressive pistons. Fronts are pretty far off though.