Rough Track or Poor Bushings or soften the damping?

[David Klassen]

I’ve been tracking my 2008 350Z NISMO since 2019. At the end of 2020 season, the front lower control arm bushing were done, especially on the right side. So for the 2021 season I put in SPL bushings (inner and shock) . . . and now they too appear to be shot. I could set the damping on the coil overs to be softer.

is there anybody else experiencing bushing failures?

[Joose]

Were the bolts tightened with weight on the wheels? Or up on a hoist with the suspension at full droop? That would tear them up quick

[donrolandofurioso]

I agree. One of the more common mistakes of working on suspensions is to have the car on a two-post lift (as it is easy to access all suspension parts that way), and then finishing off all the work on the same hoist. While it seems to make sense from the technician's PoV, reality is that all bushings need to be pre-loaded in a normal setting, as in tires on the ground with weight on them. If the technician did not do that for whatever reason, then the suspension bushings will be pre-loaded in an unnatural position, and they will wear prematurely. Two years is way too early to have bushings fail, especially if the car is barely ever driven during every day duties.

[nopistons]

Can you elaborate on the type of bushings you installed?

The website only looks to be spherical bearings, and what you have pictured looks like derlin. Unless of course it's the teflon being squished from the spherical bearing race!

In any event, either have a finite life. Spherical bearings can be rebuilt though.

[David Klassen]

I had a very helpful chat with an engineer from SPL. He runs these same bushings, also on a 350Z, under very hard conditions, with no issues. We talked about possible causes to explore before replacing them and ruining another set. In order of probability: 1) shocks might be bottoming under heavy braking (I’ve got upgraded brakes, so yeah, heavy braking!), spring rate could be increased from 12kg/mm to 16kg/mm, maybe add a stop bumper; 2) check the compression rod bushings, worn bushings will change the suspension geometry under heavy braking, they may need replacing.

@nopistons these are SPL spherical bearings, in some of my instances, it’s just a dust ring being pushed out, not a major issue.

@Joose @donrolandofurioso the bushing work was done @ Speed Factor Racing . . . one hopes that they did it correctly . . . in any case the engineer @ SPL acknowledged that improper tightening might add a little binding, but since they are spherical bearings, that’s not a high probability cause

[nopistons]

22 hours ago, David Klassen said:

1) shocks might be bottoming under heavy braking (I’ve got upgraded brakes, so yeah, heavy braking!), spring rate could be increased from 12kg/mm to 16kg/mm, maybe add a stop bumper;

If this is true and you are bottoming out the shock under heavy braking, then your shock settings are the culprit, not necessarily the spring rate.

What suspension do you have? I'd honestly step back and look big picture before deciding on a single aspect of the system. Remember, your damper valving has to support the higher rate springs or you will just send the existing dampers to the bin.

Also, too much spring rate at gimli will bounce and unbalance the car in corners and under braking, while adjusting your compression and rebound rates front and rear, will allow the car to squat and settle, which by your description is what you are after.

I'm generalizing of course but its using the entire system rather than just throwing parts at it.

More to the earlier point, you could simply have warn out dampeners.

Good luck!

Edited February 13, 2022 by nopistons

[David Klassen]

@nopistons  Thank you for you comments.

I have BC Racing series BR true coilovers. I put them on in May of 2019, after one of my rear HKS Hipermax shocks broke @ HPDE. I bought the car with the HKS shocks.

They are 1 way adjustable, with damping set a couple of clicks softer than full hard (30 clicks total adjustable range).

When ordering these shocks there is an option for different springs, I just went for the default of 12kg/mm (front), 5 (rear). The options offered are 12 - 18 (f), 5 - 18 (r), using Swift springs. This would indicate to me that these shocks can handle the stiffer springs.

The SPL engineer did suggest that before I go the route of stiffer springs that I should do a test to see if they are bottoming, fasten a zip tie to the shock rod, near the bottom, get up to 80 km/h, slam on the brakes, then see if the zip tie has been shoved to the top of the rod.

When you suggest looking at the entire system, can you suggest what else I should consider?

[nopistons]

BC are good units.

It notes that valving matches the rates you order.

By system I mean to see what is happening over the entire car. Are you bottoming cuz the rates are too low, dampening is not high enough in the front or is the rear too little?

If you go too high in springs, you run the risk of over springing the suspension when you add the rates of the sway bar (speaking specifically for Gimli. Other tracks can handle higher rates). Many folks toss the bar and jack the shock spring rates.

Small adjustments make big changes sometimes so best to take it one step at a time. (Example: spring changes might require new alignment settings)

Best to corner weight your car with you in it and ask BC what they recommend on that weight. You might end up with 3 different spring rates and need to send in the cores for re-valving.

Just my $0.02

[David Klassen]

@nopistons @donrolandofurioso @Joose 

Thanks, I’m at least 0.02¢ richer! 
I had a great chat with BC Racing, there’s no need to revalve the dampers IF I do go to 16kg/mm springs, there’s a 4kg tolerance on the current valving 
So, my course of action right now is:

1. do some detailed inspection of the bushings and order replacements if necessary 
2. order some parts that will allow for -ve camber adjustment on the rear, the Falken Tire engineer said they likes some -ve camber (already done in the front), my wear pattern indicates it’s needed rear too
3. when the weather allows for getting the car out, have the new parts fitted, get an alignment, and get the corners weighed (do you have any suggestion who could do the weighing?)
4. 1st track day, do some testing to see if the shocks are bottoming
5. Order spring if necessary, install, align

Thanks for all your input!

[Tysawch]

something to look into could be keeping the softer springs in and adding taller bump stops. this would create a variable spring rate. Ramping effect under compression. 

As for your spherical bearings. i have seen some issues across most brands with life of them. it really seems like a longevity trade off for the solid no deflection advantages they offer.

it might be worth finding the motion ratio's of the front and rear and calculating the suspension frequency to better decide on what spring rates to use.

[donrolandofurioso]

David,I have been thinking about this for a while now...

If your car has external bumpstops to limit suspension travel, then heavy braking should not bottom out the shock absorbers at all, as the suspension should collapse onto the bump stop.

If your front coilovers have internal bumpstops, then the shock absorber should also not bottom out (it should collapse the bumpstop). If a strut/coilover has no internal bumpstop, the shock absorber typically is long enough that you won't bottom it out either (otherwise you would damage the valve stack inside or rip the housing) - you should be experiencing coil bind first.

However...whether you have bumpstops in your struts or not, the force going into the lower strut bushing is always the same, since the weight of the car and the kinetic force remains the same.. Therefore changing the shock absorber or the spring is not going to improve the life of the bushing at the bottom of the coilover.

Edited February 16, 2022 by donrolandofurioso

[David Klassen]

Quote

“it might be worth finding the motion ratio's of the front and rear and calculating the suspension frequency to better decide on what spring rates to use.”

@Tysawch Could you please offer some advice on how I would go about doing what you suggest, it’s beyond my knowledge.

[David Klassen]

@donrolandofurioso  there are internal bumpstops on these BC Racing shocks.

all this conversation about spring rates and bumpstops have me thinking that my issues may have more to do with suspension geometry under heavy braking. The fellow @ SPL (designer of the bushings, tracking a 350Z like mine) suggested the mushy stock compression rod bushing will allow the suspension geometry to distort under load. It’s on my replace list because it’s the weakest component in the system now (step 1 above).

[Tysawch]

57 minutes ago, David Klassen said:

@Tysawch Could you please offer some advice on how I would go about doing what you suggest, it’s beyond my knowledge.

its also beyond my personal skill set still. I had Professional Awesome racing do all the math for my evo last year. i resprung to there recommendations and it completely changed the car. with there help on a couple things i was able to go from a 1.05 to 1.03 at gimli with less hp. 1.05 was ran on 30psi with the old 94 oct. ran this year on 24psi and 91.  if your looking to take a swing at doing it yourself HP academy does some online courses based around motorsport suspension and everything else.  i would check them out

[Tysawch]

they do race consulting and some really cool DIY aero parts

https://professionalawesome.com/

here is a link to hp academy. they offer courses and also put up lots of videos on YouTube with some great information 

https://www.hpacademy.com/

[David Klassen]

@Tysawch thank you, I’ve checked out the links. What was the consultation fee for your tuning?

[Tysawch]

8 hours ago, David Klassen said:

@Tysawch thank you, I’ve checked out the links. What was the consultation fee for your tuning?

want to say it was 400usd. at the time kinda seemed like a lot but considering the results money well spent. (i have also ran alot of ideas past them that they have just helped me save money by not chasing rabbit holes of diminishing returns) they are some seriously smart dudes and everything they will advise is backed by math or data off a car 

[David Klassen]

I’m looking for someone to do corner weighing, any recommendations?

[Tysawch]

not sure who has scales in mb. i had weighed at the track one weekend and used that to help factor in on getting my spring rates 

[David Klassen]

On 2/10/2022 at 7:27 PM, Joose said:

Were the bolts tightened with weight on the wheels? Or up on a hoist with the suspension at full droop? That would tear them up quick

Not particularly relevant to spherical bearing bushings.

[David Klassen]

On 2/15/2022 at 11:44 PM, Tysawch said:

they do race consulting and some really cool DIY aero parts

https://professionalawesome.com/

here is a link to hp academy. they offer courses and also put up lots of videos on YouTube with some great information 

https://www.hpacademy.com/

So I’m taking the HP Academy course “Suspension Tuning & Optimization”. I’ll probably follow that with “Practical Corner Weighting”. 
Thanks for the links!

[David Klassen]

@Tysawch @Joose @donrolandofurioso
 

Upon further inspection I’ve determined that the bushings (spherical bearings) are not worn out. I had observed 3 things:

1. teflon rings pushed out of the bushings
2. Bolts looked like they were off centre
3. markings on the outer portion of the spherical bearings

I was able to rotate the lower control arm around it longitudinal axis. As I did that, the anti-sway bar moved too. It’s a flaw in the design of the lower control arm that the sway bar end links mount off the side of the control arm. Normally the OEM rubber bushings or aftermarket polyethylene bushings would resist that twisting action, but spherical bearings allow for some twist until the inner part hits the outer part. This is, sadly, normal for this setup and the three observations above are symptoms of that twisting. 

[Greg Eastwood]

Interesting discussion on suspensions and their operation. There is no doubt that the rough track condition at the moment is a factor . Premature wear on suspension parts and sometimes failures have been seen on road race cars and many other Time Attack cars. When the WCMA issues a bulletin to race car drivers to get their front suspension yokes magnafluxed for cracks due to several similiar failures, you know there are some contributing factors to your situation.