Is my coilover spring rate too high?

[AlbatrossCafe]

I installed Stance coilover suspension along with TTT control arms and tension rods on my car this winter. I have 4k springs front and 5k springs rear. My car is lowered about 1/2" compared to stock.

It handles well, but is very stiff. I hit bumps and occasionally bounce into the ceiling and the car sounds like it has just been smashed lol. I have the 15-way adjustable coilovers adjusted as soft as possible. 3 questions:

1. Is the only bumpstop in these cars in the coilover or strut itself? I didn't see any other.
2. Is my spring rate too stiff? I don't track my car.
3. Will the springs break in? I have about 300 miles on the current setup and they feel the same as new.

 

Sakura Garage recommended 4k/5k springs for "Street" applications. I'm wondering if that is typical around here or if that is a bit much for everyday driving.

 

Edited August 13, 2018 by AlbatrossCafe

[rturbo 930]

First thing's first, I'm not a suspension expert, and my car doesn't drive, so I have no direct experience with Z suspension. But I've been around here a while, so here's my take.

Your springs rates translate to 280lb/in and 224 lb/in. John C on HybridZ has said that anything over 300lb/in is pointless since at that point, the chassis starts flexing, at least a 240Z. Most people who have put together coilovers seem to go with something like 225/250 or 200/225, or something to that effect, not 280, but apparently all the mainstream coilover manufacturers seem to think that this combo of 4k/5k is good, I couldn't tell you why.

Shocks can also make a difference. My E30 has stiff suspension (310 front, 570 rear, IIRC), and I started out with Bilstein gas shocks, and recently switched to adjustable Konis. There was a noticeable difference in ride quality, and I haven't even messed with the settings on the Konis yet to see if I could improve it further. I have no idea what quality shocks you have there, but that could have something to do with it. I'm not sure if BC coilovers are really all that good, lots of people use them and like them, but I'm skeptical of their quality.

Lastly, it could just be you. I don't know what you were expecting it to ride like, but obviously it isn't going to ride anything like it did stock. You may have been expecting something that just wasn't realistic.

[AlbatrossCafe]

15 hours ago, rturbo 930 said:

First thing's first, I'm not a suspension expert, and my car doesn't drive, so I have no direct experience with Z suspension. But I've been around here a while, so here's my take.

Your springs rates translate to 280lb/in and 224 lb/in. John C on HybridZ has said that anything over 300lb/in is pointless since at that point, the chassis starts flexing, at least a 240Z. Most people who have put together coilovers seem to go with something like 225/250 or 200/225, or something to that effect, not 280, but apparently all the mainstream coilover manufacturers seem to think that this combo of 4k/5k is good, I couldn't tell you why.

Shocks can also make a difference. My E30 has stiff suspension (310 front, 570 rear, IIRC), and I started out with Bilstein gas shocks, and recently switched to adjustable Konis. There was a noticeable difference in ride quality, and I haven't even messed with the settings on the Konis yet to see if I could improve it further. I have no idea what quality shocks you have there, but that could have something to do with it. I'm not sure if BC coilovers are really all that good, lots of people use them and like them, but I'm skeptical of their quality.

Lastly, it could just be you. I don't know what you were expecting it to ride like, but obviously it isn't going to ride anything like it did stock. You may have been expecting something that just wasn't realistic.

Thanks. That's what I wanted to hear since I have not been here long. Over certain bumps it almost feels like my frame just moves up and down instead of the wheels lol. I did a lot of research and I think my shocks (Stance) are a decent item, which leads me to believe it has to be the spring rate if what you said (300lb/in is a theoretical "limit") is true. I have owned a Mazda RX-8 in the past, and that thing was half as stiff as my car now but still handled very well. That's what I was going for. Really, I just don't want the car to feel like it is gonna fly over a small bump in the road or crumble when I go into a pothole.

 

Weird that this is Sakura Garage's lowest spring rate option on their site ?

[Zed Head]

This has come up before, and I don't know how the Sakura product is adjusted to set ride height, but preload can make the low speed ride stiffer.  If you adjusted ride height by compressing the spring you would add preload.

You might see if you have used the wrong method to set ride height.

[cgsheen1]

Stock Stance USA XR-1 coilovers use 175mm long springs and minimum rate they show is 4K.  They have listed 3K (168 lb.) springs in 200mm length.   If you're interested, talk to Stance USA Customer Service about those springs on your struts and ask if your struts would need to be re-valved to use them.  That is important to know.  The 3K springs would be just over an inch longer than your current springs IIRC.  That means your lower perch would need to drop just over an inch.  At your current ride-height you should have plenty of thread to lower the perch on the strut tube.

(You could move your 4K springs (or strut) to the rear and use the 3K springs on the front.  Stock 280Z spring rates were 103 lb. front and 198  (see below) 128 lb. rear (3K=168 lb. vs. 103 lb. - 4K=224 Lb. vs. 198  128 lb.).  Your springs would be softer than they are now, still stiffer than stock.  edit: the information sited below may change you opinion about the 4K springs...

The 15-step damper adjustment is for damping - it doesn't change the spring rate ("stiffness"), it dampens compression and rebound of the spring.

Edited August 15, 2018 by cgsheen1

[Captain Obvious]

18 hours ago, cgsheen1 said:

Stock 280Z spring rates were 103 lb. front and 198 lb. rear.

Seemed odd to me that the front and rears would be so wildly different, so I took a look at a couple years of the FSM... I haven't dug deep into it, but there's definitely a typo in there somewhere.

You're right that the FSM (for 1976) lists the rear spring rate at 2.28 kg/mm or 197.7 lb/in. But the problem is that 2.28 kg/mm does not convert to 197.7 ln/inch.

If you do the conversion manually, you'll find that 2.28 kg/mm is in fact 127.7 lb/in. So my suspicion is that they typo'd a number and that 197.7 should be 127.7.

As further supporting evidence, the 1977 FSM lists the fronts as 103, but the rears are listed as 128 lb. (not 198). So it seems they realized the mistake and fixed the typo in 77 moving forward.

[cgsheen1]

Thanks for that research and clarification.  The same error is in the 1975 280Z FSM.  We rarely work with lates ('77-'78) and I've always taken the published spring rate (in ft lbs) in the '75-'76 FSM as gospel (never even looking at the kg/mm figure).  Going to edit my post above.

 

[Captain Obvious]

I took a look a one year further back in the manuals, and the spring numbers are all over the place. The 74 manual even seems to indicate that the front left and front right springs were different. Do people really believe that to truly to be the case? The fische has all sorts of numbers and left and right are different!   

All I can say is that I'm glad they got that all sorted out by the time they got to the 280!

[Patcon]

It is my understanding that on the 240z the front springs are indeed different

[Chickenman]

Yep. Fairly common on other cars as well. I believe it has to do with Road Cambers and the fact that the majority of the time the car is only operated by the driver. Then again, I could be wrong with that theory.

[LeonV]

It's likely to do with wanting the car to sit level visually, given unequal corner weights. When people see cars sitting wonky, they may think something's wrong...

[grannyknot]

10 hours ago, Captain Obvious said:

All I can say is that I'm glad they got that all sorted out by the time they got to the 280!

Do you know what the spring rates are for the 280, is there a difference front to back?