Coil-overs and mechanical stress?

Thesmoke90

The rear suspension of our cars have a split shock/spring setup (called divorced, I believe). If I were to replace that setup with coil-overs in the rear, would that add a lot of stress to where the shock is bolted in? (Since the stock springs are removed, it seems like there would be more stress on the shock / shock mounting area because we are moving the spring to the shock via a coil-over setup.)

Hope you guys understand what I mean. It seems like switching from a 'divorced' setup to a coilover setup would put all of the suspension forces into the single shock area, instead of distributed between two different areas like the divorced setup.

I haven't heard of people having issues with this, I just want to know for sure before punching a hole in my frame.

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Zezus

i think there is a company that makes reinforcements for the towers.
I've never heard of anyone running into an issue with the "True rear" coilover style
Some manufacturers offer oem style as well.

BettyZ

My guess is, most people don't put enough miles on their Z / sell it before they notice an impact on the metal.

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NorthStyle

I've been running true-style coilovers for 4-5 years now with both street and some track driving. You'll be fine.

JARblue

Plenty of guys on the track run true type coils. You'll be fine.

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OptionZero

Agreed

I think the THEORY is correct that there is more stress at the mounting spots but in practice basically no one is going to feel it. Maybe at racecar levels, but those folks will have the means to reinforce the area

Note that the bigger issue os the geometry change that affects SPRING RATe and its effects
T

gomer_110

This ^^^^^^. Going to a true type coilover will drop the required spring rate dramatically. This is where people get in trouble if they didn't do the math or have someone do it for them.

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2011 Nismo#91

I frequently run over these at high speed and don't need any reinforcement.

OptionZero

Read this thread for spring rate discussion when going to true type vs divorced type

Aero and Suspension Tuning With True Type Coilovers

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AlWakRa

And I thought the curbs in my local track are hard on car

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Jhill

So I went oem style as this was part of my concern as well and also the coil overs I went with don’t have a true type option so that made that easy. That said one thing MCA pointing out when I was considering going that route is that the cars bottom out bumper are on the shocks in oem setup so when the car bottoms out (which is more frequent with oem softer suspension) all the vehicle weight is sent to the strut towers which is a lot more force then hitting regular bumps at speed. So this does make sense to me especially if the z uses longer mcu bump stops on the shock in oem form as many manufacturers do which makes the bumper act as part of the suspension by adding progression and not just a limiter (I forget if they did or didn’t when I removed stock suspension). For me I only change ride height when going to a track day and in those situations I’m already swapping brake pads so I’m kind of in for a project anyway so the added time of being oem type isn’t too big a deal but I am kind of jealous of the ease of adjustment on true type. I do wish there was more clear answer on if you should preload the oem type or not, some manufacturers say to preload the springs and others say not to. In oem suspension the springs are not preloaded but then the shock have more stroke to play with too.

cv129

That's my concern too, and pictures of BMW shock tower failures scarred me for life.

I think mine maybe the only non-caged Z34 that has strengthened rear shock towers after the "true-type" conversion. Others that have strengthened the rear shock towers are all byproduct of roll cages.

But like others have said, we have not heard of any shock tower failures, in the Z34 circle nor the heavier G37 coupe and sedan side of things.

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Jhill

Yea the bmw towers and subframes were too thin so thats not exactly a fair comparison because they crack even with stock form. Maybe I wasn’t clear in my description of his explanation but he was pointing out that in stock setup the largest hits (bottom out) still send the force to the shock towers not the sub frame. Some vehicles (mostly trucks) that use separated spring/shock setups still have the bottom out bumper on the frame. Converting this type of suspension to a true type coil over would be more concerning because the towers were never intended to handle a harsh impact. That isn’t the case in the z because the shocks still have the bottom out bumper therefore the largest impacts are still getting sent to the towers. So like I said the route I went didn’t offer two versions and I hardly ever change ride height plus if I went true type I’d want to replace the bushing in the knuckle where the shock mounts with a spherical bearing since that bushing would see more force and I wanted to stay relatively oem for NVH. But this explanation would be more comforting to this deciding to go true type.

Rusty

Makes sense.

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Zyonara91

Nothing beats looking at a car hitting an apex while going over these things. The sheer mechanical grip and ingenuity coupled with the driver's focus is something to respect and behold.

Great picture.

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