No, shocks don't carry the car's static weight whatsoever (except for some tiny amount from the gas pressure). You missed my point entirely. I will calculate the load on those shock mounts for you, if I can find the shock damping. I'll tell you whether it's plenty of the car's weight, or "plenty of stress" as you called it. (Is there a difference?)

Jump up and down on a bathroom scale and tell me how much you weigh then. The shock is seeing some % of that added dynamic weight, depending on the damping factor and how quickly the car can compress it. Going over a speed bump quickly is where I expect the shock mounts would see their most stress.


True. But exactly how much more is the debate.


Show me, seriously. I've seen the same for you in general, but I hadn't seen the need to jump in and stop the presses for it. Maybe I will from now on.

 

Here you go Larry:

Stroking the shock and spring through 1.5" of travel (3/4" up, 3/4" down) This translates to about 2" up and down movement at the wheel. I also multiplied the corner weight by 3 to account for the mechanical advantage of the suspension that the spring sees.


Shock damping ratio = 6000 N*s/m (wild *** guess)

Spring rate = 115500 N/m (88-91 Z51 spring rate)

Stroked at ~1/2 second cycles with a smooth sinusoidal-like function...

Spring pad sees an additional 4000 N of load beyond static weight, = 900 lbs

Shock sees 2000 N of compression = 450 lbs

So with my wild *** guess numbers, the shock sees half of the dynamic loads that the spring does.

This all depends on how fast the system has to respond. Hitting a pothole could put huge dynamic loads on it, you'd have to know more to calculate it, or use a force guage.

But the key is the static weight X mechanical advantage of the suspension means the spring pad is already seeing 2400 lbs to begin with.

So with my crude assumptions:

Stock... shock tower is carrying -450 to 450 lbs of load.
Coilovers... shock tower is carrying 1050 to 3750 lbs of load.

Doubling the speed of the shock movement doubles the load on the shock to equal the spring, 900 lbs and 900 lbs.

Doubling the damping constant of the shock halves the dynamic spring load for that cycle, putting them both at 450 lbs.


I thought the dynamic weight increase would be a much bigger factor. But who knows how far off my assumptions are. Either way, it looks like the shocks will see at most, 25% of the load the springs will. Putting coilovers on could increase the load on the shock towers by a factor of 5. The speed of the shock movement is critical, so this all assumes I'm in the ballpark.

But what the Hell do I know, I'm just some idiot that lives in his mother's basement and reads Car & Driver.

 

Good to see you've moved up in the world.


Good post.

 

Thank you, Kevin.




Oh, you haven't?

You called BS on my statements in two threads in the last week; both this thread and the thread on swaybars, statements that are true, by the way.
Hey, I can accept being called out when I'm wrong...and I expect it.... but calling BS when I'm NOT wrong will garner a response every time.
You can call BS on me, and I can tell you that your calling BS indicates that you don't understand the subject..... that's the way it works, no?
No hard feelings here, I know you well enough to let it bother me.

Larry
code5coupe

__________
not easily impressed....

 

I ran the sim with it hitting a 1" curb in the road at 60 mph, and the tire taking half the displacement. This put 11,000 lbs on the shock tower, and only 2,000 additional on the spring.

I haven't seen a single racer on here break a front shock tower, so who knows what the safety factor is on there.

Easy to sit there and armchair quarterback it while someone else does the design, and the racing. I don't mind being told I'm wrong, but for you to assume I don't understand the basics on how a shock works, is what gets to me.




Larry, would you be interested in a Speed Ventures event on Dec 1 or 2 at California Speedway on the Grand Am course? I'm working on getting a group of newbies together. Let's let the cars do the talking.

 

Larry
code5coupe

__________
Often wrong, never in doubt....

 

No but I was thinking of running it without shocks and welding the sway bar to the frame, I heard it's the hot ticket to quick lap times.

The willows are too damn far.


RE front shock mounts, I'd be more concerned about camber change than the mount strength. The camberbrace would probably become a necessity at this point, if it isn't already.

 

Actually, even EM advises strengthening the front shock towers on early C4's for coil-overs. They'll be doing mine in the next couple of months (but mine's a '93, so no problem).

 

Here we go again Can the shock supports handle the weight??? All the math and speculation in the world or the countless track and street miles we have had under our setup. Well you all know where I stand. About 9 or 10 years ago we got a call from one of our customers. We were informed that a car we built went off the road at a extreme speed. We asked why it happened and what were the results. Well the driver loss control at well over 100 mph. Launch the car in to the air into a dig. The car hit hard on all four tires and bounced and hit again. The car remained on all four and didn't go upside down, thank god. After seeing the car after the event, all shock towers and the lower rear mount were all in prefect condition. You guys talk about speed bumps and stuff like that, but I can't even think about the forces in this event. I have never seen any directly related shock towers, and or mounts fail on any coilover car we have built or sold parts too. This is our 17th year of selling coilover conversions. I can't count how many cars that we have set up.

Randy
PS Some of you guys remember this agreement. The chevy 350 was never design to be bored and stroked to a 383 or bigger. Yet thousands of people have done it and no one has any concerns. What if a rod comes out the block at 6200 rpm and pukes oil all over the rear tires and you crash. Running a car at speed and at the limit there is always the what if.

 

randy should know, he,s the man!
and i can vouch for his products and design/service.
after three years on with his coil over setup its still going strong with no problems and no wear what so ever.
a great coil over kit.
way to go randy!
regards
shae

 

Having said that mind pm'ing me a quote for my 93

 

While the forces on the chassis in that instance were probably far beyond what most cars will see, the forces on the shock mounts were no greater than what they are on cars going through a sharp dip (gutter, driveway entrance, etc.) at speed, and once you bottom the suspension, the forces on the shock mounts drop to zero.

My concern is the cantilevered lower rear mounts. Coilovers put extreme leverage on an aluminum component, and any metallurgist will tell you that aluminim has a fraction of the fatigue strength that steel has.
E.g. it isn't a one-time overstress that necessarily causes that part to fail, it the case of many repeated stresses that causes failure (in stressed aluminum). For race cars, which are driven for relatively few miles, and receive thorough inspections between events (including ultrasonic or fluorescent penetrant inspection), I see no problem putting on an aftermarket component that overstresses a stock suspension piece. Street cars are an entirely different matter.

I'm not saying C4 coilovers are killers, they aren't. I'm saying they have their place...on the track....and car owners need to know the ramifications.


Larry
code5coupe

__________
not easily impressed....

 

The rear knuckle, we have bent them over 3 inches on purpose, in the rear toe link. Those things are damn strong!!!

Randy

 

Let me know what they re-enforce, if anything.

Thanks

 

Larry, do you have a link to the failed knuckle?

I'm sure there are a bunch of coilover cars being street driven on a daily / semidaily basis. How long they've had coilovers, I dunno.

Also remember that the rear coilover mounts will only have to hold the weight of that corner plus dynamic loads.

The front towers, while they look more stout, have to carry substantially more load due to the mechanical advantage the lower control arms have on them.

 

the real question here is how many forum members have broken the shock towers by using coil overs? so far none of you.

 

yeah three years like i said in my above post have driven with coil overs on a semi daily basis !
no problems what so ever,
regards
shae

 

You'll probably crash and die tomorrow. Larry has his fingers crossed anyways.

 

wtf, who is going to crash and die ?
do you think there is a need to talk sh*t like that ?
you are joking arent ya ?
i thought so.
shae

 

I wouldn't wish that on my worse enemy. I have had too many friends die over the years. Most of them in daily driver crap and rockets.

Randy