Has anyone strengthened the rear arm using Gaz Coilovers?

[f0xy]

Has anyone done any strengthening on the rear arm where the bottom of the shock bolts through using (full) coilovers on the back?



A couple of people have mentioned the same thing to me, but I've been searching on various forums regarding as to whether its putting more load on the bolt/thread? Dont want to go hammering it round on slicks to have the thread rip out.

Its all in bits at the moment so strengthening the ARB mounts on the arm and chassis, but was wondering if anyone had done anything regarding the shock mounts.

[Demlotcrew]

Nothing to worry about.

Andrew

[Mikey_Boy]

^^^^ +1

No worries at all there

[harry_p]

i expect plenty of people will tell me i'm wrong, but it's one of the reasons i don't really like the idea of a full rear coilover conversion on an e30.

i've seen similar setups bend / snap bolts on other cars where a single coilover has replaced a separate spring / damper setup, and as you can imagine, if it does let go you'll know about it!

i don't know of / have never seen any car designed from the outset to use a single weight bearing strut which would be supported by a single bolt that's not supported at both ends.

would it be possible to add a triangulated support to the arm without adding too much weight or getting in the way of anything?

[randomspeedfreak]

would it be possible to add a triangulated support to the arm without adding too much weight or getting in the way of anything?

the hub is cast so difficult to weld to i believe,

maybe change the bolt for an allen head one and support the head end of it with soem bracketry coming off the trailing arm?

[f0xy]

Thats the only way I could think of doing it - supporting the head side of the bolt from the arm itself which should be easy enough to weld to. I need to make up some plates to strengthen the ARB tab, im guessing thats common practice?

Although if people are saying it will be OK im not sure whether to bother... I just want it to be solid and can drive it as hard as I like without any worry...

[Demlotcrew]

Dont worry about it, drive it hard, it wont fail

[Jhonno]

I'd say it was nothing to worry about either.. NEVER heard of one snapping (on an E30) as a result of full coilovers being fitted.

[Demlotcrew]

Not even one has broken, concentrate on what REALLY needs doing to the car.

Those flexi brake lines would be on my to do list right at the top.

[f0xy]

Well ive already reshelled it once, so im trying to get the bits done that I didnt do last time while its stripped down. Strengthening the rear setup (ARB mainly) and changing the pedalbox are priority... Brakes were spot on.

[HairyScreech]

the hub is cast but its a weldable alloy as the rest of the trailing arm is fabricated, so it can be welded.

really a bolt like that should be in double shear, and mounting the spring on that part will alter the loading.

if it was mine i would do it as its better to err on the safe side with such critical components.

as to it NEEDING doing, well as above experience has shown it doesn't need it but its better with it.

[Demlotcrew]

Sorry but thats just complete bolox, nothing needs doing to the arms, BMW motorsport ran extremely high spring rates and never was there a failure, their DTM arms had even less metal and withstood 400nm rear spring and very very highly valved dampers (using stock bolts), Gaz are much softer, I can guarantee the damper will fail before the arm does.

You wont add anything except weight and complexity.

[f0xy]

Ive seen the DTM/etc blueprints and replica wishbones available, and as you say there is no strengthening on the shock mounting point - I was just wondering what anyone else thought. With regards to the ARB 'tabs' I can move them by hand so with an uprated adjustable polybushed bar I think thats a definate job to do..

[Demlotcrew]

I have DTM arms, i can take as many photos as you need, but not too many so you can copy them, because that way ill loose my advantage

Yes i would reinforce the ARB mounting point on the arm.

Andrew

[bodger]

what about the shell where the damper attaches, is this man enough to take the extra load?

[Demlotcrew]

No its really weak, the best thing to do is to fit an E36 rear turret, just rivet it on with alloy 4x10mm rivets, job done.

[f0xy]

Yeah, I already strengthened the turret on the previous shell (until it went into a wall @ Oulton), so I'm going to be doing it again on this one considering im running the solid/offset top mounts.

I'l just strengthen the ARB pickup on the arm along with the bracket on the shell and see what two days of abuse can do once its back together.

Last time I ran standard droplinks (from an adjustable/polybushed rear bar), are they up to the job over longer periods or is it better to convert to a rosejointed item - what do people run with similar setups?

[Mikey_Boy]

^^^

Rosejoints every time!

[Phill172]

Interesting this came up, as I thought it too when I fitted my old coilovers, still even to this day I have never had an issue, the car gets a real hammering everytime I use it im not exactly gentle. Atleast its good to know they are fine

[f0xy]

Rosejoints it is then.

Last question - I'm going to replace the bottom bolts anyway as I dont think they are even the same. What rating are they stock?

[fowler]

they will be STD 8.8 tensile strength should be marked on top thats a m1281.5 thread if my memory serves me right

[HairyScreech]

Sorry but thats just complete bolox, nothing needs doing to the arms, BMW motorsport ran extremely high spring rates and never was there a failure, their DTM arms had even less metal and withstood 400nm rear spring and very very highly valved dampers (using stock bolts), Gaz are much softer, I can guarantee the damper will fail before the arm does.

You wont add anything except weight and complexity.

as i said, experience has shown its ok in this application, but that doesn't mean its the best way.
but very clearly its not RIGHT.

A bolt in double shear has significantly better chances of bearing a load vs a bolt in single shear. FACT.

http://en.wikipedia.org/wiki/Structural ... ing_theory
http://sector111.blogspot.co.uk/2012/01 ... ained.html

unless you have some information that can prove a bolt in single shear is magically better and all engineering theory up to this point is wrong.

as harry said: "i don't know of / have never seen any car designed from the outset to use a single weight bearing strut which would be supported by a single bolt that's not supported at both ends."

You now why that is? because a correctly designed suspension member would be put into double shear where possible.
No designer worth his salt would put a damper in single shear out of choice.

Now unless you want to re write the laws of physics then i suggest you unbunch your panties, wind your neck in and accept the fact that double shear is the correct way to mount a damper/coil over.

[Demlotcrew]

Sorry no information to prove single is better than double, everyone knows the basics.

My point is that the stock configuration is more than adequate to bare the load, unless you have some information that can prove otherwise, stop spreading internet bull.

Nothing needs to be done to the arm at that point, BMW would have put in a significant margin of safety.

[harry_p]

i am sure they would, but the road cars don't have all their rear weight on the one bolt, and yes, dtm cars are going to have a hell of a hard time, but i've yet to see one smash over typical b-road potholes at 100mph. most normal peoples suspension is pretty much fit and forget for thousands of harsh bumpy miles, whilst i expect dtm cars got their major load bearing bolts swapped after every round!

if they had wanted to, would they even have been able to alter the way the damper is mounted within the regulations?

[HairyScreech]

Never spread any internet bull, if you read i said its not really correct but it has not been seen to fail publicly.
Thus, the collective experience says that it SHOULD be ok.

The way i read the first post is:
"is this ok, it seems odd to me and i have worries about the longevity of this.
Is single shear ok or should i put it into double?"

Now as i said, for less than a kilo and a bit of fabrication, i personally would put it into double shear because double shear is the right way to mount something like that and that applies to any highly loaded component.
I personally would rather add a small amount of weight to make sure a nasty crash couldn't happen.
The mass you would add would be easily saved elsewhere on the unsprung side of things, be it in the wheels, disc bell, calipers or the coil over itself.


From the pictures i have seen the dtm arms are of quite different construction to a normal arm, certainly the late type ones.
I am aware the early ones were simply normal arms with strengthening.
I don't claim to know for sure but i would have thought the bmw teams would have checked that bolt pretty much before every session and its anyone's guess how often it was changed.

Now the key here is that bolt loaded the way it is HAS to be tight, any motion/play there and the bending moment caused by single shear could see the hole ovalised or the bolt fatigued.


In the interest of the collective knowledge of the e30 community as a whole i'm happy to work out the shear and bending stress imparted into the component, if half an hour can address what is potentially a safty issue then its time well spent.

We know the bolt is an m12*1.5
a uts of 800n/mm^2
with a yield of 80% (640n/mm^2)
We can assume the spring is a 400n/m (edit - this cant be right as it makes no sense in real spring rates, did you mean 400lb/in?)

How long is the damper throw roughly and how far from the trailing arm does the damper mount?
* damper throw ~ 5"? full sag to full bump?*
*about an inch from the trailing arm? 25mm?*

On the coil overs does the sleeve through the bottom joint go all the way through or is it simply a pair of spacers?
*looking at the gaz golds i assume no its just the bolt doing the work*

[f0xy]

Just to to add - should have mentioned earlier. This car is NOT road registered, never will be and will never drive on a public road - so the driving conditions are going to be slightly different as there aren't any potholes. Its track/drift only, and is mostly run on full dunlop slicks in the dry.

For the sake of pretty much zero weight I might just weld it into a double shear while its off the car, I'l have a proper look tomorrow evening when I go down to the unit as I'm going to be doing the ARB stuff anyway.

[HairyScreech]

give me 20 before you do anything and ill tell you how much margin of safety there is assuming the loading on the last page.
if anything it will be absolute worst case.

[GeoffBob]

with a yield of 80% (640n/mm^2)

I'd expect it to yield in shear at closer to 50% UTS.

For an M12x1.5mm with roughly 85mm^2 cross-section that'd require around 3400kg for it to snap. The situation is complicated, however, by the fact that the point at which the force is applied is a fair distance outside of the point at which you would expect to see the bolt shear (just inside the hole). That is to say, there is leverage, so I would expect to see the bolt shear at a lower figure. I suspect, however, that you would need to bounce the car out along the track on one wheel to achieve that sort of load .

But don't take my word for it, I'm just thinking aloud is all. I am no expert in this regard.

[HairyScreech]

going at 80% uts as the bolt is stated on the last page as a 8.8 grade.
Thus 800n/mm^2 and 80%
a 10.9 is obviously uts=1000n/mm^2 and 90% yield.

Although the yield strength is of little consequence as we want to be so far below that for fatigue since the loading is cyclic.

[Demlotcrew]

Its been 55min, we are all waiting.

[HairyScreech]

Well as it stands with that spring rate the bolt is out of there before shear is even considered.

Are you sure thats to right rate?

400n/mm is ~2000lb/inch
400n/m is ~ 2.3 lb/inch

Either way the numbers dont make sense as im looking at most road coilovers and seeing 350-500lb/inch.

[Demlotcrew]

Ok so lets try 60nm.

[redcar]

SR20DET are really light and powerful engines, only a genious would fit one!!!!

That's what you meant

[HairyScreech]

60nm could be in the ball park. do you know what most people are running?

Whats your thoughts on the damper travel?
I'm thinking my guess at 5"/127mm is too much.

3" / 80mm more appropriate?
i just went for the mid spec from the gaz gold universal range for lack of a proper value.

[Demlotcrew]

I have no idea what people are running, so I chose 60nm as a base delta.

Not sure what the specs of the Gaz dampers are, but lets say 80mm to as to get some data.