WTH Spider Rear Racing Suspension!

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ace124
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Re: WTH Spider Rear Racing Suspension!

Post by ace124 » Wed Aug 28, 2019 1:43 am

The rear hubs are lancia montecarlo.
As Steve said this is full Gr 4 suspension.
There are indeed 2 spherically jointed tie rods that attach to the hubs for toe adjustment.
The front is really advanced as well. Adjustable blade type sway bar, fully triangulated, spherically joined arms, with tension rod for caster adjustment, custom cnc spherical bearing strut tops, coil overs etc. Its crazy the level of development between stradale and gr 4. stradale is just that....a road car. GR 4 cars were really race prepared specials. The above refers to the 131 btw.
124 gr 4 front end was closer to stradale version.
Also as Steve said.....you gotta have deep pockets ;-)
This is not from RSD although they do make similar.
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fiatfactory
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Re: WTH Spider Rear Racing Suspension!

Post by fiatfactory » Wed Aug 28, 2019 6:06 am

Yes it's wonderful... you could have a 131 abarth stradale or 124CSA experience with a technically quite correct replica, but minus the huge price tag... the "real" ones have simply become too collectable and valuable for us mere mortals to own, but if you are of "modest" means you can build a decent replica and enjoy it. Base rust free chassis for a 124 spyder or a 131 2 door are not sky high value... sure it might be a financial step up from rice boy tuner prices for the needed parts, but it can be done without having to be an insane skilled fabricator as people are turning out the speciality bits...

But we are getting off topic... we were talking 5 link rear suspensions.

Couple of notes (engineers pardon the pun) on some of the ideas above...

The concept of adding a second trailing arm.

doing this would increase the roll stiffness. The trouble is it's hard to "measure" by how much, and the same effect could be had by using other methods, without some of the negative effects.

It's difficult to quantify the abount of added roll stiffness this would provide, This is because we are relyng on the effect of what I believe is known as "elastomeric ridgidity" which is the couple of forces needed to deflect the rubber bushing. Coupled as it's a function of the rubbers (or urethanes) DURO rating as well as the design of the bush itself, as some shapes lend them selves to having more ridgidity.

Weight of the additional arms. Basically half of the arms length / mass is considered to be "sprung" and approx half would be considered 'unsprung".. the simple rule of thumb is that you should do most everything you can to try and reduce the amount of unsprung weight the vehicle has... the wheels / tyres tend to stay much more firmly planted to the pavement when unsprung weight is reduced.

It's petty obvious that as soon as anything binds, the total "roll couple" - the sum of the things that contribute to the total roll stiffness - shoots off the scale, weight is going to transfer diagonally across the chassis - really quickly - and that's when you'll have the rear end swapping ends with the front, so that's something that should be avoided at all costs. Easy to test any changes made, with springs removed and the tailsahaft disconnected, to smoothly move the rear axle thru it's usual range of movements should be exactly that, smooth, no binding as the axle moves up / down both wheels together or one wheel up one down... smooth is the key. Now your always going to get some "elestomeric ridgidity" if you use a rubber/urethane bush... could you get the same amount, and perhaps a better control of the portion of the roll couple by doing the same thing another way? yep.. and it has zero nett negatives.

If you have ever looked at the early 124 lower arms bushes... the sleeve has a pressed on steel washer on each side of the bush, i.e the inner crush tube extends past the rubber and pressed / peened onto the crush tube is a fat steel washer. This steel washer was deleted in later models, bush retained the same shape but replacements became one piece. Later cars changed to a different bush again.

which method you choose depends on usage. Earliest type setup and a steel washer is an old school racer trick, cheap, effective. The rubbers also tended to last a really long time.

The usual one piece rubber bush with no steel side fat washer.. well they don't really last that well... that tells me the rubber is 'working" too hard for it's duro rating / weight that it's controlling / spring rate / roll stiffness for a standard car.

Later model bushed lower arms last a LONG time, this tells me the bush is much more suited to it's task.

if the car is for a few track days from time to time... using the later arms and maybe loosing the bridge girder bumper bars would be more than enough elestomeric ridgidity without having to add an extra arm? Perhaps just adding a fat steel washer to either side of all four lower bushes that squashed the existing rubber into its housing a little tighter, and this will improve both the life of the replacement bush as well as the roll couple component improvement as well as still keeping the NVH low...

and looking at the pics of the parts again another thought ...weight of springs... I use a progressive spring on the rear, partly as it is needed to ensure the spring remains captive when the suspension is at full droop, but also because the first two/three coils basically collapse flat (fitted with this end to the top to again reduce the unsprung portion of the springs mass) so a then you get a shorter and overall lighter spring to get the same spring rate (as you done need to have such thick spring wire) and the the added bonus of small ride height adjustments are simple (you. can cut one of the collapsed coils on most progressives, sometimes 2) and this is a 1/2 and 1" drop ... and then a light spacer can give you fine (6mm) adjustments, which you sometimes need for levelling if the chassis has a little twist (seen this more than once so not uncommon).

To sort of answer the question about "improvements and freedoms" in vintage / historic racing classes.... here in Australia (and likely quite similar n most parts of the world) the position of rear suspension attachment points (especially f they are the type that are also "bolted" to the bodywork like a 131 rear is or 124 / 131 front cross member mods sort of apply under the same rule) is free but the NUMBER of attachment points can't be added to. Fitting the lower triangulation 3rd lower link just means you swap the panhard rod attachment on the diff for the triangulation attachment point at a different pl;ace on the diff, still 5 link,

The triangulation removes all sideways deflection caused by the panhard rods attachement points arc of movement, it also sets the height of the rear roll centre - it's a very very important change for the better.. Not my or anyone in particulars "idea" at all, it's a well known and documented method of real axle location, and simply what I always thought was the best of the available methods to locate the rear axle in our application.

If you loo at old skool racing pictures of even 1950's Fiat 1100's /1300/ 1500 with leaf springs, and you'll see trianguluation attachments from the front leaf spring attachment pivot back to right under the rear diff housing, nothings new.

SteveC
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Re: WTH Spider Rear Racing Suspension!

Post by miker » Wed Aug 28, 2019 11:51 am

"and then a light spacer can give you fine (6mm) adjustments, which you sometimes need for levelling if the chassis has a little twist (seen this more than once so not uncommon)."

What do you use for a spacer? And how is it fitted?
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Thu Aug 29, 2019 1:39 am

Gentlemen,
I am really enjoying this. Keep it up. It mostly confirms my ongoing research. I have also learned quite a bit about bits I didn't know existed. For me and my almost exclusive tarmac street car, and tarmac-only racer, it is interesting to hear what your folks have thought out and done. As for my racer's rear suspension, I have achieved a set-up that just does NOT bind, and has neutral movement with deflection and cornering. If I was to get a wind-fall of money, I might purchase the IRS described by Ace124. There are plenty of dirt roads in Colorado, that are often frequented by amateur rallyists. It's a real 'thing' in Colorado. But for me, I keep to Tarmac with both of my Spiders, and do the dirt in my Jeep.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
ace124
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Re: WTH Spider Rear Racing Suspension!

Post by ace124 » Thu Aug 29, 2019 1:08 pm

The IRS set up really is quite expensive. If it means anything....my live axle car was faster than an irs rear end car on smooth tarmac.
Dirt or rough euro hillclimb circuits are a different matter.
The only issue i had with using an A arm for lateral location on a live axle, was the mounting point under the diff housing broke a few times and rather than re engineer it i gave up on it. Ill see if i can find a few pix. I also box the housing and reinforce the axle tubes. From memory the first lotus cortinas had a similar setup albeit with leaf springs, but later dispensed with it as they too had issues. Leaf springs by nature do provide some lateral location, but they still had problems with the A frame locator. Im sure google will come good with some history.
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fiatfactory
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Re: WTH Spider Rear Racing Suspension!

Post by fiatfactory » Fri Aug 30, 2019 3:39 am

Looking at the pictures posted of the triangulation and it's attachment points another thing struck me, it wouldn't be legal for historics. certainly not in Australia, in it's current form.

Rule book is pretty tight on the number of attachment points... by using the two ADDITIONAL mounts (PIVOT points) this is technically a 6 link..that's the whole reason tuning tools like a Watts linkage isn't allowed in this form of racing as it's adding an attachment point.

The triangulation I use is same but different, like I said no ;pictures from back in the early 90's of how I did it first time... but easy enough to visualise with some "back of envelope" sketches.

First up... going to arms with Heim joints all round for a circuit car is a big leap in the right direction if the class allows it. It completely frees you from the shackles of Elastomeric ridgidity and allows you to precisely tune the amount of roll stiffness the car has. It remove all bind / preload from the rubber bush, and deflection is zero.

Once you fit heim joints to the rear, first thing you'll "feel" is the chassis will have gained understeer. there's been a nett loss of roll couple at the rear from removing all the rubber. Now is the time a 124 chassis can benefit from the addition of a rear sway bar, and it becomes a useful tuning tool.

back to lower triangulations

This is how I have seen "most" people attach their A arms to the lower diff housing mount
20190830_150551.jpg
20190830_150551.jpg (446.78 KiB) Viewed 3321 times
there are a few problems with this method.

To get enough rotational deflection (which this point will see when only one wheel goes up) the bush needs to be quite large, the centreline of the bush is the pivot point and this is the rear roll centre. The ideal RC point (iMO) is about as high as you can get it to the bottom of the diff housing (of course this changes with overall wheel diameter)

this type of setup has lots of possibilities to bind and then transfer a huge spike in load to the other parts of the system... that's when bits break... not good.

The way I did it looked a bit like this
20190830_150540.jpg
20190830_150540.jpg (464.78 KiB) Viewed 3321 times
Using a hi-angular Heim joint (3/4 or 19mm size with stepped spacers to allow plenty of rotation) it never broke, and allowed the roll centre to get about as high as it needed... it would also allow for easy RC height changes with a few spacers and more length (if you went 15inch wheels for example)

My attachment point at the forward end of the triangulation was quite different to your method in the pics.
20190830_150523.jpg
20190830_150523.jpg (370.81 KiB) Viewed 3321 times
and doing it this way fulfills the rulebooks requirements in historics
the front heim joint of the lower control arm should be fully screwed in . seated on it's locking jamb nut at the front end.... never had one fail here, but exposed threads would be a weak point

you need to make the bracket for the forward triangulation attachment a bit like shown in the envelope sketch, needs to wrap around the tube.

the rear central heim joint really needs to be level with the car at rest too, to make sure it has full range of pivot, you'd be amazed at how much it moves, and tarmac rally / targa type use really needs more supple spring and roll rates to ride over rougher roads.

SteveC
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Re: WTH Spider Rear Racing Suspension!

Post by engineerted » Fri Aug 30, 2019 10:13 am

Steve, correct me if i am wrong, the Lotus Cortina attached their "A-frame" to the end of the diff similar to your first sketch but also use a swivel.
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1978 124 steet car
1974 124 EProd race car
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fiatfactory
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Re: WTH Spider Rear Racing Suspension!

Post by fiatfactory » Fri Aug 30, 2019 12:24 pm

yep, a pivot or swivel would work... a rubber bushing or something else that didn't have enough pivoting motion wouldn't ... that was my point... things break when anything binds

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Re: WTH Spider Rear Racing Suspension!

Post by engineerted » Fri Aug 30, 2019 1:53 pm

Yes, Agree. One thing that concerns me, is the short moment arm between the hiem joint on the bottom of the diff and the lower trailing arm axle mounts and its ability to control pinion climb (axle windup / down) during acell / decells. This seems like the joints would take a beating every time you up-shift / down-shift? I run a three link with a parhard bar on the race car, Hiem links all around except for the upper link on one end (chassis side). I have urethane bushing there to dampen/cushion the torque reversals.
1978 124 steet car
1974 124 EProd race car
Farmington Hills, MI
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Sat Aug 31, 2019 2:28 am

Gentlemen,
This thread has taken on a life of it's own. I am conflicted as to whether to disclose my design, or keep it confidential. It is a tri-link, which is not unusual, but the details are not like what has been posted by various contributors, and solves the specific problems encountered by some of the posters to this thread. Jim Scuria would say no, I suspect, but Ted in particular might benefit in his racing efforts (maybe Jim, too).

It would take fabrication skills to build, but this is certainly a doable project for a racing 124 or 131 vehicle. Let me know what you think, please. Standing by.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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