Project pendolare

As you can see, there are marked differences between the pendolare layout and that of the standard Fiat. The most obvious is that the arms are no longer made of pressed metal sections. Instead the two "legs" of the arm are made from thin-wall round tubing and fabricated into the required shape.The inner arm, the one closest to the centerline of the car is longer, and moved further forward toward the car's center or rotation. This increase in length would have lessened any effect on bump steer over the travel arc of the suspension.

With the standard Fiat swing arm, the rear spindle location would have been in-line with the centerline of the arm. Here we see that that tubular arm makes a very sharp, upward turn as it attaches to the hub carrier tube. This would seem to have at least two beneficial outcomes. First, by having the axle effectively above the arm, the wheel has been raised in relationship to the chassis, allowing the car to achieve a lower stance. Second, with the ever increasing power of the one liter motors, it was evident that a more robust axle design was needed and allowed for an CV joint at the outer end of the axle.

In the previous iteration of the TCR, Abarth had already abandoned the cross pin and stones idea on the inner end of the axle, instead using a short axle with a bell and a CV joint. The outer end of the axle retained the Repco cross joint and rubber filled sleeve, as it would fit inside the standard pressed metal swing arm.

Now we see that the Repco cross joint has been abandoned altogether. In its place is a CV bell, so that the axle now has CV joints at both ends of the axle. Given the ability to further lower the rear of the car (or allow for greater suspension travel, as we will explore later) it may have been that the limit of angularity was reached on the Repco cross joint. In doing so, and opting to go to the larger diameter CV joint, the arm had to be redesigned as the CV "bell flange" could not have fit inside the standard Fiat trailing arm.

Top shock mount - TCR

There is further evidence of this when we look at the top of the rear shock absorber mount. It is obvious that the "pin" type mount has been abandoned in favor of one using a uniball. Also it appears that the effective location of the top mount has been raised 50mm or more.

The lower mounting of the rear shock absorber is now contained within a fabricated section between the two arms of the new pendolare trailing arm.

The outer arm of the trailing arm is also constructed of tubular steel. It too has been relocated, this time further toward the outside edge of the chassis. Although the absolute length of the arm appears to be same, as the overall wheelbase of the car is still 2 meter, due to its new location the arms tends to wrap in for the required tire clearance, and then join the other arm where they meet at the hub carrier tube.

In the photograph and drawing above you can see the amount of lateral relocation that has taken place for the mount. This new location really gives effect to the "trailing arm" nature of the the suspension by drastically reducing the the amount of camber change that would take place during suspension travel. You will note that the attachment point is still slightly angled, so the arm is not entirely a pure trailing arm, hence the semi-trailing arm description

This evolution of the trailing arm provided for a completely different "feel" to the rear suspension. The new suspension was much softer in the rear, and given the amount of both shock and arm travel now available, this might have been quite disconcerting to drivers used to the older, stiffer suspension.

Feelings differ as to which was better. I have talked to drivers that have used both and some prefer the stiff setup, while others were able to easily adapt to the new softer pendolare suspension.

The pendolare suspension did change one troublesome characteristic. The roll center for swing axle type suspensions is at the same height above the ground as the ring and pinion, and cannot be adjusted. However with a semi-trailing arm arrangement the designer has the ability to move both the "instant center" (IC = the intersection of a plane through the rear axle and a line from the outer pivot point of the trailing arm) and the "roll center" (RC = the intersection of a line drawn between the tire contact patch centerline of one tire and the vertical plane through the rear axle). By manipulating the relationship of the inner and outer trailing arm pivot points it is possible to lower the roll center of the car. In the case of the TCR I believe that instead of raising the outer point, the inner point was lowered, in essence achieving the same effect. Those of you wanting additional information could refer to an excellent article on the subject at http://e30m3performance.com/tech_articles/susp-tech/roll_center/index.htm While this discusses the rear suspension on a BMW A30 type chassis, the principles are much the same. Changing the roll center would have had a more than trivial effect, although it may not have been fully appreciated by some drivers, not able to adapt to it.

With a lower rear roll center, this would have changed the "roll couple" of the automobile. Roll couple is the relationship of the front and rear roll centers to each other, and their effect on the roll effect on the rear and front ends of the automobile. A lower real roll center would have increased the amount of chassis roll, at the rear of the car, that was available before lifting a rear wheel. As the TCR is a rear engined car, with a weight distribution of roughly 37/63 (front/rear), this was an important development. With the standard suspension the rear end of the car would have approached the limit of chassis roll much earlier than the fully independent front suspension, where the roll center was adjustable. It is my view that with the new pendolare rear suspension, the TCR was a better balanced car. I make this conclusion because I have seen cars with the earlier rear suspension who must run a limited slip differential, due to wheel lifting. Yet cars with the later pendolare suspension are able to negotiate the same corners, sometimes at greater speed, without lifting a rear wheel, thus negating the need for a limited slip.

As mentioned earlier, the pendolare suspension also upgraded the axle, and even the brake systems. The construction of the pendolare is such that it has a round tube with a four bolt flange as the mounting method for both the axle/bearing tube and the disc brake assembly. When I first saw photos of the trailing arm I was confused by how it was constructed. But, after some careful examination it dawned on me as to what was done, and why. As the whole trailing arm assembly is welded together from fabricated parts, there would have been some distortion where the two arms are welded to the carrier tube. Abarth solved this problem by making the "bearing carrier" separate from this carrier tube. See photos below.

Here you can clearly see the "sandwich" of three components. In the very inside you have the "carrier tube", with four threaded ears, welded to the two arms of the trailing arm and threaded to accept the allen bolts. Moving outward, you next see the brake bracket, and then finally the "bearing/axle tube with four ears matching the ears on the carrier tube. All of this is held together by four allen head bolts.

After seeing this I realized that it had to be done this way. You see, he need two things. First, a way of attaching the brake mounting bracket and, more importantly, a perfectly round bearing housing.

Since the carrier tube would have distorted during the fabrication process, the easiest way to accomplish both tasks was to make a machined axle/bearing tube that would slip inside of the carrier tube, at the same time capturing the brake bracket.

Here are some additional photos of the rest of the assembly.

The axle/bearing tube, as it was holly machined, would suffer no distortion and would simply slip inside the carrier tube. The photo clearly shows that the axle was mounted with two tapered Timken type bearings. The splines on the axle would have been for the CV flange/hub assembly and the whole affair would have been cinched up by the large nut. As you can see the axle was quite a bit beefier than the standard Fiat 600 affair.

Of course not very many of the TCR cars were produced with this suspension and many of them that were, have been well used. It appears that somehow many of the arms developed moisture on the inside and thus started to rust from the inside out. (just like steel boats) Being thin wall tubing, many of the arms are now substantially weakened.

In conversation with one of my customers, a project team has been formed to investigate how to best provide for restoration of pendolare suspension components. It could be that there may be original drawings available within Centro Storico Abarth. According to several sources, including Mr. Engelbert Moll who spoke with Mr. Colucci before he died, when Abarth closed down the records were simply put in unmarked boxes and sent to various places, including Centro Storico, Hiro Kosaka at Gallery Abarth in Japan, and even the local rubbish dump. Needless to say, the boxes that went to the dump are lost forever. Members of the project team will contact each of the repositories, where we think there may be some information, to see if we can get access to it. Further, I have been able to get a set of arms that, while being need of restoration, are adequate to take measurements from as an alternative means of generating drawings. This was not an easy task, as owners of original cars do not like to give up vital parts of their cars. However, Antti Rinne has kindly allowed the project team to "borrow" his set of pendolare arms so that accurate measurements can be taken.

Other TCR owners have kindly provided photographs and measurements to confirm what would have been the dimensions of an original set of arms. Of course we found variances, like the set of arms that had been "heated and bent" to provide additional positive camber, after having been DRASTICALLY lowered for ice racing, resulting in too much negative camber, even with the improved geometry. This only confirmed just how much you could lower the rear ride height with the pendolare suspension.

Yet another rear suspension version?

It may be that at some point in the evolution of the TCR rear suspension the wizards at Abarth might have considered other iterations of rear suspension designs. The photograph below obviously shows a double a-arm rear suspension. The chassis is Fiat 600 based.

The photo quite readily show a cast aluminum or magnesium upright, with an upper and lower a-arm in place of the fabricated arms discussed previously . The rear shock/spring assembly looks to be attached to the lower a-arm in about the same location as in the pendolare setup. The upper end of the shock is attached in the standard location.

Why was it never produced? I can only take an educated guess. It is likely that this design was abandoned, because the FIA had changed the rules to such an extent that the TCR, as good as it was, simply could not keep up any more. There was a succession of events that foreshadowed the demise of the TCR. First, Ab Goedemans, the 4 times winner in a TCR in 1968, was killed at Nurburgring driving an Abarth sports car. Hezemans took over, but did not perform as well as Abarth wanted. 1969 saw Abarth back on top again, but the victory was short lived. Then the FIA changed the class limit to 1300cc and Hezemans defected to Alfa Romeo. Abarth did field cars in 1971 at Monza, but after practice all cars were withdrawn, as they were clearly uncompetitive in terms of overall class winners. That was the end of the TCR. If this was an Abarth developed, further iteration of the rear suspension, the cessation of competition activities for the TCR could have been the reason why it never went into production.

Thanks to Trevor Barrell I can provide a further update on this suspension. As you can see, the axle is obviously carried in a special aluminum upright casting. This casting is interesting as it can be seen to have a "twist" to it. I can only assume that this was done to keep the arms from interfering with the axle. According the the Fiat Abarth book by Deganello (page 39) this suspension was an iteration pursued by Abarth. According to the caption, this suspension was tested at Vallelunga (probably in 1967). However the FIA disallowed the use of the suspension because in their words " the design varied too greatly from the previously homologated pendolare type suspension and the originally homologated pressed steel, triangular trailing arms". It is obvious that the new parallel trailing arm arrangement would have been very effective, but Abarth could apparently not convince the FIA that the original mounting points, dictated by the two previously homologated suspension designs, had been maintained for this new suspension type.. The rear transverse link of both a-arms was obviously in a new location. Even the trailing link looks to me to be different as well. I am sure that Carlo Abarth did his best to convince the FIA stewards, but this was really pushing the envelope. As homologation takes some time, and is usually only done once per year, my conclusion that it was never homologated due to the demise of the competitiveness of the TCR automobile due to rule changes instituted by the FIA.

Note: I do seem to recall that a suspension very similar to this was used by Dick Ward in Perth Australia, for his Go-Gear Abarth HIllclimb car. In order to maintain tire contact with the road with really wide tires (probably 10" wide in the rear) a trailing type suspension must be used, or the tire will not maintain a flat contact patch. Dick's car has formula car front and rear suspension, and is powered by a Mazda rotary motor.

The last photograph shows just how effective the new rear suspension systems were in getting the car's stance as low as possible. Even though this is a photo of a car at the end of what appears to be a left hand sweeper, putting the right hand suspension in compression (bound), take note of how far up in the fender well the rear wheel is, with virutally no body roll. This clearly shows that lowering the rear roll center and balancing the front rear roll couple can work wonders.

Here is some additional information that has come to light from information provided by Luka Basara from Hungary and Fred Winkel from Holland. It would would appear that the last TCR suspension may have been a design developed for another Abarth car. It appears that the Abarth 1600 OT Berlina and the 2000 Mostra had similar iterations of this trailing arm suspension.

The photo on the left is a close up of the 1600 OT Berlina suspension. Obviously it has two shocks per side. If however you were to remove the rear shock, what you would have left over is remarkably like the latest TCR suspension. It has upper and lower transverse links, and although these photos do not show it, it would have to have a link running forward in semi-trailing arm fashion. The lower transverse link goes to the bottom of what could be a cast or fabricated upright. I cannot tell from the photos which it is. The axle arrangement is similar to both the pendolare and the latest TCR double a-arm arrangement.

On the right hand photo you can see that the fabricated upright has the same "twisted" aspect as the TCR cast aluminum upright. As both of these car would have had much wider rear tires, it would have been necessary to devise a suspension that had better camber control.

It would appear that several of the cars produced around the same time frame had incorporated in them similar design features. Now this makes perfect sense, as likely the same design team would have been involved.

Going back to the pendolare design, things are moving ahead nicely. The first set of machined parts is taking shape. The following photos show the machining of the axle taking place, as well as a second photo with all of the components, except the brake caliper bracket fully machined.

Some of these items will now be combined with the tubes for the arms, and placed in a welding jig to put the whole assembly together. As more photos become available during the assembly process I will put them on this page.

The Pendolare project is moving along. Miles Renton-Skinner, the gentleman doing the fabrication, has actually finished the first arm. From the photographs below it looks like a real work of art.

The man himself

As you can readily see, there is a great deal of detail work that has gone into making an exact replica of the original arm. First the entire arm assembly had to be documented, as we had been unable to find any technical drawings. Our search for these drawings included contacting the major Abarth collectors around the world and culminated in sending a letter to Fiat Centro Storico in Italy requesting their help in this project. Major collectors like Mr. Moell were gracious with their time, but doubted if any records were still available. No drawings were ever uncovered, and NOTHING was ever heard from Fiat Centro Storico (the letter was even written in Italian, so they could not claim a language barrier). Considering that no information about them was obtained, Miles documented all of the dimensions of the arm assembly himself.

Next, all of the "machined" parts were duplicated in qaulity steel, working from the originals and the notes Miles generated. Then came the job of bending the tubes. This meant developing the process of bending the tubes, likely with packed sand on the inside to keep the pipe from buckling or crimping. Then the sheet-metal parts had to be laid out, cut and bent for the area where the lower shock mount is attached to the arm.

Definitely, this was not a project for the "faint of heart". As you can see Miles has done a fantastic job of recreating a faithful replica of the original arm. While the "welding time" to assemble the first arm may have taken 15 hours, the overall time required to produce the first arm would account for many more hours.

While the photos above show one of the finished arms, Miles thought it might be of interest to see the "jig plate" that was made to assist in assembling the major structure of the arms. The arm shown on the jig plate is the original unit that was borrowed from a TCR owner. Miles has secured the major fixing points to the steel jig plate (which is thick enough not to distort when working the arms). Then there are aluminum "templates" held in place with Cleco holding fixtures to indicate the "arch" of the arms. It looks like Miles made these templates, which have a right angle element, with the use of a metal stretcher. Very nicely done. Due to the curvature and the right angle element at the base, these would be very rigid.

The hub carrier, and arm ends, are then secured to the jig plate and the arms are bent to follow the curvature indicated by the aluminum templates. Once these are final fitted, then they can be tack welded in place. I am sure that most of the final welding was done on the jig plate, so as to eliminate any chance of the arm moving around during the welding process.

Stay Tuned - We are getting closer. In future chapters I will go into the formation of the chassis modifications to hang the arms. I understand that Miles will be working on the chassis attachment points, as well as making the TCR style front suspension shock turrets.

Important Notice - Many Abarth enthusiasts have noted that the likely cost of a completed set of pendolare arms, as faithful reproductions of the original design, will be quite high. This would seem to be a reasonable assumption. The final cost has not been computed.

In order to make the benefits of this suspension design available to the larger Abarth community, I have commissioned a less expensive version of the tubular rear suspension that utilizes either the standard Fiat 600 bearing carrier and axle, or the Scuderia Topolino bearing carrier and axle system. This design allows the fitting of Fiat 124 type rear disc brake calipers.

One of the principal benefits of the tubular rear suspension design is the ability to lower the car without generating large amounts of negative camber. We have incorporated this feature, yet retained the original chassis mounting locations. We have also retained the original shock absorber mount "type" and location. This allows coilover shock absorbers to be mounted in place of the original spring and shock. The incorporation of large spherical rod bearings make these arms fully adjustable.

For further information about this new tubular rear suspension please refer to our "Specials New" tab on the opening page of the Scuderia Topolino website.