Blade Adjustable Rear Anti Roll Bar – S2 elan.

Many high performance sports cars are fitted with both front & rear anti roll bars. Generally, the bars as fitted are of the non-adjustable variety, this is the norm for factory-tuned, road going suspension systems, because the torsion loads applied by both front and rear are tuned to match & compliment the chassis and handling.

But what if a rear ARB is being retrofitted to an existing high performance classic car? The chances of selecting the correct bar will probably be based more on guess work, than that of a known quantity.

There was once a famous Chapman quote “Make it adjustable, and they’ll get it wrong”. Well that analogy may have had merit back in the early days when suspension design was in its infancy, but today, the science and computer software allow the enthusiast to explore and play with suspension settings and other things just as they do in Formula One circles, well, let’s not get to carried away there, the average enthusiast won’t ever have the mega budget, or the cutting edge engineering expertise of the F1 boys, but the enthusiast can learn much from what they have done in F1 in the past…. one only has to do some research in the right places.

During the second resto/rebuild of the writers S2 elan, a plan was hatched to include some advanced tweaks and mods to the chassis, especially where the rear suspension was concerned. The front suspension is sorted and taken care of, so we won’t be discussing much in that area, apart from maybe mentioning the front roll bar specs.

One of the very special tweaks that the writer wished to include on the Elan chassis was to build and retro fit an adjustable rear ARB, but the requirements called for the design to be very compact, and was required to be manufactured and installed in such a way that no brackets were welded to the chassis or to the lower “A” arm tubes, the reason being, that if the ARB did not work out as planned, the unit could be removed with out any remaining evidence of the modification and or the fittings.

This special mod was completed some months ago, but so far, we’ve only shared this with one or two Australian lotus elan owners, one in particular is a regular race entrant at various race tracks in Australia, but we thought that perhaps it was now time to share the mod with other elan owners. The following photos and article rovide some of the detail.

The picture above illustrates the rear ARB. A pair of special blades were manufactured, the blades are a common Formula race car design, they allow variable amounts of stiffness which can be readily dialed in, eg, when the blades are rotated from the flat position (Softest setting) through to the hard setting (Blades turned on edge) the variable adjustment will allow fine tuning for optimum handling results.

At the time of fabrication, road testing was not possible due to the car not being road ready. But once the rebuild was complete, road testing was carried out, the blade setting was initially set on the “soft” setting, further increases in bar stiffness will be made in small increments during testing to see if, or what other changes in handling may be experienced. Blade adjustment can be quickly carried out with an hex Allen key.

The blades are not adjustable from the cockpit, the general feeling was that for a road car, on-board adjust-ability would be more trouble than it was worth, yes, rally cars have that provision, and so do many other competition cars, but this elan is not a race car, and the project is a DIY design and build, the thinking behind the rear ARB idea was to achieve good, or better than standard handling results coupled with a low cost self built product, and having traveled over 6000KM of road testing we have certainly achieved that end.

We did not let ourselves become bogged down with endless calc’s & pondering’s that one can get oneself into with a project like this, lets just say, it has been based more on a rule of thumb, but at the same time taking on board a lot of detailed info sourced from what many other enthusiasts have applied to their cars. (No previous elan rear blade ARB info of the type we were looking for could be found anywhere)

The blades were carved (Via Lathe & milling machine) from a solid billet of 4140  steel. The front ARB specs are as follows: 19mm Dia. The rear ARB is: 12mm Dia hollow (2mm wall) 4140 Aircraft quality tube, coupled with rose joints attached to drop links and fabricated brackets attached to the lower rear A arms. Some changes were also required to the rear underneath section of the fibreglass body, but again, no real major mods were required, and the problems that were presented were solved with some applied commonsense, and a bit off quiet thinking.

This is a pure DIY project, the entire set of ARB components were machined and fabricated in house.

Before embarking on this project, many hours of online research was carried out, but the research proved fruitless as far as finding info about blade adjustable ARB’s far the lotus elan was concerned, so we took what we could find from other applications and applied plenty of self trained engineering nous to come up with the end result.

With increased driving distance the final adjustments are made to the elan and it is proving to be quite a nice little performer on the road, it turns into corners beautifully, and the rear end is really planted to the road (The car corners much harder than previous) and as of yet, has not shown any untoward handling characteristics, but that may change as the driving becomes a little quicker, and the cornering a bit more adventurous, but so far, the results are very satisfying after the fitment of the rear blade adjustable ARB.

If your elan runs a CVDS conversion, there is one other input function that the rear ARB provides, and that is the reintroduction of transverse torque loading to the chassis which duplicates the spring loading effect that the original rubber donuts provided, the writer has driven the elan for several decades with the (Full race spec) CVDS and has never encountered any handling problems.

But we are happy to report that the rear blade adjustable ARB has vastly improved the overall handling of the elan, and being adjustable, allows roll bar stiffness changes in small increments…. IE, to dial in the handling that you prefer.

The photos show close up detail of some parts of the rear ARB, it is compact and unobtrusive, no one would ever know that a rear ARB is fitted, unless of course they took a good look underneath.

Following Is A Caution:
Do NOT under any circumstance consider carrying out this ARB modification with the body bolted to the chassis, the proper time to incorporate this rear suspension mod is during a full body off rebuild or restoration. It is imperative that a bare rolling chassis is presented for the project.

The above photo shows the custom machined and fabricated bracket that securely clamps onto the lower A arm tube, and connects with the drop link that has a rose joint top and bottom.

Click Here To Purchase:
New ebook Release – How To Build Adjustable Blade Type ARB.
If You Enjoy An Engineering fabricating Challenge, And You Have In Your Workshop A Bit More Than A; File – Hacksaw  and A Few Spanners, Then This Could Be For You. Yes, you need a lathe, mill and welding skills.

Mind you, one or two elan owners have already said they have no idea how to build the ARB even after being provided with all of the detailed information. But I’m telling you it’s doable if you have a bit of Colin Chapman Lotus nouse in you.

This ARB Was Designed and Built by Col Croucher – elantrikbits.com

Now Go Read All About It – And If  You Get Just A Little Bit Excited – Whip Your Credit Card out And Purchase.
What you get is about $800.00 Bucks worth of engineering know how and info for Only $29.95 , that would have to be the bargain of the year.

Disclaimer:
This is a project that the writer found to be extremely successful, other persons copying this design may not enjoy the same or any success at all, if you decide to copy this design, you are deemed to accept absolute and full responsibility for your own workmanship, materials chosen and employed, as well as your applied fabrication and welding skills, if you are unsure of how to fabricate certain parts, or uncertain about anything mechanical, you should in the first instance seek professional advice, help and guidance.

Update On Rear ARB 6,500 Km Later.
The rear ARB upgrade has been one of the most profound improvements made to our S2 elan. If you think your standard elan handles fairly well, then you would be astonished at the the increase in rear end grip and the ability to corner much harder and quicker than previous, I have had a couple of blokes who own stock elans, and when taken for a drive in our S2 their reaction is “Oh my God, this thing is awesome” what have you done to it. There is also one other important mod involved and that is setting the rear suspension camber to 1 Deg Neg.