Bump Stop Limiter

Aeon Bump Stop (Rubber Spring) And Aluminium Bump Risers.

The First Thing We Should Discuss Is The Aeon Rubber Bump Stops.

Ownership of a Lotus elan is a never ending learning process. The writer has owned an S2 Elan for nigh on thirty five years, and certainly wont claim to know all there is about this model, because lotus ownership and maintenance is a constant learning process..

Take the rear suspension for instance, several years ago the rear suspension of the S2 was dismantled for general service work, that job led to the discovery that the Aeon rubber spring bump stops were never fitted to the rear struts, if you are not familiar with these, they are the double convoluted shaped rubber bump stops (They actually should be called rubber helper springs) that slide over the rear strut rod when assembled to the rear strut assembly.

If you read through the Lotus elan factory workshop manual, particularly the section that deals with the rear suspension, you will find that there is hardly a mention of the Aeon rubber bump stops, surprising really, when you consider just how important these items are. The only reference the writer could find was that they are actually detailed in the illustrated rear suspension drawings in the manual.

The photo below clearly illustrates the rear suspension of an S4 elan that does NOT have the Aeon rubber bump stop fitted, but the customer (When informed about the importance of them) soon ordered a pair to install onto the car.

The importance of rubber bump stops.

When the car is fully loaded with two occupants plus some luggage in the boot, the rear suspension will most likely thump and crash and bottom out when the car is driven over sharp road undulations and pot holes, damage could result to the rear strut inserts, the chassis upper lotocone mounts, exhaust pipe and muffler, and other items as well.

Every elan should be fitted with these essential suspension parts, because as you will find out, there is a big difference between the over all handling of an elan that does not have bump stops, compared to one that does have the aeon bump stops installed, the difference is quite remarkable.

Yes, it is a bit of a job to fit them, and not everyone will have the tools and or facilities to do the job, but if your elan does not have the rubber bump stops fitted, it would be a very wise move to go buy a pair today and organise a time to install them yourself or have them installed by your trusted mechanic.

Another problem that may arise by not having the Aeon bump stop fitted is that the upper lotocone chassis mounting bracket, through undue force could eventually crack, or at the very least be bent upwards at the wrong angle. Many owners strengthen the bracket to safe guard against any damage.

The Aeon Rubber Bump stop Is A Very Important Part Of The Elan Rear Suspension.

The first thing you will notice when driving your elan after having bumps stops installed is that it will put an end to the crashing and banging from the rear suspension over rough roads, the rear suspension will be more compliant, the handling of the car will also improve significantly.

Now, as I said, your elan may already fitted with the rubber bump stops, but there are elans out there that do not have them installed, because I have come across missing bump stops when helping customers with various things.

While speaking about missing things, did you know about the aluminium bump limiting spacers or risers that can be fitted to the elan?

What Is It With The Bump Limiting Spacers?

Do you enjoy touring with your wife/partner in your elan?
Have you ever noticed that with the two of you on board, plus the extra luggage loaded into the boot or trunk, that the rear of the elan has a tendency to bottom out and at times the muffler and exhaust pipe may scrape on undulating road surfaces making a terrible noise, which you don’t want happening while on a trip, or worse still, having the exhaust pipe damaged or ripped off the car.

Well Here Is Another Little Discovery About The Elan.
In the Lotus workshop manual, there is a section that actually describes the rear suspension and mentions the “bump limiting spacers.”

These spacers are simple cone shaped aluminium caps, the original items were die cast, but can be quite easily DIY machined.

The caps are placed onto the top of the strut tube, the strut shaft passes through the spacer, the spacer cones are designed to limit the suspension travel in conjunction with the Aeon’s with two people and extra luggage loaded into the boot… they are designed to reduce suspension travel and eliminate the scraping of the exhaust or muffler on the road surface, but the major benefit is significant improvement in the handling.

They Work In Conjunction With The Aeon Bump Stops.

The bump limit spacers provide 22-24mm of extra height above the top of the strut tube, and during excessive suspension travel such as would happen on full bump, the Aeon rubber bump stops engage and compress onto the top of the limit spacers but because of the raised height of an extra 22mm, the suspension travel will be much less than normal, thus preventing the exhaust etc from scraping on the road surface, except on the very worst of road undulations, so that has to be a good thing. The Aeons prevent sudden bottoming out, and banging and crashing of the rear suspension.

The photo above shows that the normal amount of ride height and shock travel available is still sufficient, even with the limit spacer… the bump limit spacer height could possibly be increased from 22mm to 24mm and everything would still work OK.

Below is the compression travel of the aeon bump stop – simulated with a garage press.

The rubber bumps stops are resilient and flexible without being too hard, they provide optimum bump control of the rear suspension of the lotus elan, the photo above show’s the Aeon (Or rubber spring) as they should be called, at normal ride height, the bump stop is sitting on top of the alloy bump stop limiter.

The photo below illustrates just how much the Aeon rubber will compress, which is about two inches or 50mm, quite a bit of travel. Now if the bump stop is on your elan, and you are packed with two people on board plus a boot full of luggage, then there is much more weight for the rear springs to control … I think you will realise now that the extra 22mm to 24mm of the bump limiter stop height will help to control the full plunge and suspension travel, and prevent the annoying bottoming out of the elan suspension…. but it all happens with excellent progression.

The bump stop limiter will also have the effect of controlling roll oversteer to some degree, which should make your lotus elan driving even more enjoyable.

The Aeon Rubber bump stop or rubber spring as used on the lotus elan is not new, they have been around for a very long time, and employed across many industries, especially in the heavy trucking industry, they are also used in many automotive applications.

The original Aeon bump stop as used on the elan has the following code numbers: Aeon Type 505 – Brit Patent.
But are they still being produced in the UK? That I am not sure, maybe you know.

The elan rubber bump stop design is called a Double Convolution.

Double Convolution.
The double convoluted (round) rubber springs offer the widest selection of ride quality and load capacity. Because of their longer deflection curve, fabricators specify the taller double convoluted rubber springs that deliver a perfect balance of ride quality and load capacity. (Ref: Timbren web site)

The next time you are speaking with your Lotus friends, you might care to ask if they have Aeon rubber bump stops, and the bump limiters installed on the struts of their elan, and listen to what their replies are.

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Feed Back Notes – A few weeks Later.
Time to let you know what difference the Koni shock rebuild and the bump limit spacers have made to the elan. Well, long story short, it is all good.

Previously, I had noticed that when cornering, (left or right) the front tyres would scrub on the flared guards, this should not have been occurring, but since the rear shock rebuild and installation of the bump limiters, the tyre scrubbing has ceased, and the elan rides much better over quite rough-bumpy surfaces (I used to be very cautious) and the rear shocks feel great – we are still to do the front shocks, which will be done very soon.

Post Rebuild Driving Notes- Update
Since both the front and the rear shocks and suspension work has been completed, it is only fair to report back on the overall improvements or otherwise. We are happy to report that the S2 is now a much better car to drive, with superior handling and corning ability, in fact, far greater than previously experienced.

Long Story Short: Install the correct Aeon rear bump stops – Rebuild and re-set the rear koni strut inserts (If Fitted). Install the latest Celasto front bump stops – Rebuild and reset the Koni shocks (If fitted) – Install the alloy bump limit spacers – They bring the Aeons into action sooner and help to stabilise the rear suspension when pushing really hard.

The S2 is now a formidable road car, and tackles all kinds of road with much aplomb. We are not just saying this to vindicate the large amount of work that has recently been carried out, the improvements are there, and can certainly be experienced while driving, which became apparent the other day, when an excellent blast with a Golf GTI was had, and would you believe that in the really tight and twisty stuff the elan certainly had the wood on the GTI. I know there will be people who wont believe that, but imagine that, a fifty three year old Lotus elan being more than challenge for a modern hot hatch. And now with the brand new 1700cc Hi Spec road engine, it has brilliant performance.