Needing some new dampers and springs for my Series 3 Seven, I checked on-line for options.
Following is information I found or was provided with by various companies or distributors.
Original specification used by Lotus.
According to published information, and confirmed by Peter Lucas (designer of the Lotus Seven Series IV), Lotus had a very good association with Armstrong Patents for the supply of dampers for the Seven and their other road and sports racing cars. The Armstrong dampers for a Seven were not adjustable in any way.
It appears that Armstrong Patents Co. (later named Armstrong Equipment) discontinued the manufacture of dampers in the 1980s, selling the company to Tenneco U.S. They are also known for designing and producing ‘Heli-coil’ screw inserts.
I could not find a source for the springs, but Peter Lucas wondered whether or not the data was passed to Armstrongs to enable them to supply a complete spring/damper unit assembly. He advised me that the Lotus Purchasing Department usually, but not exclusively, had control over which component supplier was used, and generally Armstrong Patents were chosen. He thought their demise in the 1980s sounded about right.
Peter Lucas provided the following design criteria:
“I always designed road car suspension systems in my interpretation of Chapman’s design philosophy.
- Keep the tyre in contact with the road surface at all times.
- Use soft spring rates with suspension frequency compatibility.
- Control the damper bump stop and hydraulic settings”.
He continued: “I would have no data for the bump and rebound valving as although we (Lotus) reported any issues found with the initial settings on the prototype units from Armstrong during our development testing, they used these observations to establish their own final specifications for the valve settings, subject to Lotus approval. Lotus were responsible for specifying the spring specifications, but I cannot recall whether the data was passed to Armstrongs to enable them to supply a complete spring/damper unit assembly or not. Obviously any commercial arrangements like this would have been organised by Lotus Purchasing Department”.
Information from Mick Lincoln – original co-director of Redline Components, confirmed that Lotus Seven Series 2 and 3 cars had 105 lbs./inch springs on the front, and 75 lbs./inch on the rear as standard. He suggested to continue with those rates – without adjustable spring seats, as these were not necessary for regular road use. He advised that Spax had become the damper manufacturer chosen by the original Caterham management and Redline, after supplies of Armstrong dampers for the Seven had ceased to be available in 1976.
Lotus Spring Specifications.
A 1964 Lotus Factory parts list for the Series 2 shows that the front spring free length should be 11-15/16 inches, and the rear 16 inches (i.e. not mounted on the damper).
The Lotus Seven Owners Manual which covered the Series 2 advises the following:
Front: 10-3/16 inches free length for chassis 1000 – 1053 + 1083 – 1131
11-15/16 inches free length for chassis 1054 – 1082, and 1132 onwards.
Rear: 17-1/4 inches free length for chassis 1000 -1028
16 inches free length for chassis 1029 onwards.
Tony Weale in his book “Lotus Seven – Restoration – Preparation – Maintenance” (Osprey Automotive Series), advised that “the early Series 3 rear dampers were actually slightly shorter than those (later) specified, extra length being found necessary to improve clearance for the larger wheels and tyres of the Series 3”. He further advised that “spring rates have been changed at various times, and during early Series 2 production there were changes in spring length while the optimum ride height was being evolved, but the front damper specification has not changed throughout Series 1, 2, and 3 production, and a single type of rear damper has now been standardised for all live axle cars”.
I have a set of very used Armstrong dampers and springs that have been removed from the car with the following measurements:
Front: With the springs mounted on the dampers, the springs are 9 inches long end to end. The dampers measure 12-1/2 inches long from the centres of the mounting bolt holes.
Rear: With the springs mounted on the dampers, the springs are 14-1/8 inches long end to end. The dampers measure 19-1/2 inches total length end to end, or 18-3/4 inches bolt hole centre to threaded rod end.
I have a set of the original DSK auto-cross springs purchased in 1980. David Kaplan advised the following:
DSK Street Springs – Front: 85 lb/in. Rear: 60 lb/in. 1.9 inches i.d.
DSK Auto-X Springs – Front: 125 lb/in. Rear: 90lb/in. 1.9 inch i.d.
Tom Robertson Competition Springs – Front: 140 lb/in. Rear: 100 lb/in.
DSK noted that the auto-cross springs fit standard length 303 front, and 305 rear Spax shocks with adjustable spring collars. Front free length is 10-3/4 inches long, and rear is 14-1/4 inches long – which exactly matches up with the set that I have.
The Tom Robertson springs were used with Spax 392 front shocks, and 393 rears with spherical bearings on the bottom mount. Tom Robertson won the SCCA National Championship in his D/Production Seven in 1977.
A contributor to the lotus@se7ens forum advised that he used Spax AS164/392G shocks on the front of his competition Seven. Springs were 10 inches collapsed and 13 inches extended. Rear shocks were AS164/393G and were 13”inches collapsed and 17 inches extended.
Dave Bean Engineering
In Dave Bean’s ‘Elan – Plus 2 – Cortina Performance Manual ELN.1’, he provided the following spring rates for the Lotus (and early Caterham) Seven:
Stage 1 – Standard Replacement – Front: 115 lb/in. Rear: 75 lb/in.
Stage 2 – Performance Road/Slalom – Front: 150 lb/in. Rear: 115 lb/in. (ride height 1 inch less than Standard).
Stage 3 – Pro Solo/Road Race (Limited or no street use with ride height minus 2 to 3 inches) – Front: 160 lb/in. Rear: 115 lb/in.
He added: “These are our recommendations for the applications listed”. (He also included rates for the Elan and Plus 2). “Obviously, these do not cover them all; and there will be differences of opinion on the ideal spring for a specific application. We have no intention of differing with learned chassis engineers over rates and lengths”.
Dave Bean’s thoughts on Spax shocks mirrored those of other dealers/users at the time he published the manual. He believed that they were good value, and continued to endorse Spax for use on Lotus cars, since they had sorted out their quality control problems. I cannot find a printing date for this manual, but it is a handy accompaniment to the ‘English Ford Racers Catalog’ of 1988. Both publications contain handy advice for Lotus owners, with many parts listed for Sevens. However, I do not know how much stock they actually carry these days (2021) that is shown in these aging catalogues.
Caterham Cars under ownership by Graham Nearn and David Wakefield.
From indications in a Caterham parts catalogue for cars produced by them from 1973 onwards, Spax became the damper of choice for live axle cars, later followed by Bilstein for the De-Dion cars. Other manufacturers such as Koni were chosen by owners for their quality.
Lotus Seven Club forum contributors, for their predominantly Caterham built 7s, mention Nitron, Leda, Avo, and Gaz as dampers of choice. A number of posts on their site (still available for viewing by non-members) from the early 2000s up to 2010, provided negative reviews of Spax dampers. Confirmation from a couple of retailers of Spax (Spyder included, who later refused to carry them due to product deficiencies), advised that Spax was the subject of a few takeovers, and quality control suffered. Since that time, Spax has reinvented itself, and Chris Mintoff at Redline, and Mick Beveridge at Xtra Special Sevens fully endorse Spax and use them on their cars.
In a January 1981 ‘Road and Circuit Impressions’ article in Motor Sport Magazine, the magazine tested the Caterham Pushrod Seven that Graham Nearn and company had succeeded in being accepted in the British 1980 Prodsports Championship events. Produced by Clive Roberts, the car started the year racing on the old production settings: Spax dampers allied to 75 lb. rear springs and 105 lb. fronts. Due to the original springs sagging, another supplier was sought for the race car. It was then passed to Chris Meek (a noted race car driver of a class leading Panther Lima 2.3), to fine tune the suspension using the new springs. The rates changed to 90 lb. fronts, and 70 lb. rears. The article noted that current production rates (1980-81) for a road going Caterham Seven fitted with the Ital axle, were 100 lb. front, and 55 lb. rear.
James Whiting noted that this track car had to be based as much as possible on a ‘standard’ road car to be permitted to race. By softening the springs, the car was riding on the bump stops thereby stiffening the suspension and increasing camber angles riding so low.
James has a lightened 1960 Series 2 Seven used for the road, but has fitted 225 lb. front springs, and 110 lb. on the rear. Tyres are 155 x 13.
Caterham increased the poundage of their springs for De-Dion production when the live axle was downgraded solely for ‘bottom-of-the-range models’. John Tipler in his book advises the following: “When you improve one facet of a design, you very often expose weaknesses in another, and so it was with the (Caterham) De-Dion set-up. Now the front suspension looked jaded.”.
Tipler describes the standard Lotus cost-saving front suspension set-up of using the anti-roll bar as the forward component of the top wishbones. Caterham devised a double wishbone arrangement with separate anti-roll bar for their De-Dion fitted cars.
Just my personal observation, but the following cars: Lotus Mark 6; Lotus 37 racing car – as originally produced by the factory; original Elite; Lotus 11 with live axle and De-Dion rear suspension; Lotus 12 Formula 2 car; Lotus 15 (using the anti-roll bar in front, and also modified later to fit behind the top arm); all used the same front suspension set-up with the anti-roll bar being used as part of the top suspension ‘wishbone’. All were very successful road and racing cars. Note: The Lotus 37 was originally raced in this form by John Berry at Lotus, but later modified to double wishbone front suspension with separate anti-roll bar – possibly by Tim Goss when he took over ownership of the car.
Suggested Damper/Spring Combinations For Road Use.
Currently (2021), Chris Mintoff at Redline Components, suggests Spax dampers with adjustable spring seats for road-going Sevens. He can provide these with springs, but does not have a device to attach the springs to the dampers.
His advice: “During my time at Redline I have increasingly supplied the adjustable spring platform Spax dampers (front and rear) to my customers with Lotus Series 2 and 3 cars and have no intention to change. I run these on my own cars. The adjustable damping allows the ride to be tuned depending on the use of the car, the adjustable platforms allow the overall ride height and front to rear pitch of the car to be set.”
The spring rates are: Front: 125 lb./inch, and Rear: 100 lb./inch. The front springs are 11 inches free length, and the rears 14 inches free length.
He notes that the reduced unsprung length of the springs from the original 12 inch/15.4 inch springs is allowed for with the adjustable platforms.
Mick Beveridge at Xtra Special Sevens concurs, and adds the following: “I actually prefer the adjustable platforms. If running the softer springs it helps to be able to raise the rear when there is two in the car. Springs I have to use are the 125/11 (front) as the 100/11 tend to be a bit soft. 80/14 rears only if you can get them, as most (companies) don’t list them so you have to use the 100/14. The 105/75 springs are almost impossible to find now. Many of the old one-off shops have closed, and the newer shops want a minimum order or are not interested. Many race shops/spring suppliers have moved on to the more common set lengths”.
Spax Performance Ltd., will sell direct to consumers. They advise the following:
“The 28 stage damping stiffness adjustable – with adjustable spring seat dampers for the Series 2/3 are:
Front G775 – open length 12-3/4 in./326 mm, closed 10-5/8 in./271 mm, 1/2 in. bonded bush top and bottom, for 1.9 in. i.d. springs.
Rear G776 – open length 17-3/8 in./441 mm, closed 13-1/4 in./337 mm, stem top, 1/2 in. bonded bush bottom, for 1.9 in. i.d. springs.
The 28 stage damping stiffness adjustable – with fixed spring seat dampers are:
Front G303 – open length 12-1/2in./318 mm, closed 10-3/8 in./264 mm, 1/2 in. bonded bush top and bottom.
Rear G305 – open length 17-3/4 in./451 mm, closed 13-1/4 in./337mm, stem top, 1/2 in. bonded bush on the bottom”.
Tony Weale advised in the appendix to his book that the Seven Series 1 uses the same Spax damper and spring combination as the Series 2 and 3 on the front of the car. The Series 1 with live axle uses G304-180 or G304-AS180 (adjustable spring seat) on the rear. He also quotes for Series 4 cars (70-74) as using G620-S180 or G620-AS180 (adjustable seat) for the front of the car, and G655-S180 or G655-AS180 for the rear. A check with Spax can confirm if these designations are still current (i.e. if ordering from a company other than Spax), as they seem to have dropped the S/AS-180 designation from their numbers.
Spax is VAT registered, and this tax may be taken off for export to certain locations. The G775/776 dampers were quoted at the exact same price each. The G303/305 are cheaper than the G775/6, and the G303 front damper was quoted as 10 U.K. Pounds Sterling cheaper than the rear. Note: Spax does not supply springs for their dampers.
Redline (VAT registered) quoted slightly cheaper for the G775/776 dampers. Chris Mintoff added suitable springs to the order, and the shipping cost still came in lower than the quote from Spax – even though the weight was considerably more with springs added.
Mick Beveridge is not VAT registered for export. His usual supplier closed shop, and he is currently looking for a suitable supplier.
James Whiting did not advise regarding my request for information on Leda Dampers. Leda have been in and out of business, so a note to James may help in confirming if they are still available.
Avo Shocks – manufactured with steel or aluminium body, are given positive mention by some Caterham owners on the Lotus Seven Club site, along with Gaz shocks. Gaz produce alloy bodied units, and recommend their spring supplier for advice.
Bilstein recommends that anyone interested in their shocks for a Seven should contact Caterham directly.
A check of the Koni site did not list Lotus for damper options.
Nitron list the Caterham De-Dion model.
Note: These web sites were checked in early 2021, so as always, an up-to-date check is recommended.
My appreciation to the following:
- Dave Bean Engineering Inc.
- Mick Beveridge – Xtra Special Sevens U.K., for Seven parts and restoration.
- Peter Lucas, Former Designer/Draughtsman at Lotus.
- Chris Mintoff – Redline Components U.K., Seven parts supplier.
- Spax Performance Ltd., U.K., Steve Meads – Sales Rep.
- John Tipler, “Lotus and Caterham Seven” – Crowood Press Ltd. book.
- Tony Weale, “Lotus Seven – Restoration/Preparation/Maintenance” – Osprey Automotive book.
- James Whiting, Appletree Works, Lotus and Caterham Restorer.