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I set out to have a high quality racing suspension coil-over system several
grades above the original, with height and corner weight selection. I wanted a
system that could be adjusted for different track conditions and different tire
choices. I connected with TrueChoice Motorsports as a recommendation from Koni,
since TrueChoice has the capability to custom design systems.
I talked with Greg at TrueChoice, Suspension Manager 1-800-388-8783 and described
my application; he was unaware of any previous M100 Koni shocks and verified with
the factory that a standard shock was not available for the M100 application.
I sent Greg a set of original Lotus shocks, springs, yokes and all the related
parts for both the turbo 16” and non-turbo 15” suspensions. The shocks
and springs were measured, tested and put on a dyno to verify the spring and rates.
Greg has all the information available for the valve selection, gas pressure setting
and shock lengths. The shocks are the same size for both suspensions.
Greg worked with his technicians and an independent suspension designer that
produces components for the Formula 1 and CART cars for a front shock bracket.
I spent $800.00 for the design and fabrication of the brackets above the cost
of the shocks and parts. Several brackets were attempted before the final was
accepted. The brackets are water jet cut and machine full welded to the shock
tube with an additional sleeve support for added strength. The front shock also
required the gas charging nozzle to be relocated to the bottom of the shock and
removing the bottom eyelet to accommodate the bracket. Eibach springs were selected
based on the availability and selection range as well as the quality. I chose
the 2.25” ID. The front and rear shocks are also modified to have the top
eyelet replaced with a hardened stud as the originals. The rear shock only requires
the top eyelet to be modified to a stud.
The system allows for a range of over 5” of spring adjustment for corner
weighting and adjustable rebound and bump with 10 positions available to meet
individual and track needs. The standard spring set up would be for a two-passenger
ride. I would suggest that if you want to use the car for extensive racing and
auto crossing that the springs be selected for a single driver. TrueChoice has
these spring rating based on my corner weighting setting, although they might
differ based on your car weight distribution and your own weight. I do feel that
the springs selected will fit a range of people and cars. If you will be racing,
these should be selected per application. The springs are cheap and can be exchanged,
if not scratched or damaged. A quality shop that sets corner weight can help suggest
the proper spring if the spring you selected doesn’t give the balance and
even ride height you want. The bump damping is only adjustable by removing the
top shock stud nut prior to rotating the adjuster. The rebound is fully adjustable
when mounted. This system is the same as the suspension used on the Lotus Sport
Elise 190 and 340R used in the states for racing. The only difference is the shock
is externally adjustable, since it doesn’t have the special bracket that
the M100 has for mounting, but uses eyelets on both ends.
The Koni 3011 series racing coil-over-shock was chosen for the application,
since it has full independent adjustability for rebound and compression (bump)
damping and has been successful in racing since 1986. The shock is completely
rebuildable and has a variety of valving giving it 4-6 times the adjustable range
over other shocks. It is lightweight at only slightly over 3#. It will also accept
either 2.25” or 2.5” springs. The eyelet mounting for the rear shock
is a swivel bearing that will allow for suspension movement. The tube diameter
is 50 mm, where as the standard Lotus is 40 mm. The base cost to purchase a 3011
Koni race shock is $500.00 and the Eibach spring cost is $55.00 or $550.00 per
corner, $2200.00 per set. The following modifications are required to fit the
The modifications to fit the front shock to a M100 requires the gas charging
valve and bottom eyelet to be removed and relocated, the top eyelet to be removed
and replaced with a hardened stud and the shock mounting bracket to be fabricated
and welded to the tube housing. These will bolt into the car directly without
any further modifications. The Koni shock will use the existing rubber grommets,
washers, studs and stud nuts for mounting. I used the existing spring top bracket
with the 3 studs to mount the shock into the car. This modification cost is $300
per front shock or $800 per shock.
Eibach Spring and Front Koni Shock assembly $855.00 each
The modifications to fit the rear shock to a M100 requires the top eyelet
to be removed and replaced with a hardened stud. The Koni bottom eyelet is ½”
instead of 12 mm for the Lotus shock or .008” to large. The suspension bracket
on the car needs to be drilled out to ½” and a new grade 8 –
2-1/2” x ½” bolt/nut used. There is plenty of room to drill
this hole out and it is much cheaper than a custom eyelet to be 12 mm. The Koni
shock also comes with a set of bushing/spacers to be placed between the Koni shock
eyelet and the suspension bracket to allow for swivel movement. This modification
cost is $50.00 per rear shock or $605 per shock.
Eibach Spring and Rear Koni Shock assembly $605.00 each
Koni web site
Cost for 4 Koni 3011 shocks and 4 Eibach Springs $2220.00
Modifications to 4 Koni shocks to fit M100, $700.00
Total cost per car is $2920.00
This cost for a suspension is high and not for everyone, but then these are a
high quality racing shock and not a cheap $200 damper. I have used them in my
past 4 races and several track days and have been able to make adjustments to
the suspension and lower my track times. I try to keep the suspension as soft
as possible, since the best traction is when all four wheels are on the ground
and this system will help to do that while allowing only minimal side roll. I
thought that some may want a superior system and wanted to share what I had put
As an alternative, check out these shocks offered by SJ
SportsCars in England
These are 'Gaz' fully adjustable shocks, available for about £50 which
is half the price of the Lotus part. See www.sjsportscars.co.uk
for more info.
As another alternative, please check out these
shocks offered by Chris Neil in England
Write-up by Dave Schmid