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Chat with a Lotus technician

5K views 56 replies 25 participants last post by  khamai 
#1 ·
Just got off the phone with a Lotus technician. Here is the info I gathered:

Bushings on LSS package are unchanged from stock - pretty stiff

Touring option adds roughly 12 lbs. to the car

Wheel weight savings are 3 lbs F and 7 lbs R on the LSS

Spring rates stock vs. LSS F 42.5 47.5 N/M
R 60 65

Cheers,

Jeff
 
#52 ·
Tripledigits said:


Spring rates stock vs. LSS F 42.5 47.5 N/M
R 60 65

If those spring rates are in N/mm, then in lb/in we have approx:
STD LSS
F 242 271 (12% increase)
R 342 371 (8% increase)

Well, heck. In a 2000lb car, those rates seem downright reasonable, and with well-tuned dampers I wouldn't expect them to result in a "harsh" ride. (Admittedly, this is coming from a fellow who drives a 3500lb car with 600 lb/in springs on all four corners as a daily driver. (And occasionally plays with a 2400 lb car on 700F/325R springs.))

I'm violating all sorts of rules in buying this car: no test drive, first year of production, colour unseen in person - and now, worst of all, second guessing my choice not to get LSS. I don't believe the "hairshirt" comment at all with those spring rates - perhaps Lotus underestimates us "soft" Yankees?
 
#55 · (Edited)
How a spring acts depends on where it is attached, and the angle. Imagine that the lower end of the spring is attached to the middle of the suspension arm. In that case, the spring will be compressed 0.5" if the wheel moves up 1". This means that you have a motion ratio of 0.5.

To quote Fred Puhn: "First, the stiffness of a suspension is not the stiffness of the spring all by itself. The important stiffness is that seen by the wheel or the body, which may be different on account of leverage." He uses the example above, and for an 800lb/in spring in the middle of the suspension arm, the vertical stiffness is 200lb/in. In the general case, you multiply by the motion ratio squared (Puhn uses the term "mechanical advantage" for the inverse of the motion ratio).

Edited for correct definition of motion ratio, see http://www.rc10.com/racerhub/techhelp/marc/Handling.5.html.
 
#57 ·
ConeFusion said:
How a spring acts depends on where it is attached, and the angle. Imagine that the lower end of the spring is attached to the middle of the suspension arm. In that case, the spring will be compressed 0.5" if the wheel moves up 1". This means that you have a motion ratio of 0.5.
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Ultimately engineers are most concerned with "Wheel Rate". Spring rate is a component of the Wheel Rate, as is the sway bar and bushings.
 
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