spring rate query

[Bare]

I'm confused about the spring rates currently used.

I sold my Series 3 7 after a few years. I replaced it with an Europa... primarily for the reason that I was tired of having my teeth rattled by the Seven.

The ride while stiff by anyone's yardstick was "plush" in comparison to the 7.

Now according my Workshop manual for the Europa: the front springs were 100lbs and the rears were 72lbs!!...(yes I'm aware that it's mid engined ;-)..However the Series 4 used the Very Same suspension and although unloved WAS the widest selling and smoothest riding 7 made... at least by Lotus.

The Europa weight is 1550 lbs, and the weight distribution is claimed as 45% front 55% rear.. over the years it NEVER bottomed even when there were two of us 200+ lbs Fatties squeezed in somehow.

I have extensively Autocrossed this car, and the settings were V good if not optimal.

Now I see spring rates of 200, even 250lbs onna front of a Seven... this to me at least ..seems absolutely absurd..basic Math, experience and sense indicates that with springs this hard there is no suspension (just think of the money wasted on shox;-)

Given the seemingly widespread usage of hi rate springs.. what am I not understanding/missing here?

Any insight would be greatly appreciated .. is there also a "baseline" setting, one that most people end up preffering?

 

 

 

[scooby dooby doo]

if (among others) any of these are different then the ride will be different:

the spring mounting angle

the suspension geometry

the pickups position

the sprung/unsprung ratio

wheelbase

track

padding in the seat

damper settings

tyre side wall stiffness

etc

etc

 

HOOPY 500 kg R706KGU

[Lawrence_Z]

72 lb/inch springs would compress about 6 inches with your corner weights, this is quite a lot

 

what length are your dampers?

 

 

 

Lawrence

 

[scooby dooby doo]

unless the wheel rate is 6 to 1, then its only going to compress one inch. (or is it 1 to 6 i mean )

 

HOOPY 500 kg R706KGU

[Bare]

the rears "compress" about 1" from empty car when I plunked my self into the car. Again there is apparently NO problem whatsoever with those rates.

Shock angles are oem 'Lotus' ..as in ..the same..as Caterhams.. suspension geometry !?.. oem.. no welding in of new pickup points if that's what you mean.. 'adjustment only' changes would give inconsequential variations;-)

What I'm struggling to understand is the widespread use of what seem to me to be ludicrously stiff springs on a 12 to 1400lb car.

Although in fairness I have recently seen a Seven with 100lb fronts.. and while I have not been in it, the owner seemed ecstatic about what he felt was a marked improvement in not only the ride but in the roadholding as well.

Has anyone here actually experimented with low rates? To confirm or dispute these annecdotal results

[Peter Carmichael]

Lawrence,

 

Quite a lot of the six inches could be taken up in preload.

 

It is perhaps easier to consider for the rear of the car where the Caterham springs act almost directly, similar to any Lotus live axle arrangement. Here, I have had success using 120lb/in and don't think there is benefit in going to harder than 150lb/in. (but this is with presurised gas dampers that contribute 15lb/in in themselves)

 

The front on Caterham's has changed considerably from the Lotus years. The latest chassis have different pickup points on the chassis and have widetrack wishbones. These have an action ratio of 1.63:1 giving a wheel rate ratio of 2.66:1. So in this case, 250lb/in springs have a wheel rate of 94 lb/in.

 

Not looking so out of order now, is it?

 

Principal tuning might focus on damped ride frequency in heave. It is a good idea to have different frequencies front and rear so that the car doesn't osscilate in the pitch sense. Normally the front is aimed at having a lower frequency than the rear. Damping ratio can be presumed to be between 0.2 and 0.4. Mass distribution can be calculated. Normally it sort of works out. Target damped frequency is ~1.2-1.4 hz. This gives a good "sports car" ride.

 

The ride quality of a seven is dominated by the rear springing because you are sat over the axle. Also some of the tall OHC engines hang underneath the chassis and give less than 50mm (2 inches) clearance. These two concerns can make it more feasible to have the higher frequency at the front of the car. The higher spring rates of 300-400lb/in used by race teams are usually making use of this effect. The stability under braking is improved. Anti roll bars are detuned to maintain front/rear grip balance.

[DaveMorris]

Bare,

 

I hope to G** that you understood that last one because it went STRAIGHT PAST me.

 

Think I'll read it again a couple of times and see if anything sinks in at all ❗

 

Dave.

[scooby dooby doo]

Dave = the front suspension geomertry has changed so you need stiffer springs to get the same result as on a much older car.

 

(Note to self - get on and read Tune to Win)

 

HOOPY 500 kg R706KGU

[wonkey eyed barmaid]

stealing another suspension thread...

 

anyone know the standard spring rates on a '99 Classic Vx? (Bilstein suspension).

 

thanx!

p.s is the front anti-roll bar on this car upgradeable to a better one? (only half wishbone on top, and no widetrack remember).

i have probs with tyres catching clamshells when on lock with car 2-up - would this help?

[Graham Sewell]

Grant,

 

As Caterham will not admit, the problem with tyres catching the clamshells is solved by bending the wing stay upward to give greater clearance. The only other methods are:

 

Change to 60 profile tyres

Change to height adjustable dampers and raise the car.

 

Cheers,

 

Graham

 

Low tech luddite - xflow and proud!

[Lawrence_Z]

Quite a lot of the six inches could be taken up in preload.

 

Ah! preloaded dampers I still have the scars.....

 

My thoughts.... until PC replies

 

Colin Chapman believed in soft springs, with stiff dampers and antiroll bars to control roll....in those days dampers had to move a fair bit more before they were effective.

 

while current thinking is for stiffer springs, softer roll bars and better dampers.

The stiffer springs control roll better, yet still allow suspension movement in a high load corner. The better dampers allow for less overall travel.

 

Stiffer springs transmit more energy into the tyres, which equals more heat, equals more grip.

 

Chassis bracing, Petty strut, race bars, and/or a full cage reduce chassis flex and allow higher spring rates again, more heat, more grip.

 

Dampers now tend to have higher low speed damping and relatively less high speed damping, with a tendency away from the traditional 3:1 bump rebound philosophy. (still can't find anybody to explain the reason for this 3:1 ratio to me)

 

Getting back to the Europa tho', although the only data I could find was for my old Esprit, I'm still not convinced that the Europa had heavier front springs than rears.

 

Lawrence