Help with Spring Rates & Shock Rates?

I'm looking to get my overdamped and oversprung setup fixed by changing spring rates and damping rates.

250lbs front + 300lbs rear is where I started. Too stiff. Changing to H&R springs (unknown spring rate, but I assume lower rate) made the car a lot faster in the corners.

JVL recommended 175-160 lbs. up front. I'm guessing that's probably about right given his experience and the above observations.

Car is a 1900 lbs Geo Metro

Setup is going to be:
Front & Rear Bilstein 36mm inverted, ~6" of shock travel
Front 2.5" coilover spring
Rear 5" spring in stock control arm location

Approx. front corner weight: 570 lbs.
Approx. rear corner weight: 400 lbs.
Front motion ratio: ~6:7
Rear shock motion ratio: ~3:4, spring motion ratio: ~5:8

Anyone have any recommendations on how to choose corresponding rear rate, and how to choose damping rates to match the springs?



Edited 2 time(s). Last edit at 07/31/2013 01:17AM by ofensus.

To do the math (and, thereby, enjoy the complete derision of some posters), you need to split your corner weights into sprung and unsprung.

Let's say that I knew those values (I can measure them later), then how does one get the damper rates from the spring rate?

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ofensus
Let's say that I knew those values (I can measure them later), then how does one get the damper rates from the spring rate?

by what is called "praxis"

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praxis (n.)
1580s, from Medieval Latin praxis "practice, exercise, action" (mid-13c., opposite of theory), from Greek praxis "practice, action, doing," from stem of prassein, prattein "to do, to act" (see practical).

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practical (adj.)
early 15c., practicale "of or pertaining to matters of practice; applied," with -al (1) + earlier practic (adj.) "dealing with practical matters, applied, not merely theoretical" (early 15c.), or practic (n.) "method, practice, use" (late 14c.). In some cases directly from Old French practique (adj.) "fit for action," earlier pratique (13c.) and Medieval Latin practicalis, from Late Latin practicus "practical, active," from Greek praktikos "fit for action, fit for business; business-like, practical; active, effective, vigorous," from praktos "done; to be done," verbal adjective of prassein, prattein "to do, act, effect, accomplish."

Somebody, looking at previous established, successful examples, looks at weight, and available travel---in your VW struts without spacers an available 188mm travel or about 7.5"----and thinks of similar applications having that travel and weight, and chooses a spring.
Then, looking previous examples, chooses a damper to control the spring.

Your car with conventional struts and conventional geometry, is easy in front.
It is the rear that is an especially difficult design to do something worthwhile.
I believe your rear stuff is more or less the same as the Suzuki MkI GTI from the 80s:


The "socket in" deal is always a bitch to deal with because of the size of the hole you must poke the suspension part--strut /shock/whatever into and the way it passes thru---and hangs way down.. The diameter is about 45mm.

Unfortunate in that suspension units worth considering tend to be 50mm OD...
And in real world examination shows that the material thickness of the pinchy part is thin, and would be "Way thin" if bored to 50--and that's ignoring the placement of the pinch bolt which "grazes" the side of the shock/strut..

Next: if the unit cannot pass thru and get pinched, logic says the strut/shock think must be above the knuckle---and this leaves insuffcient room for more than about a 4" travel unit---and I think we can all agree that 4" travel on a gravel car is just a tad short--by about 3-4"...

Add to that the spring being jammed between the lower arm and the body separate and difficult to give the spring more travel leads us pretty inevitably to a simple solution..something easy to make, and easy to install kinda of like this:


Which can be made tall enough that adequate travel AND A SPRING can be easily accommodated above the pinch point...

Then spring and damper choice is a snap.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I promised the guy "complete derision." Please try harder.

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Iowa999
I promised the guy "complete derision." Please try harder.

We explained that you are here for purely social reasons, and all your posts here show that its what your intent and desire is: chat..

This guy is actually out in rallies---the point of this forum is to get guys out in rallies---he already did the route you believe in, and he, like all who go that way, fucked up royally and spent a lot of money to do things way way wrong, in the order of twice as stiff on springs and damping rates as he should have.

That is not something funny for assholes to come here and make fun of, it's a sad thing..and it will cost him money to make right, and tyhat ain't a fun thing.

Why don't you go bully some undergrads and let the adults here get this guys car working?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

John,

I shaved the rear strut bodies down about 0.3mm to get them to fit in to the stock knuckles. I'm trying to stay in stock class for now (I know how much most people hate it), but maybe down the road I'll fabricate my own knuckles and weld the tower.

I've already been running on those rear shocks, so I'm not worried too much about fitment of the rears, and have the travel back there. My concern there is just with the rates for now as they're overdamped.

I'll try to look around for more examples of spring + damper rates, but the car is a lot lighter than almost everything out there, so it's hard to find a comparable setup, let alone one that performs well.

I guess I'll come back to this thread tonight with all the data I can search out on other setups.

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ofensus
John,

I shaved the rear strut bodies down about 0.3mm to get them to fit in to the stock knuckles. I'm trying to stay in stock class for now (I know how much most people hate it), but maybe down the road I'll fabricate my own knuckles and weld the tower.

I've already been running on those rear shocks, so I'm not worried too much about fitment of the rears, and have the travel back there. My concern there is just with the rates for now as they're overdamped.

I'll try to look around for more examples of spring + damper rates, but the car is a lot lighter than almost everything out there, so it's hard to find a comparable setup, let alone one that performs well.

I guess I'll come back to this thread tonight with all the data I can search out on other setups.

OK if you want to but I'd think you could get closer to solving it by more details of what you now have in the rear.
What shock, what travel, what spring , what valving, .? In back..

(You won't find anything with any details, its all ""I'm happy with..........."

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Rear is:
F4-V36-0066-H0 shaved bottom to fit in the stock collar moved the mounting tabs around a little bit so the shock is in the middle of travel at 0.5" above stock ride height. Shock travel (compressed bumpstops to full extension) is about 5.25" according to spec sheets (don't have actual measured values with me)

Revalved to 330/170

Right now, H&R lowering springs are on the car, in stock location. Not sure the rate, and they're progressive/have dead coils.

Quote
ofensus
Rear is:
F4-V36-0066-H0 shaved bottom to fit in the stock collar moved the mounting tabs around a little bit so the shock is in the middle of travel at 0.5" above stock ride height. Shock travel (compressed bumpstops to full extension) is about 5.25" according to spec sheets (don't have actual measured values with me)

Revalved to 330/170

Right now, H&R lowering springs are on the car, in stock location. Not sure the rate, and they're progressive/have dead coils.

This?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Yes, exactly that.

Slightly larger image:
http://www.redpepperracing.com/gallery/d/252068-1/F4-V36-0066-H0_+1984-1987+CIVIC_CRX+rt_+front.pdf

Oooh. That gives me a thought for my own purposes... what's the diameter of the narrow bit at the bottom, eg-proximately?

I think they're about 1.83" on the lower portion. This is based on guestimate extrapolation from measurements I do have handy.

Cool, thanks.