DrKlop

iTrader: (3)

I always thought that cutting springs was not a good idea. I also know that everyone on the .org would agree with this fact. However, I found this interesting article in the book called “Chassis Engineering” by Herb Adams where it is suggested that cutting springs is actually the best way to go. Take a look at it and post what you guys think.

JSutter

iTrader: (46)

hahah no. what is this from the 1940's? give me a break. have fun bouncing and watching the spring fall out.

JClaw

iTrader: (17)

Thanks, but no thanks. Coilovers for me.

DrKlop

iTrader: (3)

well, yea it is pretty old but it's only 1993 and even if the book is 12 years old why would somebody recommend doing something that will give crappy handling?

NmexMAX

iTrader: (22)

Reason we like our lowering springs, is because they're progressive, and it doesn't put any more thermal cylce stress on the metal.


And the first reason I mentioned (progressive rate) is because some of us actully use our Maximas as daily drivers.

Seems as if the main reason this guy likes the cutting method is because he likes to know what he gets when he gets, and doesn;t like to wait for 'new' springs to 'settle'.

Also, by doing this by hand, especially when it's still thrermally active, it's the luck of the draw, what if you get a cramp, or something happens, and you're left with a funky shaped spring after it cools. And re-heating it shouldn't be an option since it will further alter the mechanical properties beyond what you already did in the first thermal cycle.

DrKlop

iTrader: (3)

But wouldn’t it solve the problem of not being able to find the right springs for your car? (like I have, one set is too stiff, the other set is to low, the third set sags in the back etc..)

Also, doesn’t this article make all the people who said in the previous posts that “cutting springs will never give you good results” wrong?

NmexMAX

iTrader: (22)

Back in the day, some A32 memebers would cut their IIRC Sprint springs one coil in either the front or back in order to elimiante as.s. sag or something of that nature.

Most people have expereince with moronic idiots that cut 2 coils off, and end up having virtually no suspenstion travel or dampening whatsoever.

1/2 coil is good, as he article suggests, but hacking them using a saw would be best option, if one were to go this route, which I wouldn't.

Reason being, is because when you use a torch (read: introcude heat) you change too many properties to actually know what you're getting in the end.

njmaxseltd

iTrader: (19)

Cutting springs increases the spring rate, as stated in the article.
Increased spring rates ride harsher, impact bumps harder and rebound harder.

Aftermarket PROGRESSIVE lower springs keep the spring rate reasonably close to the factory springs until the spring is compressed. Thats why they ride better then cut springs on good roads. A Progressive spring also handles much better by eliminating body roll. A cut factory spring wount do that.

Cut springs don't give you better handling or a nice ride. Aftermarket progressive sport springs is the way to lower your car correctly and increase it's handling properties.

That article looks like it was written in the 80's. Welcome to 2006 people.

NmexMAX

iTrader: (22)

for the suspension guru

ThurzNite

iTrader: (13)

Hey, I read that book about a year ago. It's got some interesting info. As for the springs, progressive springs is the answer.

Jae

DrKlop

iTrader: (3)

I'm not arguing that progressive springs are better, what I'm trying to say is that cutting springs will not ruin suspension and will make it better than stock. The reason I posted this is because I saw a million of posts stating such things as “don’t even think about cutting springs,” “cutting springs = rice” “you will always get crappy handling” etc.

Obviously, professionally fabricated springs are always better but what if you can’t find exactly what you are looking for? Since we now have an article written by a professional, cutting stock or aftermarket springs could possibly be an option now…

maxgtr2000

iTrader: (29)

It depends on what you cut and who cuts imo. Most vehicles do handle better a little lower and I think that is what the article was saying. It was also a conservative cut. Half a coil on a stock spring is what? Maybe an inch. But these kids see cars with coilovers can't afford them and figure they can just take the cheap route and cut the springs until there is no gap. now that is rice and stupid. You know, it's kinda like people that WANT loud exhausts, fart cans, etc.

NmexMAX

iTrader: (22)

That depends on how many coils are cut.

moo moo

I still wouldn't cut my springs.

tripleGmax

iTrader: (8)

in 1993 were aftermarket springs easy to get and cheap? i wonder if this is his reasoning?

Mr. Blue Sky

iTrader: (1)

I don't feel too safe cutting my springs either, though I do own a car that had the springs cut by the previous owner and there are no other major issues other than a harsh ride. I went the cheap-o route and just used lowering brackets to get the look I wanted in my max. When I don't like it anymore I figure I can take them off and go back to my previous stock setup.

tommygunzit

has anyone heard of problems with cutting springs and causing accidents? that is one that was done as per article instructions.

InfinitiJ30

Last time I checked, books that were published in the early 40s contained more knowledge then the magazine that we read today..good read..

MacGarnicle

iTrader: (1)

No offense to those with strong opinions on the matter... but Herb is an engineer with a suspension company. I seriously doubt there is absolutely no merit to what he's saying and I'd probably listen to his advice over anyone elses..

The only thing I can think of that would discredit his advise, is if it were outdated and new theories have replaced the ones he's suggesting..

d00df00d

iTrader: (4)

Talking about about "dampening curves" doesn't exactly help his credibility. The correct term is "damping".

Plus, he fails to mention that all of his advice assumes that the factory suspension:

1. produces enough preload that, even with the shorter spring length, the spring won't come loose when the suspension is at full droop; and
2. has enough travel to keep from bottoming out with the new, shorter springs, which may or may not have enough rate to keep the car off the ground.

sixty8panther

All I think of right now is my buddy Renato who's from Brazil and
his crazy stories of VW Polos with cut springs. He had one as
did most of his friends. Out there I guess Chevy & VW make up
most of the Automotive market.

irish44j

iTrader: (38)

....only with linear springs....

Norm Peterson

I'm floating this old one back to the top only because the "cutting springs?" thread over in "Advanced Suspension, Chassis, Brakes" was closed.

Cutting springs IS a valid mod . . . but only if you know enough about spring design to know what you're getting into. Some of the caveats have already been mentioned, but the bottom line is that those who simply hack off a coil or two just because "it seems about right" are probably poster children for the "do not do this" side of the discussion. On the other hand, if you trim a slight amount, and on springs whose end details don't matter where they are cut ("tangential ends"), it is entirely acceptable.

The "heat while cutting" thing is also overdone, at least if you're trying to cut with acetylene. Get the cut done quickly using a big enough rig to get the cut started right away and you're still OK - set the coil on its side in a shallow pan of water if you're that concerned about how far the heat effects might extend. Remember that more than half a coil is always bottommed out against the seat, so if it loses a little of its temper it's no big deal, as it isn't flexing anyway.

If I'm not mistaken, Herb Adams has also suggested flattening the (heated) end coil slightly. At best, that's an application-specific thing to try, and it may not apply to these cars. I'd need more information than "Herb does it" before I would (and I have cut springs on a couple other cars).

DISCLAIMER: This is in no way a blanket recommendation or even a suggestion to cut springs. It's only mention that under the right circumstances it is certainly OK to do so.


Norm

MorpheusZero

iTrader: (10)

Cutting the portion of the spring that is already compressed will do nothing to the spring rate, it will only screw up your geometry and push the front roll center further down into the ground, making the front of the car roll more and giving it more of an understeery roll axis (for 4th and 5th gens), without stiffening the springs at all, or by a negligible amount if at all, which 4th and 5th gens NEED in order to handle better. Stock rates are like floating on water and not only is that horrible for transitions but it is unsettling even in sweepers, it does not feel right tossing the car around, although it does encourage smooth driving.

Norm Peterson

True, at least for adjacent coils that are stacked solid at static ride height. I don't think the 5th gen's coils are that way, but I have some aftermarket springs on another car that are. The stacked-solid end coils act much like tender springs on short coilover springs to keep the main springs from going loose at full droop. Cutting those coils would be unwise on two accounts.

Being able to lower a strut-suspended car for *SP or ST* in SCCA Solo but not able to legally correct the kinematic roll center is an annoyance that tends to drive you into even stiffer springs and bars just to cut the roll down and manage the camber loss in addition to what you might want to be doing with lateral load transfer distribution. Mechanical grip ends up being somewhat sacrificed. That seems at least mildly contrary to the original class philosophies, and is partly why I play as a weenie entry in 'Prepared' instead.


Norm

Norm Peterson

Roll center and roll axis effects may be more subtle than that. If anything, it makes it more difficult to balance for both sweepers and transitions, but it doesn't necessarily make either one bad.

A relatively higher rear RC by itself is actually more of an oversteerish thing, at least transitionally. It's the greater front roll stiffness that you may end up with for steady-state balance (to keep from being loose in a sweeper) that ends up making the roll stiffness portion of the equation more heavily understeerish that will hurt you where the ability to use more throttle early on corner exit is concerned. More so with sticky tires than with, say, generic all-seasons.


Norm

MorpheusZero

iTrader: (10)

Front RC being lower than the rear RC is an understeery/"pushy" roll axis, both in a static (sweeper) or dynamic (transition) roll condition--it does not matter. Front and rear roll rates also contribute to under- or oversteery nature of a car but you really cannot fully make up for one (crappy roll axis) with the other (roll stiffness F to R).

MorpheusZero

iTrader: (10)

Funny example but check this out:

http://youtube.com/watch?v=2OBhP6wPuvI&feature=related

If you pay attention you can tell that he's got an understeery roll axis, the front of the vehicle tucks in and it does the three-wheel salute so characteristic of Golfs, Maximas etc in autocross before it goes full 2-wheel.

Norm Peterson

Nope. RC effects by themselves are (mostly) linear and without regard to roll (unless roll causes large RC migrations). Roll, on the other hand, varies with time, so thinking only statically misses a lot.

A "roll axis" that slopes downward from rear to front is initially oversteerish, since the lateral load transfer begins immediately with load transfer through the RC's. In the initial stages before any roll has had time to develop there is no camber change due to suspension motion and no lateral load is being transferred through the elastic suspension components (springs, sta-bars, and shocks/struts). With more of the LLT going through the rear, you have a mild oversteer condition. That's a good thing, as it provides a more nimble initial feel.

It's the normal factory tuning of the elastic bits that then has to make the total steady-state condition one of understeer and one of the reasons why cars with steeply sloped "roll axes" are associated with understeer. It's what you see in comparing calculated front and roll stiffness numbers (aka roll couple distribution, as distinguished from the overall picture of total lateral load transfer distribution). A "looser" RC situation requires "tighter" elastic tuning to meet normal production handling behavior targets.


Norm

Norm Peterson

Once you go 3-wheel, all bets are off on the normally computed load transfer numbers - the system has gone nonlinear and from that point on all further LLTD is 100% front which is as heavy of an understeer tendency as you can have. With only the front roll stiffness to combat further roll.

I'll have to wait until I get home to see the video (internet filters, y'know).


Norm

MorpheusZero

iTrader: (10)

Naturally. I was just pointing out that it had a similar characteristic as FWD cars with stock or near-stock suspension put on an autox course. Also, three-wheeling is much less likely to happen with afternarket, stiff springs as opposed to ones with stock rates.

As for the roll axis argument, it seems that you are correct in that an "understeery" roll axis does promote initial response as the outside front will bite hard into the pavement, and it also seems that in doing so more of the load/weight is transferred to the front wheels, as opposed to a car with an "oversteery" roll axis that loads the rear more in a static lateral lean condition. I am hesitant to translate that; as it stands it could mean a number of different things.

I will concede that I am arguing a bit over my head here as I am going off my intuition and what I have read as opposed to actual experience or simulation, but I still just do not see a Maxima handling well with stock or near-stock spring rates. Hell, I had Konis and stock 5-speed SE springs and it was still a boat.

Norm Peterson

I think I'm beginning to see a disconnect or two.

The terms "roll center" and "roll axis" tend to imply far more than what they actually are. Your car (only its sprung mass, actually) does not necessarily rotate about the roll centers. All that a roll center is in this sort of discussion (as opposed to banked cornering a la NASCAR, which adds some complexity), is that it is the height at which a horizontally applied force does not produce roll. Nothing is implied about situations where roll is present.

You cannot even assume that the suspension on the side that goes into 'bump' travels as far into bump as the other side moves into rebound (IOW, that all you get is pure roll, without any net 'heave'). Kind of another way of saying that the "roll center" tells you absolutely nothing about where the center of the roll rotation might be. Consider what would happen if you were to swap the RF and RR springs on any car out for solid steel bars (their "spring stiffness" could be considered "infinite" for all practical purposes). The car would then rotate in roll about points somewhere near the bottoms of the right side wheels, not the points determined by the kinematic "roll center" constructions.

Roll centers are really just kinematic conveniences for calculation purposes. Limited calculation purposes at that. If you ever pick up Circle Track magazine and read Bob Bolles' columns, you'll find that he talks about something he calls a "moment center". It's the same thing as the old "roll center", but he has renamed it in his discussions as a way of getting rid of the baggage that the term "roll center" carries with it. Elsewhere, I've seen the term RC (just like that, not spelled out) used for a similar reason.


When you first start to turn, there is zero roll. Since the sprung mass has a moment of inertia opposing roll, roll builds much more slowly than the lateral forces develop. That means that suspension position (and velocity) also lag the development of lateral force. Load transfer that occurs through the RC's happens as fast as the lateral force can build. More load transfer at the rear from a higher rear RC can only be an oversteer effect.

Thinking in millisecond time steps, roll gets started relatively slowly at first, and the load transfer distribution through the springs and sta-bars starts adding to the RC effects. So does load that is generated in the shocks/struts as the suspensions develop some velocity. For handling effects related to load transfer, it's only the total load transfer at any point in time that matters. Very early in the turn, the total lateral load distribution (TLLTD) can easily be 80% or more at the rear, because nearly all of it is going through the RC's (think 3" front RC, 12" rear RC) and almost none through the springs/bars/shocks. That would give huge oversteer if this distribution was allowed to stay there all the way to ultimate cornering grip. But by a quarter of a second or so later, the roll couple contribution (which might be over 80% front) drags the total back to where it's slightly more biased to the front than the car's static weight distribution. Shock tuning can modify this somewhat within this time period. You start out "loose" and the springs/bars/shocks tighten things up. Because time matters, I think you'd need to plot all of these effects separately as well as the total, all on the same time scale, to see this better.

One guideline is to choose your springs, bars, and RC heights such that the TLLTD is about 5% more front biased than the static weight; that tends to produce mild steady-state understeer.


Edit: The coupling of what is basically a roll rotation with pitch due to a sloping "roll axis" still needs to go back to the true centers of rotation, not the kinematic constructions. This is a bit more complex, as lateral migration of the RC and moment effects due to the weight acting downward get involved.


Norm

Matt93SE

iTrader: (44)

One of the big issues never mentioned in this thread or the article is the TYPE of vehicle and suspension that's being discussed in the article. just because it says "street driven vehicle" does not mean "Maxima".

He mentions "most front springs rates range between 300-350lb/in. Trimming the coils will increase the rate by approx 10%. [b]But the true purpose of trimming the front springs is to lower the car for better aero and better handling, not to increase the spring rate."

Therein lies the problem here.

1. The Maxima suspension does not use a wishbone or a-arm suspension. It uses MacPherson struts. the wheel rate of the suspension is very near the spring rate- at least compared to the RWD double a-arm or wishbone type suspension usually used in RWD cars.

2. Stock Maxima front spring rates are in the range of ~120lb/in. This is WAAAAY too soft for performance use. Eibachs use ~220lb/in. Coilovers use ~450lb/in up front. Cutting the stock Maxima spring won't actually change the spring rate at all because the bottom coil is bound anyway. all it'll do is remove a 1/2" of 'spacer' down there. It'll also decrease the free length of the spring, but won't increase the rate much, if at all. Even at the "about 10%" listed in the article, you're looking at ~130lb/in which is still still about 200lb/in too soft for a performance car. The frequency of our suspension is on the ballpark of 0.2hz when it needs to be in the range of 0.6hz (minimum) for decent handling and transition response in corners.

3. Lowering the ride height of a MacPherson strut design car only damages the handling because of the camber curves and roll center- or 'moment center' if you want to follow the new convention trying to be spread by those that don't like the old terms.

It also does more damage because of the suspension travel built into these cars by the factory. they have crap for bump, but have huge rebound. why, I don't know, but they do. It sucks for performance. I also sucks when you try to lower the car more than 1" because you then run into only about 1-1.5" of bump travel, but have something like 5" of extension. Ever thought you were trying to lift a 4x4 when you were jacking your slammed Maxima up? yeeesh.

Norm Peterson

Just for a more apples to apples comparison, Herb Adams was typically working with Camaros and spring motion ratios more like 0.55. Most MacStruts are ~0.95 motion ratio. The point here being that the front wheel rate in a Camaro with 325 lb/in front springs is pretty close to 100 lb/in, which is in the same ballpark as that for the Maxima front (at 120 * 0.95^2 = 108 lb/in, if I may use your spring rate number).

I don't know where ride frequencies of 0.2 and 0.6 Hz are coming from, but that's deep into seasickness territory and quite a bit softer than old Cadillacs/Buicks/Oldsmobiles. OE ride frequencies in nearly all cars are more nearly 1.0 Hz or slightly higher. Quick and dirty numbers for the Maxima are ~900 lbs unsprung mass (curb weight only) with a wheel rate of 108, which gives just under 1.1 Hz, undamped (it's still a little over 1.0 Hz with two average size adults in the front seats). There is no firm boundary between ride-oriented and performance ride frequencies, but by around 1.5 Hz you are getting into a much more performance/less ride quality oriented setup. About where 225-ish front springs puts your 5th gen Maxima.

Lowering a strut car is always a mixed bag. The total lateral load transfer is reduced, which would improve overall grip if nothing else changed. But since the geometry starts going away on you, you need some extra spring rate just to keep roll (and camber loss) under control.


"Moment center" may not be the best term either, at least as far as most enthusiast discussions involving cornering without banking/pavement camber are concerned. But if using either it or the shorter "RC" helps get people to separate the forces that eventually cause roll to happen from the roll displacements themselves it's a step in the right direction. The longer that people stick with terminology that tempts confusion, the longer that confusion over this item will continue.

Then too, there is an approach using "anti-roll" that may be the best way to estimate suspension movements and from which you can determine (estimate may be a better word) geometry changes in independent suspensions. It's sort of like anti-squat/anti-dive/anti-lift/anti-rise turned sideways in the car to resist roll instead of pitch, and seems to be related to discussions about "force-based roll centers". Out of curiosity, does anybody [else] here subscribe to Mark Ortiz's "Chassis Newsletter"?


Norm

MorpheusZero

iTrader: (10)

Yeah, I did a few calcs with GC's 450# springs and it came out to about 2hz. That means Eibachs are about 1.4Hz, which sounds like about the right ballpark from what I have noticed when I hit big bumps. Stock at a spring rate of 120#/in would be roughly 1Hz... I am not sure where you're getting your numbers Matt.

Matt93SE

iTrader: (44)

I was pulling the frequencies out my ****...
and a 3rd gen front end is so much heavier and softer-sprung (around 1200lb on each wheel) that they do bounce about .6hz..

..I'm running 450lb/in springs on my Maxima and I notice it runs ballpark of 1hz (w/ damping) now over big bumps.. so I was simply extrapolating the crap numbers I have now to even more crappy numbers on a stock suspension.


either way, cutting coils on a Maxima is a BAD idea. these cars need much stiffer springs and only a slightly lower ride height. i.e. Eibachs or proper coilovers. most anything else lowers the car too much.

Norm Peterson

I think you're still missing something.

SQRT(386.4 in/sec^2)/(2 * pi) = 3.13 (approximately)

Frequency = 3.13 / SQRT( [Sprung Corner Weight] / [Wheel Rate] )

I do not believe that any normal production car spring gives a 40-ish lb/in wheel rate.


1200 lbs - 75 lbs estimated for unsprung weight = 1125
Say, 120 lb/in wheel rate

Frequency = 1.02 Hz


Are you taking SQRT only of the (weight ÷ spring rate) part

or are you doing a SQRT of the 3.13 constant as well?


Norm

perkman87

iTrader: (6)

on my 2000 I hadB & G springs, and for the front i cut half a coil out. It drove fine, handled great. it was 3" drop front, 1.7 rear. Looked great with my 18" zinnetti fives. Ill try and dig up a picture. The only problem was that I would go through CV joints every 3-4 months. Didnt bother me after buying the first set of cv's they were warrantied for 1 year haha, and my old shop guy would replace them for mcdonalds.

overview

IT handled great, but cv joints will goo fast esp with agressive driving.
Only reason I did this is b/c the gap for the front wheel was still not to my liking. would never do it again . coilovers only. It was a cheap fix.

All this on koni blues.

never get B & G sprigs makes the car sit bulldog

Matt93SE

iTrader: (44)

The numbers I'm mentioning are physical observations of my cars on the road, not calculations telling me what they *should* be. (not dissing the calculations at all. I'm an engineer myself and rely on my math to do the designs, BUT I often see something different when the stuff gets into the real world...)

Also, my observations will include some slowing of the oscillations due to shock damping and the rates are simply guesstimates by me based on what I've seen.

(ever watched a 3 gen with blown struts driving down the road? they look like a boat out on the lake bobbing through waves, not a car driving down the road!) As said, the car bounces something around once every 1.5-2 seconds, which is 0.5- 0.667 hz.

Norm Peterson

That's forced vibration, which differs a bit from the free vibration that most calculations provide answers for. I think that near-nonexistent damping allows large displacements over a wide range of forcing frequencies rather than only within a narrow band about the free vibration frequency, and the car is only following what the road is inputting. IOW, you're mostly looking at what the road does, not what the car would do if left to itself and excited just every once in a while.

I'm aware of the effects of damping (more of it tends to lower the free vibration frequency). It takes about 65% of critical damping to lower the free vibration from 1.0 Hz to 0.6-ish, which is hardly representative of dead dampers. But I'm just starting to absorb what forced vibration does. Dixon's Shock Absorber book (2nd ed) is out . . .


Norm