I've heard in the past that progressive rate springs can have some undesirable handling characteristics as they change rate throughout the suspension's movement arc. Is this true?

I'm looking at springs for a daily-driven MINI that is tracked 3-4 times per year. The M7 Springs are attractive as they offer good ride quality and better handling as well. Are there downsides to their progressive nature?

 

Yes, you're right; progressive rate is not really intended for hardcore
performance, but more for streetability...which I believe how over 95%
of our cars are driven. The variable weight distribution on the corners
from progressive rate springs can be controlled dramatically by using the
right rear swaybar and perhaps some struts/shocks if you see the need
for them.

Linear rate makes it easier to define how much roll, dive, squat you
may have as the rate will not change.

But for your 3-4 track days, the progressive rate springs + rear swaybar
should be plenty. :smile:

 

Sounds good. I just purchased the ALTA 22mm swaybar and am going to have it installed soon. We'll see how I feel about springs after that. I'm trying to do things one step at a time to (hopefully) complement each step with the best subsequent parts.

 

I think you may want to consider the suspension as a whole system. Adding one thing at a time sometimes can take you places that will make some issues worse before they get better. For example, adding Camber Plates, will allow you to ajust front camber, but there is a change in ride height just at the front that only coil overs can cure.....

So think about what you want to build to, and then add the parts to get there. Think of it more like you know your destination when you start you trip, as opposed to just starting the drive, and seeing where you get.....

Matt

 

Good idea, but sometimes the budget will limit how much I can do at any one time. Is it a bad idea to put on a rear swaybar without changing the springs? I haven't read anywhere that people have had bad experiences with this.

If not, I think I might just start there. Tires would probably be my next addition. Then springs, struts and camber plates.

 

I don't think adding just a rear sway bar will cause any problems. I think you'll enjoy the change in 'tightness' due to improved weight transfer.

However, I do agree with the earlier suggestion that you try to think about the suspension system as a whole. Infact, try to think of the entire car as a whole. Everything should mesh together well and be in balance. If you add more power, you should remember to increase braking ability and tweak your suspension so you can enjoy the increased power.

My car is a daily-driver, but I track the car 3-4 times a year. I like a stiffer ride, and want to feel like I'm driving a track car everyday, so I did M7 springs, Alta 22mm rear sway and rear control arms all at once. I had to "save my allowance" to get there, and it took me a while, but it was definately worth the wait. Now that I've got the suspension where I want it, it's on to adding more power with some engine mods.

Good luck - and enjoy whatever you end up doing!

- - m

 

Some progressive rate springs are actually dual rate springs - be careful as you may not be getting what you want.

From my perspective; if I could find damper/linear rate spring combo that I could live with, that would be my path. But I've certianly used pregressive rate springs in the past. One of my chief concerns with even a true progressive rate spring is that as the suspension compresses, the rate of the spring changes. This would be fine except that all four corners do not compress at the same rate; imagine driving down a road that has lots of turns with deep undulations. Each corner will potentially be at a different rate due to different compression lengths.

Bigger sway bars paired with light spring and damping rates may present a potential hazard if you're not careful; swaybars work as the car leans. the rate of lean is defined by the springs and dampers. Soft springs and dampers allow the swaybar to 'come-on-line' quicker - the car leans faster. When I say faster I'm referring to the rate of lean which springs and dampers affect. If you choose a big swaybar, you should concern yourself with slowing the rate of lean.

Ultimately, most heavier spring and dampers do not reduce total roll, just the rate of time it takes to get to total roll. This often misleads people to believe thier car rolls less. It is more accurate to say that the rate of lean is changed, or is less. I've seen plenty of 2,500lb front drive cars with near 1000lb/in springs that have have tagged bump stops.

 

I have the M7 springs on my car and love them! I have riden in quite a few Mini's with springs as part of doing big brake installs and like the M7's best for a car that is driven mostly on the street. They have a nice ride ride under normal driving but feel very sporty the second you start pushng the car harder. Yu will not feel these psrings sudendly get hard. They just feel nice and firm when pushing the car hard and have a very nice ride under normal driving.

 

I second RLmini's views.

I have an 04 MCS and added the Alta 22mm sway bar first. The car cornered pretty flat with the bar on the soft setting. I then added the M7 springs and found the car was just as predictable entering the corners and quite a bit flatter when really leaned on. The M7 springs are smoother on the highways and stiffer than stock when you get in the corners hard. The last track day one of the instructors took the car out & thrashed it pretty good and thought the car was just about neutral in handling. I could dial in a little more over steer with the bar or the tire pressures.

Since tires & wheels matter, I will note that at that time I was running the S-lites and Yokohama AVS ES100s in 205/45/17.

Bill

 

CooperSS and RLmini'

First, Strom, sorry for robbing your thread with this question.

Do either of you feel your car has any tendency toward trailing throttle oversteer with a 22mm bar? Curious???

Thanks

Michael

 

meb

Definitely not with the soft setting.

Next track day, I will try the stiff setting :smile: I hope my reflexes are up to it.

Bill

 

Bill - Any more thoughts on the suspension? Have you tried the stiff setting yet?

matt

 

I haven't tried the stiff setting yet, our next track days are Aug 13 & 14.

By then I may have replaced the M7 springs with Leda Coil overs.

We will see.

Bill

 

Correct me if I'm wrong, but don't dampers affect the rate of lean vs springs and bars affecting the amount of lean? And I think the need for lots of roll rate control (stiff dampers) with big rear bars comes from the high effective spring rate at the wheel when under cornering load. The stiff dampers are needed to control wheel movements then.

Soft springs/stiff bar/stiff shocks results in a high impact ride. Softening the shocks to match the springs results in loss of wheel control only in a corner when under load(bar rate is high). Of course stiff springs/soft shocks results in a bouncy ride all of the time due to lack of wheel control at all times.

The bumpstop observation may come from the fact that most japanese high performance vehicles actually corner on the bumpstops as very high-rate progressive springs: http://www.virkki.com/jyri/miata/bumps.html
So even if you have linear springs you may actually effectively have a progressive suspension!

 

My concern here is with using too large a rear bar, for example, with light spring and damping rates.

Soft spring rates paired with strong dampers will cause a sluggish response; the spring will not return to mean quickly enough.

Soft damping paired with heavy springs will cause an unsettled condition.

In either case, improperly matched sway bars will cause additional stabilty problems. Imagine a really large rear bar paired with the first example; sluggish ride motions and a larger, responsive rear bar...recipie for disaster.

Yes, dampers control the rate of lean, and, the characteristics of the spring's compression and rebound motions...which is pretty much what I wrote in the last paragraph. Unfortunately, I was probably in a hurry - like now - and included springs along with dampers and characterized both as controlling the rate of roll/lean elsewhere in my reply. That is incorrect.

I'll have to read the link again when I have more time. My initial reaction is one of surprise, but I don't know everything. The big question is, how does a bump stop affect spring rate when the two are not conncected physically in any way? On the other hand, if a damper comes into contact with a bump stop, it begins to stop working. If it makes a hard contact - the bumpstop is completely compressed - there is no more suspension movement, the wheel ceases to grip and control is lost - the car will skid; you might as well have a 2X4 between the wheel and car because the spring is useless under this condition. I'm very suspect of that information...

 

Isn't this what 90% of NAM users install? That is, H-Sport or other relatively light springs with a 22mm or so rear bar.

Yes and no Michael. It depends on the design of the bump stop. Some bump stops are a very hard rubber, which is only designed to keep the damper from bottoming out. As you said, it may as well be a 2x4 there because the spring rate will be infinity when the suspension hits this bump stop.

However, there are also bump stops that are designed as part of the suspension travel. These bump stops are made of a softer rubber or foam composite material, and will give a very high spring rate. The strut can compress another inch or more once it hits these bump stops.

matt

 

Yes, I was trying to explain that too large a bar with too soft shocks would be a disaster for exactly the same reason as stiff springs/soft shocks--the rate is too high for the shocks to control.

Bump stops that have an infinitely high "spring rate" when they hit will act as you describe. However Japanese sports cars, like the NSX or S2000, typically ride around barely touching their very soft and progressive foam bumpstops even at a standstill. They are not used merely as travel limiters, and do not have infinitely high spring rates. They are integral components of the suspension, and contribute as much to effective spring rate as the springs. When people lower such cars and compress the bumpstops further, the effective spring rate is higher. Uninformed people who cut down the bumpstops in these cars to "regain some travel" discover the car suddenly handles far worse than stock--and that's because they've lost the progressive characteristics of the bumpstop and end up with an unacceptably high "bump stop rate" when they hit. As you noticed, any race track at speed is bumpy enough to regularly tag the bumpstops--even with very high-rate springs. Too high a rate for the shocks is always bad, and bumpstops have a rate too. Note that 1" of bumpstop compression can equate to 2" or more of wheel travel.

So we must consider bump stops as well when we are discussing the predictability of a progressive rate suspension--particularly as polyurethane foam changes rate with humidity and temperature!

 

I just thought of something--the "rubber cone suspension" in the original Mini can be considered to be a progressive bumpstop only with no springs. Those rubber cones served as the only source of spring rate in the Mini.

 

Matt,

Isn't this what 90% of NAM users install? That is, H-Sport or other relatively light springs with a 22mm or so rear bar.
When I write, I tend to isolate relationships and characteristics, because...well that's me, and, it can be less confusing. However, placing some of my comments in a context is a little harder for the reader - I'm not easy to follow, never was. So yes to your above question. However, the H-Sports 300lb/in rear spring - correct? - and 195 front spring present me personally with some challenges; I do find the front rate, in a vacuum, too light for spirited highway driving. My overall direction was to point out that too strong a damping rate with this spring will cause a lazy reaponse. I am merely trying to throw some information out at the reader in an effort to alert he or she that this condition will occur - as will the opposite - and, that a car with lazy responses up front combined with a responsive back end might not be the ticket to fast driving. I'm not describing a well controlled neutral or slightly oversteering condition. The above scenerio would make for a very difficult driving machine. And to be very clear, I'm not knocking the H-Sports springs. They are not for me, very personal choice here. Any soft spring mated to a very strong damper will cause a lazy return to mean. This is relative as well.

BFG9000 & Matma92ser

Regarding the bump stops, well I've just learned something new. Niether my Type-R or Civic Si had these bumpstops. Explain how effective these types of bumps stops are over say 200,000 miles of driving. I cannot imaging a syntheitc foam bumpstop in operation for a long period of time. I'm still a little confused about why this type of set-up exists; limited suspension travel being one, but without seeing this configuration I'm a bit blind - I'm visual.

If there are merits to this type of system, why isn't it more commonplace - is it?...after market Mini comes to mind with its limited suspension travel.

I read the article again. While the actual bumpstop application is sinking in, why does the writer of the article suggest cutting this style bumpstop? And if so, Would the top, or stiffest rate portion, be the portion to cut? Otherwise the transition from spring to bumpstop could be somewhat abrupt...

Thanks for the clarification.

Michael

 

when I had H&R coilovers, they had built in bump stops, probably to prevent internal damage. Now I have Ledas which have no such bstops. they definitely require them, as I found bottoming out was nasty, so I am using the stockers, suitably fitted.

 

For what it's worth. I have the M7 Springs with a RSpeed 22mm rear anti sway bar... and I LOVE the combination. I did the mods at different times, do I got to gauge what each one added to the car. I love it... and find no undesirable effects of the progressive springs.

 

I totally agree. I do not like the H-Sport spring rates for my own use. Hotchkiss has a very solid rep, so I would tend to give them the benefit of doubt, but I still cannot make sense of these springs.
I used the Koni cellular polyurethane (feels like foam) bump stops on my previous car's coilover suspension for about 3-1/2 years and 50,000 miles. Then I sold the coilovers to someone else and the bumpstops were still in excellent shape.

There does appear to be very little good information on bump stop suspension tuning. Some spring manufacturers say to cut them, some say reuse the whole bump stop, some say use aftermarket...

matt

 

Matt,

I'm still absorbing the bumpstop thing. So, in the absence of a big light turning on in my head I have a couple of additional thoughts/questions.

I'm not sure, me personally, I would categorize the bumpstops you've made me - the rest of us - aware of along with what I might call a traditional bumpstop; traditional bumpstops, as jlm wrote, help prevent damper damage, perhaps, among other things. In lowered cars it is somewhat necessary to remove a portion of these types of bump stops to retain travel, to keep the suspension working - refer to my 2x4 analogy above.

The 'other' bumpstops appear to function in a very different way. I would also imagine that when modifying the dampers in that system, one would also need to explore what the new relationship with the bumpstop is???

I too used Koni dampers and bumpstops with a few of my previous cars, but these were more or less the same shape, but definately a different material. I do not beleive what I used is what you are referring to since I think both the material and shape would differ quite a bit - much more sophisticated - if it were to fill the role of a spring???

I'm just throwing this crap out there for the sake of discussion and learning.

Michael

 

For a photo of what it looks like, check out:
www.motivational.net
Click on products to see the Koni bump stops.

 

Matt,

Okay, got the skinny, or some of it anyway.

So, these are called Micro Cellular Progressive Jounce bumpers - I like the old name, but I guess different requires a different name. These, as you described, are progressive in nature.

The reason(s) these exist, I'm told, is that smaller lighter springs can be utilized in production cars. Smaller and lighter usually means less costly to build. Lighter springs provide better ride characteristics and the new fangled bumpstops provide more control in the curves - progressive damping...we've got yesterday's control along with today's ride. Progress!

I'm also informed, as was one of my questions above, that changing the spring rate will have a deleterious affect on how this sytem works; the spring frequency and the bump stop frequency are designed to work in harmony. They must be compatible or the ride will suffer. The million dollar question, does the Mini incorporate these? If so, this may explain some of the poor ride characteristics some have experienced after installing springs on an otherwise stock car...

Also, as you wrote Matt, cutting these is a no, no! Mine came with my Koni set-ups and I did not cut them...lucky me.

Regarding this subject in general...amazing what vapor escapes from my brain. These bumpstops have been around for a while.