QA1 Spring Rate: Straight from the Horse's Mouth

[marin]

Remember how I used to hope that I can get away with a softer spring rate on my car?

I ordered QA1 Pro-Coils with Small Black Progressive Rate Springs.
I was WRONG

QA1 discontinued their Progressive Rate Springs alltogether and now sells only linear rate springs.

I gave them info on my Camaro (wheel/tire combo, want autocross/track competence) and they said they'd probably go with 450#/in linear rate springs.

They removed the progressive rate springs from their offering because they've been receiving complaints about their consistency. Now I know why Dick Guldstrand flipped when he heard I was running progressive rate. Herb Adams also mentions in his book that absolutely no one in racing uses progressive rate springs despite what aftermarket wants you to think.

I should have known, but at the time I was ordering these from (fromer) Speed Merchant, they weren't even offering linear rate springs. One more thing to go back and revisit once I have the rest of the car taken care of (but before I install SFCs)..

Another thing I am getting from them is new upper shock mount bushings (they are supposed to be only finger-tightened. oops.) and spanner wrenches that are actually usable.

Do not hesistate to post replies saying "I told you so." I deserve it

[John Wright]

Sorry marin. I know it sucks when a plan doesn't come together.
How are the shocks valved compared to the one's with linear springs? I guess, what I'm asking is can you use the shock bodies as is and add the linear springs or are they valved different to compliment the springs?

[79T/Aman]

progressive spring sound good on paper but fail in practice I do try to get a point across every now and then ( but more so lately I know) because I see more and more big ads about what amounts to just BS., just like interlock bushings HA HA! stock ones are interlock, or progressive leaf springs another sales highlight, all multi-leaf springs are progressive by their design.

[marin]

John: They confirmed that I can just swap out the springs. I just called the QA1 tech and he said that while you might need to play with the adjustment they did not change any of their internal setup when they changed over to linear springs.

79 T/Aman: I did not buy into the whole "progressive" talk, they just did not offer linear rate at the time of purchase. What really is my mistake is in being too optimistic about how soft of a spring rate I can get away with... it seems 250-350#/in really is too soft even according to the QA1 tech reps.. (With regards to interlocking, there are non-interlocking solid body mounts such as the Comp. Engineering ones which ask you to use alignment holes, so I think it does make a difference; interlocking mounts are a much tighter fit)

[79T/Aman]

Marin, not bustin you at all just kind of making a point of how some companies think they just found the majic bullet, as far as the bushing goes I was not talking about CE but the fact that stock ones are interlocking but that feature is praised as a god sent on aftermarket ones.
Yes you are very right about 350 springs being too soft because that at the wheel translates as about 140# so the spring has to compress a hole lot to support just the weight of the car at rest

[1981gMachine]

From herb adams book he was saying about leaving bump stops in due to their progressive rates when squished.

[79T/Aman]

correct Herb advocated using soft springs and if you pushed it hard the soft spring would compress to the point of contact with the bump stop but this makes the suspension unstable and if pushed realy hard the rate would skyrocket and can cause lose of control but the other thing that needs to be remembered is that that trend in suspension is based on 30 year old tire technology

[Silver73]

Originally Posted by 79T/Aman

correct Herb advocated using soft springs and if you pushed it hard the soft spring would compress to the point of contact with the bump stop but this makes the suspension unstable and if pushed realy hard the rate would skyrocket and can cause lose of control but the other thing that needs to be remembered is that that trend in suspension is based on 30 year old tire technology

This sounds important but I don't know if I understand it. Can someone elaborate?

[Batman]

The spring compresses to the bump stop. Since the spring can no longer compress, any compression is the result of the bump stop compressing. Bump stops have a MUCH higher spring rate than actual springs, so all of a sudden your handling characteristics will change dramatically.

[marin]

The idea in modern race car engineering is to run the car with the softest springs possible. This is so that the car absorbs bumps and holes instead of flies over them. Absorbing bumps and holes means that the tires are in better contact with the pavement for longer, which means more traction.

A bump stop is located on the lower control arm.
As the wheel goes over a hump, the lower control arm will raise. When the lower control arm raises, it is compressing the spring, which resists at, say, 350 pounds for every inch of travel.

If the wheel goes up too high, the lower control arm will hit the frame. To avoid this, the engineers put a rubber bump stop on the lower control arm.

If you push on the rubber bump stop it exerts resistance.
If you push on the spring it exerts resistance.
If the lower control arm is moving up, it is moving against the spring. If it moves up high enough, the bump stop will begin contacting the frame and add extra resistance, so the lower control arm will have to overcome both the spring and the bumpstop to move further up.

If you can make the bump stop from soft rubber and have it the shape so it comes in contact slowly, you have a progressive spring that is combined with a regular spring.

Here you can see Danica Patrick complain about the stock setup of Porsche 911GT3 and Dodge Viper being too twitchy, jumping around.. And this is at 160+ MPH. So if some of the stock setups are too harsh for her on 160+ MPH, it should tell you something about what spring rates are the best realistically.

The problem with our cars is that after you lower the car by an inch or so, you are left with not even an inch of travel before the stock bumpstop starts hitting the frame. Tricky.

If you, say, reduce the available suspension travel by half, you have to double the spring rate -- provided you leave everything else the same. Stiffer swaybars will limit the wheel travel somewhat since the car is not going to roll as much in turns and it's generally going to resist having one wheel compressed while the other is not.

I could write pages and pages about this, since I've done my homework, I think. I will not actually swap out the current springs until I can get decent track time with the car.

What I will probably end up doing is buying multiple springs and multiple bump stops and experimenting on track until I find what I want.

[John Wright]

Marin, While you are experimenting...Don't forget about the tall progressive S-10 bumpstops. This bumpstop will be tall enough that it contacts the frame at ride height, so rates up go very quickly as the spring and the bumpstop continue to compress.

[79T/Aman]

sorry but Danica complains about everything but again this brings up another point, THE DRIVER is part of the whole car and what may work for one driver may not be for another but the safe set up is to go with a moderate to heavy spring set up, IMHO banking on the bump stops to add needed rate is like a bandaid on a shot gun wound because the bump stop is inconsistant and will make the car unpredictable.
BTW the soft spring set up is not new technology, Herb Adams advocated it over 30 years ago but it has made a big come back in the circle track ranks in the past few years BUT it was found to be very driver and track senssitive and needs a lot of fine tunning this is why it is not the best route to go for the street the "track" is never the same and most enthusiasts don't do much tunning to their suspension given it is adjustable in any way.

[marin]

Okay, here's a good quote:

"The current consensus in racing is that the best handling comes from a very low spring rate with high roll stiffness -- whether from stiff anti-roll bars, a wide spring base, or by keeping the center of gravity and roll center together."

Paul Van Valkenburgh: Race Car Engineering and Mechanics

ISBN 096174250X

This guy worked in Chevrolet Research and Development and people in Penske Racing, Mark Donohue, etc. so I think I should be taking his advice seriously, right?

John, I agree with T/Aman here, using bump stops for the whole length of suspension travel I think is too unreliable --- if the bump stop comes off or starts wearing out the ride would be impossible (or even dangerous). I would keep the bump stop on the more extreme ends.

Using bump stops as a part of suspension will make the suspension a little less consistent, but I will try to avoid higher spring rates as much as I can, because driving this car even with the 250-350#/in and all-solid suspension is a rough enough experience that makes me keep my hands firmly on the steering wheel even in normal street conditions.

I find it hard to imagine that you would get traction on anything but a glass smooth race track with springs over 450#/in. I mean, seriously, did you guys try things out on the track/skidpad? Does anyone have any numbers, videos, etc? I'd love to even just watch a video of how a car with a 400+#/in spring acts on a bumpy street. I imagine it wants to just fly over the bumps and maintains minimum traction.

Another note: There is no rubber or polyurethane anywhere in my active suspension. It is all heim joints and solid bushings -- no room for flex anywhere, except in the chassis but I cannot afford to put SFCs until I tuned everything else.

(Oh, and as far as Danica goes, she has good things to say about Lamborghini LP640 ... I know, who wouldn't... and she also likes the setup of the Z06 Corvette (except she wishes it had more power in the top end ), so I think there's more to it than her just being picky...)

[1981gMachine]

I think the idea behind stiffer springs is that, you would think they keep the tires planted at all times. But Softer springs let's your suspension work the way it's designed. I myself have very soft springs on the front with all poly bushings in the car. I really need to get different springs for the rear as they are too stiff.

In my head i see this: A car is going down the road, and hits a pot hole. The stiffer springs plant the tire into the hole quicker then the softer springs. Which makes for a harsher ride. That's what I see and can't imagine anything else happening.

[marin]

1981gMachine,

Actually, a car that goes over a pothole "falls" into a pothole or flies over it, springs are not really "too fast" or "too slow" to accommodate the pothole.

What you should be imagining is a car going over a bump and the wheel temporarily raising to accomodate a bump while the rest of the car remains flat (level).

With a spring that's too stiff, the car would raise over the bump together with the wheel, making the whole car lean to the side, losing traction on the opposite wheel. The opposite wheel loses traction because it leans to the outside (de-cambers), reducing the size of the tire-ground contact patch thus reducing available cornering traction.

I am kind of new to all this stuff, so if I got this wrong, someone correct me, but things are usually tuned for bumps not potholes.

By the way, I think I can walk through the pothole example and show you how it still works out the same as going over a bump, but it's way more complicated, it's kind of like the car encountering bumps on three wheels and being flat on one (the wheel in the pothole) ... except it's not. I am going to leave the rebound rate of the shock out of this story for now.

You usually hope that the holes in the road are smaller than the wheel width, and most of the time this is the case -- the car just goes straight over them, so usually potholes are an anomaly, not something you tune your suspension for. You want to think about bumps, not potholes, as those are far more prominent and they can be as small as you want them to and will still make your wheel raise.