Case Study in Spring Rates - need feedback

[Boundary Layer]

I’ve always been an advocate of high spring rates in drift cars, as a stiffer spring rate does promote a faster weight transfer during a shift in momentum, even at low ride heights where there is less leverage – an effect caused by the spring’s greater natural frequency. I’ve also always used lower spring rates in the front than in the rear. So it was eye-opening to me when I noticed that Suzuki uses higher spring rates in the front of his drift setups. Even more eye opening was the realization that there are several people that do so.

So as a first reaction to this, I posted a blunt message questioning Suzuki’s methods – probably a mistake, I realize. Sorry Suzuki, my impulsiveness got the better of me.
But next, I got out my pencil and paper and started doing some mechanics.

I took a fairly plain example, a car with perfect 50/50 mass distribution, the actual curb weight of the car is irrelevant. Then, to turn it into a complete deathtrap, I gave the car solid front suspension – of course I know how impractical this is, it was for the sake of the example.
If such a car is subject to a lateral load, the outside front wheel will receive 100% of the cornering load thereby reducing the effect of any driver input to that wheel – whether it be steering adjustment, or acceleration in the case of an AWD machine. The rear outside wheel will receive none of the lateral cornering load so long as it doesn’t also have a solid suspension setup. The net effect of such a setup is the outside front tire will be suffer a loss of coefficient of friction relative to the rear and as a result operates at a higher slip angle than the rear tire. In more general terms, the front outer wheel is being grossly overworked, this results in a loss of grip and an increase in the amount of understeer.

This is an extreme example, generated only to simplify the math for myself – to the point that there really was none. But take this example and apply its general idea to any car that has either a relatively neutral mass distribution. Stiffer springs support a proportionally greater percentage of the cars's mass. Therefore, the effect of having stiffer front spring rates as opposed to softer ones (assuming all other things equal) will be more understeer.

Now of course, this can be remedied or overcome with other settings/tuning, and some technique, but I don’t understand the point of employing such a setting, if your desired results are the opposite.
Such a car does not theoretically handle any better (drift wise), and it certainly doesn’t hold the road any better – infact if taken far enough stiffer front springs increase the likelihood of lifting the front wheels to the point that they could lose contact with the road over a bump or curb due to their greater stored energy, while the softer rear ones would stand a greater chance of staying planted.

So I guess what I’m saying is, even after considering the idea more fully - and despite briefly discussing it with Swift , I still don’t understand why stiffer front springs are necessary. But, after doing about 20 laps in a relatively tame S2000 with such a setup, and observing its characteristics, I did cook up a few theories:

Theory #1
Having stiffer front springs than rear springs generates more understeer under lateral load. This will also translate into a car (FR) that reacts less to countersteering inputs and is more sensitive to throttle input in mid-drift. Without any physics to back this up, I theorized that such a setup could potentially yield longer smoother drifts once oversteer has been established.

Theory#2 (I find this far less likely, but it did cross my mind)
Setting the front springs of a car stiffer is an easy, effective way to trim excess oversteer. Of course, the amount of excess oversteer would be determined by the individual, and on a car by car basis. For that reason, I find this theory unlikely, since Suzuki said he generally began tuning by setting the front spring rates higher than the rear on ALL his cars.

So, to those who use stiffer front springs than rear springs, I pose the question “why?”
I’m not being critical – no quite the contrary. I’m willing to learn, as the actual logic behind it is still fuzzylogic to me.
If anyone can explain it to me, or let me know if I’m on the right track anywhere here, I’d be quite appreciative. I gave the search button a try, but was unable to find anything of relevance on my own.

 

[Delphic Reason]

You are overanalyzing this a bit, me thinks...

The stiffer front springs allow the rear to be more easily upset, making it easier to initate a drift... Also, the softer rear springs allow the rear of the car to sit a bit lower than the front (under load), which just makes for easier weight transfer and control of the rear wheels as they are sliding around (sometimes over somewhat bumpy pavement). The front springs being more stiff helps keep the front wheels in control (planted) durring this process (weight transfered to the rear)... Most of the D1 drivers use a slightly softer rear spring setting for these very reasons...

Furthermore, you have to realise neither the front nor the rear springs should be over tightened... They should be adjusted slightly offset, keeping the balance under load... If the front spring rates are set too far from the back, it will indeed cause some problems, just as it would be if the rear was set too tight in comparison to the front (causing understeer in a drift situation)...

 

[Boundary Layer]

first off, thanks for the quick reply DR
i was aware of the theory pointed out in your last paragraph, maintaining drift is all about force equilibrium. So taking extreme measures in car setup will invariably lead to a car with volatile handling characteristics. This is known to me.

I think I'm starting to understand what you mean. Let me expand on your remarks and we'll see if I'm getting it or not:
ok, so under neutral load, with stiffer front springs, more of the car's mass will be supported by the front. Now, with the load transferred closer to the rear it goes without saying that some of the load will be taken off the front springs and distributed to the rear ones (all lateral loading neglected). So the objective is to get settings such that with weight transferred to the rear, the front and rear springs are supporting the car almost equally (with a bit more emphasis on the rear).
If this is the case I'm going to find the nearest trashbin, light it on fire and then climb in, for not thinking of it myself.

however, part your first paragraph is still puzzling me a bit.
All of my intuition is telling me that stiffer front springs will have a tendency to want to support more of the cars weight. Thus, less of the front tires available grip will be available for initiating any sort of change in vehicle heading. However, you say "The stiffer front springs allow the rear to be more easily upset, making it easier to initate a drift". I'm not seeing that, all I'm able to invision is a box full of understeering. I'm thinking that technique, or other settings would have a larger contribution towards upsetting the rear tires in this configuration. The stiffer front springs only serve to take weight off of the rear tires.

 

[Delphic Reason]

first off, thanks for the quick reply DR
i was aware of the theory pointed out in your last paragraph, maintaining drift is all about force equilibrium. So taking extreme measures in car setup will invariably lead to a car with volatile handling characteristics. This is known to me.

I think I'm starting to understand what you mean. Let me expand on your remarks and we'll see if I'm getting it or not:
ok, so under neutral load, with stiffer front springs, more of the car's mass will be supported by the front. Now, with the load transferred closer to the rear it goes without saying that some of the load will be taken off the front springs and distributed to the rear ones (all lateral loading neglected). So the objective is to get settings such that with weight transferred to the rear, the front and rear springs are supporting the car almost equally (with a bit more emphasis on the rear).
If this is the case I'm going to find the nearest trashbin, light it on fire and then climb in, for not thinking of it myself.

Yes, very good...

however, part your first paragraph is still puzzling me a bit.
All of my intuition is telling me that stiffer front springs will have a tendency to want to support more of the cars weight. Thus, less of the front tires available grip will be available for initiating any sort of change in vehicle heading. However, you say "The stiffer front springs allow the rear to be more easily upset, making it easier to initate a drift". I'm not seeing that, all I'm able to invision is a box full of understeering. I'm thinking that technique, or other settings would have a larger contribution towards upsetting the rear tires in this configuration. The stiffer front springs only serve to take weight off of the rear tires.

With the vehicle under load (in a drift) the rear is going to be sitting a bit lower than the front, so the front springs need to be more stiff to keep them planted and in control (in a FR)... This does not apply as much to AWD's, which utilize very different techniques... Of course, the techniques to come into play when setting up a vehicle to drift... You shouldn't set up a car to do something that you aren't actually going to do... You should always set up a car to be effective with the techniques that you use... Of course, if you use all techniques (depending on the situation) the car needs to be set slightly more neutral to be able to be effective with a wider variety of techniques...

Furthermore, the stiffer front springs act almost as a pivot point for the rear to slingshot around... If they are set to be too soft (in comparison to the rear) this pivot point will be nonexistant (or at least reduced in effectiveness)... Think of it as a compass (geometry tool)... When you are creating a circle using the aforementioned device, you press hard on the center (the pointed non-pencil end (front wheels)), and you put slightly less force on the outside (the pencil end(rear wheels))... This allows you to control the pencil while keeping the inside edge planted... The same goes for drift settings... I know it's a bit of a crude example but it gives a decent, albeit simple, overview of the basic idea behind the spring settings...

Now that I have said that, let me state not all vehicles need to be set in this way... It all depends on the base level weight distribution, drivetrain, and techniques (among other things)... As you previously stated, many things can be done to counteract how you choose to setup a vehicle, but some things are just counterproductive and cause the user (driver) more work than is necessary...

Good topic by the way... There haven't been any good conversations like this in the drift forum for quite some time... 👍

 

[Suzuki]

DR please delete, double post.
sorry.

 

[Suzuki]

ok, let me just say this. i havent read through the whole post, nor anything you asked in the quiz thread as i dont have much time right this sec. ill read over them later. but the reason for my not replying is that my computer has been down, and theres only one other computer in the house amung 4 people.
but, wow, im suprised to see any topics started from something i do. not that its bad. i dont mind you questioning me either. i just cant be on much untill i get my computer fixed, which should be this weekend. then ill get on and answer all of your questions.
sorry for the late reply, and me not being around much. everything will be fixed soon.

EDIT: from what i can tell, this is a very good convo/topic. ill have to read over it later.
the lowest ive gone on spring rates are something like 6.5 fr 4.5 r on my AE86SS, setup for feinting.

So as a first reaction to this, I posted a blunt message questioning Suzuki’s methods – probably a mistake, I realize. Sorry Suzuki, my impulsiveness got the better of me.
But next, I got out my pencil and paper and started doing some mechanics.

no need to be sorry man. assumption got the best of ya. you assumed that since i didnt reply i was mad, or whatever. im not. ill be happy to answer any question you ask me. ill share my setups, thoughts on your setup, anything. but as i said, my computer has got a virus, so im trying to sort that out.

 

[chishifu]

Well well.. someone's taken time to really question in depth something i've been curious for quite some time. Haha, remember me asking you this several months ago DR? didn't wanna be rude and keep buggin you, but i'm back.

Anyways, i'm somewhat skeptical and won't just take at face value that under neutral load, stiffer front springs means more of the car's mass is supported by those front springs. Why would this be? I mean, you just said, it was neutral load so weight distribution is equal along the car. It's an oxymoron imo. How can neutral load have more of the load in the front? Maybe i'm just misinterpreting this.

Oh, and Tankspanker, i think i'm beginning to understand DR with his planted feel =P The compass idea actually does clear things up a bit. Your understeer and his planted feeling are the same. THe settings aren't too extreme, so during middrift, the understeer provides a solid base upon which we can adjust car-balance, etc.

However DR, I still don't seem to understand your logic when it comes to saying that a softer rear helps initiate drifts. Sure it sits lower, but weight is transferred more slowly as well, which promotes grip in the rear. It's how i'm seeing it, if you could describe the physics in a certain scenario, it would help tons.

ChiShi

 

[Boundary Layer]

Anyways, i'm somewhat skeptical and won't just take at face value that under neutral load, stiffer front springs means more of the car's mass is supported by those front springs. Why would this be? I mean, you just said, it was neutral load so weight distribution is equal along the car. It's an oxymoron imo. How can neutral load have more of the load in the front? Maybe i'm just misinterpreting this.

prepare yourself, here comes the mechanics
ok, the neutral load means that the chassis is resting on the suspension/drivetrain without any positive or negative acceleratory forces acting upon it.
now i just lost my train of thought

oh right,
So, for lets say you have some front springs with a spring rate of 6kgf/mm and rear springs with 4kgf/mm (because the numbers are nice) and the sprung mass of the vehicle (the portion the suspension hold up) has a lovely 50/50 fore/aft distribution, and we'll assume the ride height is initially adjusted to the same level at both ends so there's nothing more to confuse things. Take as a very crackpot type of example - 2 olympic powerlifters and 2 other medium build guys supporting some sort of heavy load. You would naturally assume that the powerlifters will support more off the mass than the other 2, though the other 2 do still offer some support.
Same holds true here. The front springs will support more mass because they have greater capacity to do so, despite the cars balanced mass distribution. Thats the best I can explain it with words.
I have some distributed load formulas laying infront of me from my stress analysis class involving a couple of integrals that might help explain things, but calculus is a boring topic, and doesnt generally translate well into text.

So, under the previously described neutral loading, an equilibrium point will come about when the weight is being supported 60% (30% per each) by the front and 40% (20% per each) by the rear springs. Any more or less at either end, and the springs would be being over or under utilized and would adjust to this neutral point.
Lets say you step on the gas, a positive acceleration generates a moment about the cars center of gravity and pushes the load towards the rear - loading the rear suspension. The rear springs will push back trying to re-establish the equilibrium and center of gravity. Same goes for braking - only opposite .
Hope that helps.

(I feel sorry for the readers of this thread. I'm trying to condense my posts, really I am. I get carried away.)

 

[Swift]

Well, I've learned almost everything I've learned about spring rates from DR, so no need for me to be an echo.

But just to make it really simple. Having higher spring rates in the front makes the front tire a "pivot point" for the rear. This also helps to trace the corner that you're drifting with your front tires.

Ok, just thought I'd bring it down to no-tech level. heh heh.

 

[Boundary Layer]

Well, I've learned almost everything I've learned about spring rates from DR, so no need for me to be an echo.

But just to make it really simple. Having higher spring rates in the front makes the front tire a "pivot point" for the rear. This also helps to trace the corner that you're drifting with your front tires.

Ok, just thought I'd bring it down to no-tech level. heh heh.

heh, fine
so then in trying to maintain a no-tech, or a low-tech level.
I thought it would go without saying that the front tires act as a pivot for the rear tires, being that the four tires offer the vehicles only direct contact with the road surface, and the the front tires are the tires that ultimately generate rotation in the car. The rear tires are only available to continue or promote that rotation by maintaining a condition of slip, but have no ability to directly initiate the rotation - imo, their input is all secondary to the steering when initiating a drift.
That is to say, the rear tires will only ever rotate about a point between the the front tires, as the front tires are the only other contact points on the road.
-editted in for clarity- The rear tires rotation about any other point in space is partially due to the relative motion of the front tires about that point. -end of edit-
I've stated this in other posts in other threads also.

So I fail to see how spring rates will affect the placement of this point, as Swift and DR claim. This is why I was so silent after you made mention of this on AIM yesterday Swift, I didnt understand what was significant about your comments. They seemed fairly straightforward to me.
The rear tires will necessarily rotate about a point between the ttrackwidth of the front tires. All that the spring rates will alter is how the driver inputs change the cars behavior or rotation about this point. I did some more testing to verify this for myself (and wrecked a few more decent drift settings ), and found this to be true.

-this is all in reference to an FR drivetrain, AWD behaves differently-

 

[Swift]

heh, fine
so then in trying to maintain a no-tech, or a low-tech level.
I thought it would go without saying that the front tires act as a pivot for the rear tires, being that the tires offer the vehicles only direct contact with the road surface, and the the front tires are the tires that ultimately generate rotation in the car. The rear tires are only available to continue or promote that rotation by maintaining a condition of slip, but have no ability to directly initiate the rotation - imo, their input is all secondary to the steering when initiating a drift.
That is to say, the rear tires will only ever rotate with relation to a point between the the front tires, as those are the only contact points on the road. I've stated this in other posts in other threads also.

So I fail to see how spring rates will affect the placement of this point, as Swift and DR claim. This is why I was so silent after you made mention of this on AIM yesterday Swift, I didnt understand what was significant about your comments. They seemed fairly straightforward to me.
The rear tires will necessarily rotate about a point between the ttrackwidth of the front tires. All that the spring rates will alter is how the driver inputs change the cars behavior or rotation about this point. I did some more testing to verify this for myself (and wrecked a few more decent drift settings ), and found this to be true.

-this is all in reference to an FR drivetrain, AWD behaves differently-

Hmmm....well first I'm glad you made the distinction from AWD and FR, very wise move.

You keep saying the front tires are the only ones that have contact. I assume you mean they are the ones that have traction. And that is true, however, when you're drifting correctly (DR correct me if I'm wrong), the rear tires are performing a different kind of "traction". It is this traction that, as you have described, allows you to modulate the throttle to control the speed and direction of your drift.

Now as far as the pivot point goes. Either I'm totally off my rocker, but when I stiffen up my front end on my grip cars, the car controls better. I'm not talking super stiff, but just a little more then stock on most cars. So in my experience, increasing the front spring rate a bit helps to keep grip on the front end while I'm drifting. And it does matter where that point is because that's going to directly effect your throttle control and counter steer. Obviously, every car has a different weight distribution so each cars point will be slightly different. However the principle will remain that same. Get the rear end "out" and use the front tires to trace the corner.

Did that help at all?

Oh yeah, SAVE YOU SETTINGS! 💡 this will keep you from loosing the settings that do work for you while your tweaking others.

 

[Boundary Layer]

You keep saying the front tires are the only ones that have contact. I assume you mean they are the ones that have traction.
...
Oh yeah, SAVE YOU SETTINGS! 💡 this will keep you from loosing the settings that do work for you while your tweaking others.

oh sorry, i've edited my post to make it more clear

I thought it would go without saying that the front tires act as a pivot for the rear tires, being that the four tires offer the vehicles only direct contact with the road surface, and the the front tires are the tires that ultimately generate rotation in the car.
...
That is to say, the rear tires will only ever rotate with relation to a point between the the front tires, as the front tires are the only other contact points on the road.

and yes, perhaps saving settings wouldnt be a bad idea...
hehe. well I do occasionally, just not often enough. You might think I would learn, but I have a habit of making things tougher for myself than they really need be.

I've reread this thread a few times and Chishifu's post has made me think we may all be saying roughly the same thing from about the 4th post onwards, but with some slightly different terminology - and we're getting each other's meanings crossed up. I might devote some time this afternoon to creating some diagrams to illustrate what I'm trying to say. Then we can see if we're all on approximately the same page. A picture is worth a thousand words, afterall.

I have a few more semi-incomplete thoughts that I might post later. For now, i'm going to hold off and stew on them a bit, at least until i get my diagrams up.

 

[Konig32]

ok, let me just say this. i havent read through the whole post, nor anything you asked in the quiz thread as i dont have much time right this sec. ill read over them later. but the reason for my not replying is that my computer has been down, and theres only one other computer in the house amung 4 people.
but, wow, im suprised to see any topics started from something i do. not that its bad. i dont mind you questioning me either. i just cant be on much untill i get my computer fixed, which should be this weekend. then ill get on and answer all of your questions.
sorry for the late reply, and me not being around much. everything will be fixed soon.

EDIT: from what i can tell, this is a very good convo/topic. ill have to read over it later.
the lowest ive gone on spring rates are something like 6.5 fr 4.5 r on my AE86SS, setup for feinting.


no need to be sorry man. assumption got the best of ya. you assumed that since i didnt reply i was mad, or whatever. im not. ill be happy to answer any question you ask me. ill share my setups, thoughts on your setup, anything. but as i said, my computer has got a virus, so im trying to sort that out.

This is why Suzuki is a cool dude lol

 

[Suzuki]

This is why Suzuki is a cool dude lol

heh, thanks.
computer is up and running, just need to install a few more things.
i should have aim tomorrow, so tank if you want to chat we can.
and yes save your settings if you find a good setup!! i just kicked myself in the rear for not saving my FD settings that i just made, and were quite good.

ive got a DFP now, and im lovin it! i finally figured out why i was oversteering badly on every corner. its the steering assist. i had it on sim, switched to pro and that oversteering problem is non existant like it was! major diff between the 2 with a wheel.
im out for the night.
later

 

[Ryen49]

Heres a post by TANABE USA on DRIFTING.COM. IT has alot of good professional information that may help.
http://www.drifting.com/forums/showthread.php?t=6741

 

[Boundary Layer]

thanks Ryen. that thread didnt really help in regards to the focus of this thread (Tanabe's own initial post especially), but reading through the physics in Whiskey's post over there helped me out with some other questions that have been in the back of my mind for awhile. Im going to have a look for the "Advanced Suspension Thread" that is mentioned over there

edit: and there it is
http://www.drifting.com/forums/showthread.php?t=4943
it says exactly what i said in my first post here (in regards to spring rates)

I'm by no means saying that anyone here is wrong - nor am i saying that i think is wrong to have higher spring rates in the front on a drift setup. After playing around with my own settings, and some of Suzuki's 👍 , I'm gradually coming around on this point. He showed me first hand with some (very very mushy ) Trueno SS settings that you can build a perfectly capable drifter that has higher front spring rates than rear.
I just dont feel that I'm necessarily being given the right reasons to do it in this thread. I'm slowly converting though.

My thinking has changed slightly after reading the 'advanced' thread at Tanabe, and an article by Nissan Tuning Legend, and SCC columnist Mike Kojima (I idolize this guy).
The thinking now is that the actual ratio of front and rear spring rates isnt as vital as I had initially thought. I'm starting to think it may be more important just to get each end working properly on its own, before stepping back to see which end is actually stiffer. The actual ratio will only help determine how the sprung mass is distributed over the wheelbase vehicle. The settings at each end independently determine the amount of over/understeer. Of course this will depend somewhat on the load they support....and so the tail-chasing begins
...this isnt quite what i mean, but im having problems getting the proper words composed.

This is not a complete thought yet, when i think about it my thoughts tend to run around in circles, as demonstrated. I havent expressed my thoughts nearly as well as i can explain them to myself, but it captures the basic concept that im mulling over. I've been reading a lot of articles, and I have even talked to a few of my profs (engineers) that i've worked and studied under on research projects of theirs, and this is where everything has helped to lead me. Call me compulsive but its a topic of some interest to me.

I probably just need more time and practice with some of these settings to realize their potential on my own - without getting any numbers or sketches involved.

anyways, ya, the issue is still on my mind. If others want to continue the discussion, fine by me. I think for now, I'm going to just experiment on my own and draw my own conclusions.