sig_a

Doesn't an over-stiff front axle produce understeer? Assuming the front is too stiff causing excess understeer, softening up the front axle will help. Overdoing it will result in snap oversteer.

I've listened to many 911 classroom instructors advise reducing throttle to correct understeer at mid corner on long, steady-state turns. This "fix" will unload the rear, thereby reconnecting the front resulting in tighter rotation around the shorter, inside line. What they're getting at is many times the solution is driving technique rather than suspension set-up.

Jeff Lamb

I was thinking about the "steady state" handling issue a bit further and I think for most of us, we don't get to really focus on this type of car setup issue very much because we are all rightfully more focused on corner entry and corner exit issues. At many of the road courses we run, there aren't many corners where we have to deal with the "steady state" phase of various corners because most of the corners don't really have much of a "steady state" phase to them. Like I mentioned earlier, for many corners, we transition fairly quickly from the corner entry phase to the corner exit phase with relatively little time spent in a "steady state". Despite this, I still think this is a good issue to debate because we can learn something from it and we will find tracks where knowing how to best setup the car for key corners that need good "steady state" or "mid corner" handling will be a big help.

Therefore, to try to help guide everyone's feedback in the proper direction, lets focus on car setup issues to achieve the maximum mechanical grip in the "steady state" portion of a corner and avoid introducing other variables such as aerodynamic downforce, driver skill, etc. The best example I can think of where setting up the car purely for its best "steady state" handling would be a time trial at a track that is perfectly round and has no banking. In this case, I am assuming that any given car when properly driven would be at its absolute fastest when both the front and rear are gripping equally and any attempts to go faster would result in the car sliding directly sideways (meaning the car is setup perfectly neutral and has no understeer or oversteer).

If you were testing your car at this perfectly round and flat track (or a giant skid pad as JustinL pointed out) and you were experiencing understeer, what can be done to change the car setup to dial out the understeer in your quest to achieve the maximum mechanical grip that can be obtained from a car setup with a perfectly neutral balance?

Jeff

beentherebaby

For those who are serious about proper suspension set-up I'd suggest any of the following references before your start changing things:

Chassis Engineering by Herb Adams

How to make your car handle by Fred Puhn

Competition Car Suspension by Allan Staniforth

Any of Carroll Smith's "Engineered to..." series of books such as "Engineer to win"

It's real easy to get off in left field and create a monster vehicle to drive if you don't have a good understanding of the complex interactions of changes to the suspension. These references will give you the basics, not the solution which can only be derived from actual testing IME.

AudiOn19s

While I think there are general guidelines this thread highlights the fact that nothing is ever completely cut and dry.

Getting someone with knowledge that knows the platform you're driving or knows how to setup a car is priceless.

E46 M3's are a good representation of something is not as it seems. They understeer EVERYWHERE in stock form. The solution for that car is actually more front spring and big front bar. I still have relatively soft springs on the front of my car but a massive sway bar. The combination of the car being heavy, not having enough roll control in stock form and having a terrible camber curve in the front results in loss of front contact patch. By adding stiffer springs, sway bar and adding negative camber you keep contact patch loss at a minimum and gain front grip despite the fact that comparatively the front is much stiffer than the rear. A few here have riden in my M3 and it doesn't drive half bad now.

Andy

onefastviking

+1

It's really harder than reading a book. You must do many years of trial and error before you begin to understand it. Hiring a pro will help you understand it much faster. Well worth every penny.

Set up and changes require many variables to be addressed, the largest, imho, is WHERE in the corner you are feeling what. Corner entry, mid corner, and corner exit all require specific different adjustments.

Thats all for now, it's late and most really don't seem to be getting it. It really is one of those things that either you get it or you don't and have no clue. It's ok, it took me many years to get where I am and I know there are others that know more than I. I do ok, and I learn more all the time. The guys I set up,coach, and build cars for all seem happy with the results they get. Thats good enough for me.

Veloce Raptor

This.









Professional Racing and Driving Coach

M758

I have been carrying that magazine around with me to the track since april 2006. Very handy. My last track day I used that article to help resolve my LSD balance issue. I had my 944 balance well with an open diff, but never quite dialed it in with LSD. I reread that article and made 1 change and it transformed the car. The car ran great right up till I shifted into 3rd gear at 100 mph. ops:



Really that cheat sheet is guide. Read the article and you will see that there is little that is cut and dry with suspension tuning. You need to be prepared to try things. Adjust the car and refine technique. The cheat sheet helps, but it cannot solve all handling issues so don't expect it to. I have been using that for years as guide. I use it to first think about where the car is not working the way I want it too. I first try to tweak lines and see if that helps as I can do that from lap to lap. If not I will consider the response of the car and possible changes listed. Then make a change and try to feel what is happening. Did the change work the direction intented? Did it go too far or not enough? What did that change do every where else on the track? If my problem was a lack of stability can I as driver now learn to push harder to take advantage of the extra control. I have always believe if the car is completely undercontrol you are not going fast enough. So if I adjusted the car under control I need to push to go faster.

onefastviking

All very true about this article and all the books that are out there and available.
You have actually summed up why I so strongly reccommend hiring a pro coach. You look at these items and are not sure if you need a driver change in line, car set up change, car maintenance issue (loose diff, worn out bushing,etc) or what, so you start making changes usually with mixxed results.
Someone like myself or VR, (and I know there are many others out there but VR is the example I run into on a regular basis since we share home tracks) we listen to what you are saying about the car, then ask VERY specific questions to hear the drivers opinion of what is happening, then we review Data and video to support or possibly add some more information, or even disprove what the driver really "thinks" is happening. Then once we are armed with that knowledge as well as already knowing as complete a history of the driver as possible we can then decide if we have a car issue, or driver issue, or track issue and make the appropriate reccomendations. It usually results in a quicker and more positive result. Go figure right.

I can not even begin to count the drivers over the years that have told me they are flat out, seriously, just to look at the data or video (watch the tach) and see something different than they "think" they are doing. A quick review with them, some minor driver adjustments, and faster laps always follow. I won't push a driver over their comfort level as well, slow easy steps always works best as the comfort levels increase then so do the results.

Hope that helps,

sig_a

onefastviking:

You bet ----- the diagnosis has to be correct. Sometimes it's obvious, most times it's not.

Since we are talking about mid corner understeer, I would diagnose this as an extreme example being caused by too much roll stiffness in the front suspension. Fred Puhn says "The car would corner flatter if more roll stiffness were added to the rear suspension--and cornering speed would be improved." (see page 44 "How To Make Your Car Handle) That may or may not be the total remedy, but isn't Mr. Puhn basically correct here?

onefastviking

It looks like in his example he is refering to a car that is lifting a wheel a considerable amount and I would recommend other changes there.
When discussing a small oversteer mid corner I would just tighten the front bar, so long as it wasn't driver induced nor track induced.
If doing a new set up on a car I would probably change spring rates to see if I could improve it there, although a number of other variables would need to be considered before making that recommendation.

Larry Herman

I tried to answer Jeff's question about steady state cornering and it evolved into what will be an article, but I couldn't get it finished, so here is the first part.

-------------------------------------------------------------------------------

One of the biggest difficulties in understanding how to improve or adjust the handling of one's car is the comprehension of grip: what it is, how it works and how to work with it. When I talk about balancing the car to an advanced group of drivers, I like to present the basic premise, devoid of aerodynamics or other influences, that a car has the most grip when it is sitting in the paddock! Pretty profound huh? Each axle has fairly even weight on both sides; therefore the tires have the same pressure against the tarmac, so they are both contributing equally to the grip. Why is this so? Because of the fact that as you increase the load (downward pressure) on a tire, its grip (ability to resist sideways pressure) will increase as well. The grip increases but not quite as much in relation to the load, and this is the phenomenon known as diminishing returns. When a car is cornering hard, transferring most of its weight onto the outside tires, it actually has less grip. It is also the biggest reason that light cars generally handle better than heavy cars.

This single most fact is what balance is all about, and why a change in roll rate, either accomplished through springs, sway bars or even through shock dampening can make a profound difference in the understeer/oversteer characteristics of a car. As the car accelerates, brakes and corners, it is constantly transferring weight from back to front, and from side to side. This changes the respective balance of grip from front to rear, and creates the tendency for over or understeer. And depending on the car’s front and rear roll rates, and the amount of weight being transferred, the change in grip can be pretty dramatic.

Let’s take a simplistic example to illustrate what I am trying to explain. A Boxster (or Cayman) is a fairly neutral car with about a 50/50 weight distribution and similar sized front & rear tires. In Jeff’s example of a “perfect skid pad” as speed is slowly increased, more weight will be transferred from each inside tire, to each outside tires until they get to maximum grip. If the driver continues to feed in a little more speed, the slight shift of weight on the back tires should provide enough extra grip so that the front will start to slide (understeer). If the driver lifts off even infinitesimally, the weight will shift back towards the front and the rear will begin to slide (oversteer). Most drivers have a pretty good grasp of this. But now how do we tune this so that we can still have a little oversteer as we are adding throttle? By adding roll stiffness to the rear, or reducing it at the front. I am a big believer of adjusting the end of the car that I want to control, so if I want to add oversteer while the car is accelerating, I will stiffen the back end.

How does it do this? In my classrooms many hands get raised; “because it transfers more weight to the outside tire” is the typical answer. And that would be wrong, because there are only 3 things that affect the amount of weight transfer in a car: #1 weight, #2 center of gravity and #3 track. So what is going on here? Increasing the roll stiffness at the back of the car will help keep the overall platform more level, keeping more weight on the inside front tire, thereby increasing the grip at the front of the car.

winders

I'll probably get in trouble for this....but....

Larry,

"Load transfer" is a more appropriate term to use than "weight transfer". The only time weight transfer actually happens is when the center of mass is moved relative to the wheels.

Weight is a force and is equal to mass * gravity. The overall load (force) can be greater than the weight (mass * gravity) of the car. For example, a car that weighs 2000 lbs generating 1.2g's of lateral acceleration has a load equal to 2400 lbs shared by the tires.

The car doesn't suddenly weigh 400 lbs more because it is pulling 1.2g's in a turn. You shouldn't use weight when describing loads because it is derived from mass assuming 1g.

Scott

sig_a

Larry, Thanks -- your efforts are very helpful.
------------
Fred Puhn writes in bold: " Here is the secret of chassis tuning:" (pg. 41 How To Make Your Car Handle)

THE SUSPENSION WITH THE HIGHEST ROLL STIFFNESS WILL RECEIVE THE LARGEST PORTION OF WEIGHT TRANSFER CAUSED BY BODY ROLL.
------------
(Scott: It is helpful to think LOAD when reading WEIGHT)

winders

What Fred says is true. Although he also incorrectly uses the term "weight transfer".

Scott

JustinL

So the original comment that sparked this discussion was to dial out front understeer in mid corner you want to stiffen the front spings or ARB. Is there any truth to this?