Luis

[QUOTE]Originally posted by Schatten
[B]FYI - I put together a handling chart, its from an old Yokohama brochure.

VisualEchos

You guys trip me out. You make me happy to just be part of this organization. Keep up the good work! Can I make a suggestion? Forgive me, but I don't really plan to autocross my car. However, I am fortunate enough to live in an area with a lot of snakey and smoothe backroads... So, I am interested in just slightly tweaking my suspension to make the car more predictable and less twitchy. I am considering lowering the car(just springs), and getting the Mugen front sway bar, as well as a strut-tower brace. Beyond that, does anyone have any beneficial commentary? Thanks for any reply.

Andrew

Luis

My "beneficial" commentary would be for you to not do any of those things you propose.

The money would be better spent on a pair of new wider wheels and appropriate S02 Pole Position. I now believe that these tires are much more communicative when at the limit. They telegraph the driver much sooner about impending doom than do the stock S02, although these have substantially higher grip and would be better if you were looking at shaving the last second off your times. Just watch the front to rear traction bias.

Another good use of money is to learn to use weight transfer to help out with handling. You can xfer weight by several methods: throttle lift, throttle push, braking, shifting and steering. Some of these things can be done simultaneously like braking and steering (trail braking) or shifting and braking (Heel & Toe). So you see, it's actually quite complex.

To learn about this is easy. Get yourself on a reputable driver education school.

The S2000 will be transformed from the wild beast that is today to a tame, totally predictable, twitchy as a dead cat, rock solid car. Believe me

VisualEchos

Luis, thanks for your reply...love that "impending doom" phrase, use it quite often myself. I drive my car HARD. I live at the limit, but I don't think I would make a very good race car driver because I tend to take the "funnest" line instead of the fastest, that's why the oversteer tendancy bothers me a bit, and was looking into physical correctors. I've always viewed racing, even autocross, as work really. I drive to have fun, but I want to protect my investment...no ditches or trees for me thank you. I can talk "heel and toe" and apexes all day long, but it has to be fun for me. The tires are the most important performance part on the car IMO, and as you stated, I will be getting wider and more translative rubber in the near future. I was just thinkin' out loud, thanks again for the reply.

Andrew

Schatten

This is merely a suggestive chart. There are other factors of course - but when you are at the track, and for the most part, have these items to adjust, or even just a few, its a good reference.

[QUOTE]Originally posted by Luis
[B][QUOTE]Originally posted by Schatten
[b]FYI - I put together a handling chart, its from an old Yokohama brochure.

Master Apex

I quote this from the book of suspension tuning; one I read when I was tuning my 86' Celica GT-S a long time ago.

Because of springs in the suspension, the body cab roll or lean....The weight transfer causes body roll not the other way around....

Total lateral weight transfer = Weight Transfer(WT) due to body roll + WT due to roll center heights + WT due to unsprung weight.

WT due to body roll is a.k.a roll stiffness;
The suspension with the highest roll stiffness will receive the largest portion of weight transfer caused by body roll.
Roll stiffness can be adjusted by sway bar.

Front Weight Transfer due to body roll = Front roll couple/Front track width

Rear Weight Transfer due to body roll = Rear roll couple/Rear track width

The total of WT due to body roll is the sum of both.

Therefore, with similar suspension on front and back, the stiffer front sway/anti-roll bar would have higher tendency to understeer.

Luis

oh gosh!

As I stated before weight transfer has NOTHING to do with suspension items!!! Please guys, get over it!

You could have a rigid 1 billion pound per micron of deflection chassis and NO suspension and the same weight transfer would still occur!

I'll give another - last - go at this subject and then give up !

[a bit of generalization on]

Assume the s2000 weighs 1200kgs and is perfectly balanced. That means that, in static conditions, each side is loaded with 600kgs and that each tyre is loaded with 300kgs. OK so far?

When you turn you generate a lateral acceleration. Assume for the sake of discussion that you are going left round and round in circles with no corner entry and exit to avoid going into a another level of detail to deal with these transitions.

This lateral acceleration generates a lateral weight transfer THAT IS ALWAYS THE SAME regardless of suspension items. Let's assume it's 400 kgs.

So now we have 1000 kgs on the right side of the car (we're turning left, remember) and 200kgs on the left side. Short of designing another car with different wheel bases and mass distribution, there is no escaping these numbers.

Now comes the billion dollar question:

How do the additional 400 kgs that the right side is carrying, get distributed to the front and rear right wheel? Those 400kgs get distributed depending on spring stiffness.

If spring stiffness is the same back and fore, then the front and rear right wheels are loaded with the same additional 200kgs bringing the total load to 500kgs per wheel.

If spring stiffness is not the same, weight transfers proportionally more to the wheel with the stiffer spring.

Assuming an extreme case of having a solid suspension at the front (no spring) you would have ALL the lateral weight transfer going to the front wheel. So, in this extreme case, the front right tyre would be loaded with 700kgs and the rear right tyre with the same 300 kgs it started with. As front to rear spring stiffness bias increase, so does the weight transfer bias. Ok, so far?

And now comes the trillion dollar question:

Why would transferring more weight to the right front wheel than to the rear right wheel induce understeer? I hear you say. My teacher told me that tyre grip is dependent on the tyre load, so if there is more load at the front than at the rear the front should stick better, thus inducing oversteer, right?

Well, wrong. Your teacher sucks.

The fact is that in our conditions, there is lateral weight transfer but NO front to back weight transfer. The total weight loading the front wheels is the same as the weight loading the rear wheels and thus the right to left weight bias is now higher at the front than at the rear!

This is key to explain why stiffer front springs induce understeer.

A car understeers when the front grip is lower than the rear grip. We know grip is dependent on tyre load (the teacher was right, there) but we also know that grip is not directly proportional to tyre load. In fact, if you double the weight on a tyre you do not get double the grip. You get less than double. There is a law of diminishing returns operating here!

Thus there is less grip available if you load the front of a car with say 400 kgs on the right wheel, and 200 kgs on the left wheel, than if those 600kgs are evenly distributed (300kgs on each wheel). This is the reason why stiffer front springs will tend to generate more understeer. I hope this is becoming clear.

Let's reinforce with an example. With 400kgs of right to left weight xfer the resulting loads are:

Front: 600kgs
Rear: 600kgs
Left: 200kgs
Right: 1000kgs

If we use a car with springs with the same stiffness the resulting tyre loads are:

Front Left: 100kgs
Front Right: 500kgs
Rear Left: 100kgs
Rear Right: 500kgs


If we use a car with stiffer front springs, the 400 kgs will be transferred unevenely with a bias towards the tyre with the stiffer spring. Let's assume its 250kgs to the front and 50 kgs to the rear. Keeping in mind that there is no front to back weight transfer, the resulting tyre loads would be:

Front Left: 50kgs
Front Right: 550kgs
Rear Left: 150kgs
Rear Right: 450kgs

Now, 600kgs of load distributed the way I show above allows the rear of the car to stick much better than the front (remember the law of diminishing returns!), resulting in a tendency to understeer.

[a bit of generalization off]

This, I think, proves the point. Cdelena and Jason were right and Rev wasn't.

But beware. Real life always keeps some surprises up its sleeve! So I'm sure Rev can come up with a setup that - in real life - may disprove this point. There are just too many things at work for generalizations to be blindly applied with confidence. That, I think, does not diminuish the value of getting these things right in the first place.

[Edited by Luis on 01-18-2001 at 07:51 AM]

cdelena

Luis, thanks for a great explanation of the theoretical behavior. It is the starting place to understand the actual results, which as you mention, may not be the same.

The thing we are all anxious to see is some reports from the field. Most of us do not have the time or funding to sort out changes. On one hand we are fortunate that the car is so good in stock form that change in not imperative, on the other it does slow the R&D efforts we would like to see.

The Reverend

Once again, there is one incorrect generalization being made that stiffer springs reduce body roll. This just is not the case. My HKS springs are significantly stiffer than the stock springs and I have more body roll than stock. Since I changed all 4 springs and the ride height, I can't really base much on what effect the spring rates have had since too many variables have changed and the ratio of front to rear spring is not too far off from stock. However, I think the car has SLIGTHLY more understeer (but it's damn close to the stock balance).

Also, Luis, you keep saying that spring rates have nothing to do with front to rear weight transfer. If we took corners in a bubble with perfectly smooth roads and never used the throttle or brakes, this would be true, but in actual use you couldn't be farther from the truth. In drag racing, we find that spring rates make all the difference in the world as they enable you to transfer more weight to your drive wheels. This is why FWD drag cars often use a welded rear suspension (esentially an infinite rear spring rate) and a soft front suspension. It transfers weight to the front wheels.

Anyway, as for what you want to stiffen or soften for more understeer or oversteer, I'll wait on that until I have a chance to talk to some people on the subject.

Jason Saini

Rev... I hate to break it to you but increasing spring rates will always reduce body-roll. A swaybar is merely a form of spring. So by your logic, a larger swaybar could *increase* body roll somehow? Not on this planet.

There have been books written about suspension tuning. There are so many factors that haven't even been touched here, such as roll-couple distribution, bump-steer, camber loss, etc. To try and dissect the S2000's characteristics would require a book. And that's the rub here...

We are all trying to describe characteristics within a very narrow window of information. Inevitably something must be left out in the interest of avoiding a 2000 word post (sorry Luis!)

For some of you who are grappling with these concepts, my best advice would be to pick up a book on suspension tuning, and read it repeatedly. All of these concepts tie together, so it requires multiple reads to truly understand the dynamics involved. I'll be the first to tell you that I don't have them mastered, and I have been reading about them and racing cars for almost 10 years. Anyone in the racing world will tell you that they haven't mastered the concepts either... you are always learning something new and gaining new insight.

To ever claim that you are a suspension 'expert' is just false, as true supension experts are the guys working for Professional race teams, or desiging race cars.

There have been allot of truths tossed about in this thread, but an equal number of false information. Still more of the information is vague. I urge people not to look to this as their only source for information. Get out there and find some books on this stuff. In the meantime check out the Physics of Racing series. Don't just rely on this link, either... go out and get some books.

http://members.home.net/rck/phor/index.html

You have your homework assigment... now go study!