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Old 12-24-2001, 07:34 AM
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Default ITR vehicle dynamics

Don't know if this is a repost?

If so I'm sorry,"not really." I feel that this post answers alot of questions for newbies and vet's alike. There may be some interpretation but, It's definately worth reading.

recently posted by "Yoda is god" on SHO:
Understanding Vehicle Dynamics ...ITR's

Not sure if you guys have seen this. I posted it in the Si/SiR forum, but it was post on another board for ITRs.

Understanding Vehicle Dynamics

Before we start we have to have an explanation of common vehicle dynamics terms. We had better understand the
common ways to describe the different aspects of vehicle dynamics before we even turn a wrench, so here we go:

Friction circle: This is basically a vehicles performance envelope. It's expressed in lateral G’s, accelerating and braking
G’s. When graphed, the friction circle looks like an egg with the X axis lateral G’s and the Y access braking and
accelerating G’s.
Understeer: This is when, at the limit of vehicle traction, the front of the car slides first before the rear. Race car drivers
call this "push". This is the way that many cars come set up to behave from the factory as it is the most predictable for
average drivers (like the Type R). The crash mode for understeer is that when the limit of adhesion is exceeded, the car
will plow strait ahead off the road nose first. This is not the fast way to have your car set up, but is best if you are an
inexperienced driver. When the car understeers you should regain control if you let off the gas, unless of course you run
out of road first. (That is what air bags are for.) It is not efficient for extracting maximum lateral G’s because the car will
dynamically use the front tires excessively for turning, overloading them while the rear tires basically just hold the back
of the car up - scrubbing off significant speed. Front wheel drive cars tend to exhibit understeer as the final terminal
mode of balance.
Oversteer: This is when, at the limit of vehicle traction, the rear of the car slides first before the front. Race car drivers
call this "loose". The rest of us call this "spinning out", "spinning a shitty", "doing a brodie" or even crashing. The final
crash mode of oversteer is backwards, tail first into the woods or in the worst case spinning round and round with the
driver as a helpless passenger. Since the infamous days of Ralph Nader and the Corvair, most auto manufactures avoid
oversteer like the plague. Oversteer is difficult for an inexperienced driver to handle because recovery requires judicious
use of countersteering and throttle feathering to control; fine motor skills that only some of us can deal with. Although
oversteer looks neat and macho it is really a slow way to drive except in maybe pro-rally on the dirt . Oversteer is slow
on the pavement because hanging the tail out bleeds off a great deal of speed going through a corner. Conserving the
momentum is the fast way around as turn.
Neutral: This is the fast way around a turn where all four wheels slide evenly. Since the total friction circle traction of
each tire is being used, all the available grip that the tires have is being put to the ground. Racers call this "drifting".
This not to be mistaken for the idiotic Japanese Option Magazine video stuff which makes a mockery of proper driving
technique. Neutral is the fast way around a corner most of the time. Neutral is also the hardest handling mode to
achieve for the suspension tuner.
Polar Moment of Inertia: Or PMI as we will refer to it, is a description of how a cars mass is distributed along the length
of the vehicle. A car with a high PMI is like a rear engine, rear drive car like a Porsche 911 or a front engine, front wheel
drive car like our beloved Type R, same thing only the poles are different, so to speak. A car with a low PMI would be a
mid engine car like a Boxster. Low PMI cars have most of their mass about the middle, high PMI cars have the mass at
one end or another. Low PMI cars are the easiest to get a neutral balance out of due to the balanced, centralized mass.
High PMI cars like to oversteer, in the case of the 911 or understeer like our cars. To get a feel for this phenomena, hold
a bowling ball in one hand and rotate it back and forth by twisting your wrist. Now get a set of dumbbells of the same
weight, grab the middle of the bar and do the same thing. Bet the bowling ball wants to rotate easier right? Guess what
type of car will be easier to get neutral!
Slip Angle: This is the wonderful thing that allows us to tune our cars suspensions despite the design limitations caused
by the PMI. Proper manipulation of slip angle is the great equalizer and is what suspension tuning is all about. Slip angle
is the difference in which a cars wheels are pointed vs the angle that the tires contact patch is placed on the road. The
main thing that affects slip angle is the manipulation of the individual load placed on each wheel while cornering. This is
the key for suspension tuning. A front wheel drive car has most of the weight on the front wheels. So the front wheels
run at higher slip angles and develop understeer. Conversly the same for a rear wheel drive, rear engine car developing
oversteer. That is also a reason why a mid engine car with equally loaded tires will be more or less neutral. Slip angles,
weight distribution and PMI are the main factors in how a vehicle will handle.
Because Type Rs are front heavy, front tire overloaded, front wheel drive cars, does that mean that we are condemned to
econobox hell for driving fun? Heck no! By design we can not change the basic layout of our cars to significantly change
the PMI or weight distribution but we can sure tweek the slip angles of the tires to achieve world class handling out of
our killer compact sport transportation units.

The easy way to tweek the slip angles are with anti-sway bars and springs. Shock absorbers, going against what people
think that they do, are not really for changing the handling balance. Shocks mostly act as spring dampers and affect
understeer/oversteer balance mostly only in transient (which is big word for a change from straight line travel to turning)
maneuvers like initial turn-in and zig zaging around slalom cones.

Changing to heavier springs changes the slip angle differential by resisting the cars tendency to roll on the end of the car
that they are installed on. The resistance of the heavier spring to compression causes more weight to be transferred to
the outside wheel of the end of the car that they are installed on as the car tries to lean over in a corner. This causes
that wheel to proportionally run at a higher slip angle than it normally would. If you put heavier than stock springs in the
rear of your Type R while not changing the spring rate of the front, the car would tend to understeer less.

Anti-roll bars work in much the same way. Antiroll bars are torsion bars attached to the cars chassis and are linked to the
right and left control arms. Antiroll bars offer resistance to independent side to side wheel movement. This is how these
bars limit sway in the turns and hence their name. While limiting roll, the bars also cause weight transfer to the outside
wheels. By altering the diameter of the antiroll bars or installing them where there were none before adds yet another
chassis tuning element. If you were to increase the size of the rear antisway bar on an Type R you would be increasing
the amount of weight transfer to the outside rear wheel, thus causing it to run a bigger slip angle. This would give you
more oversteer.

Tire pressure also can affect the slip angle. Higher pressures reduce the slip angle and lower pressures increase it. A
great deal of suspension tuning can be done for free by adjusting the tires pressure.

Alignment also has a great deal of effect on a vehicles handling balance. Caster and camber affect how a tires contact
patch is positioned on the ground by compensating for a tires tendency to flex and lift the inside tread while cornering,
By helping keep the tread flat, these settings can increase or decrease the available friction circle traction on an end of a
car thus affecting balance. Toe in or out can affect balance also by changing how a vehicle turns in
Old 12-24-2001, 07:36 AM
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(continued...)

Suspension adjustment-->Affect on vehicle balance--> Symptom of TOO MUCH adjustment

Front spring rate increase. More understeer .Terminal understeer, front of car hops in corners, excess wheelspin in FWD
car

Front spring rate decrease. Less understeer. Too much oversteer, oversteer then understeer if spring is so soft that the
car bottoms under lean, car bottom excessively with a jolting ride

Rear spring rate increase. More oversteer .Too much oversteer, hop in corners, twitchy

Rear spring rate decrease. Less oversteer. Car understeers, if way too soft car understeers then oversteers as car
bottoms out under lean, car bottoms out excessively with a jolting ride

Front antisway bar stiffer. More understeer. Terminal understeer, Lifts inside front tire off the ground which can cause
massive wheelspin, also not good for most effective tire usage as inside wheel is now doing nothing

Front antisway bar softer. Less understeer. Oversteer

Rear antisway bar stiffer. More oversteer. Big time oversteer, Can cause the inside rear tie to lift off the ground which is
not two bad on a FWD car.

Rear antisway bar softer. Less oversteer. Understeer

Front tire pressure higher. Less understeer. No traction as tire is crowned so more understeer, bad wheel spin, jarring
ride, center of tires wears out

Front tire pressure lower. More understeer. Edges of tires wear quickly because tire is folding over, feels mushy, tires
chunk because low pressure means more heat build up

Rear tire pressures higher. Less oversteer. No traction as tire is crowned so more oversteer, bad wheel spin on RWD cars,
jarring ride, center of tire wears out

Rear tire pressures lower. More oversteer. Edges of tires wear quickly because tire is folding over and cupping upward,
feels loose in back, tires chunk because low pressure means more heat build up

More negative camber (Front) Less understeer .Poor braking, car is road crown sensitive, twitchy, tires wear out on the
inside edge

Positive camber (F) More understeer .Poor braking, car is road crown sensitive, twitchy, tires wear out on the outside
edge You almost never want to have positive camber unless you are a dweeb

More negative camber (R).Less oversteer, more rear grip, less breakaway warning when limit is exceeded/-3 degrees.
More oversteer, car feels twitchy in back, tires wear out on inside edge

More positive camber (R) More oversteer Car feels twichy in the back, tires wear out on outside edge

Ride height too low Car twitchy with unpredictable dynamics

Toe-in front. Car is stable while going straight. Turn in is average. Car has slow twichyness under braking, feels odd, kills
the outside edge of tires.

Toe-in rear car is less likely to suddenly oversteer when throttle is lifted. Weird slow rocking movement in back, feels
slow but still unstable, wears the outside edge of tires.

Toe-out front. Car turns in well, works pretty good in FWD cars as they tend to toe-in under load. Car is real twitchy
under braking, car is very road crown sensitive, car wanders on straight road, kills inside edge of tires.

Toe-out rear. Helps the car rotate, useful on tight low speed courses and slalom events. Not to good for street driving,
causes lift throttle oversteer, car makes violent side to side rocking motions in rear, tires wear more on insides
Old 12-24-2001, 07:37 AM
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Default Re: ITR vehicle dynamics (1GreyTeg)

damn anton...just print it out and bring it over...i'm too lazy
Old 12-24-2001, 07:37 AM
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(continued...)

Basic Rules (again adapted from material from elsewhere - edited for content)
Here are some general basic rules if you want to improve your cars handling:

If you race in sanctioned competition, read your rule book before performing any modifications at all to your vehicle. It
would be a pity to buy a fortune in trick parts only to have them declared illegal by an official. Beware of SCCA’s Street
Prepared rules as many hot and popular street car mods would put you out of this class.

Do not lower your car too much! This perhaps is the number one no no. It is a symbol of a truly ignorant person with
regards to suspension dynamics. Lowering looks really cool and can make a significant improvement to a cars cornering
capability but going too low is detrimental to both handling and even safety. Going too low can cause bumpsteer, where
the tie rods and control arms are traveling different arcs resulting in the wheels steering themselves with no steering
wheel input. When a car is so low that the suspension bottoms under cornering loads, the end of the car that bottoms
first will violently slide out. Super low guys are convinced that they are driving super touring cars but if you take them
out on the track they will suck incredibly. Our Type Rs have a short travel suspension as it is and cannot take being
lowered more than 1.5-2 inches at the most. So install some good springs such as Eibach, H&R or Ground Control and DO
NOT CUT THEM MORE TO MAKE YOUR CAR LOWER. If you have the Ground Control springs do not adjust them to lower
your car more than two inches except if you are going to compete in car shows where the car will be a stationary display.
You want to maintain at least 1-3/4" of travel.

Buy and install matched components from a single manufacture. For instance do not put H&R front springs in with Eibach
rear or a Suspension Techniques front bar with a TMC rear. Suspension manufactures usually offer these parts as a tuned
set with rates, etc. made to match each other. So unless you really know what you are doing don’t mix and match. Good
stuff for our cars is made by Eibach, H&R, Mugen, Spoon, TEIN, Ground Control and Comptech.
If you are using high performance springs, try to wait until you can afford the shocks also. Performance springs store
more potential energy when they are compressed. They need a shock with more rebound damping to keep the car from
bouncing all over the place after you hit a bump. Really good shocks like Koni or GAB’s are adjustable so you can tune
your shocks to the springs. Performance springs with stock shocks usually feel floaty on high speed undulations. I find
that that feels a little spooky. Performance spring’s quicker rebound characteristics also seems to wear out stock shocks
quickly making them get super floaty. I prefer Bilsteins because of their auto adjustability and durability.

Limiting body roll is good. Our Type R’s sit high, and have fairly soft springs from the factory. They roll quite a bit. Install
stiff springs and swaybars with matching shocks, and lower the car to a reasonable level. Limiting roll keeps the weight
from transferring excessively, allowing the inside tires to work more in a turn. Limiting roll also helps keep the car from
bottoming in a turn and keeps the car out of the bumpsteer zone. Type Rs like ours do gain some negative camber under
roll either so limiting roll helps keep the tires from folding over.

Having adjustably is good. Having the ability to adjust shocks, camber and toe is very useful when trying to extract G’s
from your car. On a showroom stock racer optimizing the alignment and tire pressures alone can make the car corner a lot
better and have faster lap times. As front camber is not adjustable on our cars (unless you purchase a kit) it is important
to make it so. Mugen and Skunk make high quality camber kits. These will slightly harshen your ride but will sharpen turn
in due to the elimination of squishy rubber with metal bearings. Rear camber adjustably is not critical on most FWD cars.
If you are racing Solo II stock class or Showroom stock and don’t want to cheat, you can get about ½ degree more
negative camber by loosening all of the suspension bolts and having someone hold the wheel in the negative position
while you retighten everything. No one currently makes an adjustable set of antisway bars for our cars but Ground
Control can make you some custom ones if you are willing to send them your car for a few weeks. In fact, it would be no
problem for just about any decent race shop to whip some up.

Align your suspension and optimize your tire pressures. In the previous paragraph, I said that alignment and tire
pressures can make a huge difference. IT IS TRUE! If you are poor, you can still make big improvements in your cars grip
by just playing with tires pressures and the car’s alignment. Try the poor boy technique and dial in some front negative
camber, increase the front tire pressure, decrease the rear and set your toe. Boy will you see a difference. Try to find a
place that does racing alignments near your house as alignment is where people really get ripped off as it is almost
never done correctly. Most hacks just throw a car on the rack and if it falls somewhere within in the wide factory specs,
don’t touch a thing. What you need is a blueprint type alignment where the suspension is adjusted exactly to spec. Most
repair shop dorks don’t understand this and will argue and tell you that that is not necessary. A race prep shop will
understand. When your car is aligned, it should be done with your weight in the drivers seat and with the technician
bouncing the car after every adjustment to settle the suspension. Set your tire pressure before you take the car in.
Remember that you must realign the car if you lower it!

Cut your bumpstops. It is important to cut the rubber bumpstops on your shock shafts to get a little more wheel travel
out of lowered suspensions. Cut an inch or one segment out of the front and rear ones. Do not go crazy and remove the
bumpstops or cut off more than half of them away. That can cause the suspension to bottom out possibly breaking it. If
the car suddenly gets real bouncy, that is what probably happened. The only solution is to get new shocks.

If you are racing, run R compound tires on the widest wheels that will fit. These tires can get more that 2 seconds for
every 30 seconds on a slalom course or 3 seconds for every minute on a road course. These tires usually have a vestigial
tread and a really short tread life so you don’t want to run these as a daily driver tire. Also R type tires only have about
10 good heat cycles in them so their stickiness will decline quickly in daily use, leaving you with a fast wearing, not so
sticky tire.

Don’t over tire or wheel your car. Our cars will go the fastest and handle best with the widest, lightest 15 inch wheel that
will fit. 16, 17 and 18 inch wheels which look radical, really slow the car down because they are heavy and the bigger
diameter screws up the gear ratio. There are few R type tires out yet in these big plus sizes to my knowledge yet either.
The widest tire that you should run unless you have a turbo or some other ungodly power is a 205. Wider tires will result
in more drag that our relatively low power engines can accelerate. A 205/50-15 works well in most cases and a wide
variety of R compound tires are available in this size. The maximum rim width that the Type R can run is 7 inches with a
43-50 mm offset. Since this always comes up, the bolt circle measurement on our wheels is 5x114.3 mm. The
competition wheels that impress me the most are the Spoon and Mugen wheels. These wheel are forged so it can be
much thinner than a cast type wheel. It weighs like 11 lbs which is twice as light as a regular wheel. Any forged or
semi-forged wheel under 13 lbs is great. Remember that 1 lb on the wheel is worth about 10 on the car due to the
wheels rotational inertia.

Tire pressures rise considerably during a run/race. Take notes of your tire pressures before and after every run so you can
start with a cold pressure that will increase to your desired hot pressure during a run. Bleed your tire pressure down after
every run to keep it constant.
Old 12-24-2001, 08:09 AM
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Default Re: ITR vehicle dynamics (1GreyTeg)

Good info.

I would suggest everybody read <U>Going Faster: Mastering the Art of Race Driving</U>. This is the book for the Skip Barber Racing School and is an amazing resource that is full of information regarding vehicle dynamics, car control, and track driving.

I give it

Amazon: http://www.amazon.com/exec/obidos/AS...504602-8707866
Old 12-24-2001, 10:44 AM
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Default Re: ITR vehicle dynamics (Flux)

Good info.

I would suggest everybody read <U>Going Faster: Mastering the Art of Race Driving</U>. This is the book for the Skip Barber Racing School and is an amazing resource that is full of information regarding vehicle dynamics, car control, and track driving.

I give it

Amazon: http://www.amazon.com/exec/obidos/AS...504602-8707866
When Skip was asked why he didn't make this book required reading for his driving school students, he said that if they read the book there would be no need to attend his class.
Old 12-24-2001, 11:19 AM
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Default Re: ITR vehicle dynamics (1GreyTeg)

Holy $hit did you type all that???


btw good reading...
Old 12-24-2001, 11:35 AM
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Default Re: ITR vehicle dynamics (Bbasso)

LMAO......damn he must have been bored. I hope you copied and paste
Old 12-24-2001, 01:42 PM
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Default Re: ITR vehicle dynamics (ITR1150)

This not to be mistaken for the idiotic Japanese Option Magazine video stuff which makes a mockery of proper driving
technique.
This thread was good till I read that....now it's all crap no matter what he says....
How idiotic is that comment? Has anybody ever tried drifting like those "idiotic Japanese Option Magazine video" guys?

I'll bet more than a few of us will end up crashing and burning before we realize how much finite control it demands outta "idiotic driving"

RagingAngel who takes offence to ignorant comments such as these.....

Old 12-24-2001, 01:51 PM
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Default Re: ITR vehicle dynamics (RagingAngel)

Understood R.A.,

Thats why I wrote in the beginning that it's open to interpretation. I also STILL think that it is some very important useful information.

I did NOT write this and neither did Yoda is God on SHO,"Which is where I got it from." It came from an old post here on HT in the Type-R forum., but the R forum moves so fast that we sometimes miss good posts and need to revisit useful stuff.

I always read all of a post and decide wether it has some validity and before dismissing it. I also tend to save important technical information and posts that I might find helpful or someone else could use.

So No hatin here, I understand your opinion with that comment but, it does not negate the rest of the post.

Alot of good Plus some not so good does not Equal All Bad in my books IMHO.

Good luck,

A.
Old 12-24-2001, 01:58 PM
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Default Re: ITR vehicle dynamics (1GreyTeg)

1GreyTeg:

No problem on my part....it's still a Great post.... I'm just P.O. at the world at the moment cuz I don't get to spend Christmas with anybody special....

so yeah...I had to go out and do something meaningless and attack at post on HT.com....

Took a deep breath.... and now things are......the same..... I'll feel better when I watch some Option Videos.....hahhaa....

Merry Christmas guys....


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