we all love the fc for its neutral handling, but as balaced as it is, there is still a fair bit of understeer present at turn-in, espcially with tighter radiusus. yes, i know this could be eliminated by widening up the line and trail breaking, but is there a mechanical solution? with stiffer shocks and springs, would uprating the rear sway bar to something stiffer like racing beat balace out the car further, or would this just lead to porsche like snap oversteer i read about in anothe thread? i dont need a track biased stiff *** racing machine, but i like to have a car thats as capable as possible for my weekend jaunts up the mountain.

 

The cheapest way is to adjust tire pressures.

 

New tires, look at the Yokohoma AVS E100. Very cheap, awesome tire. Also Kumho's are great and even cheaper.....
As far as the suspension goes, take a peak at the IBOC Lowering kit they make for the 7.

 

run 255's in back, 225's in front.

 

More stick in the rear is not going to cut down on understeer.

Get a rear sway bar and set it to the stiff setting. Probably about $140 and an easy install.

 

Rear sway bar and the staggered setup mentioned above totally cured it in my car.

 

ive always been preaching the wonders of stiffer rear sways. also stiffer springs.. 255's in the rear will decrease grip. theres less lb/in of gripping power.

 

Less lb/ft that what? A 175 series tire? I don't get the extent of your point but I do know it's wrong. You're the first person I've ever seen in my LIFE to say that a wider tire in the rear will decrease traction........

 

think of it as a function of pressure. i heard this somewhere which is why you dont want tires too wide. if you have a narrow tire, the amount of pressure per square inch is higher (between the tire and the ground) than with a wider tire. theres a sweet spot between too narrow and too wide.
then again.. i guess rubber does grip less under higher pressure or something like that..

 

That doesn't make sense? It's a surface area problem! The wider the tire the larger the surface area that touches the ground.

You're suggesting that the pressure in wider tire creats a smaller foot print which is completely wrong. Just look at NASCAR or drag races, how many skinny tires do you see?

 

yeah thats not what keeps um from grabbing dude... its the amount of surface area touching the road... thats why DRAG RADIALS hook up good... its called FRICTION... plus the makeup of the tire has a lot to do with it too...
I'd say a rear SWAY bar will help a lot... better than a strut bar... and i THINK both would give you oversteer.

 

"Narrower is better" on tires, is good only in the following situations:

1. you're off-roading in shallow mud with a hard packed base, or just zipping along a fireline trail
2. you're in a rain storm
3. you're driving through light, fluffy, dry snow which your car can snowplow through
4. basically all situations where the maximum pressure needs to be applied to the ground to stay in control.

In situations such as dry roads where the most surface area touching the road helps with lateral grip, or the deep mud or deep, wet snow, or sand at the beach, where you want to float on top of the obstacle, or when rock-crawling when you air downyour tires for more grip, wide tires are more helpful.

i know there are more situations, and i have a book that talks about all the different situations where you want narrow vs wide tires, but i don't know where the book is offhand.

~suds

 

Ack, so many peole talking, but no one knows what they are saying. Look grip is a function of weight, and friction. Rub your hands together, now press them against eachother really hard and rub them again. Harder to make it slide yes? Now go drag a floor mat across the ground, then cut it in half and have someone stand on it while you drag it. Are you catching on yet? Wider doesn't mean alot if you aren't getting the weigh to the tires to use it. Yes, in general wider is better because there is always weight on the tires(well not always, but if there isn't your in trouble) but, wider tires also couse alot more drag, take more effort to rotate etc. etc. Why do you think some of the best SCCA Miatas run 195s?

 

Another cheap way to reduce understeer is to just install front suspension bushings leaving the rear bushings stock. Of course this is not ideal. Also mess with your alignment settings.

 

I also had some understeering on my TII. Then I installed the racing beat rear sways and endlinks... That understeer is almost gone now. I can only notice a hair of understeer.

 

Try this FREE mod first. Unbolt the four bolts on top of each strut up front, jack the car up, pull the struts out of their respective purches. Then rotate them so the center bolt/strut shaft is closest to your firewall and inboard. This will give you more camber and caster angles. Then go about with the other mentioned mods above, start with shocks and struts (ALWAYS get both, don't get springs and stock struts,, just plain stupid and ghetto. You'll need dampers with heavier dampining for those stiffer springs), then sway bars, bushings etc.

~Mike...............

 

While my comment about adjusting air pressure may sound flippant, the simple turth is it works. Check out the Nascar guys, they make as little as 1/2 lb psi adjustments.

With my 16x7 rims, I was getting too much understeer on one particular entrance ramp I used to take. A strut tower bar and adding 2-4 psi increase in the front can take a lot of the understeer out. If you have adjustable shocks, make the front stiffer.

You want the front of the car to stay flatter and the rear lean a little. A little understeer is desireable. In a curve a slight tap on the brake, while still in the throttle can plant the front and reduce the understeer. It takes practice.

 

If you want to have less understeer, do anything that makes the back end stiffer, like increasing tire pressure or spring rate or using a stiffer rear bar. All of you have some truth in what you are saying but are leaving out some details. Under/oversteer is an issue of weight transfer during cornering. When you corner, centrifugal force causes the weight of the car to shift to the outside of the car. If the rear end of the car is stiffer, the weight transfer will press the rear tires down on the pavement harder than on the front, and consequently the rear tires will take more of the cornering load, use up their traction and slip more than the front, causing oversteer, or spinning out into the weeds beyond that if you keep on it. If the front is stiffer the front will take more load and slip more, and the car will plow or push, basically refuse to turn any tighter unless you slow down. If you are on a track with nice wide run off areas have fun and make the car as tailhappy as you want, if you lose control you'll probably just look like an *** and laugh about it later. But on the road a little bit of understeer is nothing but good. Thats what keeps you off of someones front porch or out from under an oncoming truck. Save the powerslides for the Fast and the Furious so you don't run over somebodies kid on a bicycle.

 

On the wider tires sticking more issue,.. the reason it works is because rubber has a unique property of its coeficient of friction effectivly increasing as the load put on it decreases.... if tires were made out of something with a constant coeficient of friction, like steel tires on a steel road,.. there would be no change from 2 inch wide tires to 10 inch wide ones because the grip is going to be a constant function of the load x the coeficient of friction x surface area, but with rubber tires on an asphault road, the coeficient of friction isnt constant so you want to decrease the load per area ratio of the tires, thus increasing there effective coeficent of friction and thus increasing grip.

you can see this with a block of nice sticky rubber and a window,.. if you try to just push the block without putting much force on it, the block will stick alot and not want to move,.. if you put load on the block it will actually slide alot easier then it should for the load your placing on it,...


I cant believe people are talking about running bigger tires in the rear and a stiffer front suspension to get rid of understeer,.. makes me wonder how many of you actually know what it is,.. you want to stiffen up the rear if you want to get rid of understeer, not the front.......

 

Technically, there is no such thing as centrifigal force. It is lateral force. I agree with the rest of what you said.

 

Good point, Drago...

Everything I've run across says that to balance a car, stiffen the end of the car opposite of the end that's losing grip first...

Maybe increase the negative camber on the front to give a little more contact patch when you're really leaning into a turn, and a little more toe-out... Both of which will increase tire wear, so you need to balance the cost issue of this versus swapping anti-roll bars, springs and shocks, or just try a little more trail-braking with your current setup.

 

Well, we all know that friction=traction, and friction can normally be calculated simply by taking the normal force (force of gravity, depends on the mass) and multiplying it by the coefficient of friction between the two surfaces. Surface area never comes into the calculation, so wider tires shouldn't give you more traction, right?
I don't agree with drago on the above... I have never seen anything about an altered coefficient of friction with rubber due to a larger surface area with asphalt. Doesn't make much sense, b/c wider tires will get more traction on concrete surfaces, as well, and chemically, a changing coefficient of friction makes no sense. I'd like to see the references behind that one.

After talking with an engineering grad a little while ago, I learned the correct formula for calculating friction in anything but an ideal situation:

a wheel G with force P pushing or pulling it on a rough surface and F as frictional force:

sum Fx = m(a)x P-F = m*ag
sum Fy = m(a)y N-m*g = 0
sum MG = IG*alpha (this is where area comes in, the polar moment of inertia which for a rectangular contact is (1/12)*length*width^3)
=> F*r = IG*alpha

As you can see F is proportional to the WIDTH OF TIRE CUBED. Where integration comes in is b/c IG for a tire is not a perfect rectangle, but it is really close to being one. Same equation applies for tire moving sideways and the length of the tire becomes the width.

 

You can make any car, no matter how well set up it is understeer.
That being said, the cheapest method to correct understeer is to simply not overdrive the car in/through/out of the turns.

 

An engineer on my robotics team told me this in high school,.. i had asked my physics teacher why wider tires exibited more grip when the equation he gave us showed that it should not matter,.. he didnt know so i asked our cunsulting engineer and he told me about that property of rubber. This page explains it better than i can,..even has a nice lil graph,..

http://calcul.com/ian/thesis/node22.html

 

You lost me. Do you actually understand this stuff or are you just belching out equations that an engineer scribbled on a napkin?

How and why would you calculate the polar moment of inertia if a massless entity (i.e. a contact patch) ?!!

I don’t know what you are trying to prove but it DOES NOT apply to rubber (at the proper temperature) on pavement. Friction is one of (if not ‘the most’) un-characterize-able aspects of physics. You are better off following documented trends then some generalized equation.

Drago86 and others are right about the ‘unique’ properties of rubber. The literature has been provided for you.


As far as the comment regarding SCCA Miatas running 195’s... A competitive Miata would only use 195’s if the tire size is limited as such in that class. You will never see a 195 on anything competitive outside of a stock class.

…and on the topic of eliminating under-steer… I personally would not correct the problem by stiffening the rear. You would essentially be decreasing the grip in the rear and hindering the overall performance of the car. Instead, try to increase grip in the front. A set of camber plates would work nicely here. As long as you get the car aligned, 1 to 1.5° of camber will have a minimal effect on tire wear.