Chriz88DX

iTrader: (1)

ok I have run into a little problem the stance on my rx7 is al most complete but the rear wheels are sunken in but the front is hella flush.
so I have two choices I could either adjust the camber in the back to make it flush with the body or do wheel spacers.

now the only problem with that that I have is that I know that increasing my rear tire width will cause under steer. and it is already a under steer happy ride. but if I dial in more positive camber will it make my car over steer like crazy. (it would be more controllable) I am just really stuck and don't know which to do to fix the problem


specs on my car;
na s4 FC

front and rear sway bars
tanabe gf210 springs
kyb shocks/struts
wheel size is 17x8 with 245/40/17 tires +40 off set
night sports camber arm

jjcobm

iTrader: (18)

Well think about it this way, ideally to get the most grip out of the tire you want to have 0 camber which equals to having the entire, if not most, of the tire contact patch on the road surface. As you approach a left corner, negative camber on your passenger side tires will help keep the surface area of the contact patch on the road as the lateral g-forces come to play. Since you are turning left, the g-forces push you towards the outside of the turn (right side). On a straight away, with a lot of negative camber on your tires, you will not be using all the contact patch on the tire, thus you will not have full grip.

Now, to answer your question about how camber and tire size (we will assume bigger rear tires) affects the vehicles oversteer/understeer characteristics. Remember as you approach the corner, with the right amount of negative camber the lateral g's will make the camber approach 0. If you add a bigger tire, you increase your "grip" around the corner (a.k.a contact patch), thus making the rear of the car push the front of the car more. That is understeer.

So if you want your car to have a bit more of an oversteer characteristic and you want to correct this using only camber, you can dial in a bit more positive camber in the rear in order to lose "grip" on the corners, forcing the tire to have less contact patch on the road and thus eventually making the rear of the car slide out. You can also increase negative camber on the front tires if you don't want to touch the rear tires, this will make the front grip more than the rear, causing the back tires to not grip as much as the front which will equal oversteer. As you can see, you basically want to make the rear somehow have less "grip" than the front.

By the way, if you have ever watch nascar, this is why the cars are preloaded and look lopsided. The right side tends to sit higher than the left side, so they can compensate during the latteral g's on the many left hand turns to make the suspension sit ideally during the turn.

Another method you can use to correct understeer is to add a thicker rear sway bar than the front of the car. If you want to correct oversteer you can add a thicker sway bar on the front of the car than the rear.

Here is a really cool website I found that list everything out for you. You can try some of these methods if the ones I described above don't fit your needs:

http://www.timskelton.com/lightning/...orrections.htm

Hope that helps out.

Chriz88DX

iTrader: (1)

This helps out alot

I have been reading that having athicker front sway bar is better for over steer

also if i dail in close to 0 camber in the back (no real camber adjust ment in the front) dsst still funtion

and i have 245 40 17 tires front and rear

thanks in advance

jjcobm

iTrader: (18)

well you don't want 0 camber when the car is in static (not moving), as when you turn into the corners your tires will in return have positive camber when the lateral forces push the tires towards the outside of the turn. While this is good for straighaways since you have full tire contact on the road (0 camber) it will suck on turns. Hope this doesn't confuse you.

You could try less camber on the back, but don't go to 0. If you don't have anymore adjustment in the back, it would be time to play with the front to make it grip more, and have the rear have less grip.

DTSS is for correcting toe during turns.

Chriz88DX

iTrader: (1)

ok i under stand so i am guessing i will need to look into camber plates for the front huh

that would help out a lot

jjcobm

iTrader: (18)

Basically you can mess with front camber, or try to make the rear have less contact patch with the road (compared to the front) by other methods. You can probably decrease the rear camber a bit, but like I said, just don't over do it. Try it out.

The other methods are thicker rear sway bar, ect. Remember, there are many ways to correct understeer and make the car lean more towards oversteer when setting up a suspension. You might even have to use a combination of decreasing rear camber just a bit, then add a thicker rear sway bar, maybe even adding wider front tires. Take a look at that website I gave you, but you are on the right track....

MOD EDIT: Don't add wider front tires. Buy coilovers w/ camber plates instead.

jjcobm

iTrader: (18)

By the way, this will give you a better idea as to how a sway bar will affect the roll stiffness of the suspension. This is out of my engineering class's chassis design book:

Stiffness = D^4

Basically it says sway bar roll stiffness equals diameter of the sway bar to the fourth power. So if you have a 1 1/4 inch sway bar, it will be 2.44 times as stiff as one that is 1 inch theoretically, assuming you have it properly mounted to the chassis and control arms. That is a big difference for just a 1/4" change is thickness.

Chriz88DX

iTrader: (1)

touge driving is the best here in the ga mountains lol

ok i get this ok one more question lol would the racing beat adjustable sway bar end links help me to soften the rear bar

jjcobm

iTrader: (18)

I just noticed a mistake on what I told you. I confused the front and rear sway bars and how they affect the understeer/oversteer of the car. I caught my mistake as I was reading up on adjustable sway bar links. Whoops, I should get an F for that, hopefully anyone reading this will get to see this part....

Softer front sway bar + stiffer rear sway bar = Oversteer
Softer Rear Sway bar + Stiffer front sway bar = Understeer

So instead of doing what i mentioned before of keeping the upgraded front bar and stock rear. You need to do the opposite and keep the upgraded REAR and stock front. Since you want to make the front wheels less stiffer during chassis roll, and the rear stiffer to the point they break loose (its more complicated than that, but thats the simple version).

So about the question regarding the adjustable sway bar links on the rear. Using those on the rear you can adjust the stiffness of the rear sway bar without having to upgrade to a thicker one, since the shorter the lever arm (sway bar link), the stiffer the bar becomes. So yes, just tighten it up (make the lever arm shorter) and see how it feels to you.

Sorry about that mistake, hope I didn't end up confusing you or anyone else, but I double checked about 4 times to make sure I didn't misinform you again so you can trust the correction!!!

(I will try to see if the mods will let me make corrections to my previous posts, that way anyone reading it in the future doesn't get confused)

Roen

iTrader: (2)

There's also a matter of using which components to make wholesale changes to your car's setup, and using which components to fine tune the setup. To make large wholesale adjustments, you use things like shocks and springs. Shocks need to be valved properly to the use of the car, and consequently, springs need to be matched to the shocks. Most people don't give a rat's *** about the finer details, so they buy pre-valved coilovers and hope it feels good. An educated consumer would take whatever shocks he/she would buy and have them dynoed, ensuring that the shock forces are matched and proper for their application. To make fine adjustments, you use things like alignment or sway bars, in order to slowly shift the car's characteristics into something that you like. You shouldn't be making any huge changes though.

You won't be able to use camber plates for the front with that setup. You would need to go to coilovers first. Essentially, you're only able to make small changes right now.

Since you've went to 245 already, (which btw I think you should've stayed at 225), you've noticed that your car has more understeer than before, thanks to the camber arm. Your car is probably also slower on the straightaway due to people overlooking the simple fact of having a wider tire causes more rolling resistance, which slows your car down. This is why you should never get more tire than you need.

If you're thinking about going turbo in the near future, then it makes sense. Otherwise, you're making the car slower by making the engine lug 4 heavier, wider tires around. If you're going to stay NA, I would use these tires up, then get some 225/45/17 tires.

To address the problem at hand, there's not a lot you can do right now, without completely removing whatever performance benefit you got from having larger tires in the back. With your setup, the only thing you can do, as mentioned before, is remove rear grip. You never want to remove grip if you don't have to. Unfortunately, in this case, you have to.

I wouldn't mess with the camber yet, I would install the stock front sway and the upgraded rear sway and see how that feels. If it's still understeers too much, take the front bar off entirely. If that still doesn't work, then start changing your rear camber and make it more positive.

You should definitely look into coilovers.

jjcobm

iTrader: (18)

Thanks for the corrections Roen. I think that pretty much sums up everything. If the stock front and upgraded rear wasn't enough, also remember to tighten up the links for the rear sway bar to stiffen it up a bit also.