Steiner

iTrader: (3)

I'm reluctantly subscribed to this thread because when it gets bumped it serves as a painful reminder that I really should have a roll center correction kit to go along with my KW3 coilovers.

belizelittle39439

iTrader: (4)

For the EVO the front end was made to be higher; though in general the purpose of a forward rake was to give more downforce to the front of a vehicle. That's why I gave that example (since most people apply forward rake for the downforce). As we talked about before, the only reason why our car's dont do so well simply lowering is due to our macpherson struts, correct?

And although the other things aren't "necessary"-- it's only a couple more hundred dollars and get's you closer to a better handling package overall. I myself have only done the roll center kit and the rear bump steer kit. This helps my lowered car with the understeer, and seems to have helped to tame the rear end a bit. To me it's a matter of balance.

And by the way...thanks again for tipping me off on that kit way back when and also maintaining an adult composure when exchanging information. It's helped me quite a bit with getting things just how I want/need them.

madmax199

iTrader: (20)

I know you got the point, I just dont want some fellow evo members to slam their front end, dragster style, because you mentioned that lowering the front potentially helps downforce .

belizelittle39439

iTrader: (4)

True True. But you're too late because I already see that all the time in the show and shine threads....

madmax199

iTrader: (20)

If that's the case then ; to each their own.

Jeff_Jeske

iTrader: (66)

It has been noted that the roll center kit is less effective on cars with stiffer suspension.

belizelittle39439

iTrader: (4)

That's a good point Jeff.

To elaborate, let's say we have an EVO with say 5k springs all around. Now, we take that vehicle and lower it using coilovers and retain the 5k spring rate. The center of gravity (COG) decreases, but due to the new geometry the roll center (RC) decreases even further which increases the roll couple (distance between COG and RC). The roll center correction kit would aid in this case by correcting the geometry of the vehicle and shortening the roll couple lever thereby "naturally" decreasing the car's tendency to roll.

Now to use your point Jeff--in that same scenario above, our EVO gets lowered with coilovers but now they use a 10k spring rate all around. The increased tendency to roll caused by the RC length is still there--but is now masked by the stronger spring rate. The car will naturally try to roll just the same as in the first example, but that roll energy is dampened by the stronger springs. The diminished effect could also be seen with a stronger swaybar I would think.

ghamatos

iTrader: (4)

It never crossed my mind that negative rake would be the right setup. Nor knew I that it is factory setup (thought it was even = 0 rake)

I have an EVO 9 with custom built Bilsteins PSS raised (because of offroad driving) 15mm front and 20mm rear (was at 30mm rear with very bad oversteer reactions at middle to high speeds, very sudden) from the factory setup.

How much negative rake has the factory setup? I mean how much should I lower the rear so I don't shoot the opposite direction?

belizelittle39439

iTrader: (4)

Most people are setting it where the front fenders are about an inch higher than the rear fenders...as far as dealer specs...not sure.

madmax199

iTrader: (20)

I do not agree whith that statement Jeff and this is why:

1) With the car sitting still (static) The RC is a fixed point in the suspension geometry and is independent of springs and SB rates. When lowered (still static) the RC changes to an unfavorable location thus resulting in that unwanted increased roll. The RC kit simply put the roll center back to a more favorable location and reduces the roll while keeping the lowered center of gravity.

2) Whith the car moving (dynamic) the RC is no longer a fixed point an now migrates with body roll. The spring rates get into the mix controlling how far the RC migrates, less springs equals to greater migration and vice versa.
Still, having a better static RC helps, the stiffer spring only increases the load needed to have detrimental roll from lowering.

I understand why one might think that correcting RC after lowering is less effective with stiffer spring rates, but it's not really the case the stiffer rates only mask the problem that's still there but at higher cornering forces. Think of it this way, having higher rates may help control RC migration with street tires and be totally undriveable(pig understeer) with R-compounds because of the higher cornering forces they bring to the eqation. I hope this helps.

Jeff_Jeske

iTrader: (66)

I think what you just typed says the same thing I did but with more words.

Profoxcg

iTrader: (9)

I read on this forum that you can lower your car and as long as the lower control arms (front) are parallel to the ground and chassis you should not have any roll center issues.. is this true?

BTW I am on coilovers =) 2 finger gap in the rear (1.25") and 3 in the front (2.0"). but think I may raise the front to have a 4 finger gap (2.5")

Jeff_Jeske

iTrader: (66)

I lower the car to the way I like it to look then corner balance it. I'm not a pro driver but I think the thing handles like its on rails.

The roll center kit is cheap. If I thought the car was loose I would get it but I'm running 12k/10K with rear sway bar and R compound tires. The only thing holding me back is me.

belizelittle39439

iTrader: (4)

Those are some solid spring rates Jeff. I run 10k all around on Zeals, but I'll be switching up to 9k front 10k rear on KW's here in the next couple days (haven't installed yet). Figured that was easier than getting the rear sway and having a softer rear spring rate.

You don't experience understeer at all during cornering? Entry or steady-state?

Jeff_Jeske

iTrader: (66)

The roll center and spring rates are only a small part of the big picture. Tire pressure, alignment, traction, throttle and steering adjustments all impact how the car performs. I don't seem to have an understeer problem. I don't know why.

The only time the car gets unsettled is when I get excitable and my my transitions become a little to abrupt. I'm notorious for inflicting an oversteer condition.

I've had serveral instructors tell me that sideways is not the fastest line around the track. (It sure is fun though)

EVOs and STIs even when not dialed in are better than 99% of the cars out there. The platform itself is still better than I am. I'm still working on left foot braking heal toe shifting and eliminating coasting.