Understeer/oversteer problem need help

littleshak

littleshak

Well-Known Member
265
240
Rillton, Pa
Vehicle Model
fg4
Body Style
Coupe
I'm not sure if it's an understeer or oversteer problem. I was driving home from my camp the other day coming up a hill in a passing zone (2 lane section) that has a left turn. I had downshifted to 3rd gear to get past some traffic. The road turns to the left and as I was about to change to 4th close to 7k rpm I pushed in the clutch and the car violently pulled left. I corrected and never left my lane but it was enough to scare the piss out off me. I was wondering if anyone else has had this issue and what they have done to correct it.
I have a 2015 si lowered on Megan racing springs, running summer tires, and a 24mm progress rear sway bar and my alignment is in factory specs.
I tried to duplicate it and it seems like when the wheels are under power it wants to plow through the turn. Which is odd because of the rsb.
Any help would be appreciated. Thanks.
 
Normal front wheel drive characteristic. On power your weight is being transferred back so your front tires loose traction ability and you start to under steer and push the front end. When you let off quickly your throwing all your weight forward onto the front end so now you have more grip in the front vs rear which allows the car to over steer and adding the 24mm RSB is only making this effect more. Throttle lift in turns is how you control the rotation of the car.
 
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Ok that makes sense. I've just never had it do it that violently before. I was going up a hill so that probably explains why.
 
I just want to make sure I am reading this correctly:

So, you were on a left turn on power, lifted off the gas, pushed clutch to shift, and the car pulled hard to the left? Not making a left turn but going around a curve to the left correct?

EDIT: How fast were you going? Not playing speed patrol, just curious. I've had some significant handling changes at certain speeds.
 
Ok, so I think you simply shifted the weight forward onto the front tires and they grabbed hard in that instant where you lifted off the gas. Normal.

While you were on the gas the car was probably pushing a little but not enough to notice, on lifting the fronts dug in with the weight transfer and all of the available grip was able to be used to point the car where the wheels were aimed.

I would be very very careful around 80 mph. That was my suspected speed. I have mentioned it before when people are looking at the rear sway upgrades and that is to be careful at highway speeds. The car can become very twitchy and the rear end will want to come around on you if you are cornering hard at those speeds. My car in particular starts to rotate on sweepers at around 80 mph. I also get significant lift-off oversteer at that speed. At speeds below 80 you can stay on the gas and keep the front at the limit of traction and it will understeer but also allow you to back off the throttle enough to regain traction without issue. It is definitely a speed thing as far as I can tell.

Basically, if I am on power and lift in the middle of corner, which you shouldn't do, the *** end starts to walk around. Scary. Fortunately if the car is starting to do this it is also sliding a bit and both times it has scrubbed enough speed for the rear to settle down and grip again. If it happens just stay calm and wait for the scrub/speed to drop and the tires to regain traction.

Even with the sway bar upgrade and upgraded suspension,tires, etc... these cars will understeer in a corner. Especially if you are on power. The trouble comes in when you change anything mid-corner. Once you stop overpowering the grip of the front tires with the engine all the suspension factors will snap into action.
 
I thought @Nix might show up on this one lol my explanations are rather :meh: I remember you mentioning the RSB high speed issues before. I'm actually not sure I wanna do that upgrade myself as I like the highway stability the car has.
 
I think the 22mm is pretty balanced and makes the car feel a lot better. Its just at high speed that you start getting into "interesting things." It helps a lot with rotation and making the car feel planted.

I would really like to make a video of this one corner at work showing what the bar allows you to do. If I take it at speed and just turn in and hold the car stays flat and goes around the curve. If I get into the turn late, I can yank the wheel tighter and have the back end skid around very tightly. Its half the bar and half the alignment. If you get the bar and start having stability issues, add in more rear camber. I have mine dialed out in the rear and more in the front.
 
Chambers805 said:
Sounds like someone needs some coilovers and an alignment.
Click to expand...
Coils are a no go because I drive it in the winter. The last car I had with coils, they galled after one winter. I am thinking slightly more negative camber in the rear though.
 
Yea, you just need good struts when the OEMs let go. Do you know what your alignment specs are now? I didn't see you mention rear camber arms, with those drop springs and no arms I would suspect your rear camber is a bit negative. I saw where you said you were in spec so I suspect you have them. Somewhere around -1.5 in the rear will give you plenty of grip, same with the front.

For comparison I am running -1.2F and -0.8R and the rear can get loosey goosey but I expect it to.
 
I have the spc/dorman camber arms. Right now I think I'm at -0.75 in the rear but I'm not sure about the front.
 
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