Hopefully anyone can help.

Currently driving on 17 inch rims but I have some 18s that I purchased used. I had it wrapped in brand new michelin a/s 4 tires and thats where the problems begin.

The steering jerks left and right when driving on bumpy roads to a point where I feel very unsafe. I essentially have to grip the steering wheel tightly with both hands so I dont veer into another lane. Not only does it jerk, it feels as if the steering becomes disengaged with the tires and the steering wheel becomes very light and loose. On smooth roads, it drives fine.

After trying many suggestions from other users and failing to resolve this issue (3 tire balances, 2 alignments, front and rear suspension replaced) I finally decide to put back on my 17’s and low and behold, the problem disappears.

The issue seems to be the tires or rims, but all the tire guys have said the wheels are not bent and the tires are good.

What do you think may be causing this issue?

Specifics:
-Car: 2014 civic lx auto, 90k miles
-Car is not lowered (edit 7/12/2021, car is “kind of” lowered, I replaced the stock suspension with an OEM honda HFP (sport) suspension. Car rides stiffer and lowered by just 1/2 an inch)
-Both the 17’s and 18’s are OEM honda wheels
-17’s are 17x7 (P215/45R17) and 18’s are 18x7 (P225/40R18)
-the 18’s were made for the same car model but on a higher sport trim level, according to honda, upsizing wheels should not be an issue and is within spec. Wheel geometry should not be an issue
-I am not using wheel spacers
-Hub was cleaned with steel wire bush and sits flush with wheel. I did not check the 18’s wheel bore so I will give it a thorough check as well. As far as I could tell, it is clean.

 

Just to add, this is one response I got on the cartalk forum by a user called "Mustangman":

Your suspension does not have stiff enough springs, strut mounts and firm enough struts to control those heavier, stiffer, low profile tires. This is a common problem when a performance wheel and tire is installed on the “non sport” version of a car even if they came on the sport version. There is a lot more to the sport version than just bigger wheels and tires. That is what is causing your problem.

I used to “tune” these systems as part of my job with a major automaker, so I am familiar with the problem.

Change back to the 17s.


So I am on HFP suspension which have stiffer springs, but is it still possible other parts such as sway bars have not been upgraded leading to these steering wheel issues? I've asked around on instagram where other people have placed SI rims on LX's and they did not experience such issue, but the explaination does make sense and sounds very plausible.

 

Get someone else to drive it and get their opinion?

Was it an 18" wheel from a Civic? Has the same +45 offset?

 

I would guess front toe is off. You mentioned you replaced suspension - did that include all bushings? DId you try moving the wheels around (front to rear) just to rule that out?