We have a 2005 xA with 17x7.5" rims & 215/45 Kumho Ecsta rubber. I notice with these summer rims on the car the road seems to grab the back end & make it shimmy from side to side randomly...no pattern...just has a bit of a random wiggle when the road surface changes or is uneven. It only does it (or I can only FEEL it) with this rim/tire combo on - the stock rims/tires don't so it. The car has a fresh alignment & rides well otherwise. Just almost feels like the rim/tire combo is TOO stiff. It's definitely associated with the summer combo, and I've rotated F-B with no change.

I ordered a Hotchkis rear sway bar, thinking maybe the stock trailing arm/crossmember assy is tweaking...

Anyone else experience this? Any thoughts? Do you think I'm on the right track with the sway bar?

 

The only time I have ever noticed the effect you are describing is when I'm driving a car that doesn't have enough pressure in the rear tires. It feels like the back end wants to wobble back and forth. Whats your PSI? Adding pressure to my tires helped with the problem I had after getting new, wider wheels.
I have an 06 and after I put new 16x8 wheels on with 205/50 Kuhmo Ecstas I noticed that my car wanted to follow every little imperfection in the road (even with a good alignment). I noticed it especially on country roads where the slope of the road (to the left or right) is steeper than on most streets to encourage water runoff. If I'm more towards the left side of the road, my car liks to pull to the left, if im on the right, it pulls to the right, if the road is choppy, it likes to follow the imperfections. Im pretty sure it is just the wider tire and having a different, wider tire/pavement contact patch. Do you notice this at all? Anyway, I had them inflated close to the stock tire pressure (29 psi), but I bumped them up to 36 psi and the pulling effect was greatly reduced. You could try that or maybe even a few lbs higher. Keep in mind that a 17" wheel/tire combo is going to give you a noticeably more rigid ride anyway vs. the stock 15" combo simply because of the smaller tire sidewall size (less cushion).

 

Actually, that's exactly the effect I'm talking about...just finding it difficult to describe, but you described it perfectly! Thanks! I do know that the tires are at about 29-30 psi cold right now. I'll try adding pressure.

Do you have a rear sway bar on yours? I'm wondering if it'll help at all...

 

No sway bar. I have mine dropped on tanabe nf210 springs and have monroe rear sensatrac shocks. They both help smooth out the chopiness of the stock ride.

 

I'm not dropping it (family car), but maybe I'll upgrade the rear shocks to try to smooth it out a bit.

The sway bar (and Energy end links w/urethane bushings for the front sway bar) are already ordered & on their way, so I'll just install them anyway. Maybe they'll help.

 

I ve been rather **** about the way my car handles as a former benz driver, but never experienced that. I have gotten my rear to slip out from my under me with my upgraded front sway bar, stock tires, springs when making sharp turns.

It helps me to steer even sharper with less wheel input. Since Ive lowered it with a set of eibach prosport springs wind has little effect or feel on the car with all the wind here on the east coast the past few weeks.

I vote for under inflated tires.

 

Well, I brought the tires up to 36psi (after a drive home on the highway, so that's 'warm' temp...they were all at around 31-32). I'll know tomorrow whether it made a difference.
Also ordered the Monroe SensaTrac 5601s from shockwarehouse.com. I'll throw those in with the sway bar & new front end links and see what I end up with.

 

Dude, you want firm, get the generic urthene end link bushings from autozone and use soem grade 8 bolts and hardware from the suspension forum and crank those ****** down so 3/4 an inch of the bolt sticks out the bottom. That is such a tight feeling.

 

The increased air pressure didn't help much...might have lessened the effect a hair, but whatever the root cause, it's still present.
The Energy end links arrived today - sway bar is backordered until mid April - shocks are backordered until the end of April. Gonna be a long month.

 

Those tires looked over sized on your car, got the photo to develop today. Maybe the road is just uneven? The only alternative is that the mounts for your swing axle is loose. Sure that will flex in the car, but it would wobble, not twist.

 

They are 215/45/17...so yeah, they're 30mm wider than stock. The overall diameter is only about 3% greater than stock, though...negligible.

 

Without knowing much about suspension components or your car's history, I would still look to your wheels/tires first as the source simply because you said that you only notice the effect with your larger wheel/tire combo. Here is a link to the thread I started when I noticed a big difference in handling after I put on slightly bigger/wider wheels.
https://www.scionlife.com/forums/vie...001&highlight=
They guys that helped me out explained things like radial pull (from the directional tires), tourque steer, and bump steer, none of which I had ever heard about. Maybe see what they had to say to see if it relates to you. You could also ask other xA owners on here who have the same wheel/tire size that you do to see what they noticed after installing.

 

Thanks Grant...there's some good info in that thread. The Kumho's I have are directional.
The car does pull a little with road surface changes, but if that front-end phenomenon is what's causing the rear-end wiggle, then the rear suspension must be flexing because the wider, stiffer-than-stock tires aren't. I'm now even more anxious to see how much the sway bar helps.

 

When I installed springs on my car, yeah buddy that axle beam flexed. I thought it was rather ridget, but no and this was with a sway bar attached. Made me ready to stack the sway bars.

 

the tires themselves can cause this problem, as well as the overwidth.. "tramlining" i believe is the term

 

the wider the tire, the more u will feel the road. there is more tire on the ground to pick up more imperfections on the road. so far ive got rear sway bar, 10mm rear hub spacers, lowered 1.5", poly end link bushings, w/ 215/45-17 yoko's. still feel some drift in hard curves (15 mph) but its not a race car, it's $14k transportation. i can live with that.

 

Check the offset of your new rims too. Stock = 38 mm.

 

offset is irrelevant when the width changes..

 

I had a a$$ end wiggle on my xA. OTG spacers took care of it tho.

 

I have 225/50/15 Hankook R-S2's
& on irregular road, I sometimes need to hang on to the wheel.
It's the stiffer tires. They are more responsive to your input & at the same time, more responsive to the road's input.

At least with my car.

Oh yeah, I have a rear antisway.