Crown Sensitivity

[OLJustice]

What causes it? I've heard alignment, I've heard wider tires. I'm running 245/45/20s up front and 275/45/20s in the rear. I know that some sensitivity is normal but my car is EXTREMELY crown sensitive-to the point where driving down an unevenly paved road with the hands off the wheel will subject you to an incredible show (the wheel is turning left & right by itself up to 90* each way)! I'll try to catch it on camera one of these days.

So... what really causes increased crown sensitivity?

(Oh, and it was just as bad before I decided to go staggered)

[mikeyb]

Get a four wheel alignment done.

I'm running 255 and it's slighly more sensitive but in your case it sounds bad.

MikeyB

[OLJustice]

Alignment has been done. According to the shop, its within specs for the car make/model.

[Charg-um]

Need more positive caster.


CASTER ALIGNMENT
The third most important wheel alignment angle is caster, which is the forward (negative) or rearward (positive) tilt of the steering axis as viewed from the side. Caster is usually measured in degrees, and only applies to the front wheels because they are the only ones that steer (except for the few oddball Japanese cars that had four-wheel steering).
Caster is a weird angle because it doesn't affect tire wear directly. It's greatest effect is on steering stability, steering effort and steering return. So it is often the most ignored angle.
Most vehicles have a small amount of positive caster to provide quick steering return and high speed stability. This happens because caster forces the spindle to angle down slightly as the wheels turn. This lifts the chassis and brings more weight to bear on the wheels as they turns. The net effect is that caster helps keep the wheels aimed straight ahead for improved steering stability, and helps the wheels return to the straight ahead position after turning. Many European luxury sedans have a lot of caster for this very reason because it provides a more stable feel at highway speeds. The downside is that it increases steering effort and steering feedback to the driver.
So what happens if caster is out of specifications? If there is too much difference in caster side-to-side, it can cause a vehicle to drift or lead to one side. Some alignment specs call for a slight difference in caster to compensate for road crown. But as a rule, caster should usually be within half a degree side-to-side.
The same kind of problems that can cause camber misalignment can cause caster misalignment: a bent spindle, mislocated strut tower, bent strut, worn or collapsed control arm bushing, bent control arm or a weak or broken spring. So if any of these parts are replaced, caster should be checked and readjusted as necessary after the parts have been installed.
Ride height can also affect caster. Spring sag or overloading a vehicle can alter ride height up to several inches, which can change caster readings by up to a degree or more. This may contribute to steering instability or change steering effort. So checking ride height is also an important element of aligning the wheels. If ride height is below specifications, weak springs should be replaced. Upgrade opportunities here include installing variable rate springs, air springs, overload shocks or air-assist shocks on a vehicle that is used for towing or hauling heavier than normal loads.

[OLJustice]

JUST the explicit answer I was looking for. Thank YOU sir! This will be printed out and taken to that pompous ass alignment guy. One thing... most shops feel that all they have to do is make sure the car is within spec. What should/could I say to tell him that its necessary to deviate from spec and actually do some *thinking* and work to get this done?

Also, can caster be adjusted on our cars without aftermarket parts? If so, what physical part do they adjust (eg. they adjust tie rods for toe)? I have a feeling I'm gonna have to babysit this guy and I want to at least be able to tell if he's really doing the caster. Really not trying to spend anymore money than necessary.

[RadarmagneT]

I thought this was about teeth!

[Charg-um]

I would recomend asking around your area and seeing if there is an alignment shop that works with custom cars. They are usually more willing to deviate from spec to make it right.

As far as if it can be adjusted on our cars, I don't know for sure, but I would have to imagine the answer is yes.

To put this adjustment in laymens terms, think shopping cart. the front wheels on a shopping cart work under this principle.

Caster

When you turn the steering wheel, the front wheels respond by turning on a pivot attached to the suspension system. Caster is the angle of this steering pivot, measured in degrees, when viewed from the side of the vehicle. If the top of the pivot is leaning toward the rear of the car, then the caster is positive, if it is leaning toward the front, it is negative. If the caster is out of adjustment, it can cause problems in straight line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. Caster has little affect on tire wear.
The best way to visualize caster is to picture a shopping cart caster. The pivot of this type of caster, while not at an angle, intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster. Picture yourself trying to push the cart and keep the wheel ahead of the pivot. The wheel will continually try to turn from straight ahead. That is what happens when a car has the caster set too far negative. Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out on these cars, it indicates that something is worn or bent, possibly from an accident, and must be repaired or replaced.

[Charg-um]

Also read here.

http://www.mopar.com/street/tech1001.htm

[OLJustice]

So you're saying that caster should/could *never* become misaligned on these vehicles like toe and camber sometimes do, and that if it is off then it is definitely something bent or broken? Please say it aint so...

[Charg-um]

It sounds like that is a possibility.... May be heading to a dealer.

Does it only happen on gravel roads ? or on dry pavement as well ?

[OLJustice]

It sounds like that is a possibility.... May be heading to a dealer.

Does it only happen on gravel roads ? or on dry pavement as well ?

All roads where there is an unevenness

[Charg-um]

Sounds like the toe is out too.. Better look for a good alignment shop..

Also post any mods, even a subwoofer box, will adjust the handling.

[diboblo]

Also, see this Dodge TSB for revised alignment specs (which mentions crowned roads)...

Bob

[OLJustice]

No 'heavy' mods. i have SRT8 shocks/struts/springs, SRT8 front swaybar, SRT8 wheels.

This problem was present before I did all of the above upgrades, afterwards it just got worse. I'll be doing SRT front brembos/rotors/knuckles soon though. I'm thinking I should hold off on any type of alignment until after I install those. I'm hoping that new knuckles may 'magically' fix the problem in the process, lol.

[Hemi31]

Justice there is an adjustible upper control arm out for these cars if you need it......gonna have to search for it though.Only other way to adjust is shifting the cradle.