My English maybe challenged to the limit for expressing what I want to say. But here's a try. Parden me if I can't be more clear. ask me if you are not clear. Assumptions: 1. roads are ideal flat surface and the vehicles are driving on it at 50mph with your hands firmly holding the steering wheel at straight position(straight relative to the car body, that is. You may or may not be correcting the pulling force or not, depending on situation described in the picture). Please note that your vehicle may or may not be going straight even your steering wheel is straight. In the picture, when you see the front wheels are straight(parallel to the car body), the steering wheels are straight. When you see the front wheels are not straight, the steering wheels are also straight. 2. front track = rear track. left wheel base = right wheel base. And 4 wheels form a perfect rectangular shape. 3. all rim/tires are the same and with the same pressure. 4. there's no uneven brakes or unbalanced power steering. 5. there's not setbacks or anything like that. all alignments are perfect except the toe issues described in this picture. 6. all cambers are 0 degrees. 7. all casters are within spec and are identical from left to right. 8. In the picture, all straight wheels(parallel to car body) are having 0mm toes. 9. In the picture, all non-straight wheels are identically skewed front left to right( wheels themselves are parallel to each other) Question is: Which side will Car A pull to if you keep your steering wheel straight relative to the car body? Which side will car A pull to if you leave your hands off steering wheel? Is the steering wheel going to move relative to the car body after you have your hands off? If it moves, to which side? same question for car B, C, D, E, F Image Unavailable, Please Login
In general, a car will pull in the opposite direction of the tow angle in the rear wheels, and will pull in the same direction as the tow angle in the front wheels. In cases where there is a mix of tow in both front and rear, it is hard to say --- either there will be a prevailing net yaw moment that will determine pull direction, or there can be a cancellation effect where the car will not significantly pull at all but simply track straight and scrub against all the towed wheels (tires). .
What I don't understand is: if I hold the steering wheel tight at center, the car will go straight if I leave my hands off the steering wheel, the steering wheel will turn right and the car will pull to the right. What is causing this?
Short answer, caster. Roads are almost never flat, slight crown for drainage, add in caster and the vehicle will drift off the crown or into oncoming traffic.
Yep, what Scott said. You need to have a dead flat surface to rule out any other influences. Short of an airport runway, flat pavement is hard to find. Even runways usually are mildly sloped in one direction for drainage.
it shouldn't be the road surface because it is pulling to the right really bad. I know I need an alignment ( somebody messed with it before this pulling happens) but just want to theoretical before I do the alignment.
A and B pull right. All others pull left. The first one causes the r rear wheel to scrub. E causes left front wheel to scrub. D and F cause both rear wheels to scrub.
Fractions or minutes and seconds of a degree add up very quickly over large distances. I'd really recommend reading up on vehicle alignment, camber, caster and toe make the gimbal. The crown in the road has a significant effect on how the vehicle tracks.
Did this recently start, or is this a vehicle you haven't seen before? A number of things can cause a car to "pull", including a bent frame. From your theoretical premise, I presume you've ruled out frame damage. But check the suspension components. (I had a bent right rear trailing arm on my EVO 8 that caused it to pull slightly to the right.) Check the ride height from side to side. A weak spring might cause the car to lean. (I had sagging front MacPhersons on my Celica GT-Four that caused "bump steer" -- okay normally, but bumps would cause the car to pull.) But if the car is pulling, you should be doing full alignment on all four wheels, including steering angle inclination. As SMG indicated, mismatched caster can cause a car to "pull". But a car pulling to the side needs to have the entire alignment checked. You actually can do alignment without the expensive machines, with a tape measure, a protractor, a plumb bob, chalk, and a bit of patience. The procedures can be found via web searches. (The expensive laser machines just turn a two hour job into a 30 minute job.) Although I've had a car pull hard to the left ... in one spot only: The road had a rut in the left turn lane that pulled cars offline. (I wonder if they ever fixed that road. )
Which side of the road are you driving on when this effect happens? If it's the right hand side then chances are the car is just reacting to the camber in the road. To check it out, you need to find a nice long stretch of straight road (so you can clearly see any oncoming traffic), drive along it on the correct/normal side of the road for the country you're in (so if traffic normally drives on the right, you use the right hand lane first), let go of the steering wheel and see if the car drifts to the right. Then turn around, and drive back along the same stretch of road but on the opposite side of the road (the left hand lane if you normally drive on the right), let go of the steering wheel and see if the car drifts to the left. (If you want to be doubly sure, do the test by driving down the same stretch of road in the same direction twice, once in the right hand lane, and once in the left hand lane). If the car pulls to the right whilst in the right hand lane, and to the left whilst in the left hand lane then it's just following the camber of the road. If you're in the left hand lane and the car still pulls right then chances are you have an alignment/steering/suspension problem.
its absolutely not because of the road because , unless I am driving on an oval, no crown will make it pull like the following: If I get my hands off the steering wheel, driving at 40mph, the car will change a full lane within 50 yards! the steering wheel will rotates somewhere around 30-50 degrees. I also can visually see the Left rear wheel is having an at least 10 degree toe , it sticks out! LOL
sorry I might not express myself clearly. The point of the thread is not to solve my car's pulling problem. I know I need an alignment to get it right because me and my friend mess up with the toe for some other reason. The point of the thread is to theoretically know, that, in the conditions depicted by my drawing, what will happen?
thank you all for the input. I hate myself as I can't make my point my important point is the steering wheel. Pulls right or left is rather easy to conclude. For example, when A is pulling to the right with your hands off steering wheel, at this moment, is the steering wheel straight relative to the car body?
What is causing the pull problem is that the pair of tires on one axle do not carry the same load. The steering wheel with take on whatever angle that results in all 4 tires carrying the most even loading. Differing caster can cause this, and it is the easiest fix and the first thing one should check. But the pressure difference could be cause by: spring sag, bent frame, suspension bushing problems not yet manifest, and a few others.
ok, apologies, apologies, apologies, I finally know what I want to ask, in a clear way. A,B,C,D,E,F , 6 scenarios. suppose your alignment is perfect except the toe. if you are travelling on a flat surface with hands OFF steering wheel at 40mph. Is the steering wheel straight relative to the car body?
make sense, different loads tends to even out themselves so the steering wheel will take some moving.
It's possible for the car to "pull" to the right, even with the steering wheel straight. (E.g. rear alignment issues.) (For instance, when I had a bent right rear trailing arm, I had to steer slightly to the left to keep the car going in a straight line. Hands off the wheel, the front caster would return the wheel to center, at which point the car would drift to the right, with the steering wheel centered.) If forward motion causes the steering wheel to rotate, seemingly on its own, it means that a misalignment is causing the steering tires to reorient, pulling the steering rack and wheel along with them. A difference in front caster could cause this, or too much toe in on the left tire or too much toe out on the right tire could cause the steering to shift right. Or you might have a geometry problem causing different steering angle inclination (SAI) on the front suspension. On an alignment, toe is the last thing you adjust, after you've verified everything else. People might try to compensate for a problem elsewhere in the alignment by tweaking the toe angle, but the fix is to get to the underlying cause.
Get the car aligned {caster, camber, toe}($60-$100), then if it still pulls one way or the other, Get the car corner weighted and ride height adjusted ($500).
I did some checking, and found a thread with the corner weights for a 430, but not for a 360. A couple of older threads, though, FWIW: http://www.ferrarichat.com/forum/technical-q/52533-360-ride-height-adjustment-help-please.html http://www.ferrarichat.com/forum/360-430-sponsored-yellow-compass-group/97309-how-adjust-ride-height-360-a.html But the gist is that this isn't an easy change to get right for a first time attempt. A shop able to check your height and corner weight should be able to look up the correct numbers. But you need to do an alignment after changing the corners, so if you do the alignment and then have to change the corners, you'll have to get it aligned again. Camber and toe are fairly simple DIY alignments, but you may be into "need a pro" territory. But then, I'm more of a driver than a mechanic. I know enough geometry to do basic alignment (e.g. on a Toyota or Mitsu), but I leave my Ferrari to the pros.
Suspension is set at the factory for each market the car is heading to. There are small differences in castor left to right, and set back left to right (ie the wheelbase is longer on one side than the other). This is to counter the natural camber of the road. If you get a LHD car and drive it in a RHD country, it will handle like a pig. A decent 3D alignment can pick all this up.
