I'm really just trying to figure out the best way to take some stress of my steering components and reduce feed back thru the steering wheel. It get to violent in some situations for example during a rock crawling situation it felt like I broke my thumb it ripped the wheel outa my hand so hard. I know ps will help but I wana fix the cause and not just hide it.
Ya wheel offset and tire size will change the scrub. I love my 30" mongrels just hate the way the maverick handles. I have Been thinking of making new spindles to change the scrub just wanted to see if any one had done it and had feed back to weather it is worth it or not. Lol it's hard not to wrap your thumbs tho when your really trying to crank on it!
Ultimately you want the center of the rim/tire over the center of the balljoint. That will help with the scrub and help with turning radius. The front factory wheels are a 5+1 I believe so a 5+2 is going to push it out to about 66-67" overall width and hurt the turning radius and scrub a little bit but not enough to kill the handling of it. I've been battling this a little bit myself as I'm on a 30" tire with a 4+3 offset. I love the handling at speed as it feels like a miniature trophy truck but I know it would turn much better if I could get the tire back over the balljoint. The added stress is a big downside on mine esp with the bigger tires.
It sounds like power steering will fix your issue though if you're having trouble turning it.
So without really delving into how A-Arm front suspension systems are designed here is a bit about how to figure scrub radius. Scrub radius does not depend on your wheel and wheel offset. Your handling and handling feedback do depend on your wheel offset. Your scrub radius is fixed and cannot be changed unless you re-design the A-Arms, A-Arm Mounting points and the spindle. A line is drawn through the center of the upper ball joint down through the center of the lower ball joint. Where the line touches the ground at ride height to the center line of the chassis is where your scrub radius is. If your tire is centered on that point on the ground, then you have a 0 scrub. A zero scrub will give you the easiest steering as the wheel pivots on the axis of the line drawn through the ball joints and encounters no or not noticeable resistance. Most designers however never design with a 0 scrub. You will typically find a negative scrub of between 1/2 to 1". Basically this means that the line between the two ball joints falls inside of the tire center line when the vehicle is at right height. This offset is what provides resistance to turning which gives the driver the correct feedback to the wheel.
So to figure out what the scrub radius is, jack the car up take a front wheel off, then lower it to ride height. Block up the suspension so the arms are at right height. Take a long strait edge (yard stick) and line it up on the center of the ball joints. Mark the location and then measure to the center line of the chassis. This gives you your scrub radius (or close enough for this exercise). Then take the same strait edge and put it against the wheel mounting surface. Mark this location and take a measurement between the two marks. This is your scrub offset. You can then factor in your wheel offset to figure out where your wheel sits in relation to your scrub radius. By figuring out your offset in relation to the wheel mounting face to the contact point of the scrub, this will tell you how much positive or negative scrub you have in relation to your wheel size.
Not overly difficult, but time consuming to figure out. My last A-Arm buggy was built with 3/4" negative scrub with a BTR 4" wheel with a 1 3/4 backspace. So for an example (just plugging in random numbers): If my scrub radius is 30" to center and I have a 2 1/2 inch scrub offset using the 1 3/4 back space wheel, that would give me a negative scrub of 3/4". My scrub radius will still be 30" as that does not change.
This post may have now created more questions than answers, but hopefully it helps with the scrub radius.
Assuming the tires are 10" wide, and the 30" tall spec is accurate (15" from the center of the installed tire to the ground), and the offset of the replacement wheel is indeed a -2 and not a +2, the scrub radius is approx. +3.6". This will make for a lighter feel at the steering wheel at low speeds, and make the steering wheel much easier to turn while parking. It also allows for more clearance from the inside of the tire to the frame and a-arm at full lock. Since the factory scrub radius is closer to 0", perhaps a bit negative even, your proposed change will be for the better (unless you'd rather have a heavier feel at the steering wheel).
What this +3.6" means is that when you turn the steering wheel, the front tire rotates at a point 3.6" away from the center of the tire contact patch, and therefore "rolls" as you turn the steering wheel. To hopefully clarify this point, picture yourself sitting in a chair and holding onto a stick of some length. At the other end of that stick is your tire, attatched to the stick via a wheel bearing. While holding the "tire stick" with your arm extended, move your arm from left to right and the tire will follow a path, circling around you at a given "scrub" radius, that which is determined by the length of said stick. Now, remove the stick, stand up, and grab the tire and rotate it (not roll it) like you're spinning a coin on the table. If you rotated it long enough, you would "scrub" off the rubber tread due to friction, because although the tire is turning, it is not rotating like it did when you used the stick to turn it. That is what a scrub radius is.
There are a couple of ways to manipulate the scrub radius on a vehicle designed with unequal length a arms like the Maverick is. One, is to change the rim offset as you are proposing. This moves the contact patch of the tire either in or out (based on a + or - wheel offset). Two, is you can modify the ball joint location(s) on the spindle, in turn, changing what's known as the steering axis inclination. This is what I did on our race spindles (see attatched image). Three, you increase the tire diameter. Lastly, and you wont believe the simplest way, is to just lower your air pressure in the front tire. Here's why:
As the tires' rolling radius changes, so does the scrub radius. This is due to the fact that the steering axis is not parallel to the vertical plane of the tire, so as the centerline of the wheel gets closer to the ground, the dimension between the center of the tire contact patch, and where the imaginary line from the top ball joint, through the bottom ball joint contacts the ground (your actual steering axis, and imaginary point in space that is the reference point that the scrub radius is based upon), the dimension between these two point decrease if you start with a negative scrub radius, and increase when starting with a positive scruib radius. This is due to the fact that these two lines that I just explained, have a finite vector (that's just a fancy way of saying that they're not parallel to one another!). :sorry:Sorry, but you asked!