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Old 02-27-2018, 10:49 AM #1
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Is 5 degrees of caster too much?

Had my FN wheels and 285 Terra Graps installed this past week and I am rubbing the cab mount. With JBA UCAs my current alignment is at 4 degrees of caster and everything else in spec.

If I can get the alignment to 5 degrees keeping everything else in spec how much more space behind the wheel is 1 degree good for and will I notice the handling difference from 4 degrees? It drives great right now.
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Old 02-27-2018, 10:59 AM #2
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Quote:
Originally Posted by TeeDub21 View Post
Had my FN wheels and 285 Terra Graps installed this past week and I am rubbing the cab mount. With JBA UCAs my current alignment is at 4 degrees of caster and everything else in spec.

If I can get the alignment to 5 degrees keeping everything else in spec how much more space behind the wheel is 1 degree good for and will I notice the handling difference from 4 degrees? It drives great right now.
Are you rubbing on the mount or on the mud flap? I'm running 17x8.5" with -10 offset and 285 At3w with no cab mount rub.

I was rubbing at first but it was on the flaps, removing those fixed it.
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Old 02-27-2018, 11:25 AM #3
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Caster can be too much. But 5* is probably just fine. As caster goes up the steering may feel heavy. I don't think you can probably get high enough to cause major driveability problems. By something like 8 or 9* you start to risk "death wobble" harmonic oscillations.

1 degree of caster is about equal to 0.25" movement of the spindle center. Probably just a little less. I don't have a 3d model, so I'm just doing a rough back of the envelope calculation. It's probably closer to 0.21" or something like that.

Edit: Keep in mind that having 1/4" clearance with the body mount really isn't enough. The rubber bushings in the control arms flex a lot more than it seems like they would. I'd want at least .75" of clearance before I started going offroad much. More if you want to go fast offroad. Even though it clears in the driveway doesn't mean it'll clear offroad when there is significant force on it. I thought I was good to go with a bit more than 1/2" clearance on my setup until I hit the first hard bump while steering.

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Old 02-27-2018, 11:33 AM #4
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Removed the flaps. Definitely rubbing the body mount. More severe on the passenger side. Not sure .25 will help at full compression. Probably enough for daily driving. I like the Falken tires but Dustin at FN warned me they run large and would rub. Thats why I decided on the Nittos.
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Old 02-27-2018, 11:35 AM #5
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Can you go 5 is another question... there are max on caster, I only see people go to 4.0 with their 4.0. But try it and let us know. do you have no lift? Sounds like it shouldn't rub with 285s
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Old 02-27-2018, 11:44 AM #6
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The wheels are the root problem BTW. I'm guessing you already know that, but if you want to fix the rub - you probably are going to have to either do a body mount modification or change wheels to some with less offset.
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Old 02-27-2018, 12:17 PM #7
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Good thread, brings up questions I have. I get body rub when the wheel is turned full left or right, mostly when in reverse. My castor is current at L3.5 , R4.0.

Would tweaking the castor help eliminate this?

Things I have that impact this,, 3" OME lift, factory wheels, Toyo OC 285/75/17, JBO UCA's, 1" Spidertrac spacers.


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Old 02-27-2018, 12:17 PM #8
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Don't think the wheels are the issue as they typically have the ideal offset on the FN stuff.

Caster is relative to the two different ball joints (LCA/UCA), so you can't really say how forward or aft your tire is based on caster numbers alone. Moving the upper back will increase caster, but move the tire back. You want the lower forward and the upper just far enough back to provide decent caster 3.5-5*. Each UCA will put the ball in a slightly different place... Sound to me like the JBA puts it a little further back than most. TC is sort of the std in my book. They seem to position it just right (but every truck is different) and some UCAs are adjustable.
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Old 02-27-2018, 12:50 PM #9
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The JBA UCA's move the ball joint center approx. 22mm toward the rear of the vehicle. That motion should IIRC add about 3ish degrees caster.

I guess we should start by asking how much lift you have. If you're stock height - caster correction control arms will mean you have to push the tire way back to get caster in spec. Generally high caster arms are not a good match with 0-1.5" lifts.

(Keep in mind that the spindle is in between the upper and lower ball joints, but much closer to the bottom, so adding 3* of caster via upper control arm moves the spindle center much less distance fore or aft than moving the lower control arms to adjust caster the same amount. The lower control arms are more important in locating the tire within the fender simply because the hub center is close to the lower ball joint on the upright.)
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Old 02-27-2018, 01:14 PM #10
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Guess I should have included the lift. Wheelers 2.5 springs on 5100s (bottom perch) up front and 1.5 wheelers on rear. FN wheels are 8.5 -6 et 4.5 BS.
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Old 02-27-2018, 01:22 PM #11
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FN wheels, 285 falkens, and JBA UCAs with 2.5-3 inches of lift here and no rubbing. I have the caster at 5 with everything else in spec and the truck performs great on and off road.

But again every truck is different....so...just sell the truck if you can't get it right and start over and SAS it. That'll fix it.
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Old 02-27-2018, 02:17 PM #12
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Quote:
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Guess I should have included the lift. Wheelers 2.5 springs on 5100s (bottom perch) up front and 1.5 wheelers on rear. FN wheels are 8.5 -6 et 4.5 BS.
You should be right in the sweet spot for lift and alignment with the JBA arms. The wheels with -6 are less than an inch difference in offset. All 4runners are a little different, but yours is pretty unusual to have that rub so badly with normal 285s. Just to double check the size is 285 70 17 right?

Any chance you could take a quick picture of the rub area and maybe also a picture of the lower control arm cams? That would tell us where your LCA is set relative to the frame.
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Old 02-27-2018, 02:36 PM #13
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why not just do BMC and be done with it?
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Old 02-27-2018, 02:45 PM #14
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I have a Icon 3" lift with SPC UCA, FN FX pro with Falken Wildpeaks with +4 caster and still rubbed on the body mount. Did a BMC and all is well. Just do the BMC and be done with it.
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Old 02-27-2018, 02:48 PM #15
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Anyone in the Portland Oregon Vancouver Washington area know of a good shop to do the BMC?
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