Caster angle question for all you alignment experts

[pawzitiv]

I've just installed my new wheels shod with 285/70R17 Cooper STT's on my 2010 Trail Edition. Earlier this week I had my dealer install my OW 2.5 suspension and had them set my caster angle at 3 degrees. I've removed my factory front mudflaps and when I reverse at full lock, I'm still rubbing on the body mount frame horns at the rear of the front wheel wells. Oddly, I didn't need to pull my plastic fender liners forward for clearance in front of the wheels.

My question is if I have my caster set at 3.75 or 4 degrees rather the the present 3 degrees, will that pull the wheels far enough forward to gain a bit of clearance at the back of the wheel? I've had conflicting info; a couple of people claim that more caster will actually push the front wheels further back in the wheel wells.

So do I need more caster angle or less caster angle to gain some clearance from the body mounts?

 

[Jtraskell]

I am not an expert, I am sure Harper and other's have much more knowledge then I. My understanding, however, is that you will need "positive" caster, which moves the wheels forward. Negative caster adjustments move the wheels back towards the rear of the vehicle. According to a previous post from Harper who also has a lift, put your caster as close to 4.0 or more as possible. I do not know his tire size. I have 285/70/17 with no lift. I have 4.0 on the passenger side and 3.75 on the drivers side. (This to compensate for the crown of the road) and I do slightly rub with the passenger tire on very hard left hand turns. A very slight rub that will go away in time. Either tire wear or the thin plastic rib found on the front inner wheel well will simply be ground down a bit. Even before the lift, mine never rubbed anywhere in the back of the wheel well. Prior to changing the caster, the factory had the passenger side set at 3.0 and the drivers side and 2.30.

Hope this helps.

 

[4RBob]

Actually, more positive caster means the top of the "pivot" is leaning further towards the rear of the car. I am not sure if your wheels would be pushed back any however.

This is a short summary of alignment terms:

Wheel Alignment A Short Course

 

[FERAL 4R]

Positive caster means that the top of the upper ball joint (or strut) is tilted toward the rear of the vehicle, and negative caster means that it is tilted toward the front.

Yes, you want more positive caster to prevent rub, but, can you even get +4 degrees with the stock upper A-Arms? And how will that affect Camber and Toe settings?

On my FJ with aftermarket A-Arms, I was able to get +4 or more, but never needed it because I chopped the body mount.

Also, I never have my left/right caster set a different settings. Always the same on both sides...Some say it's for road crown and crap...

 

[Jtraskell]

Actually, more positive caster means the top of the "pivot" is leaning further towards the rear of the car. I am not sure if your wheels would be pushed back any however.

This is a short summary of alignment terms:

Wheel Alignment A Short Course

Thanks 4rBob, I knew I would screw something up on this. Notwithstanding the definitions provided in your article link, the one statement found there summed up my thoughts and I guess my incorrect definitions.

"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."

That was the symptoms I was experiencing until I got the change. This is why I thought positive caster is what I needed. Sorry for the confusion.

 

[Jtraskell]

Within your link 4RBob, there was another link under caster towards the bottom, and here is what was said.

Caster

Positive caster improves straight line tracking because the caster line (the line drawn through the steering pivot when viewed from the side) intersects the ground ahead of the contact patch of the tire. Just like a shopping cart caster, the wheel is forced behind the pivot allowing the vehicle to track in a straight line.

If this is the case, then why did most cars have negative caster specs prior to 1975 ? There are a couple of reasons for this. In those days, people were looking for cars that steered as light as a feather, and cars back then were not equipped with radial tires. Non-radial tires had a tendency to distort at highway speed so that the contact patch moved back past the centerline of the tire (Picture a cartoon car speeding along, the tires are generally drawn as egg-shaped). The contact patch generally moves behind the caster line causing, in effect, a positive caster. This is why, when you put radial tires on this type of car, the car wanders from side to side and no longer tracks straight. To correct this condition, re-adjust the caster to positive and the car should steer like a new car.

 

[FERAL 4R]

Positive caster moves the upper ball joint rearward...pushing the tire forward.

Caster is the tilt of the steering axis of each front wheel as viewed from the side of the vehicle. Caster is measured in degrees of an angle. If the steering axis tilts backward—that is, the upper ball joint or strut mounting point is behind the lower ball joint—the caster angle is positive.

 

[Jtraskell]

Yes, you want more positive caster to prevent rub, but, can you even get +4 degrees with the stock upper A-Arms? And how will that affect Camber and Toe settings?

On my FJ with aftermarket A-Arms, I was able to get +4 or more, but never needed it because I chopped the body mount.

Also, I never have my left/right caster set a different settings. Always the same on both sides...Some say it's for road crown and crap...

It may be crap, but all I can say is that right now after the setting change on all type of roads, crowned or not, I get a much better tracking and decent steering resistance. And if it is not going to effect tire wear, I think will let is stand the way it is.

 

[FERAL 4R]

It may be crap, but all I can say is that right now after the setting change on all type of roads, crowned or not, I get a much better tracking and decent steering resistance. And if it is not going to effect tire wear, I think will let is stand the way it is.

That's cool man. I said "I never have"...Not "YOU should never have"...

 

[Jtraskell]

That's cool man. I said "I never have"...Not "YOU should never have"...

I understand, thanks Feral. I just hope I did the right thing by letting him adjust it that way. Old wifes tales and the such. So far so good.

 

[FERAL 4R]

I understand, thanks Feral. I just hope I did the right thing by letting him adjust it that way. Old wifes tales and the such. So far so good.

If you are running more positive caster, and camber is different from side to side, and you are tracking straight, and you are experiencing no adverse tire wear, then you are good to go. That's a lot of commas right there buddy!

I guess my point is with bigger tires and altered suspension setups, you sometimes have to tweak the alignment settings multiple times to get it dialed in.

With bigger tires and aftermarket UCA's, I will run at 0 Camber, (tires square) .05 Toe and let Camber fall where it falls and tweak from there.


Back on topic... If you don't want to rub, then you need to get more positive Caster if you can, without adversely affecting Camber and Toe. Unless you have aftermarket UCA's, then you should be able to dial in a good start point from the getgo.

 

[4RBob]

Positive caster moves the upper ball joint rearward...pushing the tire forward.

I'm not following how moving the upper ball joint rearward pushes the tire forward? But, I personally have never set caster or know how caster is set on an IFS vehicle. I used to change caster on Jeep's (solid front axles), but that was by shortening the length of adj upper control arms to increase caster. Wheelbase was more constant, set with the lower control arms.

 

[FERAL 4R]

I'm not following how moving the upper ball joint rearward pushes the tire forward? But, I personally have never set caster or know how caster is set on an IFS vehicle. I used to change caster on Jeep's (solid front axles), but that was by shortening the length of adj upper control arms to increase caster. Wheelbase was more constant, set with the lower control arms.

I may be wrong, and I am by far an expert...If you want expert, talk to an expert...but I have experience with Toyota IFS from my FJ Cruiser...And getting the front end alignment dialed in on it over several tries, and working closely with an alignment guru (tech).

I would also like to mention, when you get the alignment dialed in, mark "witness" marks on the cams and bolts. If any adjustments are made at a later date, you can visually see the difference.

With our FJC and 4Runner suspension, the Camber and Caster is set using the lower control arms only. Those silver bolts with the circular looking cams with tick marks on it you see on the lower control arms adjust Caster and Camber. The upper A-Arms are not adjustable (stock).

Setting positive Caster: They will adjust the lower control arm cams where the front bolts are more inward (On the driver side, you will see more of the cam to the right of the bolt, and the passenger side will be to the left of the bolt), and the rear bolts more outward, pushing the lower control arm forward, away from the upper A-Arm ball joint. So, technically, on the 4Runner, the upper ball joints kinda move rearward (The lower control arm will be moved the most) moving the tire forward on axis. And technically the top ball joint is the pivot, so moving the lower control arm forward, also moves the tire forward, creating positive caster.

Again, I'm no expert, and I only play one on the internet....I may be totally wrong.

 

[pawzitiv]

Thanks everyone for your responses.

I do have Light Racing UCA's so I am able to dial-in 4 degrees of positive caster. I do understand the physics of caster angle and its' effect on straight line steering stability (ie more positive caster gives more stability but requires more effort to turn the wheels).

My question relates more to where the caster pivot axis is on the 4Runner. If a line is drawn between the UCA and LCA and the LCA ball joint can't be moved far enough forward, the UCA ball joint will need to move rearwards to get more positive caster angle.

I think I'll first fully flex out my new suspension and then drive my 4Runner fully loaded for a few weeks to get the ride height to settle. Then I'll go back for another alignment and get the alignment tech to dial-in 4 degrees of positive caster. If 4 degrees doesn't help my rubbing issue, I can always go back to less positive caster .. it's just the cost of another alignment.

 

[4RBob]

Ok Feral, that makes sense. So you are "effectively" moving the upper ball joint, but really adjusting at the lower CA, therefore changing wheelbase slightly.

 

[4RBob]

pawzitiv, sounds like increasing your caster MAY improve your rubbing issue. but, even if it didn't, why would you want to go back down again? 4 is still within specs and not too "heavy".

 

[FERAL 4R]

My question relates more to where the caster pivot axis is on the 4Runner. If a line is drawn between the UCA and LCA and the LCA ball joint can't be moved far enough forward, the UCA ball joint will need to move rearwards to get more positive caster angle.

You are correct. The pivot is the upper ball joint. If you have LR UCA's, set them to 0 (zero), take it in for alignment and tell them to loosen the top nut on the LR UCA to dial in the Caster to +4, if that's what you are shooting for.

It also helps to find a good alignment tech...

Ok Feral, that makes sense. So you are "effectively" moving the upper ball joint, but really adjusting at the lower CA, therefore changing wheelbase slightly.

Exactly.

 

[Jtraskell]

Ok already, I am on my 5th beer and just got home from shooting an 79 on a course with a 131 slope in 95 degree heat. After reading 15 posts that seems to explain everything that I said was either wrong or right, jargon aside and notwithstanding my incorrect definitions, did I ultimately give the OP the correct advice? Thanks in advance for your support.......positive criticisms are always welcome..lol.

 

[pawzitiv]

Jtraskell .. I can't say if your response is on the money or not. Stock 4Runners don't have any caster adjustment in the upper control arms; it's all in the lower control arms. Now that I have adjustable upper control arms things start to get confusing because now I have 2 places (each side) to adjust for more caster angle. In addition to having straight line tracking stability, what I'm really after is increasing my wheel base by about 1/4" to get the front tires a bit more forward in the wheel wells.

The fact that you are running 285's on a non-lifted 4Runner and have 4 degrees of positive caster on the passenger side with minimal rubbing gives me cause for hope. Thanks.

 

[Jtraskell]

Jtraskell .. I can't say if your response is on the money or not. Stock 4Runners don't have any caster adjustment in the upper control arms; it's all in the lower control arms. Now that I have adjustable upper control arms things start to get confusing because now I have 2 places (each side) to adjust for more caster angle. In addition to having straight line tracking stability, what I'm really after is increasing my wheel base by about 1/4" to get the front tires a bit more forward in the wheel wells.

The fact that you are running 285's on a non-lifted 4Runner and have 4 degrees of positive caster on the passenger side with minimal rubbing gives me cause for hope. Thanks.

Not that it helps your issue, but I do feel better now, thanks.