Mid-Travel: Too much caster?

Here is some good info about IFS and UCSs.

https://www.youtube.com/watch?v=_68Hc8GtLko&t=297s

https://www.youtube.com/watch?v=l1tTelhdEiM

https://www.youtube.com/watch?v=huMztKaHsUE&t=11s

https://www.youtube.com/watch?v=InQnp42pfts

https://www.youtube.com/watch?v=LAYGdcKSA3o

 

specs from my most recent alinement... and it feels spot and great going down the road. Lifted and with JBA UCA's..

 

Caster added at the UCA does not help tire fitment because it moves the wheel backwards. However, caster added at the LCA does. I think this is explained in the videos I linked.

 

Thanks! I was sure I had imperfect information but it's good to stay refreshed

 

I ran high 3s, lows 4's in caster on a full mid-travel upper and lower, and it was fine. My LT setup now runs even more. If you can run big tires with OEM spec that awesome but these trucks make that hard to impossible since most UCAs have built in caster.

 

Thus the SPC UCA (and some others) that have adjustable caster and camber.

 

The numbers are all pretty meaningless because every truck is different. I’m also lazy and don’t do my own alignments. Before an appointment, I just max out caster at my LCAs and let the tech make minimal adjustments from there to get it to drive well while maintaining the max possible amount of caster for tire clearance.

When you get your truck back, test drive it and if it’s not right, have them make it better until it is right. Sometimes a measure of compromise is required on non stock trucks.

 

Too little caster, like a shopping cart "caster" can cause bump steer and touchy steering. This would be more and more noticeable the more negative the angle goes below around 1.5* Too much caster, like a motor cycle chopper, causes heavy steering and slow return to center or no return to center steering thus having to manually center the wheel. This becomes more and more noticeable going more positive from around 3.2*

 

Please explain your understanding of what you think bump steer is or what causes it?

 

Bump steer is exactly what the words imply. When there is suspension travel, the steering angle changes, so if you hit a bump and you come out of it, your truck seems to go in a different direction and you have to correct it manually, on the fly. That's why the example of a shopping cart wheel applies. Just watch a shopping cart wheel as it hits every little imperfection in the floor. BAck and forth, back and forth, toe in toe out, toe in toe out. Obviously, what causes it is the low caster angle, when the UBJ is vertically parallel or close to parallel, to he LBJ.

 

You say the steering angle changes when there is suspension travel. But why does the steering angle change?

 

Because the toe changes when the suspension travels. Positive caster helps negate the effects of the toe change within suspension travel.

 

So why does the toe change? And if positive caster helps negate it why would people recommend that this guy should degrease his caster from 4.5 down to something like 3.8? What he is most likely feeling is what is referred to as feed back not bump steer.

 

Ok, so we all have put taller springs on the front of our trucks. Without adjusting any of the cams, on the front or the rear of the LCA, your Caster, camber, and toe all change, just by making this change. If you were to take it to an alignment shop right afterwards, your caster would be decreased, your camber would be increased, and your toe would be toed out on both wheels. This is a permanent representation of uptravel of the suspension thus you have to dial back the caster/camber angle THEN adjust toe once proper caster/camber angle is acquired. The OP described a "dead zone" . When you have too much caster, steering is not as responsive as it is with less caster thus giving the steering a "heavy" feeling

 

What kind and size of tire?

 

Ideally you would want the upper and lower control arms and the tie rod all the same length between pivot points and the pivot points in the same plane. This way all 3 elements are always parallel to each other and you have no toe change as the suspension cycles.

This is not possible in a road vehicle due to space. Also on a road vehicle the tire doesn't simple move straight up and down but up and back which helps absorb the bump. They also degin in toe changes as the suspension cycles for their desired handling affects but this is all designed at the standard ride height. When you raise or lower a suspension too much you get undesirable affects which people call bump steer. You then add in different wheel offsets and tires and some people have it worse than others.

 

I understand this but was trying to see if the one I was asking did. I think a lot of people assume feedback is from bump steer. Bump steer is feedback but it is not the only thing that causes feedback.

 

I only answered the question the OP asked. 4.5* absolutely would cause what the OP described as a "deadzone". Of course, there are other things that cause "feedback" (Scrub radius is another problem angle because guys change the offset of their wheels.) but that wasn't the question, the question was, which has been asked ad nauseum on here is generally how caster affects ride.

 

Lots of confusing misinformation on this thread. You need to understand caster and how changes impact your truck. Caster is an angle created by the difference between the upper and lower piviot point (ball joints) in relation to the centerline. This means that it changes from two different locations. The stock alignment adjustment is done by using the lower control arms. This adjustment only allows for specific amount of change and when you change your ride height, you can over come this with new upper control arms which reposition the ball joint. Most of these are fixed. SPC offer an adjustable ball joint which allows you to fine tune caster.

You also need to understand what happens when you gain caster using your upper and lower control arms. When you gain caster with your upper control arms, it moves the ball joint back toward the cab. This means that your tire will sit closer to the cab and when you turn, it is enhanced and gets even closer to your cab mount. The lower control arm adjustment is the opposite. When you increase caster with your LCA, it moves the tire closer to your bumper. As with the UCA, the more you dial in, the more that sweep increases. Ideally, you want caster to be on the high end of the spec, but sometimes limitation prevent this.

As for the impact of caster, you need to understand what happens as you increase and decrease caster. Lower caster means your ball joints are closer to being in line. This makes your suspension parts happy, but makes driving a challenge. Your truck will wander all over the road. Think of it like putting a lot of weight in the front of a wheel barrow. steering and lifting is light, but you hit a bump and you are chasing it. Higher caster means the ball joints are at increased angles. This make your truck track much better, but harder on your suspension. This is like moving the weight back in your wheel barrow. It gets heavy. It tracks much better, but harder on your back.

More caster is better, but as the OP has seen, it puts weight on your steering. You have to put more input to make turns. Some cars are designed for this. Mercedes and BMW love lots of caster. You can see it when the wheels are turned that you see a lot of lean from the caster. This makes them ride so much better on the highway, but they also have beefier suspension to accommodate that.

For me, I try to get as high on the caster spec as I can.

 

I agree with everything you said - save for maxing out the caster. I pushed my LCAs all the way forward prior to alignment and told the tech to get as high as caster as possible, and sure enough he was able to achieve 4.5 degrees. It created a dead zone, which I want to focus on. I'm of the opinion that steering sensitivity issues exist at the low and high end of the caster range. You already nailed low caster (constant input needed to correct wandering truck), but think about how high caster pushes the wheel out forward (like a chopper as someone mentioned on this thread). When going over bumps, the wheel is harder to control with it being so far forward. A good example is when wind hits the side of my truck on the highway. A lot of input is needed at the steering wheel to adjust the vehicle to the desired position in the lane.

My takeaway is to avoid the mentality of "as high of caster as possible". It is possible to go too high and create a steering "dead zone". Perhaps folks desire it so they don't need to do a CMC. I have a minor CMC and wouldn't mind cutting again once I bring the caster back to 3.5ish degrees.