Caster (lack of):

I too have noticed the shift to minimal caster. That started in the mid- to late-80's with the prevalence of setback axle configurations. Take an old 359 or FLC120 and it will just about drive itself down the road. With these new trucks, it feels like you have to constantly fight to keep the truck in your lane--you're worn out at the end of the day. Worst truck I ever had was an IH 9200. That truck was just plain dangerous.

 

I am a alignment tech. That is a great question. I increase caster on pretty much every truck I do. Caster is one of those rarely focused on things when it comes to trucks. I know International had general specs of only 3 - 3.5 degrees for the longest time. It was only in the last couple of years that they increased it to 5 degrees. I like to set them to around 4 on the left and 5.5 on the right. You always need more on the right to help fight pull to the right caused by road-crown. The difference in caster between left and right is called Cross-Caster. Again International increased their specs from 0.5 to 1.5 degrees. Any good alignment tech will adjust caster during an alignment. Caster can be a pain in the ##### to adjust since you can run into seized ubolts or a center bolt that is too short to accept a thicker shim. Caster can also be a big time consumer and so gets skipped by some alignment shops. For the most part I think assembly plants are relying too much on dealers to get the truck set up for either highway or local running. Rule of thumb is that local or city trucks have low caster to they turn easier and reduce driver fatigue, where as line-haul trucks get higher caster for better highway handling. OEMs simply can't be bothered with two different spec levels for caster and just assembles them with a "general" ball-park amount. I have aligned 100's of trucks, many straight from the assembly line. All new trucks need alignments. Pretty much all need the caster increased. If it isn't done right at the beginning the truck will never "feel" right.
Powell - you will be lucky if your truck doesn't have a slight, constant pull to the right. Your caster on the right should be at least 4.5. Do you have a Hendrickson Airtek steer axle? If you do, then you can't change cross caster because that axle is a hollow square tube type. Cross caster actually introduces a slight twist in the axle beam itself. Airteks won't bent that way, the spring and air bags will take it.

 

In the 1970s, the alignment shops were busy as we changed from bias ply to radials. Theoretically, radials ran cooler and got better fuel mileage but required stronger rims. With near zero caster, radials handled the same, loaded or empty. It took a giant of a man to steer a loaded truck without power steering, bias ply tires, and too much caster.

 

Don't know about US but in European Union there is some stupid rule that even the weakest driver must be able to turn the steering wheel after the power assist quits, that's why they use so little caster. Volvos are worst, DAF and Mercedes best. You must have at least 8 degrees caster to get a good handling.

 

I think its probably related to power steering pump and steering gear warranty. The harder those components work the shorter their life will be of course. There have been a lot of effort in the last 20 years to reduce the cost of components and warranty for trucks.

 

As far as who is to blame, I would say everyone. Everyone should know that trucks need more caster on the right at least. As for what is perfect, that is wishy washy. Unlike toe-in, caster has more of spec range rather one perfect number. Every truck handles a bit different, and every driver handles it a bit different. Some trucks are "good enough" with caster under 4 degrees. Most drivers don't know what it is or what it does. Unless you are an alignment tech, (not all mechanics do alignments) most managers don't know either. Again, the OEMs are being cheap, quick, average or whatever. There specs from the OEMs and specs from the axle manufacture and sometimes no one wants to stand up and say "this is how it should be". I really haven't talked to other shops or techs about caster. I know in my own shop, out of about 20 techs only 4 of us do alignments. Out of the 4 I am the only one who adjusts caster on a regular basis. I would guess there is an issue with dealerships not properly setting up trucks from the beginning. As for the p/s pump strain, I don't think so. If caster gets too high, like around 6 degrees you will start to feel every bump in the road through the steering wheel and have a shimmy. When you turn, one wheel tilts inward and the other tilts outwards. It isn't 50/50 even but the caster increase would cause minimal pressure increases on the p/s system.

 

Did two alignments this week, had to increase caster on each on. Went from about 3.8 to 4.7 on each one.