Unstable driving down the road

I'm with you but it can definitely be tires too.

 

Not doubting that a bit (The factory setting), I’m questioning the statement it “needs some pull towards each other to keep it tight.”

 

For what it’s worth, I did alignments on cars for 5 years. I agree it sounds like alignment issue. I know if the toe is off it will make one drive “squirrelly” also the castor being off can too. Every vehicle has positive castor from the factory to help it drive better. Unfortunately most truck alignment shops set the toe and send the truck down the road. If you take it to an alignment shop, it needs to be a good one that understands your problem and what you are trying to correct.

 

*And those are REALLY hard to find. I live in a pretty good sized city. Trucks everywhere. ONE known truck alignment shop and I've asked around for years. I just don't see how this happens but so far it's the way it is.

 

Too high tire pressure on the rear tandems. Try to keep them at only 100psi.

 

Same happens to me. Yesterday i replaced 8 drive tires Douublecoin and now when i switch lane the truck is acting weird, it’s kinda goes left and right and then straight up weird feeling.

 

Doublecoin tires are the worst tires money can buy. They are soft rubber. Had 1 set on a brand new trailer, and they didn’t even last 100,000 miles.

 

Lack of caster 100% does cause wander and weak return to center

 

If it's the Hendrickson air,
It's critical to add a caster wedge and lower by 1" makes the truck a whole different machine.

**When set correctly it'll have equal or slightly less front air PSI compared to rear suspension at gross weight

Class A Motorhome bus type smooth glide ride and great steering feel, extremely stable in cross winds etc