Frame resonance.

[Pinger]

What kind of tires are you running?

Continental ContiContactCross AT 265/65 - 17.

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[Pinger]

Do you have an aggressive tread off road , snow type tire?

See above post.

Yes the max inflation is 44 psi at MAXIMUM LOAD of XXXX.
If your not running at maximum gross loads , your over inflating. It must ride harshly, are your fillings getting loose yet?

It was worse before. Lowering the pressures from 45/50psi F/R to 40/45psi F/R eliminated some of the harshness.

Drop the pressure to 35. Your hard ride and aggressive tread, high tire pressure could be finding a harmonic frequency equal to or on balance with frame, body.

I've been wondering what forces the vibration and tyres was all I could think of. If so, the trend seems to be that lower pressures shift the frame resonance frequency to a higher road speed eg, from 60-65mph to 70-75mph now.

It may not " feel right " but there is a recommended tire pressure on the door jam or in the handbook.

Door jamb says 35/50psi F/R for comfort. I'm 5psi above on the front and 5psi below on the rear.
If I go with 50psi rear I'm above max pressure for tyre (as stated on sidewall). I guess I could lower the fronts to 35psi and see what transpires.

My tyre pressures were debated a few weeks back here >> https://www.gmt400.com/threads/tyre-pressures-and-wear.63644/

 

[Pinger]

Add some weight to the rig (2nd row peeps and/or add trailer) to help identify source? suspension or driveline

I think the intensity of the vibration is worse with reduced load.

Increase frequency of tire rotations?

I'm looking more that rotation has contributed to this. I only rotated them to balance off the uneven wear (more in centre of tread at rear) and would have just moved them front to rear and rear to front but instead did them as per handbook which sees them shifted side to side also. Why the need for side to side?

 

[HotWheelsBurban]

I think the intensity of the vibration is worse with reduced load.

I'm looking more that rotation has contributed to this. I only rotated them to balance off the uneven wear (more in centre of tread at rear) and would have just moved them front to rear and rear to front but instead did them as per handbook which sees them shifted side to side also. Why the need for side to side?

Maybe tire technology has improved a bit since I was in school(probably has, that was a while back) but I was always taught that radial tires were always rotated front to back, or back to front, on the same side of the vehicle. Once they've been run a good while in one direction, they should stay running that direction....

 

[SUBURBAN5]

Maybe tire technology has improved a bit since I was in school(probably has, that was a while back) but I was always taught that radial tires were always rotated front to back, or back to front, on the same side of the vehicle. Once they've been run a good while in one direction, they should stay running that direction....

The gm manual says, rear tires stay on there side but move straight forward. The front tires go diagonal to the back. Not sure if that per tire type but I though it didn't matter due to wear?

 

[Pinger]

Maybe tire technology has improved a bit since I was in school(probably has, that was a while back) but I was always taught that radial tires were always rotated front to back, or back to front, on the same side of the vehicle. Once they've been run a good while in one direction, they should stay running that direction....

That, is exactly how I'd do it - or done it - left to my own devices. GM handbook says diagonal and I obeyed. Truth be told I've never previously moved them between axles. With the smart, it wasn't even possible due to different wheels front and rear.
Many - if not all - high performance tyres are directional ie, their direction of rotation is predetermined and has to be adhered to.

 

[Hipster]

I only rotated them to balance off the uneven wear (more in centre of tread at rear) . Why the need for side to side?

center wear is indicative of over inflation, Sometimes it's about what works with how you're loaded without wearing tires out. If you run empty except for the occasional load I'd try less in the back and air up if loaded. The jamb sticker is not the end all be all.

When I'm underneath it I give the propshaft a tug to check for play in the UJs and they are fine.

That will tell if one has play, it won't tell you if it's dry and binding. If could be a dozen things; a tossed wheel weight, tossed DS weight, Pinion bearing/diff issue, tweaked rim that more prevalent on the opposite end of vehicle, separated tire belt , wheel bearings on their way out, etc. Conti's are generally top notch tires so a tire problem would be way down on the list.

I've always been under the impression radials are to stay on the same side and only bias-ply get crossed.

 

[Caman96]

This doesn’t apply to modern radials.

I've always been under the impression radials are to stay on the same side and only bias-ply get crossed.

Unless they are unidirectional.

 

[Hipster]

This doesn’t apply to modern radials.

Unless they are unidirectional.

Radials were a new thing when I learned. lol

 

[Caman96]

Radials were a new thing when I learned. lol

Trust me, I’m not modern either. Lol

https://www.tirerack.com/images/techCenter/tires/tireRotation_1.png

Seems like most tire manufacturers use these patterns. For “multi-directional” tires.