A little less air?

Low pressure on a motor bike leads to this:

Be careful lowering it too much.

low pressure can also cause the tire to be spun on the rim from torque,,,
causing the valve stem to be cut

The fattest tires you can fit on your motor bicycle are the most comfortable.

I always assemble my rear wheel with the valve stem leaning into the drive direction so I can easily see when to reset the tire on the rim by watching the valve stem. When it gets straight, I let the air out and reset it.
I lost several tubes to valve stem failure before I started doing this. It can happen very quickly if the pressure gets too low or if you don't keep an eye on it.
Certain tires are more prone to this. I tried running a Bontrager kevlar flat resistant tire for awhile but it was impossible to keep it from slipping no matter the pressure due to thin flexible sidewalls. I now run cheap thick hard mountainbike tires from parts bikes and have much less trouble. I get them off cheapo parts bikes and usually have several laying around. The harder cheapo tires wear much better than good soft grippy tires, and I'm not road racing so I don't need better traction.

I would give em a try at 60psi...
rc