I had pirelli's on an MGB and it would sit for long periods of time before driving. I did experience what you are discribing. Siince it would have leak down during sitting I decided to raise pressure 5 pounds over recommended pressure and the tire seated and quit having the bump feeling........maybe this will work for you.

 

if u research this the pirelli atr is a dual steel belted tire and will flat spot in 12 hours time. its a bad design yet its really strong.. just gotta live with it or change them out.

 

Hmm i have the 20's in the same tire and have no problems. Strange!! :/

 

I have this same tire on a s/c. These tries flat spot when sitting on concrete over night bad. Ford replaced them once with no good result. The same. I can drive it less than 2 miles and flat spots are gone. Still annoying. Pirelli recommends 44psi cold. Info from tirerack. Which I found to be way to much. Did help with redusing flatspots but when tire was warm it rode very hard. Ended up with 40 in front and 37 in rear, seems to wear nicely on this truck and ride good.

 

I had the Pirelli STRs on my 20" wheels... Same issue with them flatspotting overnight pretty badly. I only have a 4 mile commute to work, so I literally never had a time during the week that the truck wasn't 'jittering' about from the tires. Even once warmed up, the tires would STILL have a little bit of a hop to them on the highway. I took the truck to the dealership and they road force balanced them and found two to be out of spec. They replaced two of them, and while it seemed 'better,' the problem did not go away.

Long story short, the next day I drove the truck to my local Discount Tire store and talked to the manager of the store who knows me very well (I am in there mounting/dismounting race tires almost every other month), and gave me $100 credit per tire for a new set of Michelin LTX M/S2s. I now have ~1000 miles on the M/S2s and the truck is running VERY smooth.

The sad thing is, when the dealership put two new tires on the truck, I could already tell a BIG difference in the amount of tread depth between the two new tires and the other two that were original, with only 4700 miles on the odometer. The Pirellis wear very quickly, IMO, and don't really provide any better traction than these M/S2s (I do drive fairly aggressively and have found the traction limits of both tires).

The other thing is, with the STRs on the truck, I would get a second 'squish' or 'set' that I would feel in the suspension when cornering hard, and that is now gone. The cornering stability is much better.

Sorry for rambling, but I just felt I should share my experience as well.

 

My 08 came with Pirelli's also and they flat spotted too, I took them off and put on Bridgestones, smooth as glass for about 10,000 miles and now they are F.S'ing too........it's just the way it is.

 

Those tires are junk...swap them out as soon as you can...took mine off at 7K

 

At $303 a piece I think I will wear them until they are worn out........

 

You bought them or did they come on your truck ?? I don't think they are that much...

 

http://www.discounttiredirect.com/di...85&ar=45&rd=22
and $33 ea. to install and balance.