Random Thumping front right question?

[gulfstreeeam]

NOT A POLITICAL QUESTION!!!

My seldom driven '87 Targa has started a new random sympton - while driving after sitting in the garage for 3-6 weeks, everythings seems perfect for the first few miles,
then it feels like the front right tire is a little out of balance, and it progressively gets worse. I stopped to see if there's something wrong with the tire then drive off and the thumping goes away for a short while and slowly comes back.

It can't be a out of balance problem since it comes and goes, my guess- it is in the suspension, but a friend suggest it may be the calipher sticking from slowly generated heat?

[Flieger]

Is it rhythmic- that is, does the thumping frequency change with the speed?

[gulfstreeeam]

I don't think so, but I'll double check tomorrow if its not raining.

[Danny_Ocean]

Flat-spotting of the tire? Separating tread? Flip-flop the wheels and see if the problem switches sides.

[gulfstreeeam]

Will switch & check, tires 95% of tread remaining - looks great, but car parked for weeks on end too long, how quickly will tires develop flat spots?

[Flieger]

Flat spots from sitting too long start bad and get better as you drive and the tires warm up and become more compliant.