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I own a 2002 Ford Focus ZX5 that about one year ago I had the brakes and rotors repaired after noticing some grinding. Shortly after that, I noticed a thumping when I applied the brake. I took it back to my repair shop and he re-turned the rotors. This took care of the problem for a little while. About a month later the car started doing the same thumping, but now when the car was in motion - not while braking. It started off as a minor thump, but has since gotten quite a bit worse. I've read up on the problem on various places on the web, but all I keep doing is eliminating potential causes without finding the real problem. The problem seems to be worse when the tires are cold and lessens as the car has been driven for 10 or 15 minutes. It starts off as barely noticeable around 20mph and actually feels/sounds like a flat tire (without the pulling) at 60mph, then it begins to taper off around 70mph.

In that year, I've replaced all four tires. I keep them properly inflated (I check them once a month), and keep up with general maintenance. The alignment is more or less perfect from what I can tell. I've read that it could be faulty motor mounts, and they suggest you rev the engine while in park to see if the thumping occurs, which it does not. I've also read that misfiring spark plugs could cause it so I've shut the engine off while the car was in motion to see if the thumping stops and it does not. The problem doesn't seem to originate from the motor, it seems to be coming from the wheels themselves or something directly associated to them.

I do a fair share of the minor to moderate repair work on my car, but I'm no mechanic. I'm more than willing to take it to a shop, but I'd at least like to know a general idea as to what the problem could be so I don't get raked over the coals by a sly serviceman. Does anyone have any idea about what this could be?  

some tires when parked hot... will flat spot...

what kind of tires pressures are you running... on the side walls of the tire... there is a load rating and a max pressure cold ,,,   set the tires to the max pressure cold ... and see if it improves...

got any jack stands???   can you park the car as soon as you stop and put it up on stands overnight.. see if it thumps in the morning..  no thump... you found the problem...  

The side of the tire says "51 psi max press", load index is 87, load is 545kg/1201lbs. I've seen tires give a cold psi but these do not. I keep my tires around 34psi because that's what my car manual (and the sticker on the inside of the door for the gas tank) says to keep it. I don't have any jack stands but I'd be willing to try it. Before I go out and buy them though, I'd ask that would this problem likely occur across two sets of tires? The first set didn't give me this problem until after the brakes were repaired. The second set were brand new tires and gave me the same problem from day one.  

jack it up one morning.. and rotate the tire while you have you hand on the tread... you will be able to feel any flat spot...

just lift the front wheels.. as they have most of the pressure on them...

51 psi sounds like a weird pressure... these low profile tires???  

how accurate is your gauge?????  

and after a normal days drive... how hot are the tires????    HOT   warm.. cold...   if they are hot... you might try bringing the pressure up to more.. best to talk to your tire manufacturer.. or tire shop mananger...  

205/50R16, 87H... so yeah, low profile. They're the exact same specs as the tires that came stock on the car (which was the first set that started having this problem after the brake repair). Both sets of tires I've had are those specs. When my mechanic mounted and balanced the new set he put the pressure at roughly 35psi (one 33, one 34, two 35... I just figured he wasn't being overly precise). These new ones are Cooper tires. I believe the old set was Michelin.

The tire gauge I use is digital that I use at home, accurate to half a pound, but I've used an analog one at the gas station down the street several times and verified the pressure.

Typically I drive 25 miles highway to work in the morning, and 25 miles highway home in the afternoon. So... they're as hot as they could get from that kind of usage which I can't imagine is a lot.

I'll try the jack stands this weekend when I'm able to go buy some, but I'm a bit reluctant to think it's the tires that's causing the problem considering the same problem has been happening across two completely different sets of tires - one of which were brand new tires. So... devil's advocate, what would be the next most likely culprit if I try the jack stand thing this weekend and it's not the tires? A buddy of mine said shocks/struts. That sound possible?  

pump the pressure up to the side wall rating...   that is the cheepest way to see if that fixes the problem...

low profile tires really need as close to the sidewall rated pressure as you can run without turning them to bricks...

25 miles with the tire just slightly over half the normal tire inflation pressure might cause it to take a set over night...  

I have the same problem.
2002 ZTS, thump thump thump that increases with speed. very annoying.
I thought it was a bad belt in a tire, but i switched them out with the spare one at a time and the problem persisted. BF Goodrich g force sport.
It is a thumping sound that starts about 20mph, gets louder then fades out around 60mph. Seems to come from the rear, I know that there are only bearings and drums rotating back there. I don't think it's suspension. I turn the engine off, put it in neutral, apply the brakes, nothing affects it.
I am a former mechanic and can't figure this one out.
It doesn't matter if the road is very smooth/just laid new asphalt. It seems worse when the tires are cold.
Any suggestions would be appreciated.