I've been hunting down a vibration problem for about three months now. A little background info.:

Bought my Kumho Ecsta ASX 215/55/16-W speed rated tires in July (my sister's boyfriend, now my new brother-in-law, took it to Discount to get them put on in Chicago). I drove it out of the city and they were severely out of balance, alignment was done right after the new tires were put on (assumed that was not going to be a problem), had them balanced in Springfield, Il on my way back to San Antonio and that made them a lot better, but I still had a little vibration. Proceeded to take it in three more times to Discount for spin balancing and each time at least one of the tires was out of balance. By this time the steady vibration had stopped and it would just do it after the car had been sitting for a while and 5-10 min. of driving would make it pretty much go away. The fourth time I had them spin balanced, I ended up taking it to the dealer and they did alignment again cause Firestone sucks and didn't do it properly (I saw the spec sheet and the alignment was way out of spec). Still had a little vibration after they did alignment and they (the dealer) told me the tires needed to be road force balanced and wanted $110 to do it. I said to hell with them and took it over to Discount and paid them $50 to do it. It seemed ok as I drove it home and the next morning when I drove it to work it still did it. Now let me describe what the vibration is. It will onlly do it when the car has been sitting for more than an hour. After you drive it for about 5 minutes, the vibration will go away and it seems fine. The best example I can give is when I left it for four days (gone to my sister's wedding) and came back. Took it out the night I got back and it was especially bad, but once again, it stopped after about 10 min. It seems the faster you go, the less you feel it. Between 60-75 mph is where you will mainly feel it, but like I said it goes away after about 5 min. of driving.

Now to my question. I took it to the dealer the next day (Monday) to ask them what the hell was going on and why, after spin balancing them four times and then having alignment done and a road force balance, I was still getting this problem. The tech went for a ride with me so he could feel it too and he told me that because these tires are W rated, they are soft and will develop flat spots when the car sits for a while. He told me to bump the air pressure 4 psi to curb the problem. They set them to 32 front and 36 rear (+4 psi from manufacturer reccommended tire pressure). I don't know if i can believe this because I have never once seen a Lexus IS 300 or any other sport car or sedan with Z+ rated tires have an issue like this (my brother-in-law owns an IS 300 with Z rated's, got two twin brother friends, one's got a Mustang GT and the other a Z28, they've never had an issue like this with their Z+ rated tires). What's the deal here? Is my dealer filling me full of crap? Should I take them back to Discount, describe the problem, and ask for a new set cause these are defective? Are they defective? Please help!

 

flat spotting depends on the tires, but it happens so i would say its normal if it is going away.

 

That's just it, it isn't going away, it happense every time the car sit for more than an hour. It only goes away afgter driving for 5-10 min.

 

bump.

 

it sounds as if you are experiencing flat spotting which happens to some high performance tires since it goes away after the tires have warmed up .... many higfh performance tires experience this and lower cost high performance tires see this more often .... more of an annoyance than a problem

 

Thank you Luke, I was just looking for a second professional opinion. I'll take it as annoyance and move on.