The tires are the most likely culprit, but before you can conclude that, you need to figure out whether the shaking occurs at a given road speed, or a given engine speed. I know you said you notice it above 65 mph, but the next time you drive, pay special attention to whether you notice any shaking in any other gear except 5th, especially when you are between 2,000 and 3,000 RPM, which is probably the RPMs you're running at 65 mph.

If you do not feel the shaking in any other gear, you can just about rule out the engine and the clutch.

The next thing to check is whether the shaking occurs under power or if it doesn't matter. Get the car up to 65 so the shaking starts, and then let off of the accelerator to see if the shaking goes away immediately, or if it continues. If it keeps shaking until the speed drops, suspect worn, defective, or out of balance wheels and tires. If the shaking stops when you lift your foot off the gas pedal, it's likely that it's not the tires but is instead part of the drivetrain, such as a half-shaft or CV joint that's damaged, or possibly part of the transmission.

"shaking" at a certian speed or speed range, especially when felt primarily in the steering wheel is likely associated with the suspension or rotating tire assembly.

As cowboy said it might be directly associated with a tire. Radial tires sometimes can have a belt slip which forces the tire into an oval or out of round shape that does not become noticeable until you're driving at higher speeds. It is pretty obvious to the guy driving next to you because your tire appears to be noticeably shaking while the car is rolling. Of course you can't see this from inside your car.

Could be also be ball joints CV joints or someother suspension related component.

If you whacked a curb recently could also be that your rim go damaged and is no longer balanced or you could have lost a balancing weight.

hope this helps.

A quick and simple test that may or may not prove anything is to rotate your front tires straight to the back and bring the rears forward. If you do not rotate your tires every other oil change (also scheduled) then your fronts may be worn for many reasons but the rears will be much better (usually) and all or most of the vib in the steering wheel will be gone if the tires were to blame, although the car may still have a vib due to the bad tires having been moved to the back. Some people like to balance their tires every so often also but we know that costs too, many have a great place to buy good tires at a great price every couple of years anyways, what is your story.

Duane in Japan

Cowboyind, sdello and Duan,

Thank you very much for your helpful response. I will try to follow your instruction. : )

A worn out ball joint, or a bad CV are not very likely at all, same with the clutch assembly.

I suspect that there are more and more tires of poor quality on the market that are causing problems, and that tires that "last" a long time can be more liable to have thread separation(this takes time, and miles)...

Hi, earthworm, thanks you for your message.