Hello all,
I have vibration in my 1991 civic cx hatchback between around 55-65mph. Above that speed the vibration goes away. If I release the gas in that speed range I think it still vibrates/shakes. I had my wheels balanced but it didn't seem to help (not that I can verify if the mechanics actually did anything). Possibly related, the front right tire seems to bulge out a little on the bottom--not sure why.
Thanks

 

Check the wheel bearings

 

if wheel bearings are bad then it would wobble at all speeds...either you need to get your wheels balanced again or one of your wheel is out of round that it wobbles when you reach up to speed... I've had bad wheel/tire combo in the past that no matter how many time I've had it balanced it would still vibrate at the same speed as yours (bet 55-70mph)...another thing you might want to check is if your wheels are hubcentric.

 

What do you think would be the best way to diagnose the bad tire and/or wheel if I take it in to a mechanic? If I end up replacing just one tire, does it have to be the exact same brand/type of tire?
Thanks

 

Rotate your tire to see if it still shake. (Back to Front)
It might be a bad rim/tire.

 

Check the steering tie rods. I had the same problem, never had a chance to fix it but I figured thats what it was.

 

Get your wheels balanced, when wheels are unbalanced the speed you will feel it around the most is 55-65.

 

I've had a shake identical to what you descibe since I bought my car. For me, it was definately something with the crappy Mastercraft tires or a balancing issue. I just had another set of tires mounted and balanced, and the car feels like a new car: it's so freakin smooth now. So unfortunately, I can't really tell you if it's a balancing issue or a problem with the tires, but it was most definately one of the two for me.