You got quite a few different answers here. All of them are possible causes. It is a process of elimination that you need to go through. Take the simple stuff first. One bad tire or out of balance tire can cause this problem. If you can get some one to follow you and watch your tires to see which on is bouncing on you. They should be able to see it if it is bouncing that bad then you know where to start at. If they are able to tell which tire it is then you know where to start at. If they can first move that tire to a different location to see if the problem moves with it and if it does the tire is you problem and if it doesn't you know that it is something with the vehicle itself. I had a new stet of tire put on once that bounced so bad that it broke my rotary. Went back to the tire center and they had five weights on one spot of the tire, they rebalanced them and it helped but didn't take care of the problem. I went back to the tire center again and came unglued on them so they put another set on and all problems were gone.

Can be VERY RISKY to drive, but check the TIE ROD ENDS! in the front, have someone jiggle steering whel back and forth as you put hand on TIRE! If TIE RODS are bad, you wil FEEL a pop or notice play in the jiggle motion! TIRE BALANCE and NAME BRAND and AGE are other factors! Do NOT expect much from OFF BRAND name tires! Stick with MICHELIN< B.F. Good rich ( also MICHELIN) and BRIDGESTONE and even ASIAN and korean makers, like KUMHO< etc! GOOD LUCK to you always!

Yeah........front end problems manifest themselves at lower speeds . . . . rear end problems mostly show-up at 65 and above.

You can nail it down by switching the tires around, if you want to go to the trouble but if as you say you need back tires, that is probably it. Don't know if you are rear drive, front, or all-wheel: possible that it needs a 4 wheel alignment????

Tire imbalance is what's making it shake or cylinder/s not fireing. Alignment has less to do with the shake.

Probably lost a $.50 wheel weight and a tire has been out of balance, causing it to wear unevenly.

It's the wheel balance.

If the vehicle shimmies left and right you have bad inner axle joints. Most mechanics would start by balancing the tires.

You could have a tire out of balance or have a completely blown shock that is allowing a tire to hop.

An axle cv joint is frozen and no longer flexes like it should. Replace the faulty axle. Do not replace things that are not faulty..

My car violently shakes as SOON as I hit 55-60 mph. I replaced front struts and tie rods in front but car STILL shakes. Some say that it may need an alignment so I'm getting one as I type. But I can't even tell if it's the front or back that shaking. The whole car moves like crazy. I know I need back tires. Would that cause the entire car to shake. HELP!!!