If the tires are balanced but the car still shakes what could it be?

Answer 1

One of the most common problems I have found which are manifested by excess vibration in the area of tire/wheel that is not cured by rebalancing has to do with the condition of the tire. If a tire that is out-of-round is balanced, the out-of-round condition is not cured. What that means is that, while the balancing ensures that the tire/wheel assembly will not deviate abnormally from the forward/backward plane as you drive(side-to-side), there exists nothing to prevent its up-and-down movement due to its shape(oval or ellipsoid). Another common problem, potentially dangerous, is tire separation. Should a tire begin to separate, that separation may not be readily apparent without a road-test, at which time it will be noticed that the steering wheel shakes violently when certain road speeds are reached. To locate the offending tire, it is advisable to move the front tires, one at a time, to the rear of the car. In so doing, you should notice a distinct difference in the car's behavior when driven once the culprit is moved from the front. Note: If you have just had your tires replaced and the wheels balanced, there may be another explanation for the problem, assuming it did not exist prior to this: The stub-end of an old tire-valve trapped inside the tire. I have encountered this problem at various times; and, what happens is this: The tire purchase is made, and the tire man pulls your wheels off of your car. The wheel/tire assembly is put onto the tire machine, and the valve core is removed from the valve, letting the air escape so that the tire may be dismounted. The tire is then removed from the wheel. A new tire is now chosen and mounted onto the wheel. Next up is a new valve. The replacing tool is screwed onto the old valve, which is then pulled free from the wheel, out of its hole. Most of these do not come out whole. The "bottom"? Well, that falls innocently away. A new tire valve is now installed, being pulled into place with the same tool used to remove the old one. The tire is then aired-up, sealing the bead, and is moved to the balancing machine, where it is spun by computer-control and indexed for weights to be attached. This done, all is well, right? Not exactly... You see, that innocent little piece of old tire valve which fell innocently away when removed isn't actually innocent at all; but is, in reality, a nefarious little critter which has stowed away inside the new tire, now balanced--- or so it was thought... In reality, that little hunk of rubber rolled around inside the tire on the balancer just until the spin of the tire created sufficient force to make it stay in one place while the tire was spinning.... This is where it resided when the computer indexed the tire's proportional weight characteristics and where upon the rim certain weights were to be placed. Guess what: All of that changed when the tire came to rest, allowing the gremlin to fall to the bottom of the interior cavity--- and it will continue to change every time the tire moves. That is, of course, until the tire is broken back down, and the little imp is removed. Many times this situation can be detected with a good ear once the tire is jacked up and spun. If you hear something rolling around inside your tire, it's back to the tire shop. Balancing tires properly can only take place when nothing is trapped inside the tire. Another thing to consider is lug-nut torque. Over- or under-torqued lug-nuts can be dangerous, as well as a nuisance--- especially when aluminum wheels are involved. Tightening lug-nuts beyond their intended torque can warp a brake rotor, as can torquing them down unevenly or by not following the proper tightening sequence. This can result in a pulsation in the brake pedal, a shimmy in the steering wheel, possibly broken studs, and potentially the loss of a wheel while driving--- and that ain't good... And aluminum wheels: After initially mounting these and torquing them down, they require a re-torque after they are driven a short distance(20 miles or so), and a final re-torque after another 50-100 miles. This is due to the fact that the aluminum of which the wheels are made expands at a different rate when heated than does the steel to- and with which- it is bolted. If these are not properly torqued and re-torqued, the heat generated at the wheel serves to create a gap between mounting surfaces which grows--- and you end-up with lug-nuts that are only finger-tight, if that much. This is dangerous... Finally; anything which is worn in the steering or suspension can cause such a problem, as can a bad cv-joint, or a bad bearing. It wouldn't be fun to find out that a tie-rod end was bad by having it come apart while driving down the road, allowing a wheel to go whatever direction it was so inclined toward, rather than where you intended it to go through steering... A good front-end inspection goes a long way--- be safe... Hopefully, something here will be of help. Rotsa ruck.... jb