what causes shaking?

Well you can start moving combinations around, two at a time, and find out which one it is.

I am

You are going the wrong way. Those alloy wheels are prone to damage and getting bent and the cheap ones are the worse. Steel is less likely to cause problems.

I suspect the problem is a tyre. Sometimes belts shift so if you look at the tread as the wheel turns you will see it move left and right at one spot on the wheel as it spins. The only fix is replacement. It is also possible that there is a dynamic balance problem. Dynamic balancing cost more (sometimes called computer balancing) they spin the wheel at high speed on the machine.

Of course there are other possible issues, but your description seem to fit a wheel or tyre.

Don't mix old and new tread on the same axle and put the best rubber on the rear. It helps keep your car pointed in the direction you are moving in an emergency.

Have you checked the tie rods and the ball joints? With the car raised up on jacks, put your hands at the 9 and 3 positions of the wheel and try to rock it back and forth. (Make sure that your steering wheel is locked.) If it rocks back and forth (and the movement appears to be coming from the 9 o'clock position mostly) I would suspect your tie rods. If it moves back and forth but the movement looks like it is coming more from the 3 o'clock area of the wheel, check out your ball joint(s). Ball joints should be fairly firm. Next, place your hands at the 12 and 6 o'clock positions and try rocking the wheel. If it moves in these areas, I would suspect your wheel bearings.

Good luck, Bryan

Sorry to pounce on this, but the accepted wisdon is to have the good rubber on the front as it carries 70-90% of the breaking and does all of the steering. (and on a FWD, provides drive; the rears are there to stop the arse dragging)

Which is wrong. The safety experts agree that the best tyres need to be on the back. (BTW that 70-90% figure for brakes is generally not correct as well.). The problem is when a car goes into a skid, the most dangerous thing is to have the back tyres loose grip as that will result in you looking where you have been and not where you are going.

OK, I don't want to get into a flame war over this so I'll continue what I'm doing, you do your own thing, but I want to ask this question.. if the rears are doing so much, why do the fronts alwas wear out first on a FWD?

It is not a question of which tyres are doing more or will wear out sooner. It is a question of what happens in an emergency situation.

Where it not for the handling problem, I would suggest the best tyres on the front. After all you do want the best traction in mud or snow. You also want the best tread up front to reduce hydroplaning. However those who have done the numbers on the relative risks (between hydroplaning and loosing control) have indicated that the best in the back is better.

I would be tempered to reverse that if hydroplaning was a more serious threat where I drive.

Of course it all comes back to the idea that you should have four good tyres and not try and skimp on your tyres. They are the only contact you have with the road.

You are wrong, and dangerously wrong.

Have you thought about checking your rotors I don't know if you have rotors or drums on front sometimes you can get what is called Heat Checking or some call heat spots that can warp your rotors or drums you may wanna check those out too and see if you have any spots if you do you can always have them turned and then of course you will want to replace the pads or shoes whichever applies. Just a thought???

I think I'll keep my best tires on the front, thanks. Drivers who don't know how to handle a skid should probably keep good tires in the rear, but if you have the right reflexes and know what to do in a skid situation I think the traction is put to better use up front.

Just IMHO.

The front tires should match in wear and tread pattern, too, BTW. However with FWD, the rear tires can be mismatched with little effect.

I have to agree with the lawyer here... You are dangerously wrong. First, I think the statement that the front tires do 70-90% of the work is probably correct. heck, the fronts probably have at least 60% of the weight on them statically. Last time I measured it, my 90 Jetta GLI could pull 1G while braking. So I think that puts the numbers somewhere in the 75-82% just based on my crude back of the envelope guessing.

The fact is, on hard braking the rear of your average VW is just along for the ride. There's a reason why the front are 10.1" vented and the rears are 8.9" solid. Is it dangerous if your rear brakes lock before your front brakes? Sure... But so what? There is a rear pressure regulator on the axle to adjust the rear braking strength. You put the good tires up front and then adjust the rear brake power relative to the front to ensure your front brakes lock up first.

I can tell you that if I'm hard on the brakes and I try some radical steering its gonna break loose. Thats pretty obvious. Wouldn't matter if there were good tires on the back or not. You brake, or you steer, you don't do both unless you know exactly what you are doing (or have ABS).

Balancing would be my first option. It takes only a few minutes to do. I get the wheels on my car re-balanced every service additionally to switching the tyres front to back. This gives a nice and even wear with minimal noise increase.

Remco

I would like to point out that most drivers believe they are above average and it would appear that many many drivers who become involved in serious accidents have greatly over estimated they personal ability to drive and control their car. I also tend to find that people who have great faith in themselves tend to find excuses to ignore the advice of legitimate experts because they think they know better.

I am glad you have more faith in yourself than in the experts. I hope I am not involved with you while you are trying out your theory.

The only theory I was referring to was your theory that you and most other drivers have the ability and experience to handle the situation in an emergency situation. I would say I don't, even though I do understand the physics involved. Somehow I doubt that the average driver has that ability and to suggest that they should do otherwise than to follow the advice to keep the best tyres on the back is irresponsible.

Note: I would suggest that it is likely a good idea to put the better tyres on the front in the situation where hydroplaning is a more serious and common problem. The better tread on the front IS more important under those conditions.