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Discussion Starter #1
Hey all,
I have a 2000 S430 with AMG wheels and 18 / 40R - 275 tires in back ( installed by the previous owner) . I am noticing a very twitchy rear end. When I hit a bump or pothole the rear end seems to skip to the side. It is a very strange feeling that other S-classes I have driven did not do. Most were rock solid over bumps. I have had the car up on the lift and cannot find anything noticeable. The factory alignment cams are in position and there is no noticeable movement or visually decomposing bushings. I have a few questions such as, is it possible that even though the airmatic system is working that the hydraulic portion of a shock is bad? Could the tires be causing this? Anyone else have this happen?
Thx,
Jeff
 

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I have heard of other people having a similar problem with oversized wheels and tires. You should go to maybe a 17 inch wheel at the most.
My mechanic warned me against anything bigger than maybe 1 inch larger because the tires do not have enough side wall to compensate for the shocks of bumps and you can experience side to side instability.
He also said the larger wheels and low profile tires can also cause stress cracks in the strut mounts which can cause complete suspension failure. This is due to the tires not having enough sidewall to absorb some of the shock.
 

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Discussion Starter #3
I would definitely agree that a thinner sidewall would cause a more harsh ride and more stress on the strut mounts ( which are a weak link anyway in front). But I'm not sure how the sidewalls would cause a side-to-side instability unless the tires being wide are causing them to pull on ruts.
 

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Outstanding Contributor Always Remembered RI
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Do you know any kind soul who would lend you a pair of 17 inch wheels to try as this is the only way you can prove/disprove its the wheel size causing this. Personaly I think it is the wheels, but with bigger wheels the wheel bearings do take a lot of pressure so check the bearings for free play:thumbsup:
 

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Discussion Starter #5
That is a great idea and one I thought of also! It would certainly be a good test. But alas, I don't have access to another set of wheels. I'll ask around. Anyone in North Dallas want to swap wheels for 20 minutes in exchange for a case of beer?
Jeff
 

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That is a great idea and one I thought of also! It would certainly be a good test. But alas, I don't have access to another set of wheels. I'll ask around. Anyone in North Dallas want to swap wheels for 20 minutes in exchange for a case of beer?
Jeff
Way to go:thumbsup:
 

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Before you get too fancy w/ fixes, you might want to check the torque on your lug nuts. Our cars require 110 ft.lbs. and most tire places will only want to torque them to 80 ft.lbs. for some reason--I guess that's "normal." I went from OE 16" wheels to 18" a few years ago and that happened. I experience a certain "twitchieness" too and asked my MB SA and he said to make sure they were at least 110! Once I had them torqued properly, I had no more twitchieness.

Please let us know what you do...
 

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Outstanding Contributor Always Remembered RI
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Good point Jayhawk:thumbsup:
 

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Discussion Starter #9
Thanks for the idea. I checked all lug nuts with the torque wrench and they are 110+ ft lbs. One thing I also did was to increase the tire pressure from 32 to 35 psi and the car seems to be a little bit better. I'm really starting to think it's the tires . They are directional and wider at the rear so can't rotate them but I'm thinking of swapping sides ( running them backwards) for a test. I remember having a set of truck tires that pulled strangely. After replacing them, everything was fine.
 

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Thanks for the idea. I checked all lug nuts with the torque wrench and they are 110+ ft lbs. One thing I also did was to increase the tire pressure from 32 to 35 psi and the car seems to be a little bit better. I'm really starting to think it's the tires . They are directional and wider at the rear so can't rotate them but I'm thinking of swapping sides ( running them backwards) for a test. I remember having a set of truck tires that pulled strangely. After replacing them, everything was fine.
If you run your tyres in the wrong direction, it will achieve nothing and may damage the tyres,
 

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Discussion Starter #11
Eric, thanks but I differ on that as far as a test goes. I am aware that a tire is biased by turning one direction and that rotating it oppositely can create safety problems --especially on an older tire. I am trying to rule out the tread pattern causing the tire to pull by rotating backwards. Only planning to do it for a matter of minutes at low speeds around the block a few times. Wouldn't want to run it on the highway that way....
 

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Eric, thanks but I differ on that as far as a test goes. I am aware that a tire is biased by turning one direction and that rotating it oppositely can create safety problems --especially on an older tire. I am trying to rule out the tread pattern causing the tire to pull by rotating backwards. Only planning to do it for a matter of minutes at low speeds around the block a few times. Wouldn't want to run it on the highway that way....
Sorry, but what do you expect to achieve with a test like this? Think about it running tyres in the wrong direction will give you a different set of problems and not achieve the original goal of finding the true cause.:confused:
 

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Thanks for the idea. I checked all lug nuts with the torque wrench and they are 110+ ft lbs. One thing I also did was to increase the tire pressure from 32 to 35 psi and the car seems to be a little bit better. I'm really starting to think it's the tires . They are directional and wider at the rear so can't rotate them but I'm thinking of swapping sides ( running them backwards) for a test. I remember having a set of truck tires that pulled strangely. After replacing them, everything was fine.
Don't do that!
 

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I think this whole discussion might have been better addressed on the Tire Rack forum here. I would at least PM Luke and see if he will look at this thread and comment here...
 

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I think this whole discussion might have been better addressed on the Tire Rack forum here. I would at least PM Luke and see if he will look at this thread and comment here...
I forgot about the tire rack, best idea on this thread so far:thumbsup:
 

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Discussion Starter #16
I PM'd Luke but I think I may have figured it out. I put the car back up on the lift today and starting re-checking everything again hoping to find something loose. Also pulled the wheels to check bearing pre-load. Everything seemed tight and all bushings were nice and clean with no cracks. But then I started to look into the subframe mounts. With the car on the lift the upper side looks cracked and when weight is on the wheels, there is 3/8 inch of space between the bottom metal retainer and the rubber. Looks like almost 1/2 inch of vertical play in the subframe and who knows how much lateral! I'll install some new subframe mounts and see what happens. Will post the results.
Jeff
 

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I had an S500 two years ago with 18 inche wheels. I had the same feeling you are having right now. But with my S600 /17 inche wheels, I have not seen that problem at all. So, the wheels size could be the source of that feeling
 

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Discussion Starter #18
Problem Solved!

Just posting for the archives. I put some new Falken FK-245s on ( 245 -45 -18 in front and 275- 40 -18) in back and the problem is gone! Hard to believe a set of tires could cause that much of a ride problem, but heck! I still believe the subframe mounts are bad after 100K miles which made the problem worse when the old tires grabbed ruts. I will install new mounts this weekend which should further tighten 'er up.
Jeff
 

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Just posting for the archives. I put some new Falken FK-245s on ( 245 -45 -18 in front and 275- 40 -18) in back and the problem is gone! Hard to believe a set of tires could cause that much of a ride problem, but heck! I still believe the subframe mounts are bad after 100K miles which made the problem worse when the old tires grabbed ruts. I will install new mounts this weekend which should further tighten 'er up.
Jeff
Did you have them Road Force Balanced? I recently had tires/wheels balanced on a Hunter 9700, what a difference.
 
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