question on tires and ride once again(long)

[rocco16v at netzero.net (L F)]

Allyn gives pretty good advice, Stefan.

(except the part about the "larger contact patch" with 17inchers.  That's a little off-base; the patch may be wider if the tire is wider, but the patch area will be the same...wider patch but shorter)

Larry
  ----- Original Message ----- 
  From: Allyn 
  To: Stefan P ; scirocco-l@scirocco.org 
  Sent: Thursday, April 01, 2004 8:56 AM
  Subject: Re: question on tires and ride once again(long)


  >A while ago I asked  a question about why my car vibrated really badly at 
  >higher speeds. I had 17 inch rims. The replies I got where to get 
  >hubcentric rings.

  you would be shocked at just bow shitty even a 1mm misalignment of the wheel 
  center on the hub can make your ride. the rieger was simply unbearable at 
  70, it would make my leg go numb.

  > As soon as i start driving the difference is noticeable, the car shakes 
  > and vibrates at 45mph. I take it to the shop. They look at it and tell me 
  > the tires are chopping. ( the alignment is perfect and camber is as close 
  > to perfect as it can be, i know this cause i had to have those specially 
  > fixed on that car).

  ok, even a slight offset in the hub mount can give imbalance 'effects' on 
  the wheel, enough to cause choppyness. anything felt at less than 60 mph is 
  not balance, its centering / bent wheel (or bad wear on the tire from high 
  speed imbalance / offset centering). also, i assume your toe is set to 
  factory, which is a bit steep for 17's. you have a much larger contact patch 
  and thinner sidewall than those specs were designed around. 17's give much 
  less and tend to respond better on half the factory toe value. this was 
  especially noticable on the back of the rieger (275/40/17). factory toe was 
  simply too much for that much rubber on the road, and was causing very bad 
  chopping of the outer part of the tread, while wearing the inner tread down 
  to being bald (even with good camber values). moral of the story - too much 
  toe for wide rubber can cause wear that looks like too much negative camber.

  > from 55 - 70 mph (i dont usually go over 70). So now my next tire rotation 
  > is coming up and I notice that im drving on slicks in the front as in 
  > there is hardly and tread. The back looks a little better but not by much. 
  > SO all in all a set of 4 tires lasts me 10000 miles.

  ok, heres what happens. wheels arent mounted at perfect center, which causes 
  localized heating of only some of the tread, which causes uneven tread wear 
  (also chopping / cupping), which causes overall uneven wear of the tire, 
  even if it is later mounted at perfect center. for example, the 5k miles 
  with no hubcentric rings may have already done the damage - even installing 
  rings at that point may not completely eliminate vibration since the tread 
  has already wore unevenly. it may not even look like uneven wear - the 
  localized heating can make some areas of the tire give more than others, 
  resulting in something you can really only feel with the car going down the 
  road (doesnt show up on a normal tire balancer).

  > The Falken tires are yes some of the cheaper brand but im afraid to go out 
  > and by the good years or firestone for 600 bucks if they will only last me 
  > 10000 miles.

  i've got 10k miles on the kumhos on the rieger, and they still have about 
  3/4 tread wear. i drive almost the opposite of you. i beat the holy shit out 
  of the front tires every morning on the way to work (30 minutes of 
  demolition derby, avoiding idiots and crappy charleston pot-hole ridden 
  roads). also, i cant rotate mine even if i wanted to (front size diff than 
  rear size, and directional tread). i cant even rotate them the long way 
  (dismount / remount on opposite side), since my wheels were made for racing 
  and have a sharp bead-grabbing ledge. the first dismount you attempt on 
  tires mounted to my wheels result in prompt destruction of the tires bead. 
  it sounds shitty, but it does come in handy (last week i went 5 minutes on 
  the highway, took an exit ramp pretty quick, drove a couple of block, all 
  before i even realized one of my fronts was completely flat from a bad valve 
  stem).

  > The car is lowered.

  so is the rieger, neuspeed softsports over koni adjustables. probably 
  lowered approx the same as yours. no real effect on tread wear. also, my 
  camber is at -0.6 on both sides (limited by max adjustment on one side), 
  again, probably the same as yours.

  > Stefan

  hope this info helps
  Al

  Allyn Malventano, ETC(SS), USN
  87 Rieger Scirocco GTO 2.0 16v (daily driver, 200k, rocco #6)
  86 Kamei Twin 16V Turbo Scirocco GTX (30% complete, rocco #7)
  86.5 Occo 16v Trailer (rocco #8)
  90 Passat GL 16V (the wifes new daily, 200k) 


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