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2004 chevy trailblazer_ls_ext
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Discussion Starter #1
Issue: put Two different types of 265/70R17 tires on 04TBEXT4x4. (now have Mastercraft AXT SUV version). Above ~55-60mph front gets unstable vibration.

History: Put on ~2"wide hub extenders before tire change and ran with old 245/65R17's on TB. Was fine, just like w/o extenders. Steering slightly different feel. Pre-fit a on-spare a 265/70R17 size tire and moved some front wheel-well supports near front lower fairing (changed location attachment to lamp supports pulling black ww-plastic forward). Tires do not rub anywhere while operating on a smooth road. Will bottom-up and scrape upper ww-plactic in a heavy fast dip.. But this is not the issue. Fitment is OK for on-road use at all steerage-angles.

So, with new tires, several balance events, still have an aggressive front and steering-wheel L-R whip shake-wobble (more active on smooth road, like it's a coupled-driver between both wheels). Rears seem OK. the TB use to be very good at high-speeds and "settled in" well with a nice glide feel from the tires. That is now absent with this size, and can't get comfortable above 60mph.

Replaced upper ball-joints (boot-cracked not worn heavy) and checked for other suspension issue before mounting hub extenders. As said earlier, was good with 245/65's but shakes with 265/70's.

Is there something I need to do, like add some type of damper to the front suspension? I'll get tires "load balanced" next week. But I've already seen this on two different tire types now. 04TB still has original OEM struts.
 

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2002 gmc envoy_slt
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3,203 Posts
Have they rechecked the alignment? The taller tire will provide add'l toe in inches, with the same degree setting. With a larger tire, if the shop is using degrees to align the toe, as opposed to inches, you want as little as possible, preferrably zero or even a tiny bit toe-in, knowing that the wheels will slightly toe-out when driving at highway speeds on a RWD vehicle.

My other thoughts would be that perhaps you're near the max setting on camber and riding the shoulder of the tire a bit. Most AT rated tires have a non smooth shoulder and you may be feeling the impact of the raised blocks along the edge of the tires at speed. I mention this as you indicated a ball-joint replacement, which may have affected alignment and perhaps the shop didn't try to hard to get the setting near the preferred specs. - For camber, you want +/- .3 from the -.5 degrees preferred setting....ignore the +/- .5 recommended by the factory, get it closer than that with bigger tires.
 

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2002 chevy trailblazer_lt_ext
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295 Posts
I agree with the wheel alignment, but also check your upper ball joints and tie-rod ends.
 

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2004 chevy trailblazer_ls_ext
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Discussion Starter #4
A re-alignment happened, first one since I've owned the vehicle, when the bigger tires were installed.

Also, All three shops I've talked to, and these are ones I trust and two know tires, tell me that alignment will not cause vibration, just wear the tires more or less.

Seems that the 2" hub extenders might create longer lever arm on the steering. But I can't say enough that the std-size tires with hub extenders was just great.

So, one shop checked the suspension linkages (with the crow bar method) and said, 'no problems.'. Upper ball-joints replaced for boot tears only, wasn't having any mechanical issues.

The steering wheel moves side-to-side as the car rolls down the road. Some roads more than others. It never did that with my old std-size tires (used BFG rugged-T). I think that steering wheel rocking L-R is caused by tires being out of round too much, or the belt tracks sideways too much. These are new tires from Cooper (AT3 and now Mastercraft AXT, similar tread, also made by Cooper)

I'm thinking also that the bigger tire is not matched well with the spring-dampers setup. heavier tire doesn't stop it's bounce quickly enough. Bad tires just don't help either.

Recommendations on front shocks and any other dampers that could help with heavier tires?

Anyone with direct experience with this size tire. 265/70R17. out there?

I'll report my findings on the load force balance, after storm Sandy exhales (... geeezzzz... didn't we just get done with clean up from last year!!)
 
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