tire wear question

[Echomirage]

theres no tire section, and i figured its suspension related, so here it is:

after a new front end; including inner/outer tie rods, sway links and bushings, and UBJs (still stock, old LBJs), and a FRESH alignment done by an old school guy who does nothing but alignments, im getting cupping on the outside of the tires. theyre used BFG ATs, 285s on wheels with zero backspace.

the alignment was JUST done, im in the middle of a 300mi round trip, and im already seeing cupping on the front tires. they were on the rear of a previous truck, and had dead even wear when i installed them.

is this something that just happens with bigger tires? it only has a 3in body lift and torsen bar crank, so still basically stock suspension and steering geometry.

 

[Justin S]

Tire chop isn't usually from alignment, could be unbalanced tires, shocks, or even just the type of tire. The more aggressive the tread the easier they chop

 

[michael hurd]

If you cranked the torsion bars, the geometry is no longer 'stock'. It may be within a range that the factory allows for, but alignment specifications are for 'stock height' trucks.

Once the tire diameter is changed, and the wheel offset is changed, that all goes out the window.

Check chapter 17 of Race Car Vehicle Dynamics, Milliken and Milliken. SAE international.

That being said, poor shocks cause all sorts of tire issues, how long has it been since they were changed?

 

[Justin S]

I had a set of BF Goodrich All terrain T/A's on my GMT800, and they barely had any chop on them by the time they were down to the wear bars. I replaced them with some Falken Wild Peak ATs, and the rears were noticeably chopping quite a bit by 5k miles. I have since ditched those and bought a set of General Grabbers and they don't have any chop yet after 10k miles. Nothing was different about any of that other than the tires.

 

[Echomirage]

when the tires were mounted, the guy said one of them needed ALOT of weight, i think it was 4oz, if thats alot. he said to put that one on the rear, just in case. but, it was one of the 2 that were in the best shape, ie: no cupping from the previous owner, so i put it on the front. the rears are already cupped pretty bad, from the first owner of the tires.

all that being said, at speeds above 70, i got a huge vibration in the front. whether or not it was balance, i dont know. the vibration did go away when under 70.

most everything on the truck was original when i got it, including 2 plugs.

 

[Dylan1991_1500]

What these guys said above. Alignment doesn't usually lead to cupping. Cupping comes from the tire bouncing while it rotates. Bent rim, bad shock...things of that nature can cause this.

 

[Echomirage]

the rims are brand new, balance and alignment fresh. so many time for new front shocks?

 

[Nathaniel2g]

the rims are brand new, balance and alignment fresh. so many time for new front shocks?

Just because something is "brand new" doesn't mean it isn't at fault - there's a reason why car manufacturers issue recalls, and that's because something "brand new" is causing a fault..- We've received brand new rims at work that come damaged in the box and don't get noticed until a tire is half way on or already on a truck. Maybe the shop that did yours didn't notice a bend in a rim or damaged something and didn't tell you to save themselves money?

My point is that you should check everything over before you throw more parts at it - if you think your alignment is good, start elsewhere. Check rims and tires for visible signs of damage. Have another shop rebalance your wheels. Do a bounce test on your truck to make sure your shocks and t-bars are good. Take a look at your hubs and make sure they're not damaged. Take the truck to another shop and have them double check your alignment.

Things like that could save you a lot of time and money (because tires aren't cheap, and going back to a shop that caused damage or isn't doing something right doesn't help you or your truck) in the future and help keep your truck alive for much longer.

 

[Echomirage]

yeah i know......but out of the 2 things, theres a far greater chance that 20 year old, 150K mile shocks are to blame, rather then brand new, never used wheels.

 

[michael hurd]

Heavier wheel and tire combination + offset wheel = reduced effectiveness of both the spring and shock.

The tire and wheel are a lever and changing the distance between the pivot ( control arm mounting location ) and the outside of the tire changes the lever over the spring.

The job of the shock is to simply dampen the spring oscillation, when it can no longer effectively do that, the tire bounces as it rotates.

Given that Tenneco ( makers of Rancho and Monroe ) advise 50,000 mile replacement, it's certain yours are totally ineffective. It has been my experience that shocks can degrade even faster than the above stated number.