Shop bent my rims?

[flyweightnate]

I brought my car in for scheduled maintenance, and they reported back that, during a rotation, they noticed both of my front wheels were bent and required balancing. Both. And not the flange, but supposedly near the lug nuts. Alloy 17" rims on a Subaru Legacy, and I'm not doing a ton of driving off cliffs...

Weirdest part is, when they mounted a new front passenger tire in January, it was fine. And, they're directional tires. So they're suggesting I've hit major potholes on both sides in a 5 month period.

Does this seem fishy to anyone else? I did some suspension repair a few months back that required taking off the wheel, but I use hand tools and torque wrenches.

Sent from my SM-G930T using Tapatalk

[Paintslinger16]

Seems a little fishy, you should be able to feel something that is “that bad”

[flyweightnate]

Oh, I can definitely hear the road noise now. It was much more quiet previously.

Sent from my SM-G930T using Tapatalk

[foughtwolf]

As a mechanic, does kinda sound fishy. However I will say that those alloys are incredibly soft, and if some idjit with a rattle-gun just sends the lugnuts without ensuring the tire is up and on straight, they will bend the centers.

[Siress]

This was my first thought as well, and still seems most likely to me. There's no way the wheel would be bent in this scenario if using the proper torque spec.

As a mechanic, can you offer any advice on what we can do or say to ensure 100% that the mechanics that touch our cars use the proper torque specs? Particularly on lug nuts... Last time I had my tires replaced it was at a local chain instead of the old guy I usually go to, and I told them several times not to over torque the nuts because the studs won't take it, gave them the torque spec., even told them they could use my torque wrench - preset - and left it in the passenger seat with the security spline socket required for each nut. And lo', they did the rattle gun. And lo', they broke two studs. Moot point these days since I replaced all the studs with grade 8s, but still. wtf.

[foughtwolf]

If it isn’t mission critical; no mechanic worth his salt goes by torque specs, it’s by feel. However if you went to a chain I’ll say from experience it’s all about getting cars in and out. Lugs and studs are far from single use torque to yield affairs. I’d file a complaint and get them to buy or try to make em get you new rims. Shops have insurance for just such a reason.

Hell I screwed up a few weeks back and left an oil plug loose, mulched a civics engine. Shop insurance covered having the car repaired no questions asked.

[Siress]

If it isn’t mission critical; no mechanic worth his salt goes by torque specs, it’s by feel.

I take issue with that mindset. If lug nuts are not considered "mission critical", then what is?

Torque specs exist for many reasons and have numerous, peer reviewed rationale behind them - while your "feel" is a purely subjective measure for your convenience. Still, your mindset is prevalent because it's significantly more profitable to rush through a job, and fatal consequences are rare and nearly impossible to positively place blame on the mechanic that under/over-tightened the lug nuts. That's precisely why I insist on either doing my own automotive work or thoroughly checking everything myself.

[flyweightnate]

If it isn’t mission critical; no mechanic worth his salt goes by torque specs, it’s by feel. However if you went to a chain I’ll say from experience it’s all about getting cars in and out. Lugs and studs are far from single use torque to yield affairs. I’d file a complaint and get them to buy or try to make em get you new rims. Shops have insurance for just such a reason.

Hell I screwed up a few weeks back and left an oil plug loose, mulched a civics engine. Shop insurance covered having the car repaired no questions asked.

Thanks - the rattle gunner was my first thought, too. Helpful to consider that the shop has insurance for such things; it's not quite zero sum, I win - you lose.

And yeah, I can guess between 10 ftlbs and 40. But on my car, all those numbers are way higher than the small little machines at the office. No sense guessing and having something fail at 80mph while some armchair cowboy is tailgating me in an F350. Yay Dallas. So I'm more careful than my shop.

Sent from my SM-G930T using Tapatalk

[Chuck E Ducky]

Sounds to me like inexperienced mechanic cranked the Lugnuts down with to many Unga Dungas. No way to prove it. But I would find a new mechanic.

I use my air gun to put wheels on but my gun SnapOn has settings so it won’t over torque them.

The extra road noise is probably from rotating the tires more then anything.

[punkncat]

Uh, NO.

So, first off, if the center of your rim was WEAK enough to have been bent to a degree of warping a rim simply with an impact wrench it should NEVER be on a car. That is a false pretense and simply cannot be. There are extreme forces on a wheel going down the road. Even if the impact was used too aggressively it would only break the stud or strip the lug. You "might" and I say might strongly, be able to damage the center of a wheel by putting it on with something in the way, MAYBE. But by damage I mean chip or scuff, something like that. You aren't going to bend an aluminum wheel at the center with some routine activity.
With that aspect said, you also cannot balance out a bent wheel. It doesn't work like that. Even if it's masked by weight it's going to shake like hell going down the road. You will feel that.
Even IF you hit something going down the road it is almost 99% of the time either going to damage tire/edge of rim or the hub/suspension. You don't just bend a middle of a wheel doing something you aren't immediately aware of. Uncorrected for fully and you would have had your steering wheel shaking in your hand like a leaf on a tree.

They are full of shit.

I would HIGHLY suggest you go to a reputable shop for a follow up, perhaps ask them what they speculate could have happened IF anything at all. I think you were being shaken down.

I would have the 'other' shop check for evidence that they dropped your car off the lift....and as personal experience would have them check to see if there is a lock screw for your rotors just barely loose on the fronts where they saw this.

[shadow191]

Did they show you the bend? As above poster mentioned, it's pretty much impossible to bend the rim at the center. That's the thickest part of the wheel. And the torque settings for lugs is ~90ft lbs which even with an impact gun going multiple times that isn't enough to bend a wheel. Typically what happens with impact guns is they cross thread or strip a lug or stud. Worst case they can snap the stud but rarely.

Most likely you just hit a metal plate or big expansion joint somewhere. That could damage both sides. Or the balancing weights could have just fallen off if you hit something.

FWIW, I live in a city with lots of potholes and metal plates and have bent all 4 wheels on my car before. So bending 2 is pretty common.

[flyweightnate]

Went back in to see it all in person - the rims are eccentric, they're so bent, but no smoking gun as far as whether it's a train track or a sloppy mechanic.

Such is life. My car is noisier, and hopefully not much else changed.

Sent from my SM-G930T using Tapatalk

[Siress]

Uh, NO.

So, first off, if the center of your rim was WEAK enough to have been bent to a degree of warping a rim simply with an impact wrench it should NEVER be on a car. That is a false pretense and simply cannot be.

Let's think about that for a minute. Typical torque limit for an automotive pneumatic torque wrench is ~900 ft-lbs. Subaru Legacy lug nut thread is M12x1.25. Assume a coeff. of friction of 0.2 and the clamping load comes to ~114,300 lbf. The surface in contact is less than a square inch, so the clamping pressure is >114 ksi. Cast aluminum has a compressive yield strength of 109-134 ksi. From what I've read, Al wheels are typically alloyed with magnesium for various reasons, which has a side-effect of lowering the strength. Here's such an alloy that explicitly states it's used for automotive wheels, and a compressive yield strength of just 16 ksi. Safe to say...
at the very least.

It's pretty common to have compressive yield locally around the lug nut on new alloy wheels after the first 50-100 miles. This is why you always need to go back and tighten them to the torque spec again after the first few times alloy wheels are bolted on. Eventually the localized area becomes harder and harder (i.e. work hardening, more specifically Peening) and this issue goes away. Steel wheels do not have this issue in the first place because they have a significantly higher compressive yield strength. That's why the alloy wheels yield under pressure applied by the steel lug nuts, rather than the lug nut also yielding. The threads of the stud are a different matter - those typically do yield (mechanics often call it "stretch") under load and often break after a point. That's because the same load is being applied to a much smaller contact area, thus ramping up the applied pressure.

Now, considering we're at the yield strength of the material in a best case condition (i.e. wheel is seated properly when rattle gun ramps up) it doesn't even matter how much leverage is added by being improperly seated. That leverage only makes matters worse. Damage is going to occur if that load is unsupported. That's my 10min analysis, anyway. Take it with a grain of salt.

EDIT: To add, if this was the cause of the OD of the wheel being heavily eccentric, you'd see SIGNIFICANT damage around some of the lug nuts. To be out enough to cause issue at speed - maybe not so obvious. Hard for me to say without a simulation.

[punkncat]

Let's think about that for a minute. Typical torque limit for an automotive pneumatic torque wrench is ~900 ft-lbs. Subaru Legacy lug nut thread is M12x1.25. Assume a coeff. of friction of 0.2 and the clamping load comes to ~114,300 lbf. The surface in contact is less than a square inch, so the clamping pressure is >114 ksi. Cast aluminum has a compressive yield strength of 109-134 ksi. From what I've read, Al wheels are typically alloyed with magnesium for various reasons, which has a side-effect of lowering the strength. Here's such an alloy that explicitly states it's used for automotive wheels, and a compressive yield strength of just 16 ksi. Safe to say...
at the very least.

It's pretty common to have compressive yield locally around the lug nut on new alloy wheels after the first 50-100 miles. This is why you always need to go back and tighten them to the torque spec again after the first few times alloy wheels are bolted on. Eventually the localized area becomes harder and harder (i.e. work hardening, more specifically Peening) and this issue goes away. Steel wheels do not have this issue in the first place because they have a significantly higher compressive yield strength. That's why the alloy wheels yield under pressure applied by the steel lug nuts, rather than the lug nut also yielding. The threads of the stud are a different matter - those typically do yield (mechanics often call it "stretch") under load and often break after a point. That's because the same load is being applied to a much smaller contact area, thus ramping up the applied pressure.

Now, considering we're at the yield strength of the material in a best case condition (i.e. wheel is seated properly when rattle gun ramps up) it doesn't even matter how much leverage is added by being improperly seated. That leverage only makes matters worse. Damage is going to occur if that load is unsupported. That's my 10min analysis, anyway. Take it with a grain of salt.

Wut?

I saw you were speaking English and then something happened...

I worked at a tire shop for some time. Admittedly I never dealt with today's brand new Subaru rims...so there is that.
I don't know about the exact specs of the wrenches we used there, nor could I comment to the exact torque spec of each individual stud that came in. I can tell you over the course or trial and error, and the bitch process some of these manufacturers made it...that breaking a stud is the single easiest thing to do while un/re mounting a wheel. Making certain assumptions as to things like putting the rim back on properly, making sure nothing is between the wheel and spindle/rotor/mounting surface that you aren't going to warp the middle of an alloy wheel even IF you rat-a-tat it till the stud breaks. A wheel is just not that weak.
The forces that break wheels commonly come with other catastrophic damage like busted ball joints, shock towers, bushings damaged, broken spindle.

What I am saying is this. IF that rim is truly bent in a significant way, at the lugs then either THEY did something grossly negligent, or we aren't getting a whole story. If you drove a car with bent rims it isn't something that hides till the shop sees it.

And, the reason you re-torque the lugs is because the studs stretch, particularly on first install, and also to be sure they are fully seated in the spindle/hub.

[Siress]

What I am saying is this. IF that rim is truly bent in a significant way, at the lugs then either THEY did something grossly negligent, or we aren't getting a whole story. If you drove a car with bent rims it isn't something that hides till the shop sees it.

And, the reason you re-torque the lugs is because the studs stretch, particularly on first install, and also to be sure they are fully seated in the spindle/hub.

Good points all around.


Anyway, Nate, It could've been worse...