Both front tires cupping on inside, why?

[mstgeer]

Car just passed state inspection this week with no issues found with ball joints, wheel bearings, or suspension in general.

So, what is generally the cause for both front tires to cup on the inside edges? Alignment has been verified per oem specs.

Car is lowered on ST springs with Tokico Illumina II's, MOMO 17x8 (don't know offset but it is proper for the supra) and Kumho Ecsta Supra 712 tires.

Any input would be appreciated.

 

[hvyman]

What are the actual alignment specs?

What kind of driving do you do?

Are the shocks blown?

 

[te72]

Got a picture? Isn't cupping caused by the toe setting? Or is it a caster setting? I forget alignment symptoms today...

 

[hvyman]

Usually feathering is caused by toe.

Cupping is usually shocks.

 

[mstgeer]

What are the actual alignment specs?

What kind of driving do you do?

Are the shocks blown?

Car has been in rebuild mode for the past 2+ years, so maybe only >500 miles in that time frame. Do not have specs anymore but nothing has been done since alignment except sit idle and have motor rebuilt.

The car is simply street driven hard on weekends only. Mainly straight line hard acceleration, not any twisties or tracking.

Shocks do not appear to be leaking any fluid, however they are also not a stiff as I remember / expect, and I do observe a floating feeling when driving. But attributed that sensation was due to using my modified WRX (rides like a go cart) and stock 07 BMW 328xi as references.

I will try to get some pics put up after work this evening.

 

[mstgeer]

Kind of hard to capture with my limited photo skills. The light, dirty areas are the high spots. Both tires exhibit the same wear pattern on the inside of the tire

 

[hvyman]

It's hard to tell from the pics but looks more like feathering from toe. With all the new alignment machines most places will stop once it's in the green and the green is a wide area.

Best bet is to get a good alignment and get the sheet. Make sure to tell them you want it perfect. They can't charge you any different to do so.

 

[LordDigital]

LCA Bushings shot to a point where they induce significant dynamic (when driving) toe in / toe out?

Also very likely bad alignment rack that setup excessive static toe... I would check the alignment at a different shop that preferably has hunter alignment rack.

 

[mstgeer]

Thanks for the input guys.

Do the LCA and/or any other suspension bushings go bad with age or mileage ususally? The car is a '91 with approx 91k miles on it.

 

[hvyman]

It's a little bit of both and luck. Some will go out sooner than others. Tho ours seems to be pretty stout even after the years.

If the rack bushings have been covered in oil tho the rack might move slightly.

 

[mstgeer]

If the rack bushings have been covered in oil tho the rack might move slightly.

Good point, I did not think of that. Best way to check is to simply have someone turn the wheel while the car is on the ground and stationary, and look to see if there is any movement in the rack bushings and/or other steering components?

 

[te72]

Another thing that may have been slightly overlooked, it is always a good idea to keep an eye on tire pressure. Sometimes it is the simple things, but I'm thinking you aren't quite so lucky in your case.

 

[LordDigital]

Good point, I did not think of that. Best way to check is to simply have someone turn the wheel while the car is on the ground and stationary, and look to see if there is any movement in the rack bushings and/or other steering components?

Or simply check for play with the wheel off the ground... The best way to detect rack/roadEnd(s) issues is again on the alignment rack ,but you have to know a place with highly experienced mechanic with good rack and that is not easy to find.

 

[customs]

Good point, I did not think of that. Best way to check is to simply have someone turn the wheel while the car is on the ground and stationary, and look to see if there is any movement in the rack bushings and/or other steering components?

This is the best way to check for play in any steering component.

Or simply check for play with the wheel off the ground... The best way to detect rack/roadEnd(s) issues is again on the alignment rack ,but you have to know a place with highly experienced mechanic with good rack and that is not easy to find.

With the wheel off the ground you will get less resistance and thus not give you 100% accurate inspection.

That tire wear can be caused by a few things. First off I would assume that toe would be out, like previously stated. When you lower a car the effect that the toe is out will be larger then if the car is at stock ride height. Something you should look into is a "custom" alignment, assuming that all of the suspension components are in proper working order.

 

[darshy523]

correct me if im wrong, but i thought that if a wheel is off balance that could cause cupping wear on the tires also.. maybe something to check into if the wheel havent been balanced in a while. i also believe that if the toe angles are incorrect it will cause inner/outer edgewear and not so much cupping.

 

[hvyman]

Toe will cause feathering.
Camber will cause inner or outer tire wear.
Usually blown shocks will cause cupping.

 

[kanji1jz]

I would have the alignment checked, if the toe and camber settings are good then I would move on to the struts... Toe is mainly a feathering as stated previously, but with the combination of a few of these issues present I have seen cupping be a factor. It could also be the tires themselves. Do you have a staggered set up? If not, have you rotated your tires recently? If so, I would inspect the rear struts as most of the time there is cupping on the rear as opposed to the fronts.