Excessive outside wear on rear tyres

[Burgo]

Hi,

I'm experiencing some excessive wear on the outside of my rear tyres compared to the inside edges, see picture. I was told by one source that this fairly normal on Mustangs but I'm not too sure.

Is this something that can be correct via the standard rear alignment process or do I need to install some other correction kit in order to achieve even wear?

The front is perfect for wear and steering.

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[Bushranger]

My 2016 oem rear tyres at 33,000 km are slightly more worn on the outer edges than the inner edges like yours. However the deciding factor is the middle wear. I believe this is due to over inflation causing the middle of the tyre to bulge a bit (dealer pumps them up to around 40 psi when I get a service). My front tyres are far less worn albeit a tad more worn on the inner edges. I therefore would suggest a bit more pressure in the fronts and a bit less pressure in the rears. Say 34 front 30 rear (cold). My toe in for both front and rears is about 0.1 degree in each wheel. Camber for the rears is about -1.8 degrees and for the fronts is about -1.2 degrees. These were the delivered specs. I have changed my wheels now but I reckon I would have got about 70,000 ks from the fronts and about 40,000ks from the rears. I would have got more from the rears had I reduced the pressure after getting the car serviced. I drive conservatively.

 

[GT 550]

Hi Keith are the tyres still fitted and inflated in those pics? They appear concave but maybe it's the camera. What pressures are you running?

 

[Burgo]

Hi Keith are the tyres still fitted and inflated in those pics? They appear concave but maybe it's the camera. What pressures are you running?

Yep tyres are on the car in the pics. I run my tyres at 32psi cold, they do look concave in the pics but not that much in person.

 

[Burgo]

My 2016 oem rear tyres at 33,000 km are slightly more worn on the outer edges than the inner edges like yours. However the deciding factor is the middle wear. I believe this is due to over inflation causing the middle of the tyre to bulge a bit (dealer pumps them up to around 40 psi when I get a service). My front tyres are far less worn albeit a tad more worn on the inner edges. I therefore would suggest a bit more pressure in the fronts and a bit less pressure in the rears. Say 34 front 30 rear (cold). My toe in for both front and rears is about 0.1 degree in each wheel. Camber for the rears is about -1.8 degrees and for the fronts is about -1.2 degrees. These were the delivered specs. I have changed my wheels now but I reckon I would have got about 70,000 ks from the fronts and about 40,000ks from the rears. I would have got more from the rears had I reduced the pressure after getting the car serviced. I drive conservatively.

I run my tyres at 32psi cold front and rear and always maintain them at that as the dealer doesn't touch my car. I suspect that my rear camber is closer to 0º or even positive to have the excessive outside wear.
I think the wear in the middle is from the excessive outside wear and it just transitions across the tyre to where there is bugger all inside wear. I suppose I could correct it by lowering the car!
I might have a look at adjusting it this weekend myself. I've read that there is a couple of degrees adjustment on the upper arm where it attaches to the IRS.

 

[GT 550]

You'd think it was camber but I noticed slightly more outside wear on mine some time ago and I'm running 305s with factory camber and 35psi. From what you're saying it's not unheard of (possibly would be heard of more if people checked their tyres like they should) so I wonder if it's lack of rebound on the rear dampers. Rear camber is definitely adjustable but a lot of places will claim it isn't because they don't know about it. Also a bear to do apparently as the adjustment mechanism isn't friendly and can move when being tightened.

You could try the chalk test ie put a thick line of chalk on a hard surface, drive over it, and see if there's anything to tell from the imprint. Or wind on some more camber and see if it makes a difference. Lowering will have an effect but you still need to run good camber specs so fixing the problem first is the way to go or you may end up with a lowered car and a new set of problems.

 

[jacknifetoaswan]

I believe that to be a combination of improper inflation, as well as toe wear. I'd go get an alignment, and set your tire pressure to 32 PSI.

JR

 

[Burgo]

I believe that to be a combination of improper inflation, as well as toe wear. I'd go get an alignment, and set your tire pressure to 32 PSI.

JR

They're always set at 32psi and I use an expensive Michelin gauge that is accurate to within 0.1psi.

What is a bit odd is that when the last rears were removed to change over to these current ones, they appeared to be worn fairly evenly, much better than the current ones and they are the same brand spec tyre!

 

[Burgo]

You'd think it was camber but I noticed slightly more outside wear on mine some time ago and I'm running 305s with factory camber and 35psi. From what you're saying it's not unheard of (possibly would be heard of more if people checked their tyres like they should) so I wonder if it's lack of rebound on the rear dampers. Rear camber is definitely adjustable but a lot of places will claim it isn't because they don't know about it. Also a bear to do apparently as the adjustment mechanism isn't friendly and can move when being tightened.

You could try the chalk test ie put a thick line of chalk on a hard surface, drive over it, and see if there's anything to tell from the imprint. Or wind on some more camber and see if it makes a difference. Lowering will have an effect but you still need to run good camber specs so fixing the problem first is the way to go or you may end up with a lowered car and a new set of problems.

I might get a magnetic digital angle gauge and place it on my rear brakes discs and check what the camber is currently.

 

[GT 550]

You might have trouble getting access to the rotor and/or a good reading unless you take an accurate hub to guard measurement, remove the wheel and jack up the lower arm to replicate its location with a wheel attached and on the ground. Still probably quite prone to error because the car wouldn't be sitting as it would after driving it. But if you go down this route make sure you use only the middle portion of the rotor ie not the outer lip or the inner non machined part.

A better alternative is to put a straight edge across the tyre wall top to bottom, avoiding raised lettering as much as you can, and then use the gauge. Or even better use the rim beads.

PS I have to ask, what's that jigger in your avatar?

 

[Burgo]

You might have trouble getting access to the rotor and/or a good reading unless you take an accurate hub to guard measurement, remove the wheel and jack up the lower arm to replicate its location with a wheel attached and on the ground. Still probably quite prone to error because the car wouldn't be sitting as it would after driving it. But if you go down this route make sure you use only the middle portion of the rotor ie not the outer lip or the inner non machined part.

A better alternative is to put a straight edge across the tyre wall top to bottom, avoiding raised lettering as much as you can, and then use the gauge. Or even better use the rim beads.

PS I have to ask, what's that jigger in your avatar?

I was going to jack the car up using a jack and remove the wheel, securely tighten the brake disc with 3 bolts then using another jack place it under the disc and jack the car up to the exact same ground to guard lip measurement that the car had when it was on the ground with the wheels on (724mm) then place the angle gauge on the brake rotor.

The jigger in my avatar is a Badass Box, they trick the speed sensor on E-bike MTB into going faster than the 25kph preset limit before assistance ceases.

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