Front Tyres Center Wear

[fka]

Hi all

I've been looking at my front tyres as they're not far off needing replacing. I've just noticed that both fronts have a mm or two more wear on the centre strip. I'm very vigilant on tyre pressures and they're always at 36psi so I don't see how this can be an over inflation issue. You can see in the pics they're almost on the wear indicator on the centre but a mm or so off on both edges. Is this relatively normal?

Cheers
D

[mikeloadsasaabs]

Could be that the guage you are using to check the pressures is underreading, meaning that you are inadvertently overinflating them. I always wondered the fronts on my 9-5 Aero wore so much in the middle, but when I had some new tyres fitted the garage explained that their guage was state-certfied, so I checked mine against that. It turned out mine was underreading by 4psi, and obviously had been for years!

[carrera]

That sounds entirely plausible. Tyres vary in stiffness, pressures can only be advisory as there is a relationship with heat and so driving style has an effect as well. If it's wearing in the centre then run with less air in and see how it feels.

[fka]

Thanks for the replies guys.
I've checked against a few different gauges, various garage forecourt pumps which I know are also to be taken with a pinch of salt but in theory should be calibrated, and they're all within a psi or a half of each other. Also even if it were 3 or 4 psi out, that would still be within the high load/ speed inflation spec for the car which is 41psi.
90% of the time it's driven sensibly. The other 10% I'd expect more edge wear from high speed cornering, and since I drive with ESP on, damage due to wheel spin should be minimal..

[carrera]

What tyres are you running - I'm not sure but are they Michelin Primacy ??

[fka]

Spot on, Primacy 3 235x45 on 7.5" rims

[TomPaine]

I used to run my Primacys at 39 as a compromise between min and max and for a firm ride during what I think is called spirited driving; but I had exactly the same issue, and now don't go over 36 front 35 rear. As others have said an even slightly under-reading gauge might be the culprit here.

[carrera]

I run Primacy XL as well. Off the top of my head I run at 36/34 cold and have even wear, front and rear, though I have done some work on the rear suspension to get the camber correct to eliminate inside end feathering. I'll try and double check in the morning

[fka]

Hmm, it would seem to be a pressure issue then. I've just ordered one of these, seemed to get good reviews on a number of tests https://www.autoexpress.co.uk/accessories-tyres/85474/best-tyre-tread-depth-and-pressure-gauges-2018 ,in the hope I can get a more accurate reading..

Thanks

[carrera]

Sorry, I didn't get a chance to put my pressure gauge on the tyres today, I hope to be able to do that tomorrow - car and equipment are not in the same place.

 

[carrera]

Here we go, you can tell this isn't a staged picture for the cameras as it looks like I may have a slow leak from the front right.

Rears were bang on 34, fronts will be back at 36 by the end of the day. Cold weather too (that does make a difference)

I just put my depth gauge on, without messing about with fractions of a mm it read 4-4-4

[carrera]

Spot on, Primacy 3 235x45 on 7.5" rims

Just noticed this bit - I run 225/45/17 on 7.5" rims.  I think the 235 may have been a later option and I can't believe the extra 10mm would make much difference... but....

[fka]

The 235 did cross my mind but according to WIS that seems to be the standard on the 7.5" rims, 225 on the 7"
Either way I'll be fitting 225 when I change them due to cost and availability..

As soon as my new meter arrives I'll check again but I'm fairly sure they are at or around 36psi. I even knocked a psi off each of them last month since the warmer weather had knocked them up to 37.
I also have a slow leak on my nearside rear. The last one I had on the offside rear was sorted for a tenner by the nice man at my local indy tyre place, who took the tyre off and cleaned up the surface corrosion on the bead seat..

[sgould]

My Aero is running 225/40 tyres on an 8inch wide rim. But the wheel offset is 41mm which means that they sit 8 mm further out than the standard wheels.

One other small point is that the 225/45 17tyre is 94w rated for load and speed and is an extra load tyre. The235/451, also 94w is a a standard tyre, not an XL. XL on that size is 97w.

[fka]

I've just checked and mine are 94w. I know XL are specified for the car, so are you saying they should in fact be 97w?