When to change Tyres ?

[ChrisW.]

I'm posting herewith pictures of a front and rear Pilot Sport Cup2 Tyre.

When to change them is rather confusing since, when a car is used predominately on track, it is the shoulders of the tyre that wear more as the carcass of the tyre flexes against the negative camber of the geo set-up.

As you can see, the inner sections of the tyres still have good tread, but when really leaning on the car it is the edges of the tyres which are most engaged ...

I'm running 30psi all around on my GT4 when hot , peaking at 33 psi so it's unlikely that the tyres are running under pressure ... ever.


REAR


FRONT

The tread depth of the front nearside tyres from inner edge to outer edge in mm are:
FNS 1.6 / 4 / 4.5 / 4 / 0
FOS 2 / 4 / 5 / 4 / 1
RBS 1.6 / 3 / 3 / 3 / 3 (both sides)

It was an easy decision to replace because the tyres were dated around April 2019 ... due to Covid years, having wet tyres and last year running other cars ... even my new tyres are week 20 / 21 !! So they need fitting.

New tyres in mm are from inner to outer:
Front 3 / 5 / 5.5 / 5 / 4.5
Rear 4 / 5 / 5 / 5 / 5

As you can see my measurements are a little imprecise !!

What thoughts ? I have now found a spare set of part worn rear tyres now dated 2016 !! Junk ?

[bigmowley]

In my experience Cup 2s tend to only give their best for a few full heat cycles and from then on they deteriorate quite quickly regardless of actual trend wear. By a full heat cycle I mean a decent track day stint of quite a few laps, followed by a full cool down prior to another stint. Certainly there is also a time based deterioration as well, for example a two year old Cup2 will not be as effective on track as a few weeks old one again regardless of wear. I love a new set of Cup2 tyres the car always feels sharper and better to drive. I would chuck away a 2019 Cup 2 regardless of wear and fit a new set prior to a track day. It’s a relatively low cost within the context of track days in general.
On the road I don’t think you would ever notice the difference.

[ChrisW.]

Useful, thanks.

Certainly at Silverstone last week despite a few sideways moments the car really didn't want to pull more than 1.35g both left and right, although it had been good earlier in the month at Knockhill ??

As for the 2016 tyres ... kept in-case I get a puncture that can't be repaired and replacement tyres are in short supply ...

[Twinfan]

bigmowley said:

In my experience Cup 2s tend to only give their best for a few full heat cycles and from then on they deteriorate quite quickly regardless of actual trend wear. By a full heat cycle I mean a decent track day stint of quite a few laps, followed by a full cool down prior to another stint. Certainly there is also a time based deterioration as well, for example a two year old Cup2 will not be as effective on track as a few weeks old one again regardless of wear. I love a new set of Cup2 tyres the car always feels sharper and better to drive. I would chuck away a 2019 Cup 2 regardless of wear and fit a new set prior to a track day. It’s a relatively low cost within the context of track days in general.
On the road I don’t think you would ever notice the difference.

In my experience, albeit limited, I totally agree with this. I recently had new Cup2s fitted to replace a set that still had plenty of wear left. They'd had several track days and therefore full heat cycles through them and due to the oils in the rubber rising to the surface and escaping numerous times (a very obvious blueing effect) they had very clearly lost a lot of grip.

If you feel they're losing grip and they've had several days of good use already, chuck 'em IMHO.