Review Submitted by - Steve Pritchard.
Dunlop D01J 225/45ZR16 - GPS (super soft compound)
They are very solidly built. After fitting them I tried the classic rock the wheel top to determine the amount of sidewall flex. Suffice to say that it is very minimal. At least an order of magnitude lower than my Michelin Pilot Sports. Also they do not appear to be that soft...
First time out - Silverstone "Club" circuitSetup
Ambient temp - it was hot but probably only in the region of 25 ambient. I do not know track temps but would estimate 35-40 (15 degrees above ambient).
On balance, the other GT4 folks there did not like this circuit.
It is massively truncated from the GP course and runs probably a 60 sec lap time. Quite a few sections of it are low speed and tight. Most notably Luffield the final hairpin before entering the start/finish straight.
On the other hand I loved this course. With the Dunlops fitted......Grip levels were phenomenal. In several spirited sessions of driving I had two moments of trivial understeer when pushing quite hard and one or two minor step outs from the rear. However, this could not be described as anything as crass as oversteer. A slight removal of some lock, as opposed to opposite lock, was all that was required to sort them out.
Other than that the tyres just grip and grip. In all honesty I feel that the car would need a rollcage to fully explore the limits of the tyre. Grip is so prodigious that corner entry, taking and exit speeds are significantly high and an "off" is going to go on for a while..........
I was consistently one of the faster cars on course even pushing some Porsches and Caterhams around corners One thing of note was that after 5-6 HOT laps I could feel the tyres go off. Grip was still impressive but turn in was slightly less precise and cornering was a little squirmy - kind of like some sidewall flex had crept in
The tyres do run quite hot and once up to temperature they are indeed quite sticky Wear was difficult to gauge. We ran immediately after the A1 GP cars which meant a huge amount of marbles off line. Consequently, after an offline cooling down lap rubber pickup was severe. I would estimate that I had more rubber on the tyres at the end of the day than the start...
However, some micro-blistering is evident. This looks like the rubber has just started to go off a little "boiled" slightly. This I believe would have occurred when the tyres went off
Second time out - Donnington Club CircuitSetup
It was hot, damn hot. I would estimate 30 deg C air temp in blazing sun so probably 45-50 degrees track temp.
My experience here was the complete opposite of Silverstone From the very get go the car felt "wrong" compared to the previous Silverstone outing Grip felt quite limited and squirmy right from the very first lap. In fact for both of my two initial sessions this was the case. It felt as if the tyres had gone off from the very first turn of the wheel
I must admit a slight err here. After the first session I forgot to check pressures. However, after the second I did check and pressure was 41 psi (I have subsequently discovered this is out of the operating range - read on). I immediately lowered this back to the stock 37 from the first Silverstone day
At this point it is difficult to make a firm pronouncement on what made the difference. The third session was considerably better than either of the first two. Grip, although not at Silverstone levels, was much improved with sharp turn in again and minimal squirm. However, due to the first two sessions I would have to say that I did not drive it hard
Looking back at it there were a number of factors which may not have helped
2) The tyres were over inflated. Dunlop have a maximum operating pressure of 40 psi so I was outside the safe zone and presumably well out of the efficient zone
3) For the first two sessions (and particularly the first) the tyres were markedly dirty. As mentioned previously the Silverstone cool down laps left me with huge pickup and I know from experience and TV coverage that it will take a few laps to clear dirt off. It wasn't until the 3rd session where the tyres looked clean again
Readers might say that the offline pickup would have been no different at Silverstone. However, I do not believe this to be true. The short "between session" times at Silverstone meant that the tyres never really cooled down. It was at all times quite easy to pick off the surplus rubber. However, the two weeks between the final Silverstone session and the first Donnington one meant that the tyres were cool and it was notable that removing the excess rubber would require a knife.........
Overall impressions and things learned
I have to say that some of the "problems" I've had may well be user error. I have never run Dunlops before and hence really do not know the best setup. It will take a few more sessions to figure this
One thing for sure is that I will experiment with far lower pressures. A talk with one of the "pit crew" at the last Silverstone day I went to revealed much. First off was the 40 psi operating limit. I must admit I had not noticed this :(
The second was the pressures they run. I was aiming for 37-38 psi based on my experience with road tyres which invariably seem to work best in this sort of territory. However, the "tyre tek" guy was talking about pressures more in the 30-32 region.
So I **may** have been running excessive pressure which will have self perpetuated - over inflated tyres heat up faster and hence get more pressurized etc. etc. etc For my next sessions I will reduce starting pressure to 25 psi and take it from there
Also, I now wonder if the super soft is the correct compound. Despite the prodigious grip levels available at Silverstone I still feel that a set of track day focused tyres should last more than 6-7 hot laps. This is not a major concern at the moment because the basic car is not able to cope with significantly more hot time without getting a little warm itself. Now, this could again be a side effect of running excessive pressure. Or it could be a result of the tyres simply being too soft and running too hot......