Driving to and from the track on semi-slick, and perhaps slightly worn track tires.
We must plead guilty to the charge many times over. And on more than one of those occasions, we were caught out by unanticipated precipitation.
Thankfully, long before any of those outings we became well acquainted with the (low) limitations of semi-slick tires in wet track conditions, so we knew to go easy. For all of their immense capability and traction in dry track conditions, many semi-slick track tires become utterly feeble when precipitation is involved.
In wet track conditions a quality set of street performance tires is the superior choice to be certain. On a memorable rain-soaked track day the Continental ExtremeContact DW had us lookin' like Schumacher in the '96 Spanish GP… Trust.
Right, the TÜV Süd findings --
The organization released test data that corroborates the knife edge grip characteristic of track tires in wet conditions.
The test compared 3 Dunlop tires -- a semi-slick, and two street performance options.
In a wet road braking test from just 50 mph to 12 mph, the semi-slick took about 18' longer to complete the task. (Average car length is 14.75'.)
The semi-slick was also measurably less capable on a wet steady state circular course.
In conclusion, TÜV Süd found the semi-slick tire to be unsuitable for typical road use and variable conditions.
Here in the U.S., Tire Rack regularly conducts testing of both performance street tires and "extreme performance summer"/DOT legal track tires.
An analysis of their findings shows an equally large performance differential between the two types of tires in wet weather.
In a wet road 50 mph to 0 mph braking test, the aforementioned ExtremeContact DW managed the stop in 96.9'. In the same test, the Hankook Ventus R-S3 required 120.6' to complete the task.
So can you safely run semi-slicks in wet road conditions?
As much as we'd like to claim it's a reasonable and responsible thing to do, there's no getting around the objective data. Semi-slicks provide notably inferior wet road traction, and braking performance even at moderate speeds (50 mph). At minimum, it must be said that running semi-slick tires on wet roads should be avoided if at all possible.
But if the situation cannot be avoided, the risks can certainly be mitigated with prudent driving practices. Our approach is much reduced speeds, and extreme cognizance of any standing water. We've managed plenty of miles in wet road conditions with "rain-phobic" tires like the Pirelli P Zero Trofeo R and Nitto NT01 with these precautions.
Related: Track Tires vs Performance Street Tires