Formula 1's plan to spice up the Belgian Grand Prix could be scuppered by two factors.
For the first time since the 2022 Australian GP, Pirelli skipped a compound by bringing the C1 (hard), C3 (medium) and C4 (soft) compounds for the Spa weekend.
The initial aim of this was to increase the likelihood of a two-stop strategy and test skipping compounds as a method for reducing the number of one-stop races in the future.
But two factors - one more predictable than the other - threaten to stop it from being a successful experiment.
Graining is gone
Last year's Belgian GP was dominated by tyre graining on a resurfaced Spa circuit, but on the evidence of Friday this year, it appears that graining has gone.
"This was an improvement, let's say, in tyre appearance," Pirelli chief engineer Simone Berra said.
"So this year the graining is no more a limitation. It was a concern last year for the strategies and that's why almost all the teams opted for a two-stop race last year.
"And so this year, without the graining, if you have a proper level of management of the rear axle thermal decay, probably you can extend the stint lengths on both soft and medium."
It was hoped that teams would be tempted to use a mixture of C3 and C4s for a two-stop strategy rather than a one-stop with the C1 tyre.
But the performance of all three compounds has been better than expected, which means teams could run a soft-medium one-stop race on Sunday and completely circumvent the C1 hard tyre.
So why is there no graining this year?
"I think it's two effects: obviously the ageing of the tarmac, of the new patches, that obviously after one year they had increased both the macro- and the microroughness; and also the improvement in mechanical properties of the compounds. So both the effects," Berra explained.
"Also the teams that know our product better compared to previous years. Basically, the product is different and the compounds are different, but after 13 races they now have a lot of experience and based on the experience of the last year with the new surface, probably they found a good set-up not to generate graining. That's it."
Rain forecast
The most obvious element that could scupper the experiment is a rain-affected race at Spa.
Current forecasts have the chance of rain at the start of the race (3pm local time) at around 70-80% - and the risk of rain is essentially ever-present at Spa.
F1 teams using the intermediate or wet tyres would deny a chance for the experiment to play out, though it could be repeated at future events.
"We obviously will analyse in detail the data at the end of this weekend," Berra said of the experiment.
"Hopefully the weather will be good on Sunday enough to have a dry race to evaluate this experiment.
"It may, maybe it happens, it could happen that here this experiment doesn't work but it could work in another circuit. So let's see how it goes.
"Obviously if we have a one-stop C3 and C4, we cannot say that we reached our goals because our goal was a different one, was to push more towards the two stops.
"But I'm not sure that [if it] didn't work [here], then it couldn't work in other circuits where you have probably higher degradation levels. We will consider it anyway for future races.
"We are working already now to make selections for the second part of the season.
"So obviously we will gather the data from this weekend, this weekend will not define 100% if we are going to continue in this direction or not.
"So it's a good experiment, we will see the results and then we will see how to move on for next [races]."
The sprint race choice
Pirelli says teams may opt for the C3 or C4 tyres for Saturday's 15-lap sprint race, with the C4 the riskier choice but one that could prove favourable for those out of position, like Lewis Hamilton's Ferrari and the Mercedes cars down the order.
Plus some drivers with little chance of scoring points in the sprint may opt to use the C1s so they can save a set of C3s or C4s for Sunday's grand prix.
"It will be interesting to see tomorrow if there will be a different selection or maybe someone would like to try the hard compound for the sprint for the first time," Berra said.
"Not to use in the race but to use it in the sprint and to keep much more medium than they usually have [for the grand prix]."
Second-place starter Max Verstappen has just one set of new mediums left and two sets of hards, while the McLaren drivers either side of him have one set of hards and two new mediums for the rest of the weekend.
