(CNN) -- When Jackie Stewart speaks about driver safety in Formula One, it's worth listening. The racing legend was a pioneer in raising standards in an era when mortality rates were high, and his legacy has left F1 stars with greater support than ever before.
But he is still worried about one burning issue -- the controversy over sole supplier Pirelli's tires, which he says are dangerous due to their rapid rate of degradation.
The three-time world champion told CNN that drivers risked a "multiple-car accident" unless immediate improvements are made.
"I don't think that amount of rubber should be coming off the tires and be left to the side of the track," the 72-year-old said.
"If you go over that rubber it then sticks to the terribly hot -- above 100C (212F) -- tires.
"When you get to the next corner your car is now totally unstable, and when you're going to brake you'll probably lose control of your car. If there's a car close to you then that will cause a multiple-car accident -- it has to be improved."
The Scotsman, who notched up 27 wins in an F1 career spanning eight years, also blamed the tires for the exceptionally open season.
Four different drivers have won each of the four races so far, ahead of the start of the European swing in Spain this weekend.
"An issue that nobody can quite work out is how the tire wheel, tire temperatures work," Stewart said.
"We've seen a lot of winning and losing because of when people have chosen or not chosen to go into the pits."
The "Flying Scot" -- as he was nicknamed during his racing days -- agreed with Mercedes driver Michael Schumacher's criticisms of the Italian tire manufacturer.
Seven-time world champion Schumacher has complained about the quicker degradation of the tires and even likened them to driving on "on raw eggs."
McLaren team boss Martin Whitmarsh, whose drivers Lewis Hamilton and Jenson Button struggled with their tires at the Bahrain Grand Prix, has also criticized Pirelli.
Meanwhile Schumacher's teammate Nico Rosberg, who won the China Grand Prix last month, argued the unpredictability made racing interesting.
Pirelli has argued it should be congratulated for such an open, unpredictable season. The manufacturer claimed it was simply responding to calls for more eventful racing, with director Paul Hembery saying: "We are pushing the limits."
Stewart, who won the Spanish Grand Prix three times, said the high caliber of this season's drivers made it anyone's championship.
"They're probably the best bunch of drivers I've seen since the late '60s, early '70s when we had around eight or nine drivers capable of winning."
He said Nico Rosberg's win in China could finally spell a comeback for Mercedes. It was the German marque's first race win since Juan Manuel Fangio in Italy in 1955.
This week the team played down reports it could be set to quit F1. British newspaper The Times claimed UK-based Mercedes could be forced out over a power dispute arising from F1's proposed stock exchange flotation.
A Mercedes spokesman said only that they were "in discussions with the commercial rights holder."
But Stewart believes this could be Mercedes' season, saying they were "giants."
"The Silver Arrow has been winning races since the '20s and '30s and came back in the '50s and won races," he said.
"If they hadn't won that race (in China) and showed themselves to be that competitive in the ones immediately following it, I think there might have been a chance of Mercedes Benz withdrawing from Formula One."