Taking the stand at Minshull St Crown Court, King explained how he saw Devon riding the £3,000 e-bike, which he had taken from another boy following a scuffle.
King said he was angry and had told police there was “blind panic” as he sought to get the bike back.
Under cross-examination, King said he had only intended to get alongside or behind Devon.
“I saw the bike and decided to try and block it in,” King said.
Defending barrister Mukul Chawla KC asked King why he did not brake.
“I don’t know,” said King.
Chawla said: “Did you know Devon? Did you know whole stole the bike?”
King replied: “No.”
It was revealed King refused to watch CCTV footage of the crash when it was played to him by the police the next day.
“Why was that?” asked Mr Chawla.
“Because Devon had passed away,” said King, who denied intending to hurt the youngster.
Jurors have been told King has previously pleaded guilty to manslaughter.
Prosecuting barrister Michael Hayton KC queried King’s recollections.
“You’re giving a version that makes your actions sound like you’ve done nothing wrong,” Hayton said.
“That makes no sense. You drive at 30-plus miles per hour into a boy on a bike. What’s going to happen to him?”
King said: “At least serious injury.”
Hayton said: “Serious injury is what happened.”
He urged jurors to convict King of murder.
“In the heat of the moment, at speed, you did not brake,” Hayton said. “I’m going to suggest your actions in doing so were deliberate.”
In his closing speech, Chawla told the jury: “Can you be sure about what was in his mind at the time of the collision?
“Specifically, can you be sure he drove into him intending to cause at the very least serious harm?
“It’s straight forward.
“We suggest there’s not a single part of the prosecuting evidence that contradicts the defendant’s account.
“There is far more that demonstrates he had no intention of harming anybody.”
The court had previously seen CCTV and doorbell camera footage showing Simmonds-Caines riding an e-bike, which the court heard he had stolen from another boy.
King’s car was seen driving at speed on the road before veering left, mounting the pavement and crashing into Simmonds-Caines, who died at the scene from his injuries.
The footage was too upsetting for some of the boy’s family, who left the court in tears.
The trial continues.