'Boris bikes' prompted the most heated moments of Thursday evening's mayoral hustings, after the mayor was told his policy was "killing cyclists".
Liberal Democrat candidate Brian Paddick's claim was reinforced by Labour's Ken Livingstone during the televised debate hosted by Sky News in the City.
"Your office instructed TFL to remove the cycling safety measures," Ken told Boris.
"Within a month two cyclists had been killed and when the police investigation is over your office may be subject to corporate manslaughter charge. You have done nothing for cyclists."
He received a brief round of applause before Boris responded: "I think that is absolutely outrageous. Not only from a man who cannot ride a bike, but who is standing on a platform to cut investment."
Mr Paddick claimed that Boris had prioritised traffic flows over safety, but the Conservative incumbent insisted that City Hall was working hard to bring cycling casualties down.
Boris is not accustomed to being criticised over his bicycles, which received the royal seal of approval earlier this year, the Telegraph reported.
At a Fortnum and Mason reception the Queen told the mayor: "At least I didn’t have to come down here today on one of your bikes."
Mayoral fears that Her Majesty did not approve were assuaged when she added: “Oh, yes, I think they’re lovely. In fact, I notice the bike racks are often empty.”
Thursday evening's debate also saw Boris pressed over his absence from the capital at the start of last year's August riots and he and Ken trade blows over their tax arrangements.
Boris said he wanted to prevent London "lurching back to the arrogance, the waste and the broken promises of the past", while Ken reasserted his tube fare cuts plan.
"If I don't cut fares by the 7th of October this year I will resign," he pledged.
Mr Paddick appeared more focused on the other elections taking place in London on May 3rd. He said: "It is just as important to vote for the Liberal Democrats as far as the London Assembly is concerned, it's just as important as voting for me for mayor."