Like-for-like cycle sales fell 4% in the three months to 1 July, which chief executive Jill McDonald blamed on poor weather and the timing of Easter.
Halfords hopes that new bike ranges designed with Sir Bradley Wiggins and Laura Trott, who are both competing in the Rio Olympics, will boost demand.
In the year to March, bike sales at Halfords had fallen by 0.9%.
Halfords said that sales of premium bikes, which are priced between Â£500 and Â£5,000 and include the Pinarello model ridden by Team Sky, performed well over the first quarter. However, wet weather and the timing of Easter affected sales of mainstream models and accessories.
Overall, Halford's like-for-like sales fell 0.6%. Its retail division gained from strong demand in car maintenance and for child safety seats, but declining sales of sat navs dragged revenues at its car enhancement sector down 4.2%.
Halfords said in June that it expected the weak pound to knock Â£3m off its profits. Following the steep fall in sterling against the dollar since Britain voted to leave the European Union, the company said it may have further small impact in the financial year.
Commenting on Brexit, Ms McDonald said: "While the recent decision to leave the EU does create uncertainty, we are well-positioned as a business and focused on delivering sustainable long-term growth."

Mr Su was a vice-chairman of China's parliamentary advisory body.
The Central Commission for Discipline Inspection (CCDI) said he had used his position to obtain "large bribes".
State media had announced in June 2014 that the government was investigating him for corruption.
The CCDI statement (in Chinese) said that Mr Su had been expelled from the party and relieved of all positions.
It added that his behaviour had "resulted in serious violations of the law" and that "the issue of his alleged crime, clues, and evidence have been handed to the legal authorities for them to take action".
It said that Mr Su had abused his position of authority, receiving "large sums of illegal bribes" which resulted in "huge losses of government assets". The statement did not give figures.
Mr Su, who was previously the top Communist Party official in Jiangxi province, was also found to be "chiefly responsible for the serious corruption problem that has emerged in Jiangxi".
Chinese media reported in November last year that several officials from a city in Jiangxi said to have links to Mr Su were arrested.
He was one of 23 vice-chairmen with the Chinese People's Political Consultative Conference, which was seen as a prestigious position. The conference advises China's legislature, the National People's Congress.
China has been conducting a widespread crackdown on corruption since President Xi Jinping took power in 2012, and has arrested dozens of officials and others in the private sector. The authorities have also gone after those who have fled the country, and extradited hundreds of suspected "economic criminals" back to China last year.
Mr Su is considered to be among the most senior government figures caught in the dragnet, along with former security chief Zhou Yongkang who was arrested in December.
Halfords is hoping for an Olympics bounce to stem a slide in bike sales, which have continued to fall.
[NEXT_CONCEPT]
Former senior official Su Rong has been expelled from the Chinese Communist Party for corruption and faces prosecution, said the country's top anti-corruption body.