Car parts and bicycles retailer Halfords drove through a 9.6% rise in group revenue from 3 April to 26 July, helped by its acquisition of Nationwide Autocentres in February, but it issued a cautionary stance on the economic environment.Halfords said it remains on track to deliver full year earnings growth in line with previous guidance.Like for like sales were disrupted by a 'sluggish start' to the spring season. Poor weather in April and consumer nervousness ahead of the General Election and subsequent emergency Budget hit consumer appetite, the group explained. A delay to the start of our Summer Leisure promotional campaign to mid July also hampered sales.Like for like sales at its Halfords stores fell 2.1% while revenue at its Autocentres was flat. Overall group like-for-like revenue declined 1.9%.However sales growth continued at its core categories of car maintenance and cycling and gross margin remained broadly flat on the year. "We are cautious about the macro economic environment but, through the execution of our proven strategy, we remain on track to deliver full year earnings growth in line with previous guidance" said chief executive officer David Wild. Halfords said costs continue to be closely managed. Its programme of store colleague re-rostering was completed in the quarter and is expected to reduce annual costs by around £2m.