* H1 adjusted pretax profit 44.6 mln stg vs 39 mln stg forecast

* Cycling H1 like-for-like sales up 14.2 pct

* Shares up 14 pct

(Adds details, shares, CEO, analyst comments)

By Neil Maidment

LONDON, Nov 7 (Reuters) - Bicycles-to-car-parts group Halfords HFD.L posted an unexpected rise in first-half profit, buoyed by a combination of Britain's growing interest in cycling, a warm summer and improved product ranges.

The group, which is in the early stages of a 100 million pound ($161 million), three-year turnaround plan to boost slumping sales, said adjusted pretax profit rose 6.4 percent, to 44.6 million pounds.

That was comfortably ahead of analysts' average forecast for a decline to 39 million pounds in the six months to Sept. 27. and sent Halford's shares up 14 percent to 477.4 pence at 1042 GMT on Thursday.

Its shares have climbed more than 50 pecent since hitting a low point for the year in June, a month after the company cut its dividend by one third to help fund the new strategy and warned profit would not reach the 72 million pounds made in its last financial year until 2016. ID:nL6N0E40NS

Halfords Chief Executive Matt Davies said on Thursday that while first-half trading had been good, there was still much work to do at the company which trades from over 460 Halfords stores in the UK and Ireland and 290 Autocentres.

"The weather undoubtedly really helped us... When you double your sales of sun glasses you know it was better weather than last year," Davies said.

Halfords' turnaround is focused on heavy investment in its online offering, staff training, new cycling ranges and store revamps to lift sales.

Group like-for-like sales rose 6.2 percent in the first half of its financial year with the strong performance led by a 7.7 percent rise in its retail division, which makes over 80 percent of group revenue.

"Sales growth is what the market wanted and after knock-out first-quarter retail sales, strong momentum continued in the second quarter," Investec analyst Kate Calvert said.

"While still early days in Matt Davies' three-year recovery strategy, these results should help to reassure doubters that Halfords' brand still resonates well in consumers' minds," Calvert said, pushing her full-year profit forecast up 13 percent to 67.8 million pounds.

The company said a warm summer, increased stock and marketing, improved ranges, and strong British showing in sporting events including the Tour de France cycle race helped its performance. First-half underlying cycling sales jumped 14.2 percent.

Illustrating Britons' increasing interest in cycling, membership of British Cycling, the sport's national governing body, has risen by over a half to an all-time high of 75,000 and 100 new cycling clubs have been formed since Bradley Wiggins won the Tour de France last year.

Cycle repairs and car maintenance sales - both growth areas for Halfords - rose 27.7 percent and 8.8 percent respectively.

Underlying sales at the group's smaller vehicle service and repairs arm, Autocentres, fell 2.1 percent.

($1 = 0.6219 British pounds)

(Editing by Erica Billingham)

((neil.maidment@thomsonreuters.com)(+44 0207 542 2292)(Reuters Messaging: neil.maidment.thomsonreuters.com@reuters.net))

Keywords: HALFORDS RESULTS/