Don't know specifically about bike parts, but you will get stung for import VAT and customs duty depending on what exactly you are buying if its outside the EU.
Customs Duty (from HMRC website);
Customs Duty is charged as a percentage of the total value of the goods - that is the sterling equivalent of the price paid abroad.
To work out the percentage, each type of product is given a 'commodity code'. This tells you what the Customs Duty rate percentage is for that particular product, based on whether it's being imported or exported.
There are around 14,000 different classifications. The duty rate percentage for each may vary according to the country the goods come from. The average percentage is between 5 and 9 per cent, but it can be as low as 0 per cent or as high as 85 per cent.
Import VAT:
The percentage charged is the same VAT rate that applies to similar goods that are sold in the UK.
The import VAT percentage rate is applied to the total value of the goods. In the case of goods brought in this is the sterling equivalent of the price paid abroad, as shown on the receipt. In the case of goods posted from outside the EU, it is the amount on the Customs Declaration, which includes the price paid for the goods, the cost of transport, postage and packing, insurance and any duty that may be payable.
