Im a newbie to biking and picked up a used Giant OCR3 (2005) for next to nothing. The bike is in pretty good shape (needs a tune-up). My question is if I wanted to upgrade the Sora 8 speed components that are stock, could I upgrade to a 105 set? Anything special I would need besides the group? Thanks for the info.
Overall there is no reason why you can't upgrade to 105 as long the costs suit?
You have to careful with upgrades as it may cost more than a new bike complete with your favoured group.
I would presume you know that 105 is now 10 speed.
A new groupset will fit with no problems. You can keep the same wheels as the cassette will be a straight swap. You will need new cables unless these are included.
You will need a new bottom bracket as the chainset is a different mounting type and a new chain. Again may be included?
New bar tape will be required when fitting the new cables for the new STI.
[font=Trebuchet MS]Ride hard or ride home alone![/font]
Try to get last year's 105, the difference to this year is not that big. The important upgrade will happen later this year, when the shifter cables will be routed under the handlebar tape. You can also try to get last year's Ultegra, the price difference should not be that great.