I have an early 2000's Giant OCR 2 roadbike (3x8 speed) with worn out chain rings on the Shimano Sora FC-3303 triple crankset. The original rings are the SG A-type, 5 bolt, 130 mm BCD in 52T-42T-30T sizes. All I can find are used ones, and I'd prefer not to change the crankset. Can I just drop the A-type originals and go with new ones in the same bolt pattern and BCD that are close (ie 53T-39T-30T)? Thanks
Yes, you don't have to use actual Shimano chainrings, you can use 'third party' brands.
There are a few manufacturers that produce replacement chainrings in a wide range of BCD measurements and tooth counts, so you be able to get exact matches.
If you do decide to change gearing, derailleur position and chain length will need to be changed, but you should probably be replacing the chain at the same time as as rings anyway, and also checking at the cassette for wear and replacing that if necessary.
Of course you can as long as the bolt pattern matches. It may happen that the new chainrings have slight offset, you would need to adjust your front derailleur then.
What will change is the gearing. Going from 52 to 53 for the largest cogring will decrease your cadence by less than 2% (will require more effort to maintain the same speed) but these are negligible values, I'd say.
You also may have to slightly rise the front derailleur, depending on how much clearance you have right now between it and the largest cog.
You should also check whether the new chainrings will fit your chain, i.e. if they are not too thick (for 1/8 chain only while your is 3/32) but I don't think it will be the case.
For your reference, I've changed the complete crank on my old 26" mountain bike. I went from 46 to 54 the largest (if I can recall) and I needed a longer chain and the front derailleur had to be readjusted for height.
Thanks for the help so far. The original Sora 3300 triple has always required constant adjusting, and the only chainring replacements are 9 or 10 speed which means they should work, but might not depending on variables (which chain to use, etc). It's a bit spendy, but since the frame and wheels are OK for my riding my current plan is to install a whole new Sora R3000 2x9 groupset (chain, shifters,RD,FD, cassette, crankset) for around $350 and do away with the triple altogether. If it updates key components as a set and gets me another few years of riding this bike it seems worth it.
Update: I found a very fair deal from Merlin Cycles in the UK for a Tiagra 4700 groupset (mechs, crankset,bottom bracket, brifters, cassette, chain and brakes) with my preferred choices (crank length, medium rear mech, large cassette). It came in about a week through regular post (Canada) very well packaged and complete with new cable sets. Switching a 2005 Giant OCR from Sora 3300 Triple (3x8) to Tiagra (2x10) was straightforward, just had to Amazon a Hollowtech bracket wrench as I had not used one before. The next bike will be 105 with more carbon, but this feels like a good move to keep this one at a good level, and I don't miss the Sora triple so far. It feels as good as my older Dura Ace, although I know it's heavier.