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I currently run Tiagra triple 9 speed crank, 50/39/30 The BCD on the 50 being 130mm. I'd like to replace the 50t with a 52t to make it 52/39/30. I'm looking at a Shimano 105 52t chainring but it says it's intended for a double crank and 10 speed drivetrain.
But you think I can make that ring work in my setup?
Should work fine, assuming the BCD on the 105 52t chain ring is also 130 mm (and not 110 mm - compact). The 105 chainring will be profiled ever so slightly thinner for the 10 speed chain, but will not affect 9 speed performance. Make sure to orient the new ring in the correct position with the small metal tab (that catches an errant chain) pointing toward the crank arm.
First, consider this; can you spin out the 50t? If not, there isn't anything to be gained by going to a larger chain-ring. At a cadence of 90rpm and a 50t x 11t will yield over 32mph & a speed of about 42.5mph could be attained with 120rpm. Even with 50t x 13t & 90rpm, the speed would be close to 28mph. If you make the switch, you may find the front derailleur can't handle the larger chain-ring, so check the specs first. Older Tiagra derailleurs could handle up to 53t, but the design was changed for better shifting, and the current model specification shows a top gear of 50t with a range of 20t (meaning the difference between the large chain-ring & the small ring can be no more than 20t, ie. with a 50t outer ring the inner ring could be no smaller than 30t)
As long as your front derailleur can be adjusted vertically to accommodate the 52tooth chainring, the drivetrain should run fine.
The jumps between gears is not large so shifting would likely not be a problem but this will not be the quietest of drivetrains.
