There are some stiff climbs on this route as ever, 34 x 28 should be okay, as some have already said you may end up pushing in some places, but so what, its not a race, myself will ride my tourer with triple chain ring, the last climb of the day is a long slog up the bwlch-y-groes, which steepens all the way up, last section is 1 in 4, with a roughish surface, but the whole ride is great, different to ‘sportives’– although in recent years more people seem to treat it as a sportive– they miss the point, some great characters turn up year in year out, including the 12 hour record holder andy wilkinson on his legendary dolan– just hope for ok weather