Guessing, I would probably think in the 200lbs ++ range, or thereabouts. You'll reach a point where adjusting the preload will wipe out any free sag and limit total shock travel. I'm around 175lbs... in that range, or slightly higher, a stock spring installed on the rear shock can produce some decent numbers. But, as mentioned above, how you ride the bike and where you ride (street/track) will also be a determining factor. Street and dedicated track setups may vary sharply. On the front end, running Marzocchi forks, the front appears softer than the rear... so the max up front may be somewhat lower.