Originally Posted by
dsbrantjr
Why don't you find a similar bike with a rigid fork and the same wheel size (probably 26") and measure that? It shouldn't be too far different.
Well...
There can be a fairly big difference between a bike designed as a rigid and one designed for a sus fork.
If you stick a rigid fork that's
not sus-corrected on a frame designed for a sus fork you run the risk of ending up with a rather steep fork angle. Ride may get "lively" to a fault.
51 mm is very short travel, with todays measurements. Subtract 25% sag and you're left with 38 mm or thereabouts.
IME ATC for bikes definitely designed as rigids is between 395-415 mm, so unless the designer has opted for some extra crown clearance an ATC between 433-453 sounds like a decent guess.
It may not be advertised as a sus corrected fork.