Hi everyone,
I want to use an old fork I have as a starting point to know which new fork to get for an ebay frame I bought. I don't know what the frame was intended for... 80mm, 100mm, or 120mm forks.

But, the old fork is a Rock Shox Dart 1 circa 2007 off my wife's 2007 Trek 4500 WSD. Seems to be either 80mm or 100mm but I can't tell for sure from web searching. It might be adjustable between 80/100 with an internal bumper installed or left out.

I measured from the top of the dust seal to the bottom of the fork crown, and that was 100mm. Can I assume it's a 100mm fork?

Or, if there is a bumper inside to make it only 80mm travel, would it sit like an 80mm fork or a 100mm fork?

I've used it on a hard-tail I'm building up, and the bike rides nose-down with this Dart fork. So I'm pretty sure I want a longer fork when I buy a good one, but I don't know where I'm coming from. (Besides the fact that the fork is shot and it's 1/2 way through its suspension all the time I'm riding it.)

I think I'm going to go for a rigid fork, so the length is pretty important. Any advice how to know what I'm currently using?

That vintage Dart was probably 80mm. This Bikepedia page seems to indicate the same. https://www.bikepedia.com/QuickBike/...spx?item=95858