This isn’t a trick question, I am just trying to understand the effect of changing from a 100mm fork to an 80mm forks and what it does to the bike set-up.

So, the question is as per the title – does the difference in travel length of the fork also equate to an overall difference in the length of the fork e.g. measured from the drop-out to the crown race?

No – my 100mm menjas and 80mm recons have a difference of 4mm in axle to crown length.

Short answer – roughly, yes.
Long answer – it depends.

Everything else being equal (i.e. the same model of fork in two different travel versions) then the 100mm fork will be 20mm longer than the 80mm one, but as Smee says, different brands/models will have quite a bit of variation.

Depends on the brand of the fork obviously. EG a marzocchi mx comp in 80mm travel guise will be 20mm shorter than the 100mm travel version.

And the 80mm Marzocchi will probably be about the same length as some 100mm competitors… Which means a 100mm fork COULD even be 40mm taller then an 80mm fork if you happen to pick a particularly bad combo.

If you take two identical forks bar the travel, say for example a 80mm and a 100mm Reba, then the real difference in ride height is about 14mm not 20mm. This is because a 100mm fork will need to be set up with more sag than an 80mm fork.

Thank you for the feedback, it doesn’t look like a precise science. I am trying to work out the effect of reducing some 100mm forks to 80mm (a mod that is OK according to FOX) and then using them on a frame that is specced for 80mm forks.

Axle to crown length is the key measurement here, I believe. You should be able to find this on most fork manufacturer’s websites, but I’m unsure if Fox will list that length for a modified fork.

ditto, although the marzocchi reputation is based on the 2003/4/5 era forks (when they went for 1 piece cast lowers, and the 888/66’s etc). some bits form those forks were kept right upto/evolved into the all mountain forks, which were also veryyyy tall.

My 130mm 2002 z1’s were actualy the same lentgh as manitou minutes from a few years later, which were amongst the shortest 130mm forks.

The All Mountain forks were stupidly high axle to crowns. Worse fork they made. My old AM1 were 30mm higer than some other 100mm travel forks I fitted on the same frame.