Say internally reducing from 140mm to 120mm

Will forks be noticeably stiffer due to increased upper/lower overlap?

The overlap is fixed, the shortening of the fork may help but I doubt it is noticeable

What do you mean fixed? The fork gets shorter as there is more stanchion inside the lowers, no?

theoretically yes, though it is more about reduced leverage than overlap as such; the bushings in the lowers will be the same length whatever you do. There are other variables in the stiffness of the fork such as the arch, type of dropout/axle, size of disc rotor…. I dropped my reba’s from 115mm to 100mm and i can’t say they feel radically stiffer, they just climb better.

I’ve got some 08 32 floats being dropped from 140 to 100 – I wondered this too…

Oh, I see what you’re saying. Ta.

Surely it depends on the design of the fork internally…?

Or do you mean are the spring / air chambers being compressed is the ride firmer?

Yes, it depends on the fork.

A coil Rockshox U-turn fork for example does get stiffer because part of the spring is bypassed as you wind it down, increasing the effective spring rate

On an AIR u-turn fork, if you set the pressure at full travel and wind it down, then the +ve air chamber becomes smaller and this ups the air pressure and makes it stiffer…. However if you wind it down, then reset the air pressure the only difference is less travel and a more progressive rate (I think)

Second the view about Rockshox U-Turn – maximum extension results in the most sag. Winding it in reduces the sag.

stiffer fore and aft? yes.

A coil Rockshox U-turn fork for example does get stiffer because part of the spring is bypassed as you wind it down, increasing the effective spring rate

But this would only be the case on a progressively wound spring, wouldn’t it? Otherwise you simply have a shorter spring with the same spring-rate.

I think OP was talking about stiffness as in flex rather than spring rate though.

Sorry I meant fore and aft stiffness, not firmer spring

All it means is the lower legs will sit further up the upper legs, so there will be less leverage on the upper legs, so yes they will have a little less flex fore / aft.

Running revelations at 130mm on my old scandal was slightly more twangy than at 100mm. Something to do with the leverage I think.

Was the originally question not to do with how flexy the fork is as opposed to how stiff the suspension travel is?

I remember reading in a magazine (mbr – so questionable) that 2007 Fox 32s at 140mm were very flexy, but the ones reduced to 120mm (on specialized and others) weren’t noticable flexy

Yeah, I think James has hit on both mine and the OP’s question…