Greetings.

I want to have a speedometer on my Trek and I have an analogue style one that works mechanically. I'm finding that I don't have room on the hub bolt, while I see photos online of these being used with new bikes. Help! Would I need an adapter or to have the bike hub changed? I've added two images from online and two of my bad situation here!

you have 50s parts on a newer bike.

cruiser with a bolt on wheel is a better match pry out the fork wider. no looking back after that

longer axle spacers & all that ..

Folding bikes use a 74 mm wide hub most bikes use a 100mm so you could start over with a custom wheelbuild

but why not just put out $20 on an electronic speedometer-computer ..

My consultant fee being mailed now?

No Consultant's Fee!
It is a new speedometer. Also, I don't like the lcd screens, black on dark grey - I like seeing the dial.
My hub measures 100mm. The Russian bike shop guy said it would be expensive to have him make it fit. Why?!
Also, the electronic sensor type speedos are $40 here.

But also... these images from online appear to be a normal bike, standard hub...and use the old speedo.

find that one and look at it in person, then.. measure it..

you work for free yourself?

- I never asked for free.... Just wondered why it would be "very expensive." Incidentally, that guy quoted me $275 for a post-hurricane overhaul. Got it done at an older, local shop for $150. Maybe I'll try them.

measure and think ... where are the interference points?

Interference? There is no interference; the hub bolt does not have the room for the but, fork, AND the added odometer ring...