Replacing a fork with aThreaded Steerer

[DCBassman]

The plan is to replace the crummy suspension fork on the Trek Navigator with a rigid replacement. The current fork is 430mm crown to axle, 190mm steerer tube.
I'm not too fussed about losing some height from the front, it's very upright at the moment.
Questions are:
1) If I get a fork with a 250mm tube, can I use spacers above and below?
2) If I get a slightly shorter steerer, does that matter? There are already 2 spacers (5mm) between the two locking nuts.
3) Will the drop in height of the front have any significant effects?
Your expertise, as always, much appreciated.

 

[DCBassman]

Title modified!

 

[boydj]

The fork will come with a long steerer. You then cut it down to size and use spacers above and below as necessary. It is normal to leave the steerer on the long side until you are happy with the height of the bars and then trim the steerer again, leaving the steerer still slightly long to make repositioning or reselling easier.

 

[rualexander]

The fork will come with a long steerer. You then cut it down to size and use spacers above and below as necessary. It is normal to leave the steerer on the long side until you are happy with the height of the bars and then trim the steerer again, leaving the steerer still slightly long to make repositioning or reselling easier.

It's a threaded steerer according to the title, not an Ahead style threadless steerer.
Therefore, the steerer has to be cut to the correct length to suit the headtube plus the headset stack.
A couple of small spacers between the top bearing race and the locknut may be possible as the OP suggests are there currently but it would not be usual to add a significant spacer stack between the race and the locknut.
And spacers above the locknut would be pointless.

Dropping the height of the front end would have a significant effect on the geometry and handling as it would steepen the head tube angle and alter the fork trail etc.

 

[DCBassman]

Thanks for the replies. Of course, I could go the whole hog and convert to threadless, but that would mean new bearing cups needed to be installed. Apart from that, I have the tools to do it. But then new stem also.

Dropping the height of the front end would have a significant effect on the geometry and handling as it would steepen the head

How would this translate into what I would notice in use?

 

[rualexander]

The steering would become more direct and less stable with reduced trail.
You might find it fine and no problem, or you might not like it.

https://road.cc/content/feature/bike-geometry-101-learn-why-frame-angles-trail-matter-267512

https://calfeedesign.com/geometry-of-bike-handling/

You would also be altering the seat tube angle slightly too of course.
Which would probably require you to move your saddle backwards to compensate.

 

[boydj]

It's a threaded steerer according to the title, not an Ahead style threadless steerer.
Therefore, the steerer has to be cut to the correct length to suit the headtube plus the headset stack.
A couple of small spacers between the top bearing race and the locknut may be possible as the OP suggests are there currently but it would not be usual to add a significant spacer stack between the race and the locknut.
And spacers above the locknut would be pointless.

Dropping the height of the front end would have a significant effect on the geometry and handling as it would steepen the head tube angle and alter the fork trail etc.

I assumed a conversion to threadless would be the best way to approach this job. I've worked with a threaded steerer and threadless is a much better way of doing things.