I have this folder and I want to keep the small size but want to raise the handlebars. I Have a new fork coming that is 295 mm and I am hoping that I can put a bunch of spacers under the stem and top cap.
Right now, the total stack from crown race to top cap is 190mm. I am wondering if putting 80mm of spacers is too much?

New cables and housings.

New shifters and brake levers on a riser bar. Lost 1.5 lbs with this change

Brooks seat and new rubber grips

Assuming the steerer on the new fork is steel, you can use quite a tall spacer stack safely. For carbon steerers I've seen a recommendation of 25 mm max for a 1" steerer and 40mm to 50mm max for a 1-1/8" steerer. An 1-1/8" steel steerer should be able to exceed this with no problems but I wonder if 80mm will make the steering feel a bit flexy.

If you aren't doing steep grade enduro downhill with it, you can raise your handlebar with as many spacers are you'd like.

But seeing the height of that seatpost on that teen-sized 26" bike, you may want to think about getting a whole another bike with the features you want.

What material is the new fork's steerer made of? If Al there's a greater ability to handle a higher set stem (and thus more spacers) then a carbon steerer usually likes. Some forks will have spacer height limits listed in their specs or stated on a sticker. There's a good chance that longer cables might be needed too. Andy

I don't think you will have any trouble, though with that much rise had you thought about a steertube risers? I'm fairly tall and have used them on various bikes. I use a Satori version on one peticular bike, but I've had Delta and others. I prefer the Satori clamp design over the Delta.

Here's a picture of a Satori installed

The bike is a rather small bike for me but it is a folder and I want it to fold small. The new fork is a steel disc fork and I plan to mullet the bike. I will get a 650b/27.5 disc front wheel and possibly keep the 26 rear. It is going to be my travel bike here in Cambodia.

With a steel steerer the spacer limit is pretty much a non issue. Andy

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...this turned out a little cheaper than buying all those spacers. I used a piece of PVC (cut to the right length) as a temporary spacer, while preloading the bearing. Once you have the lower clamp tightened and the bearing preload is set, you can remove the PVC and install the stem at whatever height you need it.

Your primary source for this would be the fork specification. Every fork I've ever bought comes with a spec for maximum spacer height between the top of the headset and the bottom of the stem, and sometimes with a maximum overall length (which would be spacers height + stem height).

My 1" full carbon fiber fork specified a maximum of 40mm between top of headset and stem. I've had two or three new 1 1/8 CF steerer forks and they've been 35 and 40, usually 40. I believe metal steerers have much greater maximum lengths.

If you find that the specification for the fork is inadequate for getting your handlebar high enough, get a stem with a steeper upward angle.

Curious, as you are already frankensteining a foldable bike, so why would you think too many spacers is also a bad move?