CaptainPlanet

From what I understand, the fork bar's length determines how high you can raise a threadless stem, and if you want to increase the height further than what was cut, you have the get another fork and recut it. This seems like a disadvantage of threadless stems.
With quill stems, you simply raise the quill independent of the fork, and if you can't get the height you want, you can just swap in another stem.
There are also technology like quill threadless adapters so you can use threaded forks in combination with threadless stems

Is my information correct? Is there a way to raise threadless stem height further than the fork bar's height through some other adapter?

cpach

There are various steerer extenders that work OK, though I wouldn't advise them for heavy riders riding hard. They're basically a threadless stem that goes straight up parallel to the steerer with a section higher up with a diameter of the steerer. You can also get a fair amount of additional rise using a high rise stem, and in many cases different handlebars can generate a lot more rise as well.

Even with threaded stems there's a range of adjustment, and you can only get so high. Arguably, some steel forks come in extremely long before being cut and allow for higher positions for the same head tube length than any threaded system.

In a lot of applications threaded stems are genuinely much nicer, but they wouldn't hold up well to the leverage of modern mountain bikes, and weigh an awful lot more than current road bike setups.

LesterOfPuppets

Big changes generally require a stem change - Technomic for threaded, 20-30⁰ stem or maybe a tallstack for threadless. If MTB you can get bars with higher rise also.

Many quill stems just have 1-2 inches available adjustment. Many threadless bikes are unfortunately setup with less room for adjustment than that.

Trevtassie

Yep, there are plenty of threadless extenders out there. Plus plenty of angled stems of many lengths, so you can usually get where you want. If you need a mega tall bar height, then you probably need the next size up frame.

DaveSSS 

The correct term is the steering tube. Carbon fiber steering tubes should never be used with an extender. The clamp on the stem should also not extend above the top of the steering tube. Use a steeper stem angle to raise the bar height, but keep in mind that the steep angle also moves the bars closer to rider, so a longer stem may also be needed.

HillRider

Unless you later decide you need to raise the bars a lot, you can leave some height adjustability when you cut the steerer initially. Cut the steerer too long and add spacers above the stem, say 20 mm or so. Ride in that configuration for a while to determine where you prefer the bar height. During the trial period you can shuffle spacers between the top and under the stem to change the height. When you have settled on a preferred height, cut the steerer to its final length but leave enough extra for a 5 or 10 mm spacer above the stem for future adjustment.

Note that most carbon steerer fork makers limit the spacer stack under the stem to 40 to 50 mm maximum so don't try to set the bars too high if you have one of these forks.

Leebo

I never cut my steerer tubes, no issues.

Retro Grouch 

How much do you think you need to raise your handlebars?

Most of the time the cost effective way is to substitute a stem that has a higher angle. Incidentally, Quil stems generally only allow an inch or so of height adjustment too.

FastJake

Both systems have work-arounds to get the bars really high if that's what you want. If you get un-cut fork there's no kludge needed with threadless.

Both systems have advantages and disadvantages, but I don't think anyone will say threaded is superior in the context of mountain biking. I generally prefer threadless but threaded works just fine too.

As someone else mentioned, the correct term is "steerer tube".

3alarmer 

...this. There are a whole lot of various configurations for rise and reach for threadless stems. One of them usually works if your bike was already pretty well fitted.
In general, to sit farther upright, you need something that angles up and has less reach.

davidad

https://www.amazon.com/Delta-Cycle-B...KWS?th=1&psc=1

Kapusta

This is why I leave a few spacers above the stem until I am sure of the fit... and then still leave a 10mm spacer there.

And, as has been pointed out, you can just get a riser stem if need be.