Hi,
I want to build a 24" uni since I dont want to take 29er everywhere. I’ll some parta that I’ve got at home (qx 26 frame old KH saddle…) And I’d like to use 39mm wide Řím with 32 holes. And thats where I need advice this rim is really heavy (900g) is it top much for rim? KH weights About 700g I think…
I’m guessing you’ll probably use an Intense Mag30 or a Sun MTX39? This is what I have on my 24’’, pretty heavy yes, but you can really have fun on those without worrying about breaking it. It does make a difference in pedaling, the uni will have more rotationnal weight, so harder to accelerate and to slow down. It will require more energy to do so. But once it’s going the feel of it is pretty cool to me.
Sun mtx39
Yes I’m going to use SUN MTX39 since it is pretty cheap And strong rim. But I was scared to use it because I’venever ridden uni on non unicycle rim 
(altought I know there is no difference…)
I’ve had a 700c (narrow 29") wheel with a Sun Rhyno Lite rim for over three years and it has worked very well. The MTX39 looks good, at least from looking at the Sun Ringle product page, particularly since 36-hole choices are always limited. Of my 7 unicycles, only 2 have actual genuine unicycle rims. It can be done!
I’ve been running a mtx33 on my 29er. Haven’t had any problems, probably put 300 miles on it by now. I’m not a light weight rider either…