It's for looks, or for guys riding minature frames to get as low as possible. Every year the idea of what a "short" stem is seems to get more ridiculous. Consider for a moment that for a bike with Italian stage geometry, a 12cm stem was designed to go on a 60cm (C-T) frame.

I don't understand these negative comments. I already suggested that the OP might want a flat bar road bike setup, in that case you need the longest possible stem pointing downward. Another possibility is long arms paired witha now fashinable "grand fondo" geometry. I test bikes for a magazine, and I have just received a well-known Italian brand's "grand fondo" model, which has the shortest TT for a XL size I ever saw paired with the longest head tube. I had to change the supplied 110 mm stem to a 130 mm -10 degree, slam it all the way down, and the bar on this test bike is still 15 mm higher and 10 mm shorter than on my own bike. So now I'll try to borrow a 140 mm, if I can. Maybe there is a "grand fondo" frame out there which with an even more "relaxed" geometry, and the OP wants to make it fit like what he is accustomed to...

Wouldn't that make it the wrong frame for the job then?

Maybe the OP had an older "sporty" aluminum road frame, wanted a carbon frame, didn't know what this new frame geometry trend was all about, bought one and now has to make the frame fit... There are many reasons to need a 140-150 mm stem, having a frame 1-2 size too small is just one of them, so I still don't understand why you guys are so unkind to this first time poster!

The OP doesn't seem to be interested anymore, but to me it just feels better. I'm 6' with normal proportions and have 14cm of saddle to bar drop, and 60cm from saddle tip to bar center. A 54cm frame (145mm head tube) with 140mm -17 slammed stem is what gets there.

Oh ya... I also have a setback post and the saddle is all the way back.

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formerly rruff...

Well I'm 1.86m and have a relatively short femur (thus zero offset post at 78.5cm saddle height/85mm set back) plus long arms, which means I ride a 61cm with a 160mm custom stem for a saddle to bar reach of ~63cm. I've never ridden a road bike with a stem shorter than 13cm and I'm really not that tall. With 38cm bars it doesn't handle too well but its for going fast in a straight line! I have another bike with 42cm bars and 130mm stem that climbs and handles better.

A 150mm stem is not too big if that is what you need