Long Distance Competition/Ultracycling, Randonneuring and Endurance Cycling - How does stem length effect steering?

How much does stem length effect steering?

I need to move the handlebars closer to the saddle and a shorter stem seems like the only way to go. I went from a 100mm stem on my Surly LHT to a 75mm stem and the steering feels incredibly fast.

I'm also increasing the stem angle by 18 degrees
I don't care for butterfly bars which would have me sitting completey upright.

I don't think it makes a real difference. If it did, putting your hands 25mm back from the hoods would result in a massive change in ride feel, and I've never found that to be the case.

More likely is that the stem change has put you into a position that works better for you, and you're interpreting it as feeling more responsive.

18 degrees sounds like a big change, as does the 25 mm.

Look at the geometry of it...

Shortening your stem by 25% will put your hands closer to the steering axis. I'd think that it would handle a little differently. Not sure how much different, but it makes sense that it would feel funny at first.

I recently went from a 110mm 7-degree rise to a 100mm 15-degree rise and the steering feel is noticeably different.
A shorter stem means you move the bars through a smaller arc to acheive the same turn of the steerer. Steering will feel quicker/twitchier for a while with the shorter stem, but you'll get used to it.

The difference is big if you go from a 100mm to a 120mm. The 100mm stem was a quicker steer response than the 120mm stem on my road bike, but I went for the 120mm stem because it was more stable on fast downhill winding turns, I felt more at ease with how it handled.

Interesting thread topic!

I don't think it makes a real difference.

Actually, it can make a huge difference. It's not only about changing the axis. In the roadie world buying a frame that's too small and using long stems is common. Problem with that is it shifts your weight and center of gravity forward. Buying a small bike because it weighs less and compensating with longer seatpost and stem can have an adverse effect on handling. Getting compact geometry crowd to believe is almost impossible.

This might be related - I have extended the height of three bikes' stems. The bottom of my drops are now at my seat height and the hoods are up above the seat height.

All around the bikes are more comfortable but I wonder if the added height adds some flexibility to the whole front end.