daveed

Hello,
Not sure why my steering feels so gyroscopy after I trimmed an inch from the top (above the stem) of my steel 1 1/8-inch fork. I can't ride no-handed, for instance.

The particulars. Headset: Cane Creek S2 with sealed bearings (not new). Fork: Kona Project 2 (not new). Frame: Soma Double-Cross (new). Standard stem (new).

I tightened down the assembly properly, making sure there was no movement in the fork. I have done this several times with the same wonky steering result. One possible issue: The crown race on the fork isn't tight. I recall easily snapping it on the fork when I built up the bike last fall. It's not loose and it fits snugly. But I don't need a tool to remove it.

What should I be looking at, examining, doing do get back to normal steering?

rpenmanparker 

The most likely answer that comes to my mind is that the frame and fork are not well matched, i.e. you have the wrong trail as a result of the head tube angle and fork rake not being right for each other. I don't know what "gyroscopy" means in this context, but I'm assuming you mean the front end is fidgety (actually the opposite of the gyroscope effect which is to stabilize). Sounds like you have too little trail with this combination. Check the head tube angles of the old and new frame to see how they compare. I doubt it has anything to do with the cutting of the fork unless you changed frame sizes radically. But why did you remove the fork crown race at all to cut the steerer tube? That wasn't even necessary.

daveed

Thanks for the answer, Robert. I don't know what "trail" means, however. Meanwhile, I didn't remove the crown race. I just noticed that it was easy to pop it off. The fork and frame are the same fork and frame; nothing is different (same frame, same fork). I simply trimmed the fork using the proper Park tool.

By gyroscopy I mean the bike pulls a little right and left on its own, hence scary to let go of the handlebars for more than a few seconds.

rpenmanparker 

I was responding to your labeling of the frame as "new" in your original post. Is it new or not? Trail is the distance between the point where the head tube center line would intersect the ground and the center of the tire contact patch. It is determined by the head tube angle and the fork rake and is the main determinant of front end handling of the bike. Too much and the bike is sluggish, too stable. Too little and the bike is unstable, fidgety.

Homebrew01

If you have the same frame & fork, but just cut the extra off the top of the fork, then the only thing that could have changed is headset adjustment.

HillRider

Any chance you assembled the headset incorrectly? Is the inverted centering cone in the right place? Bearings oriented correctly? Do you still have a gap so the top of the steerer is a couple of mm below the top of the stem or top spacer?

rpenmanparker 

Yes, and it should go without saying, but OP, are you tightening the stem clamp bolts properly. You can't rely on the top cap bolt to secure the fork. That just sets the pre-load. Security is provided by the side bolts on the stem.

reddog3

Assuming the bike could be ridden "no-handed" before- sumpins changed.

Same front wheel and tire? Same air pressure? Wheel oriented in fork as before? Cable routing?

Others mentioned headset adjustment. You didn't remove the frame cups did you. If so, maybe they are not seated properly causing some bind. Possibly the adjustment is too tight causing a bind that won't allow the steering to self-correct. I'd back it off 'til there's just a tick as you rock it with the front brake locked- then ride it.

Then I'd look at the cable routing. Since you had the front end apart (new stem at this point?) it's possible that you have one or more cables without enough slack. The new stem is the same height and reach? Keep digging. You changed something without realizing it.

daveed

Thanks to everyone for their kind help. I have actually thought about (but haven't necessarily tested) the aforementioned suggestions -- except for tightening the stem to the steerer tube, which I did properly (backing off the stem bolt just so). Same front wheel/orientation, to be sure. As for the frame cups, I dd not remove them. In short, I reassembled the same components onto the same frame. Yes, I have the gap just a tinge below the stem.

Cables, perhaps, are the issue but I neither raised nor lowered the handlebar/stem height (only trimmed above the stem).

rpenmanparker 

What do you mean you backed off the stem bolt? Even though you can theoretically ride with the top cap loosened after the stem side bolts are tightened at the right pre-load, it is not recommended to do so.

daveed

I mean I loosened it a tad after tightening down the stem bolts. I believe there may be difference of opinion on how tight the stem bolt should be once the stem bolts are properly torqued.

rpenmanparker 

As I said, it should be okay to loosen the top cap after tightening the side bolts. It shouldn't make any difference, but I have never seen a recommendation to do that.

OTOH is it possible you are overtightening the top cap at the outset, i.e. applying too much pre-load. It may be counterintuitive, but a headset that is too tight could cause squirrely handling that you might think would only happen with a loose one. If the fork head set binds, it could make the steering jumpy in that it would resist the natural turning that comes from shifting your weight. That is how you steer without hands. If the head set is too tight, the bike could be unresponsive to normal steering by weight shifting and seem unstable. Kind of s stick-slip effect. Resisting steering then letting go all at once.

daveed

RP: Thanks for the tip! Maybe excessive pre-loading is the problem here. Meanwhile I'll be in the basement, bike on stand for awhile.

mmmdonuts

My vote is for this, too much preload makes it stick in one direction.

Kimmo

Just do up the steerer clamp bolts until they're not loose, but haven't begun to clamp. Sit on the top tube and rock the bike back and forth with the front brake on while doing up the preload bolt just until the rattle stops.

Pick the bike up and tip it side to side. The bars should easily move. Then clamp the steerer after ensuring the bars are straight.

If you can't adjust the headset so there's no rattle or binding, there's something wrong with it.

reddog3

Funny how the simplest of devices (threadless steerer) can sometimes be the most confusing. Once the preload is set, and the stem clamp bolts are tight, you can take the top cap and bolt out and stick it in your pocket. It serves no purpose other than adjustment and plugging a hole.

rpenmanparker 

Agreed that you can, but I simply said that it is not generally recommended to do so. You're right most folks don't understand this.