I converted an old Atala road bike frame to single speed/fixie. Didn't test ride the pre converted conditions, but now the back end is lighter and the bike seem unbalanced.

At moderate speed, perhaps 8-15 mph, the steering seem wobbly and I'm afraid to turn, fearing losing control. I've read Sheldon Brown's steering adjustment piece. Not sure if it's shakiness or stiffness or both. Is there a better description for both terms?

Is shakiness felt at low speeds?

I've made adjustments to tighten the threaded top race and backed off a bit because the handlebar became stiff.

Was wondering if the unbalanced bike, with the heavier chromlux rim front wheel has kind of a centrifugal effect to cause this wobbly feel. I've swapped wheel from a hi-tensile Univega bike and have the same problem.

I've read Sheldon Brown's steering adjustment piece <-- are u talking about something called headset???

I think you have a headset that is too tight, sorry for telling you this but u dont need to be a genius to figure it out when is lose and when too tight, a hint ok? when is lose the fork and the handletbar will have play, if too tight it will do like brake dancing.

About your centrifugal forces and unbalance is just an idea way out there. Big chance the setting of the bike is wrong for you or you dont know how to ride a fix gear, assuming the headset is right and smooth my choice is the last one, rider problems.

Good luck tho.

If you've got a flip-flop rear hub with both fixed and freewheel, switch to freewheel and reinstall and get the front brake working if it isn't already.

1. with the brake applied, rock back and forth, turn sideways, and rock. Adjust to get rid of the play, and then if an old headset, I'd tighten down top lock ring. Make sure you have a key'd washer between top cup/race and top lock ring and that your top lock ring (which has a lip often) isn't bottomed out. If so, add washer height. Ride the bike and pulse the front brake. Does the frame flex too much or the fork go thunk? If so check for ovalized head tube or that you've indeed adjusted the headset correctly (i.e. cups and races are flush against headtube and fork, there's no jammed seals wedged between the cups and races, etc.)

2. ride with freewheel and stand on pedals and gently do quick short squats/mini handlebar push-ups to bounce to flex frame and fork. Feeling more mushy than normal? Hopefully, that didn't cause full steerer tube/fork crown separation and your impalement, but if it's flexing or creaking or crackinly, disassemble headset, remove fork, check for cracks in steering. You may need to remove crown race and wrap a towel around steerer tube and clamp firm but non-destructively in a vise. Then try to rock the fork and look for cracks in the steerer. Now inspect downtube and top tubes near the head tube. Any flaking paint around welds/lugs? If you're feeling solid on bike, then it isn't your headset or front end frame or fork.

3. Get off the bike. Stand on drive side. Step against center of crank with your toes with sneakers on, and push down and sideways and have someone on the other side look at the right chain stay and lower rear triangle near the BB. Any cracks? If nothing and you feel the frame is solid, then you've mostly eliminated any frame issues.

4. Spin the front tire. Any flat spots? bulging spots? check all spoke tension to feel if equal. Just squeeze each crossing pair. If the rim is mostly true, but you feel a set of spokes is way too loose or tight, then you have a dinged wheel that someone tried to correct by brute spoke tension. Not a good idea because the rim's integrity has likely been compromised and the repair is just cosmetic to hide the underlying deformity in the rim. Is the weight rotationally balanced? If not, check the tire, deflate and see if someone overly enthusiastically filled the tube with green sealant goop that sank to one side of the tube and formed a spot where all of the stuff has coagulated. Replace the tube if necessary.

5. That leaves the rider. But that's unlikely, right? ;-)

I've only been riding on the freewheel side. Loosening the top race did the trick. However, if I try to tighten down on the lockring, the steering turns stiff again. There is a keyed washer that also serve as the brake cable attachment.

I'll try to play around to see if i can loosen it to the point of shakiness and then tighten the lockring.

Have you taken the fork to check it with an alignment reference tool?
steerer tube may be bent, and so crown race seat is not right .
tight and loose bearing feel,as you swing the fork , steering, may be that
even with an un pitted headset..
one blade may be ahead or behind the other , .. relative to the fork crown/steerer tube..
Ditto the frame itself..

When you tighten the lock ring to lock the top cup into place you need to actually turn out the top cup a little at the same time you tighten the lock ring against the top cup.

The "why" of it is due to the play in the threads. When you bring the cup down onto the bearings and get it feeling just right the cup threads are seated against the lower side of the steer tube threads. When you screw down the lock ring it tries to push the cup ahead so it's seated against the top of the steer tube threads. The couple of thousandths of movement this causes results in far too much bearing preload in the head set.

To counter this you need to slightly loosen the cup or to screw the cup back against the lock ring just as it makes contact. And even than you can expect a little back and forth play. To slightly loosen you turn both the lock ring and cup back together using two wrenches. To do so you'll likely need to loosen the lock ring an eighth to quarter turn. Then the cup threads will be eased off enough to turn along with the locking ring by using a second wrench on the cup while the first wrench is on the lock ring.

This is the same treatment that you use for adjusting cup &cone wheel bearings. So you may as well figure out how to do it.

Thanks BCRider for the tip.