I bought a steel replacement fork for my Klein Quantum and took it to my LBS for installation. The mechanic told me I'd guessed wrong on crown race size. The fork is 27mm, my headset 26.4. Welcome to my life. He said my options were to get a correctly sized fork or he could install a Velo-Orange Grand Cru headset. He said the headset is "notched" and can work with either size crown race. I bought the headset and had it installed with the fork. Today I took it for a first ride. The steering is fine, smooth and solid. It seems to me, though, that the front wheel does not hold center as well as it should. If I take my hands off the bar there is no center stability. It quickly dives to one side or the other. Is this possibly a result of not using the Velo-Orange headset as it was intended? Thank you for your thoughts.

If the headset is too tight it might. Is pretty obvious to know if its too tight so i wont go to discuss that and from what u say it is ok.

If the bike goes to one side or another IMO is the bike or your skills riding w/o hands. Some bikes do what you describe no matter how good you are at riding no hands. What bike are we talking about here?

The bike is a Klein Quantum. My no-hands skills are not great but I did much better with this bike before the new headset and fork.

The first thing your mechanic should have done suggested milling your 27.0 crown race seat to 26.4... and if he/she didn't have the tools to do it then they should have suggested going to another shop. I guess it's too late-too litte now

I am guessing it was a geomarty change.

I don't know anything about VO headests but that seems odd. A 27mm crown race typically means 30mm cups and a 26.4mm race uses 30.2mm cups. Do the cups fit snugly in the frame? The frame was likely designed for the more standard 30.2mm cups.

i went to 6+ bike shops and all of them denied having the tools to face a bottom bracket. This tells me two things.
1. Shops either aren't what they used to be or they don't care anymore
2. Premature failure of outboard bb bearings (common complaint) is likely a result of poor installation and not poor design

It sounds like the headset *is* being used as intended. You have an ISO headtube and a JIS fork. The VO Grand Cru is an ISO headset that has a crown race (it has cartridge bearings so they don't actually run on the crown "race") that can be used on either ISO or JIS forks.

The handling change is probably due to geometry change.

I agree with the fork idea, the fork probably has a different rake then the original fork and thus throwing the geometry off. But just because I agree with Thirdgenbird on this doesn't mean he or I are correct, it's just an assumption based on not seeing the bike.

Good to know about the VO headest (not that I intend to mix in the future)

Yup just a guess based off first hand experience

Thank you all for your ideas. I wondered if geometry could be an issue. I guess the easy solution is to keep my hands on the bars.

I missed the part about the fork... The geometry changed probably because the rake in the fork is different.

I think it's a headset problem. If the mechanic installed a 26.4 crown race on a 27.0 fork seat and the crown race is "notched" (meaning intentionally split for a tool-free installation?) then the crown race has a gap where the ends do not meet. That could cause the bearings to not seat properly and could be your problem.

Rather than the design I would be concerned that Velo-Orange Grand Cru headset comes in both JIS and ISO. A split crown race would work with sealed bearings, but my guess is they come in two sizes; JIS and ISO. Forcing an ISO over an JIS would split the race more than intended. I am also a bit confused by your LBS, I'm sure a call to Velo Orange would have resulted in a JIS crown race; it was quite common in the past as fork makers often made their forks JIS to make them more compatible. Also, if you can't find an LBS with a crown reamer, find a custom bike maker. I had a similar issue and Paul at Rocklobster pulled out a hand reamer and fixed the problem in less than a minute.

what about the new headset bearings being new?, the old ones may have been worn a bit in the straight ahead position, where the bars are mostly pointed and would make it want to stay straighter on its own. Now that you have new headset bearings, there is no worn in spot to hold the bars straight ahead. that and the likely geometry change are what I would think is going on.

1. With the bike standing next to you on the ground, lock the front brake
and push the bike back and forth. Do you feel any play in the fork/headset ?
There should be none/zero/nada.

2.Take your old fork and hold it so that the tube lines up with your frame's
head tube, alongside the newly installed fork..... get someone to measure
how far the new fork's ends sit relative to the old fork's ends (fore and
aft in relation to the BB. This is roughly how much you've either
increased or decreased the rake. You can get away with some decrease,
but past a certain point, the twitchy feeling you describe becomes more
pronounced. ( For the record, rake is actually defined as the difference
between point of tire contact patch and where imaginary line parallel to the
head tube would intersect the ground.)

3.In my experience it is never a good idea to mix headset parts....too many
variables and ways to **** up.

When the old headset was removed, the old races were also removed, so there is no legacy or worn area left to affect the new headset or steering.

That was the point of my comment.

My bad, I was just elaborating on your point well taken.

that is my point, that you may have been used to the worn bearings that would automatically want to steer straight, with new bearings you no longer have that worn area helping you steer straight and it now seems twitchy

To answer 3alarmer's questions: No, there is no wiggle at all in the headset, it's very solid. Comparing the original fork to the new one, the new one, at most, moves the wheel a small fraction back towards the down tube. The new fork was advertised as 44mm rake. I don't know the rake of the original Quantum fork, wish I did. I rode again today and did a little better. My familiarity with the new parts and them working in may both be factors. There is another fork for sale on Ebay with a 26.4 crown race and a 40mm rake. Would that change in rake move the wheel back away from the head tube?

A fork with 40 mm of rake whould move the front wheel even closer (4 mm closer) to the downtube and increase the trail measurement a bit.

Thanks, it's been many decades since geometry class.

There's also the another problem a new fork can present and that is different forks will have a different axle to crown distance, if that distance is reduced the bicycle's head tube rotates down, relative to the rear axle, thereby increasing the head tube angle and making the bike handle more quickly and thus more difficult to stay on track. A longer axle to crown distance will decrease the head tube aangle and make the bike more difficult to turn.

....so let me try again.
https://www.bikeraceinfo.com/tech/trail.html



So just to be clear, in case it is not already, increasing trail would be
a step in the right direction, if that is indeed the issue here. The simplest
way to do that is to decrease (shorten) the rake. You can also change it
a smidge by wheel and tire diameters, but not very much.


I still would look very carefully at what's going on in the headset and
the seating of the crown race........otherwise, I really got nothin' else.

Maybe like you said you just need to get accustomed to the new and
improved handling.

I wouldn't be surprised if they actually use the same slotted crown "race" and that the only difference is the cup sleeve diameter.