Bicycle Mechanics - OK, stupid question.

I noticed recently that my handlebars seem to have some kind of self centering function. What I mean is if I lift the front tire off the ground and turn the bars side to side there seems to be some type of mechanical catch which holds the bars (and front wheel) exactly in the center position (as if to ride in a perfectly straight line). I have never noticed this before and would suspect a damaged bearing except for the fact that it alligns in a PERFECTLY centered position as if the bike were designed this way. Is this normal? It is a Diamondback wildwood.

Your headset is Brinnelled. Somebody overtightened it along the way. A new one will cost you about $50.

D*Alex, Please forgive my ignorance, but what does "Brinnelled" mean?

Originally posted by Big Johnson
D*Alex, Please forgive my ignorance, but what does "Brinnelled" mean?
In D*Alex-speak, "brinnelled" is roughly equivalent to being "pokey-ed". :D

Hmn, must be an inside joke.... Am I to assume Brinnelled/pokey-ed = F.U.B.A.R.'ed?

Brinnelled: the bearings have worn little dents into the races. The bearings then sit in those dents and make steering notchy and difficult. In a word, D*Alexed, Pokeyed, or FUBARed.

Thanks, RegularGuy. Appreciate the info.

I have a related question. Does the angle of the fork determine how stable the bike is in a straight line? I would guess the greater the angle, the more the bike will want to go in a straight line and the harder it is to steer it off the straight line. Is this true?

OK, I've done some reading around this subject. It seems that the term brinelling is not always used correctly in relation to the notchy or indexed steering problem with headsets.

True brinelling occurs if the bearing is overloaded, most likely in a single event. The balls make permanent indentations into the raceway. For more info see: http://www.emersonbearing.com/failures/true.html
This could occur if the headset was hammered during assembly, maybe by overtightening too, but you'd really have to overdo it.

OK so what's my point?

The indentation patterns that occur on most headsets are a result of wear over time, as pointed out by RegularGuy. This is known as false brinelling, or more correctly, fretting. See http://www.emersonbearing.com/failures/false.html
The problem is that a headset doesn't rotate very much, so the lubricating grease film is lost from between the bearing balls and the raceway. Flex in the fork and steerer causes off axis motion ( fretting) that results in the depressions worn into the headset bearing surfaces - and so the notchy steering. Ball bearings in a headset are really a compromise - they are needed to maintain low friction in the steering, but are really best suited to an application where there is continuous rotary motion (e.g. bottom bracket or wheel bearings).

Hope that was not too long winded,

Ed

Originally posted by trmcgeehan
I have a related question. Does the angle of the fork determine how stable the bike is in a straight line? I would guess the greater the angle, the more the bike will want to go in a straight line and the harder it is to steer it off the straight line. Is this true?

Depends on the angle of the headtube too, but a fork with a greater offset (longer trail) is more stable and harder to move off line than a straight fork, which makes a bike more quick to turn.

Does the angle of the fork determine how stable the bike is in a straight line?
Partially. All things being the same, a bike with a greater headtube angle will be more stable at high speed, but less so at low speed. This is due to lateral damping inherent in a system that has more trail. However, it is not the angle that is the determining factor for high or low speed stability, but rather the trail, which is a function of both headtube angle and fork offset (rake). A course in vehicle dynamics will explain this more fully (it's usually offered as a 3rd or 4th year mechanical engineering course).

Originally posted by Ed Holland

True brinelling occurs if the bearing is overloaded, most likely in a single event. The balls make permanent indentations into the raceway.

The indentation patterns that occur on most headsets are a result of wear over time, as pointed out by RegularGuy. This is known as false brinelling, or more correctly, fretting.


I learn a lot here at the Forums.

Gee I thought it was called indexed steering and you had to pay extra or it ;-)

Thanks everyone. I have learned a lot.

Gee I thought it was called indexed steering and you had to pay extra or it ;-)

There's an idea. They could market it as a hands-free system. "rest on those long straights with the ind-X stability enhancement system"

Already available. It's called a Hopey Steering Damper. It's used in DH racing to bring the handlebars back to center. I've never used one, but they look pretty cool.