Self-Centering headset? Why?

[yoothgeye]

I have this cool older Mongoose Hilltopper (pre-buyout, 80s-90s?) that was given to me by the original owner. He did a lot of miles on it and then hung it in his garage and moved on to road bikes.

I am cleaning it up and tuning it to give to a student of mine who is in college now. While on the bike stand I noticed something interesting. The steering always automatically goes back to center, as if the headset has some sort of detent in it (I have not disassembled the headset... yet). Luckily I noticed this before taking it for a test ride. The bike rides fantastic, but if you try to ride hands free, the steering centers almost immediately and the bike tries to kill you.

The only reason for this that I can think of would be to hold the steering so that the bike could be leaned against a wall on the grip without falling over. Why else? And that may seem like a cool feature, until you ride it!


(click for video)

 

[user 135]

That is not a feature but a sign of wear caused by lubricant breakdown and/or an improperly adjusted headset. The bearings are either out of round and/or the race has become dimpled. The is also called Indexed Steering.

http://sheldonbrown.com/brandt/indexed-steering.html

 

[yoothgeye]

This is just too perfect for me to believe it to be an accident! haha

 

[Bicycle808]

Yes, Clancy's got it-- the other term for this is "brinneling". This is often caused by someone running the headset too tight. The proper fix is a new headset, or at least, new bearings, top cone, and cups. The semi-long term cheapskate fix is, if the headset is currently running caged retainer bearings, replace them with loose bearings of the same size (but add more to make up for the cage's absence). This will change the way the balls have become aligned with the dimple in the race, and you may get many more miles out of it...

But, like I said, the "right" thing to do is to replace the headset.

 

[Bicycle808]

This is just too perfect for me to believe it to be an accident! haha

It is, though. The headset is adjusted too tightly. And, unless you ride exclusively in figure-8s, the majority of your riding will be roughly straight ahead. So, as you ride in a straight line, every bump in the road is jamming the too-tight bearings into the races, until the balls have a tendency to get "stuck" in those little dimples. Over time, the problem gets worse, and it does so in an almost "perfect" way, insofar as the steering will be perfectly centered and straight....

 

[Bama Bill]

Common on well worn off-road motorcycles.

 

[c.p.odom]

Technically this is called "Fretting" or "False Brinelling". Almost all cases are caused by a lubricant issue, more so than improper adjustment. Often grease with too high a viscosity is used in the headset. Remember that grease is only a source of oil, basically the carrier for the oil. Headsets do not turn like cranks and hubs and the grease gets forced away from the bearings by road vibration leaving them almost dry. Use a light weight grease or rotate your bars back and forth before and after every ride.

 

[Bicycle808]

Crap. Now you got me worried about my grease. =P

 

[ifitsfreeitsforme]

Thanks for that education c.p.


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[user 135]

Technically this is called "Fretting" or "False Brinelling".

Is the Jobst Brandt article correct in stating that cartridge bearings minimize this problem?

 

[Bicycle808]

FWIW: In my time as a wrench, and in my time messing around at co-ops, and with my own bikes, I've never encountered a "brinnelled" headset with cartridge bearings.

Jobst Brandt is a smart guy, but he said a lot of goofy things in his day, too.... see his rants about the peril that lies within every Sturmey-Archer hub. (There were some scary ones where the coaster brake wouldn't work if you got stuck in between gears, but most are eminently reliable hubs.) I'm not entirely convinced that overtightening a headset isn't tied in with "brinneling", as most headsets I've seen with "indexing" characteristics were tight when I got'm....

 

[mikeeebikey]

I am going to be that guy.

Always believed it was from jumping. Thats it, a dent in the cup or race from a
ball bearing, it's self aligned!
Usually because the headset was loose!
But I have done in many aluminum cupped lined headset. The cartridge headsets will also.
If cups are not square, headtube bent, it will also self align.