The parts of a headset, from the bottom to the top, (so you'll know our terms), beginning with the part resting on the fork, which is the "Fork Cone Race", (also called the fork crown race). It is driven onto the fork. Next would be a bearing, either loose ball or in retainer, or possibly a needle or sealed cartridge. Over the bearing rests a "Lower Bearing Cup", made of steel or aluminum or both, this is pressed into the bottom of the frame head tube.
On the top of the head tube, we have an "Upper Cone Race" which is pressed into the top of the frame's head tube. Followed by another bearing. On top of the bearing is the "Upper Bearing Cup", above which sits the "Head Key Washer" and then, finally the "Head Lock Nut".
The headset is the single area on your bike where the most shock is experienced by the smallest amount of surface. Consider that every time you land on your front wheel, your body weight and the bike's, plus the added velocity all gets compacted onto just the tops and bottoms of a few small ball bearings. The need for a solid headset, made of quality materials can't be overstated. An inexpensive one will be replaced over and over, while one bought to the best standards from the outset will save you continual time and money over the course of your enjoyment of bicycles.
There are many ways to make headsets. The cheapest way is to stamp them completely from sheet metal. This is what you find on bikes sold at toy stores and department stores. We don't sell that type of bearing assembly. There are ways to compromise even good workmanship.
Ideally, what we want is the roundest bearing running on the smoothest race. "Bearing races" are the surface that bearings roll on. The bearing race is put under a grinder that produces an exact and relatively smooth cut surface to fit the bearing dimension. After the surface is put through a grinding step or "ground", it is then polished to remove burrs and grinding imperfections. After the polishing stage, it is now at it's best to receive the bearing and be used as a bearing race. We will tell you when a bearing race is of the "ground" variety.
Some headset manufacturers, perform the cosmetic work, painting, plating, labeling, and anodizing after they give a surface to the bearing race. This compromises how smooth the surface really still is. It may be they get away with it because most riders aren't aware of this. In the case of chrome plating the bearing race, I can just hear them say that chrome resists corrosion. If it can corrode, the headset wasn't designed to be moisture resistant enough, or stainless steel should have been used. Wherever possible, we try to tell you the steps in the manufacture of each headset. It gives you a clue about it's genuine quality and the thought process of the makers.
The Head Key Washer holds the threaded upper bearing once properly tightened in place. The head key washer has a tiny square tab that fits into a notch on the back of most forks. The head key washer with the tab installed in the notch provides a stationary fitting from which it is difficult for the upper cup to loosen. The head lock nut holds the key washer fixed in place.
Headsets come in three common sizes. "Size" relative to headsets refers to the outer diameter of the fork steerer tube. A common size, known as "standard", is the original 1" diameter. The inserted part of the bearing cup has an outer dimension of 30.2mm so the inner diameter of your head tube should be approximately 30.0mm. The size of the most used is 1 1/8", known as oversize, which was first established by Tioga calling it the "Avenger" as alternative compromise to the standard 1" and the Fisher Evolution 1 1/4" size. The inserted part of the 1 1/8" sized bearing cup has an outer dimension of 34.0mm, so the inner diameter of your head tube should be approximately 34.0mm. The last is the 1 1/4" size that Gary Fisher innovated, and is also known as the "Fisher Evolution Size" or "Evolution" size. The larger diameter will permit more ball bearings in the headset and give a greater surface area to revolve on. The inserted part of the 1 1/4" sized bearing cup has an outer dimension of 37.0mm so the inner diameter of your head tube must be approximately 37.0mm. While the different diameters are not without merit, one standard would be nice. Since all headset makers build all three why doesn't the industry agree on the 1 1/8" size for both Road and Mountain and also while at it, how about only threadless forks to simplify things even more?
There are some bearing variables. Headset bearings can come as loose steel balls which you place into a greased cup. They have been made that way for years. A more common way to see bearings is in a small steel cage that holds a number of ball (or needle/roller) bearings together in one "cage". This steel cage with the bearings in it, is known as a "retainer" or "bearing retainer". This is the way headset bearings are now most commonly seen. Roller or needle bearings are a better substitute for ball bearings. Instead of round balls there are tiny metal rollers that revolve. The needle bearings give a broader surface for the weight and shock to be dispersed over. The bearing races in needle bearing headsets are separate and thin pieces of steel laid over a lightweight aluminum piece that resembles a bearing race. This race "element" is pressed into the frame and the thin beveled steel race is set on top. These are a remarkably fine bearing arrangement, that was in fact, borrowed from the automotive industry.
Bearing retainers come with different numbers of ball bearings in them. The accepted thinking is, the greater the number of balls, the greater the surface area over which the weight and stress will be displaced. Therefore, more ball bearings per retainer is desirable. The exception, which is noted in the reviews of the headsets is the Ritchey Logic Headsets. Mr. Ritchey believes (and he has given this some research) that a larger ball bearing provides a greater bearing contact surface than several smaller ones. The real truth about whether more or larger bearings is more desirable remains unclear.
"Stack Height" is the measurement, in millimeters, from the top of the inner threads of the head lock nut to the bottom of the upper cup where it touches the head tube, added to the measurement from the top of the lower cup where it touches the head tube to the bottom of the fork race, with the bearings installed. Once again, from the top of inner threads inside head lock nut to bottom of upper cup at the head tube - and - from the top of the lower cup at the head tube to the bottom of the fork cone race. Add these two numbers in millimeters together to arrive at headset stack height. It's importance comes from the rare instance of an odd sized head tube creating too short a steerer tube on the fork. Sometimes the headset you want might requires more thread length than exists on your fork.
Triple seal is a headset buzzword of the 90's. This means there is a rubber seal or gasket in the lower bearing assembly and one in the upper bearing assembly. The "stem seal", a rubber o-ring or sleeve, where the stem passes through the headlock nut, helps prevent contaminants from dropping into the bearings.
The thread pattern used on forks known as "English" is so close to the "Italian" thread pattern that for all intents and purposes they are the same. Where you see English as a thread pattern, if you just happen to have an Italian frameset, you can substitute the word Italian. The variation is in the thread pitch, (the angle of the thread) not the thread per inch count. The distinction is not deeply perceptible to the normal standards of bike part machining. One inch headsets have 24 threads to the inch, while 1 1/8" and 1 1/4" headsets have 26 threads to the inch.
Lastly, in 1992 Dia Compe's introduction of the Aheadset began to gain acceptance. This threadless headset design eliminates all threads and the head lock nuts from conventional headset designs. The lower cup, crown race and bearing remain the same, while the upper cone race or bearing cup is now threadless and slides over an also htreadless fork steerer tube. The system is held in place by a clamp-on style stem. This system saves weight, lessens the odds of headsets loosening, makes routine maintenance easy, and eliminates weaknesses in the fork steerer introduced by cutting threads into it and thinning its tubing wall thickness. Manufacturers, appreciate not having to stock several versions of a fork. Instead they can inventory one with a long threadless steerer tube and cut them down to the needed length as they manufacture each bike. The threadless system is becoming more and more popular in all headset diameters by both Road and Mountain riders. It is our prediction that the threadless design will become the industry standard.