Mechanical Advantage

steerer, just above the crown.) 2. A row of ball or roller bearings. Revolution 3. The lower head race (pressed into the bottom of the .) 4. The upper head race (pressed into the top of the head Are threads soon tube.) 5. Another row of ball or roller bearings. to be history? 6. The adjustable race (attached to the steerer.) By Sheldon Brown The adjustable race is secured by one of the following: 7a. A keyed and lock , for threaded headsets. 7b. A clamp-on "threadless" , star fangled nut and here's a revolution going on in headsets. cap. The battle of the mountain bike is pretty much 7c. Compression rings, in the case of some threadless over, and the battle of the road/touring bike is just headsets. beginning. T There are two fundamentally different systems for Most newer mountain bikes use "threadless" headsets attaching, adjusting and securing the adjustable race of and matching stems. At present, most intended for headsets: road use still use threaded headsets, but the trend toward threadless designs is likely to persist. For this reason, even Threaded the hard-core road rider should be aware of this alternative Traditional threaded headsets fit forks with threaded design, which becomes more pervasive every year. steerers. The adjustable race on to the steerer, and a A further complication is created by the fact that many screws on after the adjustable race to secure it. bikes now come with "oversized" forks, so there are now There is normally a keyed, non-rotating washer between the six different types of headsets in fairly common use: 1" adjustable race and the locknut for extra security. Virtually threaded, 1 1/8" threaded, 1 1/4" threaded, 1" threadless, 1 all bicycles made before the 1990s used threaded head- sets. HEADSETS & STEMS Bicycles with threaded headsets use handlebar stems that fit inside the steerer tube, and are secured by Cup (2.) a wedge or expander nut, operated by a long run- Size Steerer Stem diameter Crown race (1.) Outside Threads O.D (Steerer I.D.) Inside diameter diameter per inch ning down the middle of the stem. Threadless Threadless headsets have an adjustable race that 1" Standard 30.2 mm 24 (25.4mm) 7/8"(22.2 mm) 26.4 mm slips over an un-threaded steerer. There are three dis- tinct types of threadless headsets, each of which adjusts 1" J.I.S. (3.) differently: 7/8"(22.2 mm) 27.0 mm 30.0 mm 24 (25.4mm) 1. "Aheadsetª" style threadless headsets, the most common type, require a threaded , such as a 1 1/8" star fangled nut, to be installed inside the steerer. 1" (25.4 mm) 30.0 mm 34.0 mm 26 (28.6mm) This type of headset requires a special handlebar stem that clamps on to the outside of the steerer, either 1 1/4" 1 1/8" (28.6 mm) 33.0mm 37.0 mm 26 with one or more binder bolts, or other means. The (31.8mm) stem is further secured by a or cap, which is bolted to the star nut. (1.) This is the fit of the bottom race on the fork crown. (2.) This is the fit of the races that press into the head tube of the frame. To adjust an "Aheadset"-type headset, loosen the (3.) J.I.S. headsets are used on most older and some current bikes from Asia. stem binder, then tighten the bolt that runs through the Frames and forks intended for J.I.S. headsets can be modified to take stan- cap to the starnut. This cap presses the stem down dard 1” headsets. If you want to replace one headset with another, you must take into account the stack height of the new headset. against the tapered bushing that fits inside the adjustable cup, and takes up the slack in the system. Once the slack is out of the system, align the stem There is such 1/8" threadless, and 1 1/4" threadless! (The most common with the front wheel and tighten the stem's binder bolts. The a confusing size is still 1" threaded, but the 1 1/8" threadless size is stem's clamping to the top of the steerer is what holds the array of rapidly gaining on it.) In this article I will try to demystify whole system together. Once the stem binder bolts have headsets the bewildering variety of headset systems, and explain how been tightened, the adjusting bolt that goes to the star nut is available, it to adjust them. under no significant stress, and may even be removed. takes a table A headset consists of four races, plus associated parts, to sort it all 2. "Diatechª" threadsets from Dia Compe use a special out. listed from the bottom up: pair of collars, usually mounted just below the stem and 1. The crown race (pressed on to the bottom of the fork above the top race. The lower collar has a beveled, conical

Adventure Cyclist • May 2000 The AheadSet wrong-sized stems or contrast, threadless forks are made in only and its star headset parts due to one (long) steerer length, which can easily fangled nut the confusing array of be cut down to fit a particular frame size. started the sizes in use. A lead- This offers a reduction in the number of threadless ing cause of this is stock-keeping units for repair forks, and revolution. that the headset nom- also for aftermarket forks. inal size is based on the outside diameter The down side: The major disadvantage of threadless

HT YGREG SIPLE PHOTO BY of the steerer, but the steerer is completely headsets is that there's less height adjust- hidden from view. In ment available without replacing parts. the case of threaded While you may be able to make minor stems, the diameter of height adjustments by interchanging spac- the stem is 1/8-inch ing washers, significant changes in handle- less than the nominal bar height will require that you buy a differ- size, i.e., the stem ent handlebar stem or adaptor. used with a 1 1/8- While traditionalists may bemoan the top surface, which fits inside of a matching inch headset is 1 inch in diameter. The table change, it appears that the move to thread- bevel on the inner circumference of the on the previous page lists headset dimen- less headsets is inexorable, since they offer upper collar. sions you may run across. so many advantages to the manufacturer — The upper collar has a gap at one point, and even a few to the rider. with a binder bolt to squeeze the gap Why the change to threadless design? together. (This upper collar may also Oversized and threadless headsets have a include a cable stop for the front brake, if number of benefits, some of them to the rider, others to the manufacturer. Let’s look Adventure Cycling member Sheldon Brown’s the bicycle has a rigid fork and convention- column appears regularly in Adventure al cantilever brakes.) at the advantages of doing without threads. Oversized headsets make for stronger Cyclist. Visit his Web site at http://www.shel- To adjust a Diatech headset, slide the donbrown. com/harris handlebar stem down until it bumps up forks and stems. This is primarily an issue against the upper collar. Clamp the handle- for mountain bikers, who bar stem tightly to the steerer, preventing tend to crash a lot, and the upper collar from moving upward. need stronger parts to Cycle our website There will still probably be a bit of slack in hold up to the stress. www.adventurecycling.org the headset. Threadless headsets Tighten the binder bolt of the upper col- can generally be adjusted International Bike Event Calendar with only a 5mm Allen lar to remove the play from the system. As the upper collar is compressed by the binder wrench, while threaded Adventure Cyclist Archives bolt it squeezes the lower collar downward, headsets normally Cycling Resources taking up any slack in the headset bearings. require two large, bulky 3. The YST "GeForce" headset has a open-end wrench. Bike Clubs collar that slips over the steerer, and is The 1-inch size is Bike Maps clamped to it with a binder bolt near the top adequate and safe for of the collar. The outside of this collar is forks with steerers, Tours threaded, and the upper bearing race screws but oversized forks can onto these threads. The upper race assembly be made with lighter is fitted with a binder bolt that clamps it materials, such as alu- tight onto these threads when the desired minum and carbon , adjustment has been attained. reducing weight. Even To adjust a GeForce headset, slide the when made with the YOUR BIKE CAN FLY FREE top unit down firmly and tighten the upper same materials, the com- binder bolt, securing the top unit to the bination of threadless ON NORTHWEST steerer. Then, turn the lower section of the fork and matching stem top unit to make fine adjustment to the will generally be lighter bearing play. Once the adjustment is good, than a threaded system, tighten the lower binder bolt to clamp the due to the elimination of fine adjustment threads down. the stem's quill, expander The GeForce is the only threadless head- bolt and wedge. set that doesn't use the handlebar stem as The very fine threads part of the adjustment. These headsets may used on threaded steerers be used with any stem, either external are tricky and expensive Adventure Cycling members can avoid expensive airline bike han- clamping or internal expander/wedge type. to make. It is substantial- dling fees when they book their Northwest airline tickets through the The GeForce is also the only threadless ly cheaper to make a Adventure Cycling Travel Service. This special offer can save Adven- headset that allows you to adjust the stem threadless steerer. ture Cycling members more than $100 per roundtrip. Call the Adven- without having to re-adjust the headset Threaded forks have ture Cycling Travel Service today for the program details: bearings. to be provided in multi- ple lengths to fit different Sizing confusion frame sizes of the same 1-800-735-7109 It is very common for people to order model of bicycle. By (Offer valid only when booked through the Adventure Cycling Travel Service)

Adventure Cyclist • May 2000