- Frame must take press-fit headset cups. Frames with integrated headset cups are not compatible.
- Nominal inner diameter of top end of the head-tube must be 44mm (43.95-44.00 mm measured).
- Inner diameter of bottom end of head-tube must be within one of the following:
- 44mm (43.95-44.00 mm measured ID)
- 49mm (49.57-49.61 mm measured ID)
- 56mm (55.90-55.95 mm measured ID)
- Head-tube must be between 90mm and 140mm long. Head-tubes outside of this range are not compatible.
- GeoShift headsets may have a taller stack height compared to traditional headsets. Refer to the sizing table for stack height measurements to ensure your fork’s steerer tube will be long enough to accommodate the GeoShift cups.
- All GeoShift headsets are designed for forks with 1 ½”-1 ⅛” tapered steerer-tubes. Forks that have 1 ¼”-1 ⅛” tapered or 1 ⅛” non-tapered steerer-tubes may be used with a Wolf Tooth 1 ½”-1 ¼” or 1 ½”-1 ⅛” adapter crown race (sold separately).
Notes about EC, ZS, and IS:
Nearly all head-tubes will fall under one of two categories: Press-fit or Integrated.
Press-fit head-tubes require cups to be pressed into the top and bottom ends of the tube. The pressed-in cups then house the bearings used in the headset. There are two styles of press-fit cups:
Use a bearing that is small enough to fit inside the head-tube. The bearing cup is thus housed inside the headtube, which is beneficial for reduced stack-height.
Use bearings that are larger than the inside of the head-tube. The bearing cup is housed externally. These have larger stack height values than ZS cups, but allow more room for larger steerer-tubes.
Integrated head-tubes, also known as IS, are manufactured to house bearings without the need of additional cups. Frames that have Integrated/IS head-tubes are not compatible with GeoShift headsets.
Wolf Tooth press-fit headset cups use a common naming convention that first gives the cup style (EC or ZS), followed by the nominal inside diameter of the head-tube where they will be installed (given in millimeters). For example, an EC44 cup is an External-Cup to be pressed into a 44mm tube. A ZS56 cup is a Zero-Stack cup that will be pressed into a 56mm tube. It is very common for head-tubes to be a smaller diameter at the top end than at the bottom end - these are known as tapered head-tubes.
To determine if your frame is compatible with a GeoShift headset, you will need to determine the upper inside diameter, lower inside diameter, and length of your head-tube. This information will typically be available from the frame manufacturer. If the headset that was originally spec’ed on your bike is listed as an ZS44/ZS56, that means your head-tube’s inside diameter is 44mm at the top and 56mm at the bottom. The two-letter EC/ZS designation only refers to the headset cup style, it is not a characteristic of the head-tube/frame. Head-tube length is typically listed in frame geometry charts - this value must be between 90mm and 140mm to be compatible with GeoShift.
Many GeoShift headsets use an EC44 upper bearing cup. That is, the upper bearing cup sits outside of the head-tube, and is pressed into a 44mm inner diameter tube. These are used in applications where a traditional (non-angle adjusting) headset would typically use a ZS44 upper bearing cup. The reason for this is purely spatial - by moving the bearing outside of the head-tube, more angular movement of the steerer-tube can be achieved. In fact, a 2-degree angle change in a 44mm head-tube with a 1 ½”-1 ⅛” tapered steerer-tube is only possible with an EC upper bearing cup.
Traditional ZS44/EC44 headset in 44mm head-tube
GeoShift 2-Degree EC44/EC44 headset installed in same 44mm head-tube
The only drawback to using an EC upper bearing cup instead of a ZS bearing cup is added stack height. GeoShift EC44 upper bearing cups have 10mm more stack height than a comparable ZS44 cup. If you currently have your stem slammed on the headset (no steerer-tube spacers used) with a ZS44 upper cup, it’s a good bet that your fork’s steerer-tube will be too short to accommodate the GeoShift headset. If you have at least 10mm of spacers, which is most often the case, you will simply need to remove 10mm from your spacer stack.
|Stock Upper Cup/Lower Cup||Compatible 1-Degree GeoShift||Compatible 2-Degree GeoShift|
|ZS44/EC44||EC44/28.6 UPPER EC44/40 LOWER||EC44/28.6 UPPER EC44/40 LOWER|
|ZS44/EC49||ZS44/28.6 UPPER EC49/40 LOWER||EC44/28.6 UPPER EC49/40 LOWER|
|ZS44/ZS56||ZS44/28.6 UPPER ZS56/40 LOWER||EC44/28.6 UPPER ZS56/40 LOWER|
Steerer Tube Diameter
All GeoShift headsets are designed for 1 ½” - 1 ⅛” (aka 1.5”-1.125” or 40-28.6mm) tapered steerer-tube forks. Forks that have 1 ⅛” or 1 ¼” lower steerer tube diameters may be used, but will require a Wolf Tooth adapter crown race, which are sold separately.