Welcome to the

International Spline Interface Standard web site.










Bottom Bracket Questions:______________________________


What is the best manufacturing method for the spindle?

The spindle can be easily machined or forged, depending upon the material. Machining can be quickly performed with a three-axis NC lathe. Alternatively, machining the spindle in a mill is also possible, although care must be taken in fixturing to assure the correct alignment of the spline ends. Some spindle materials may be forged, although the process must usually be accomplished using multiple forging steps.


What does the spindle designation number mean?

The spindle designation number is the nominal distance between the crank stops on the spindle. Since all the spindles in the standard are symmetric about the BB shell mid-plane (theoretically the frame centerline), one-half the spindle designation number is the distance from the BB shell mid-plane to the drive-side crank stop on the bottom bracket. By adding this number to the “chainline offset” provided by the crankset manufacturer, you can easily figure out the resulting chainline of that particular crank assembled onto any ISIS Drive bottom bracket of a given designation.


Why use the spindle designation number instead of the overall length?

The entire ISIS Drive system is based on the crank stops of the spindle. Everything in the standard is derived from these crank stop “datum planes”, including the method of measuring a spindle. Since the spline shape itself is defined relative to these stops and the taper angle is so small on the flutes, the cranks should easily slide all the way onto the spindle until they are stopped by these crank stops. Thus these crank stops consistently locate the crankarms axially relative to the bottom bracket (and hence the frame) every time a crank is installed. The overall length of the spindle has no effect on the axial position of the crank on the spindle, and thus has no meaning in the context of this standard.


The spline ends are so large, what kind of bearings should I use?

It is up to you. The outside and inside diameter of the spline shape was determined so as to make use of as much existing tooling as possible in the industry. Bearings for this bottom bracket may take any number of forms, including custom cartridge bearings, needle bearings, bushings, or loose balls. The purpose of this standard is not to standardize one particular bottom bracket design, but rather to standardize the interface between the bottom bracket and crank. It is up to the individual designer to determine the type and configuration of bearings in the bottom bracket.


Should I grease the spindle when installing the cranks?

This will depend on how the crankset manufacturer designed their crank. We have found that grease helps to ensure the cranks contact the stops on the spindle, thus reducing the possibility of the crank loosening while riding. Further, the use of grease helps to eliminate noise that sometimes exists in interfaces. The drawback of using grease on almost any interface is that it reduces the friction present between the mating surfaces, thus reducing the amount of load transfer through friction. Please refer to the instructions from your crankset manufacturer regarding the use of grease on the interface.


Crank Questions:______________________________________


What is the best way to manufacture the spline shape in the crank?

Although at first it looks difficult to manufacture the spline shape in the crankarm, the quickest and easiest method is the same used for manufacturing the majority of tapered square cranks: a broaching operation followed by one or two coining operations. The broaching operation creates the straight-sided spline shape in the crank while the coining operation creates the 1° taper of the spline flute. The depth that the coining tool is pushed into the crank determines the amount of pre-load between the crank and spindle.


How much pre-load should I design into my cranks?

This depends upon your crank material. For most aluminum alloys we have found a pre-load of 3-5mm is ideal (as measured according to drawing sheet three). The individual crankset manufacturer will have to determine their required pre-load for themselves, based on analysis and testing.


What are the consequences of using too much or too little pre-load?

If a crankarm has too much pre-load it will not bottom out against the crank stop on the spindle when initially installed. This will lead to the crank arm “walking” up the taper during some initial rides and a consequent loosening of the crank bolt. If the bolt is not constantly tightened until the crank finally contacts the stop, the result could be the crank falling off while riding or damage to the interface.

If the crankarm has too little pre-load it will bottom out on the crank stop prior to attaining a press-fit with the spindle. Depending on the magnitude of the press-fit, this may result in anything from a slight reduction in the load carrying capability of the interface to a “sloppy” fit between the crank and bottom bracket. This may also lead to creaking of the interface due to the slightly “sloppy” fit between crank and spindle.


Will this interface work for a steel crankset?

We haven’t tried but don’t see a reason why it wouldn’t work. It is up to the manufacturer of such a crank to determine the interface’s suitability through appropriate testing.


Bolt Questions:________________________________________


Why two bolt sizes?

A bicycle is used in many different ways, from leisure riding around the block to radical 30-foot drop-offs. Each riding applications places different requirements on the crankset and bottom bracket. Thus, we included two bolt sizes in this standard to allow manufacturers and riders to choose the best ISIS Drive bottom bracket for their needs. An ISIS Drive crank is compatible with either bottom bracket size, be it M12 or M15. Since the bottom bracket determines the bolt size, the ISIS Drive standard specifies that the correct bolt size should to be included with the bottom bracket.


Which bolt size should I use, M12 or M15?

Please consult the bottom bracket manufacturer to determine which bolt size is appropriate for your riding application. We cannot generally say that the M12 bolt size will produce a stronger spindle than the M15 because different materials may be used for the spindle. The bottom bracket manufacturer is in the best position to help you pick the correct bolt.


Do I really need to use a washer between the bolt and crank?

Yes, we recommend always using a washer between the bolt and crank to prevent excessive deformation and wear. Please only use a washer specifically designed for the ISIS Drive interface, as other washers may be too small or thin to support the pre-load present in the bolt. We also recommend greasing the bolt underneath the flange where it contacts the washer to help provide a more accurate torque reading when tightening the bolt.


How much torque should I use when tightening the bolt?

Again, please refer to the bolt manufacturer’s specification on the magnitude of the install torque.


Master Gage Questions:_________________________________


How does the spindle gage work?

The spindle master gage is essentially a “perfect crank” that slips onto the spindle. This “perfect crank” contains GO/NO-GO indicators that allow the determination of whether the flute geometry is within the tolerances required by the ISIS Drive standard. The GO/NO-GO indicators are based upon the distance the tool sits away from the crank stop located on the spindle. This tool does not measure clocking between the spindle ends, which is left to the manufacturer of the bottom bracket spindle.


How does the crank gage work?

Like the spindle master gage, the crank master gage is essentially a “perfect spindle” that fits into the crank and contains measurement lines allowing the determination of the amount of pre-load for the crank. This tool does not measure the shape of the splines in the crank it only gives an indication of the magnitude of pre-load the crank possesses. This tool is double ended, so manufacturers can press GO/NO-GO stops onto the tool and thus have a GO/NO-GO tool for determining whether the pre-load is within their required range.


Who manufactures the gages?

Currently Race Face will be manufacturing the spindle master gage and Chris King will be manufacturing the crank master gage. Please refer to the Tooling page on this site for more information.


Can anyone purchase the master gages?

Of course, though they are most useful for manufacturers of the ISIS Drive system and their OE customers.


Miscellaneous Questions:________________________________


Is the ISIS Drive geometry compatible with any other bottom bracket/crankset interface?

Not that we know of.


Does the ISIS Drive system infringe any existing in-force patents?

Not that we know of. We have performed several patent searches worldwide and have been unable to locate any patents that may be infringed by the ISIS Drive system. However, we do not guarantee this to be the case in any way. It is up to the individual manufacturer to perform their own legal research and protect themselves from any legal repercussions of using the interface.


Is it really “free”?

Yep, use it to your heart’s content.