# FAQ

## FREQUENTLY ASKED QUESTIONS

- Why would you mess with your bike? Don't the manufacturers and designers know best?
- What is an angleset?
- Who makes angle adjusting headsets?
- What kinds of headsets can be replaced with angle adjusting headsets?
- Will modifying my bike void its warranty?
- How does changing fork axle-to-crown length affect bike geometry?
- How does mixing wheel sizes (mullet bike) affect geometry?
- How does adding an angle adjusting headset affect bike geometry?

## Why would you mess with your bike? Don't the manufacturers and designers know best?

For most people, the bike they purchased is going to be perfectly fine as is. It’s hard to find a bad bike these days and you can usually rest assured that your money is going toward a quality bike. But it is worth noting that the people who built your bike designed it to appeal to a wide selection of riders and obviously some elements will be a compromise to keep it in the middle of the bell curve or to hit a certain price point.

For obsessive-types (myself included), squeezing every last bit of performance or enjoyment out of their bike is part of the fun. Maybe you’re looking to freshen up an older bike with a small cash outlay to hold you over for a couple years before dropping big bucks on a new ride. Simple changes can go a long way toward making a bike feel new again.

Experimenting with your bike, whether by upgrading parts, adding some bling, or changing components that alter the fit or feel (geometry, suspension) of the bike can be a rewarding, addicting, never-ending expensive hobby. I find it worth it. Customizing your bike makes it truly yours and may even help you pick up some new bike maintenance skills.

## WHAT IS AN ANGLESET?

An angleset is an angle adjusting headset used to tweak your bike’s head angle. Installing an angle adjusting headset also affects other aspects of your bike’s geometry, but the goal is typically to achieve changes to the head angle. The head angle can be slackened or steeped to achieve desired ride characteristics.

Your bike’s headtube was designed to hold its headset bearings concentrically with the center axis of the headtube, so the fork passes through the headtube concentrically. An angle adjusting headset offsets one or both headset cups from the headtube’s center axis and angles the face of the headset cups, allowing your fork to pass through the headtube at a slight angle (typically not more than 2°). Most manufacturers use standard headset bearings, while Cane Creek’s AngleSet uses spherical bearings to achieve the realignment of the steerer tube axis with respect to the headtube axis.

For the record, the name AngleSet is actually a registered trademark of Cane Creek, and other manufacturers are required to refer to angle adjusting headsets by other names. The term angleset is commonly used and understood in mountain biking circles as a generic term for angle adjusting headsets installed in frames with pressed in headset cups.

## WHo makes ANGLE adjusting headSETs?

There are a number of manufacturers making angle adjusting headsets and the list continues to grow. Some manufacturers are even including optional offset cups with new bikes, so it is clearly becoming a mainstream and manufacturer approved method of altering bike geometry.

Here’s a list of angle adjusting headset manufacturers I’m aware of. Please contact me if you find others worth adding.

9point8 (for integrated headsets)

## Is my bike compatible with an angle adjusting headset?

I’ll be the first to admit, headset standards are confusing! Park Tools is my go-to site for reading up on headset standards. Start there if you’re new to headset terminology and sizing.

Until quite recently, angle adjusting headsets were only capable of being installed in frames that used pressed in headset cups, whether those were zero stack (ZS) or external cups (EC). 9point8’s Slack-R, introduced in 2020, is an angle adjusting headset for bikes design with integrated headsets, where the headset bearings drop into cups built into the frame. So most modern mountain bikes are now compatible with some form of angle adjusting headset.

The best way to check if your bike is compatible is to look at angle adjusting headset manufacturers’ published literature and headtube/headset/fork combinations. You may need to replace a ZS cup with an EC cup to make room for the bearing to be offset. Other combinations of headtube/headset/fork may simply limit the number of degrees you can attain.

## WILL MODIFYING MY BIKE VOID ITS WARRANTY?

Maybe. Be sure to check the literature for maximum allowable fork lengths and maximum wheel sizes for forks and frames. The installation of an angle adjusting headset could potentially also be an issue with some manufacturers.

## HOW DOES CHANGING FORK AXLE-TO-CROWN LENGTH AFFECT BIKE GEOMETRY?

The Bike Geometry Calculator allows for changes to axle-to-crown either through fork travel, lower headset cup thickness, or adding/removing a bottom headtube spacer.

The simple explanation for what happens to your bike’s geometry is that a longer fork makes the front end taller, resulting in the bike frame rotating counterclockwise about the rear axle.

The figures below demonstrates this effect, with the grey silhouette representing the original geometry and the red silhouette showing the revised geometry with a longer fork installed.

Lengthening the axle-to-crown measurement, either through a longer travel fork or increasing the stack below the headtube has the following impact on bike geometry:

- Head angle slackens
- Reach shortens
- Bottom bracket drop decreases
- Stack increases
- Seat tube angle slackens
- Wheelbase lengthens
- Trail increases

## HOW DOES MIXING WHEEL SIZE (MULLET BIKE) AFFECT BIKE GEOMETRY?

The Bike Geometry Calculator allows for changes to either front or rear wheel size.

A common modification is to reduce the rear wheel diameter or increase the front wheel diameter. This is known as a “mullet” bike. The simple explanation for what happens to your bike’s geometry is that a smaller rear wheel or larger front wheel raises the front axle relative to the rear axle, resulting in the bike frame rotating counterclockwise about the rear axle.

The figure below demonstrates how the calculator handles the revised inputs.

The figures below demonstrates this effect, with the grey silhouette representing the original geometry and the red silhouette showing the revised geometry, with a 27.5″ wheel used for the rear wheel.

Reducing the rear wheel size relative to the front wheel has the following result on bike geometry:

- Head angle slackens
- Reach shortens
- Bottom bracket height decreases
- Stack increases
- Seat tube angle slackens
- Wheelbase shortens (negligibly)
- Trail increases

- Head angle slackens
- Reach shortens
- Bottom bracket height increases
- Stack increases
- Seat tube angle slackens
- Wheelbase shortens (negligibly)
- Trail increases

## HOW DOES ADDING AN ANGLE adjusting headset AFFECT BIKE GEOMETRY?

The Bike Geometry Calculator allows for an angle adjusting headset to be added. The following description demonstrates how the calculator handles the revised inputs, with the black silhouette representing the original geometry and the red silhouette showing the revised geometry.

The simple explanation for what happens to your bike’s geometry is that using a slackening angle adjusting headset rotates the fork outward and upward from its original position which slackens the head angle and lowers the front end of the bike, causing the bike frame to rotate clockwise about the rear axle.

The figure below demonstrates this effect, with the grey silhouette representing the original geometry and the red silhouette showing the revised geometry with a -2° angle adjusting headset installed.

Slackening the head angle with an angle adjusting headset has the following result on bike geometry:

- Head angle slackens
- Reach increases
- Bottom bracket drop increases
- Stack decreases
- Seat tube angle steepens
- Wheelbase (and front centre) lengthens
- Trail increases

Note that reach is a frame measurement. The perceived “reach” of your arms to the handlebars may feel reduced with a slackening angle adjusting headset installed, as the steerer tube is moved slightly rearward.

The opposite effects would be encountered if installing an angle adjusting headset to steepen the head angle.

## I added an angle adjusting headset IN the GEOMETRY MODIFICATION calculator and the change in head angle didn't match the number of degrees on the angle adjusting headset! What's wrong with your calculator?

Aha! This is the reason I built the calculator. If you haven’t already, first check out the FAQ response to how the angle adjusting headset influences geometry. Throughout these explanations, I have assumed the angle adjusting headset is being installed to slacken the head angle of the bike.

In the literature of angle adjusting headset manufacturers, the actual mechanism of how angle adjusting headsets work is somewhat misrepresented. An angle adjusting headset claiming to slacken your head angle by 2° is actually realigning (slackening) the steering axis within the frame’s head tube by 2°, but that does not mean the bike’s head angle is slackened by 2°. The slackened steering axis angle within the frame’s head tube and the bike’s slackened head angle are not the same thing as I will demonstrate below.

Refer to the figure below, representing a head tube in the thicker red outline. The solid black line passing through the headtube represents the bike’s original steering axis (center of headtube). The dashed line shows the effect of adding a -2° angle adjusting headset. The steering axis through the head tube is slackened by 2° as you would expect. Two styles of angles adjusting headsets are shown outlining minor differences in how the slackening is handled, but the result is largely the same. The image on the left side is the style used by Cane Creek where only the top cup is offset. The image on the right is the style used by Works Components where the majority of the offset comes from the top cup, but the bottom cup is also slightly offset.

When determining the impact of an angle adjusting headset on the head angle of the bike, the approach most commonly taken is to subtract (slacken) the number of degrees listed on the angle adjusting headset set straight from the head angle of the bike. A 65° head angle becomes 63°. The rest of the geometry numbers are then calculated on the assumption that the head angle is fixed and known.

My calculator takes a different approach to solve the bike’s revised geometry, treating the bike frame as a series of points in space, fully defined by the input geometry numbers and working out the various transformations each point takes with the modifications to the bike. The original geometry table is used to locate these points and then the revised geometry inputs are used to modify their locations. Refer to the figure below for the points that are fully defined by the geometry table of the bike, arbitrarily tagged with letters for the purposes of visualization.

The geometry modification calculation is completed in two phases. The goal of the first phase is to find the revised location of the lowest part of the front wheel (point FG), recognizing that the steering axis has been realigned with the addition of the angle adjusting headset, and as a result, the front hub (point G) has been raised and pushed outward. The required rotation about the rear axle (point A) to put both wheels (points RG and FG) back on the same plane is then calculated. All points in the frame are then subject to this rotation about the rear axle, and all geometry measurements are then recalculated from the distances and angles between the new locations of the labeled points. The graphic below shows a real world example of the results of each step the calculator takes.

The black silhouette in the background shows the original bike geometry with head angle of 68°.

The blue silhouette in the foreground shows the geometry with a -2° angle adjusting headset realigning the steering axis by 2°. The angle shown by the fork in this graphic is 66°. However, as you can see, the front hub is raised upward and forward from the original position and the tire is no longer in contact with the ground.

The red silhouette sandwiched between the black and blue silhouettes has had a clockwise rotation about the rear axle to put the front wheel back in contact with the ground. The red silhouette is the bike’s actual geometry with the -2º angle adjusting headset installed.

The resulting head angle of this bike with a -2° angle adjusting headset? **66.47°.**

The resulting head angle is almost a half degree steeper than you would have obtained from simply subtracting 2° from the original 68° head angle! The slackening of the steering axis by 2° is accompanied by a steepening of the bike’s head angle, and the combination of these two rotations means the result will always be somewhat less than advertised.

I suspect, but can’t confirm, there are some exceptions the above analysis (and the resulting difference between the angle adjusting headset’s rating and the bike’s actual change to the head angle) with bikes that come stock with head angle adjustabilty, such as models from Guerilla Gravity or the 2021 Specialized Stumpjumper Evo. Looking at the Stumpjumper Evo, the optional offset headcup included with the bike claims to change the head angle by 1º in either direction. Since Specialized has full control over all aspects of the geometry and the components shipped with the bike, such as the fork and wheels, the offset cup should have been designed to compensate for the clockwise rotation of the bike in the slackened position and the head angle is likely exactly 1° slacker with the offset cup installed.

BikeCAD‘s site includes a calculator to simulate the installation of an angle adjusting headset by recalculating the fork’s length and offset for a given realignment of the steering axis through the frame’s headtube. This is also an accurate approach to model the effects of an angle adjusting headset.