Proportional Geometry Render

Scaled to perfection

Proportional Geometry and stiffness delivers a dialed ride at every size

Proportional Geometry Render

Scaled to perfection

Proportional Geometry and stiffness delivers a dialed ride at every size

A mountain biker cornering on a rocky trail

Proportional Geo and frame stiffness

Proportional geometry and stiffness is our way of specifically engineering each frame size so that certain elements scale as frame size gets larger—so whatever your stature, there are no compromises with performance, efficiency, or fit. We’ve taken this concept to a new level with proportional rear-center, or chainstay length, and even frame stiffness. The result is a bike that’s dialed at every size.

A mountain biker cornering on a rocky trail

Proportional Geo and frame stiffness

Proportional geometry and stiffness is our way of specifically engineering each frame size so that certain elements scale as frame size gets larger—so whatever your stature, there are no compromises with performance, efficiency, or fit. We’ve taken this concept to a new level with proportional rear-center, or chainstay length, and even frame stiffness. The result is a bike that’s dialed at every size.

Proportional Geometry Render
Proportional Geometry Render

Rear Center and Seat Tube Angle

Chainstay length and seat tube angle are matched to the frame size (seat tube angle steepens and rear center grows as frame size increases) so that every rider, no matter what height, gets the same balance of geometry and handling characteristics.

Proportional Geometry Render
Proportional Geometry Render

Frame stiffness tuned by size

We tailor stiffness for every size to make sure everyone gets the same ride quality. Bigger riders create greater forces on larger frames, but that's remedied with our size-specific frame stiffness tunes.

Riding the 2020 Santa Cruz Hightower

[Nerd alert] Read on for a deeper dive...

Ok, let's start with the basics.

Bike geometries have always been “proportional” or scaled across a size range, so what are we blathering on about here? Well, while many attributes of a bike—like reach, wheelbase, and stack height—have always grown larger with each successive bump up in size, others have remained fixed. Chainstay lengths and seat tube angles, for example, have traditionally been the same, even across bikes that come in five or six different sizes. While this is an easier way to make bikes, it creates performance compromises on larger bikes, particularly while seated and pedaling.

A few years ago we recognized that there was more to the common assumptions about fit and ride quality, so we set about developing each frame size with a rigorous look at how to make each one ride how it really should. To do so meant unlearning what we knew and relearning with a new set of parameters and conditions. One of those things we jokingly refer to as "butt reach".

Riding the 2020 Santa Cruz Hightower

[Nerd alert] Read on for a deeper dive...

Ok, let's start with the basics.

Bike geometries have always been “proportional” or scaled across a size range, so what are we blathering on about here? Well, while many attributes of a bike—like reach, wheelbase, and stack height—have always grown larger with each successive bump up in size, others have remained fixed. Chainstay lengths and seat tube angles, for example, have traditionally been the same, even across bikes that come in five or six different sizes. While this is an easier way to make bikes, it creates performance compromises on larger bikes, particularly while seated and pedaling.

A few years ago we recognized that there was more to the common assumptions about fit and ride quality, so we set about developing each frame size with a rigorous look at how to make each one ride how it really should. To do so meant unlearning what we knew and relearning with a new set of parameters and conditions. One of those things we jokingly refer to as "butt reach".

Santa Cruz Bicycles Tallboy 5
Santa Cruz Bicycles Tallboy 5

Baby got back: ‘Butt reach’ explained

Our engineers use a scientific term to describe how relatively far back one’s derrière extends over the rear end when seated on the bike…they call it “butt reach.” And while it’s a funny (juvenile?) term, the dimension significantly affects both suspension performance and pedaling efficiency.

Generally speaking, and to a point, implementing a “steep” seat tube angle yields a better front-to-rear weight balance and rider position, as well as better suspension performance when climbing. Conversely, a slack seat tube angle can be detrimental, putting too much weight on the rear wheel, not to mention a less efficient pedaling position.

When comparing a rider on a size small frame with a 436mm (17.2-inch) chainstay length and a 77-degree seat tube angle to a rider on a size extra-large bike with the same geo, we see that the smaller rider is positioned much further forward than the larger rider. Even though the actual geometry is the same, the butt reach is different.

Riding the Santa Cruz Megatower
Riding the Santa Cruz Megatower

Tweak, tweak, goose!

For years we’ve subtly tweaked our geometries for acceptable performance regardless of size. Thing is, “acceptable” isn’t really something we’re OK with. To get the high level of consistency we wanted required more than subtlety—it required some changes to our design thinking and philosophy.
To begin, we needed a consistent baseline. This resulted in us establishing a scale of average saddle heights by frame size. Our engineers arrived at these numbers by studying fit for the bike’s use-case scenarios, plus calculations based on human scaling factors.

Proportional Geometry Render
Proportional Geometry Render

Playing the angles

From there, we made changes to the effective seat tube angle on a frame-size-by-frame-size basis. As described previously, this angle determines how far rearward the saddle cantilevers over the rear wheel at a benchmark saddle height. And while this helped bring these numbers closer together, it alone didn’t fully close the gap.

Proportional Geometry Render
Proportional Geometry Render

The long and short of it

In addition to the seat tube angle, chainstay lengths would also need to vary in order for butt reach to be consistent as a percentage of rear-center length.

The most obvious way to get scaled chainstays is to simply make longer or shorter ones as necessary. But adding the complexity of tooling up and managing numerous rear carbon swingarms in addition to the (as many as six) front triangles we already make made that approach a nonstarter.

Rather than having physically longer or shorter swingarms, we elected to use the same swingarm but move the mounting points further fore or aft to create an optimized effective chainstay length for each size. The physical result is swingarms that grow by about 3mm each time you move up in frame size. The riding result is a bike with the same riding characteristics, whether you’re on an extra small, extra large, or anything in between.

Greg Minnaar Riding the Santa Cruz Megatower 2

How stiff is your frame?

Bigger riders mean bigger stresses on bigger frames, which makes sense—they’re heavier, so when they hit the same hole/corner/drop as smaller riders, more force is put into the frame. And if the frame is bigger–imagine the longer tubes of an XXL frame compared to an XS frame–it should be built to handle these greater forces across larger, inherently more flexible tube spans. If the stiffness is not tuned accordingly, the smallest riders are left riding something that feels like a railway tie, or the largest riders get stuck trying to corner on a wet noodle. To counteract this, we tune frame stiffness for every size by adding more carbon where it’s necessary on the larger sizes—ensuring everyone gets the same on-rails handling, regardless of size or stature.

Greg Minnaar Riding the Santa Cruz Megatower 2

How stiff is your frame?

Bigger riders mean bigger stresses on bigger frames, which makes sense—they’re heavier, so when they hit the same hole/corner/drop as smaller riders, more force is put into the frame. And if the frame is bigger–imagine the longer tubes of an XXL frame compared to an XS frame–it should be built to handle these greater forces across larger, inherently more flexible tube spans. If the stiffness is not tuned accordingly, the smallest riders are left riding something that feels like a railway tie, or the largest riders get stuck trying to corner on a wet noodle. To counteract this, we tune frame stiffness for every size by adding more carbon where it’s necessary on the larger sizes—ensuring everyone gets the same on-rails handling, regardless of size or stature.