World of Bold > Technologie > Internal Suspension Technology

internal suspension technology


The Concept

For the construction of high-end bike frames, no material is better-suited than carbon fibre. Its exceptional properties enable the construction of frames with incomparable specifications, and as carbon technology has established itself, the options for frame-builders have multiplied enormously. In contrast to the days when one was restricted to classic aluminium tubing, nowadays it’s possible to use moulding techniques to create new forms.

We have recognised this potential, and gone a step further. We use the freedom that carbon gives not just for aesthetic purposes, but also for achieving new engineering goals. To this end, with the Linkin Trail we have said goodbye both to the old ways of full suspension frame-building, and also to the old kinematics associated with them.

The result is a revolutionary new concept: Internal Suspension Technology, or IST for short.

Bold Linkin _ Andrew Dodd-1

It’s what’s inside that counts

The patented Internal Suspension Technology system places the damper inside the frame. This brings a total of seven solid advantages over previous construction methods:

  1. COMPACT LINKAGE Placing the damper inside the frame removes the problem of having to build a moving structure around the frame tubes. Suspension elements can be massively scaled down and therefore kept much shorter. As well as creating weight-efficiency this shortness brings stiffness, which means that the bike is noticeably more efficient at transmitting power to the rear wheel.
  1. LOW CENTRE OF GRAVITY The damper is located in the lowest-imaginable position within the frame’s main triangle. Having both damper and link arms positioned low and central gives the bike outstanding handling.
  1. PROTECTED The damper is placed in a position that protects it from both mud and physical impact. This is much less demanding on suspension seals, and keeps vulnerable technology safe from flying stones.
  1. ISOLATED Riding forces are transmitted to the inside of the frame via a 30 mm axle. The DT Swiss damper is held by two oversized bearings in a way that completely isolates it from lateral forces coming from the swingarm. We even go so far as to fit the damper with spherical bushes at both ends, where it is attached to the suspension bellcrank and frame. This allows free-floating mounting, which means that the damper receives forces solely in the direction for which it is designed, i.e. with absolutely no damaging lateral forces. This ensures that the damper has a long service-life, as well as benefitting overall system performance.
  1. STRAIGHT TUBES The compactness of the suspension and damper technology creates space. This allows the frame tubes on the Bold Linkin Trail to be straight and able to connect two join points by the most direct line; other systems have to use awkward offset tubes to create space for a damper or water bottle. The advantages of our system are stiffness and weight efficiency. And even the small frame size can easily accommodate a large water bottle.
  1. INTUITIVE The damper is set to one of its three operational states via a lever on the handlebars: Open, Drive or Lock, selected instantly.
  1. NEUTRAL HANDLING Switzerland is known not just for being a neutral country, but also for the neutral handling characteristics of its renowned suspension technology… And so, the IST system places strong emphasis on being completely neutral in terms of the bike’s handling and braking. The compactness of the system allows kinematic axis points to be defined that have previously been impossible. Or in less technical terms: even when set to Open mode, the bike covers even the most technical uphill sections, over roots, rocks and holes, with phenomenal handling and power transmission efficiency.
Bold Linkin _ Andrew Dodd-4

The Internal Suspension Technology’s patented bellcrank-based construction is the real heart of the system. The bellcrank’s function is to transmit the external leverage forces into the interior of the frame. It’s made up of three separate elements which are joined to a high level of precision with a fine-pitch titanium bolt, and can be dismantled to allow easy fitting and removal.

The construction is based on an optimised four-bar system with a Horst link. This ensures both drive-efficiency and precise and responsive suspension characteristics.


Undoing the down-tube protector’s two M5 bolts gives easy access to the damper for installation and maintenance. This opening is also used for setting up the suspension:  the valve and thumbwheel for setting rebound also benefit from protection and ease of access.


By undoing the single lightweight titanium bolt, the two external bellcrank elements can be separated from the internal bellcrank element and thus removed from the frame. This in turn allows the damper together with the internal bellcrank element to also be very easily removed.

The over-sized bellcrank bearings are comparable with a BB30 bottom bracket, which gives the bellcrank a rock-solid foundation. Similar to the cranks on a chainset, the forces involved are transmitted via a 30 mm axle through the inside of the frame. With the Internal Suspension Technology system, the internally-fitted bellcrank acts to transmit forces directly to the damper. Very simple, very effective.


Precise engineering and perfect fabrication produce a stiff and compact bellcrank, the heart of every Linkin Trail. The illustration shows the 3D-printed prototype elements, along with the final production versions.

The conical, toothed connection system facilitates easy and correct joining of the bellcrank’s two external elements and one internal element. The chunky design ensures excellent stiffness.