Carbon bikes are quite the norm these days throughout all disciplines. Road, MTB, hybrid, cyclocross and even trickling into the downhill scene as engineers find the most advantageous way to propel humans downhill with the lightest and strongest bike. This material is so popular in high end bike frames because you can change the “layup” and fibre characteristics to suit different cycling disciplines. Two distinct carbon characteristics are Tensile Strength (measurement of force/MPa required to break the fibre) and Modulus (Measurement of force/MPa required to bend the fibre).
Lets take a look a a few of the Jamis road and Mountain Bike frames:
Xenith SL (Jamis’ top road bike):
This frame is constructed with a combination of M40/M30 Carbon which are both considered High Tensile Modulus. The frame is built using pre-pregnated (flat sheets of carbon fibres) sheets of M40/M30 carbon which is applied to Silicon and polystyrene tube forms in certain directions (usually confidential information!). The sheets are overlapped and applied in layers depending on the location on the frame and certain stresses that are applied to the area. Engineers can strengthen particular areas on the frame depending on the stresses applied to that area (rear stays, bottom bracket, heat tube…) by adjusting the carbon layup.
After the carbon layup has been decided there is another important step that is involved which influences the outcome of the frame. The moulding process! Pressing and heating the carbon sheets together to produce one solid tube and frame. Jamis uses a process called Near Net Silicon Polystyrene Vacuum which produces a very clean and tight carbon frame. Silicon joints and polystyrene (styrofoam material) tube shapes covered with bladders are wrapped in pre cut carbon sheets to make a pre form. This pre form is placed in a vacuum pre-mold which suck out all the air between the pre-form and the multiple layers of fiber. The pre-form is then placed in a steel mold and left to cure in an autoclave where the bladders inflate and the silicon expands with the heat causing the carbon to be pressed against the steel mold, creating a solid clean frame!
The entire front triangle consisting of three main frame tubes are pressed together as one piece and attached to the rear triangle separately.
Dakar XCR Team (Jamis’ top dual suspension MTB):
Fig. 2 Jamis Dakar XCR 29 Team
This bike is built with a completely different riding purpose compared to the road bike above but uses very similar type carbon to construct the frame! This frame is manufactured with just M30 High Modulus Carbon (Omniad Elite m30 Layup) compared to the road frame which also uses a higher modulus M40 carbon. Jamis doesn’t use the M40 for their mountain bikes because they need to produce a stronger tensile strength frame (see chart below). M30 provides a sweet spot to work with as it carries high tensile strength and moderate tensile modulus characteristics. Using high modulus carbon is great but it is not as strong as higher tensile carbon, therefor it is strictly used on just road frames.
Tensile Modulus vs. Tensile Strength
Come by RB INC-Sports to check out our Carbon road, MTB and hybrid bikes!
2014 models are starting to roll in this week
Awesome! Great insight to how these frames are made. 2014 models are looking great!!
Good stuff. Everyone loves carbon but don’t always know the difference between high modulus and high strength. Thanks!
Great review of Jamis’ carbon too. Not all companies provide insight like this.