Seatpost – frame
Failure: Seatposts are crushed in the frame and finally break. Carbon seatposts are usually varnished and the material generally is pressure sensitive. The frame’s seatpost clamp, however, has to be tightened forcefully to fix the smooth seatpost. By doing so, the material is stressed improperly, the tube is damaged.
Remedy: Enhance friction between seatpost and frame, so lower torques are necessary. Never use grease, the frame has to be carefully degreased. Use dynamic assembly paste.
Wheel and rim material – brake pads
Problem: The braking performance of carbon rims is often stuttering and from time to time very aggressive. Under wet conditions, friction decreases considerably. On long downhill rides the developing heat can lead to dissolution of the brake pads’ suface. The surface is not smooth and cannot conduct away heat as it is the case with aluminium. Under wet conditions there is no friction, the brake pads skid over the resin surface.
Remedy: The varnished or resin surfaces need special carbon brake pads. They have to be matched and chosen very carefully. Concerning problems with wet and heat development manufacturers have to do their homework.
Handlebar – stem
Failure: Drop bars are crushed in the stem and finally break. Carbon handlebars usually are varnished. Because of this, the stem clamp has to be tightened forcefully to fix the smooth handlebar. By doing so the pressure sensitive material is stressed improperly, the tube is damaged.
Remedy: Diameters must be accurate to a tenth of a millimetre. Therefore it is sensible to buy handlebar and stem of the same manufacurer. Assemble without grease, apply Dynamic assembly paste to handlebar and stem. Assemble with a torque wrench starting with very low torques – control if the handlebar still moves in the stem. Tighten bolts very carefully until the handlebar is fixed.
Mountain bike handlebars – levers and bar ends
Problem: Handlebars break in the areas where levers and bar ends are fixed. Besides the facts cited above this is often caused by assembly parts not fixed at the reinforced parts of the handlebar.
Remedy: Only put bar ends on carbon handlebars with special reinforcements or such which can be reinforced with cases. Use Dynamic assembly paste in order to lower the torque necessary. Do not shorten carbon mountainbike handlebars as they often have integraed reinforcements for brake levers or bar ends. Manufacturers have to indicate where parts can be fixed.
Author: jk/dz
Photos: Zedler
