Everything new when it comes to bottom brackets?

For the first mountain bikes, frame builders adopted the mass known from racing bikes. In the meantime, increasing loads in practice have shown that the terrain takes its toll ? and led to new designs. Fork steerer tubes were the first to be redimensioned, and the now established 1 1/8 inch size is being rivaled in the freeride sector this year by the new one-point-five standard. The rear axles of some downhill bikes now also have an extra width of 160 to 170 millimetres instead of the familiar 135 millimetres, and bottom bracket housings with a width of 100 millimetres (instead of the usual 68 to 73 millimetres) are being used to match. But even the weight-conscious have noticed that more is more ? especially when it comes to the bottom bracket. So the dimensions of the bearings and axles are now being radically rethought.

If one of the trade fair trends prevails, the selection of bottom bracket dimensions will be larger in future, in terms of axle width and bearing diameter: Shimano is presenting a complete solution comprising bottom bracket and cranks for the top XTR groupset. For downhillers, Truvativ has "Giga-Pipe" bearings in its range, whose axles run on up to four industrial bearings. And with the "MegaTech" system, FSA is presenting an oversized, yet very light bottom bracket with a hollow axle this fall, which runs on oversized bearings pressed directly into the frame.

Shimano XTR: A "magical" BMX crank...
Anyone who has ever held a classic cartridge bottom bracket in their hand knows that a lot of weight can still be saved here. Shimano demonstrates just how much with the 2003 XTR groupset. By combining a number of existing designs, the Japanese were able to save even more weight: As with the legendary "Magic" crank from CODA, bearing shells bolted onto the frame accommodate the oversized industrial bearings. The greater distance between the bearings ensures an extremely stiff pedal platform. The hollow drilled axle and internally hollow crank arms help to save weight, and thanks to the assembly method borrowed from BMX sports, the whole thing can be assembled or disassembled in a flash.

Sheer indestructibility at Truvativ
The competition in terms of bottom brackets and cranks, which has agreed on the alternative "ISIS-Drive" standard, is also doing a lot. Truvativ offers almost indestructible "Giga-Pipe" bearings for downhillers and jumping athletes, whose robust steel axles run on up to four industrial bearings (!). It is clear that these parts have a longer service life rather than a lower weight. However, they are also available for frames with extra-wide 100-millimeter bottom bracket housings. This oversize dimension is becoming increasingly popular for downhill bikes because the additional width of the bottom bracket also allows the swing arm bearing to be widened ? and therefore stiffer frame constructions.

FSA: Bigger is stiffer
As with the "ISIS-Drive" standard for bottom bracket axles with multiple gearing, FSA also wants to handle the "MegaTech" system as an open standard. In other words: Interested bike manufacturers and frame builders can find all the information they need to build suitable frames online at www.oversizebb.com. In addition to a special tool for milling the frame, matching bottom bracket shells made of CroMo steel, aluminum and even titanium are also available directly from FSA. Because the bearings are pressed directly into the oversized bottom bracket shell - which now measures 50 millimetres in diameter instead of the usual 34 millimetres - their dimensions can be larger. In addition, there are no bearing shells, so no thread is needed on the bottom bracket. The hollow-bored axle is also significantly oversized, resulting in a system that offers more rigidity and promises a longer service life despite the weight savings. FSA names weight-conscious road cyclists and bikers as the primary target groups for the "MegaTech" bottom bracket, which can be combined with all ISIS cranks ? but the Taiwanese are already working on reinforced versions for downhill and freeride use.

Sources of supply in Switzerland:
Shimano: until December 31, 2002 Cilo Bike Service SA/Romanel, from January 1, 2003 PLFM AG/Gipf-Oberfrick
Truvativ: Polygon Impex/Langendorf
FSA: Fuchs-Movesa/Gipf-Oberfrick