Shimano has been thinking outside the box for quite a while when it comes to dreaming up new ways to create wheelsets.
The WH-R540 wheelset is a 16/16 spoke wheelset with a 30mm or so deep aluminum clincher rim. This design is shared with the WH-7700 Dura-Ace wheelset. Using this few spokes is unique as is their method for backwards spoke orientation. The aluminum nipples are oversize and are at the hub. The rim has holes drilled just below the brake track into the side of the rim wall. Then what looks like a bladed but otherwise standard 'J' bend bladed spoke is fitted with a washer that seems to lock the spoke into the hole. Spokes are paired which can give the allusion of just 8 spokes when viewed in profile. Despite these high tech ideas this wheelset uses cup and cone bearings.
The later WH-R550 wheelset uses 16/20 bladed j-bend spokes front and rear and a slightly shallower 26mm or so deep rim. Oversize aluminum nipples are at the hub like the WH-R540. The attachment to the rim is more traditional in that the spokes are centered and are not paired. Cup and cone bearings are used.
Here are some observations from Slim's recent disassembly:
- The front hub without skewer weighs 165 grams.
- The rear hub without skewer weighs 386 grams.
- The WH-R540 rim Slim measured, which was worn but still serviceable, was also on the heavy side at 512 grams.
- Shimano has glued a special washer/spacer to each spoke. After pulling the spacer off the spoke appeared to be a standard 'J' spoke with standard 2mm threading.
- Rear hub weighs 385 grams. This is about 10% heavier than an 'old school' 28/32/36 hole Ultegra hub with traditional flanges.
- The bladed spokes appear to be standard straight pull bladed spokes with standard 2mm threads. But Shimano has added a special shaped washer that presents a larger surface area to the inside of the rim to prevent it from pulling through.
- The rear rim from a WH-R550 that was worn down to about .8mm of wall thickness weighed 440 grams.
- Spoke tensions measured using a Park Tools spoke tension meter TM-1 were 19+-1 on the drive side and 16+-1 on the non drive side. Without specifice information we were unable to translate these number to spoke tensions using the Park Tools spoke tension chart that is provided with the TM-1.