pdlpsher1 wrote: ↑
Thu Apr 05, 2018 7:50 am
Disk rims are generally wider and heavier.
They also need more spokes to transfer the braking force. Rim brake forces are transferred via the rim and not the spokes.
"Disc rims are sometimes wider." True. "Disc rims are heavier." False. Carbon rim manufacturers have universally stated that disc rims can be made lighter because they don't need to reinforce the structure around a non-existent brake track. Not only is the edge of the rim no longer subject to high pressure from brake caliper actuation, but there doesn't need to be a build-up of material to help absorb heat.
"They also need more spokes to transfer braking force." Campy Bora disc wheels have 21 spokes in the rear, do they not? In the front, yes, the difference is generally around 4 extra spokes, sometimes 6...sometimes 8. But again from a rotational weight standpoint, fairly insignificant. From a total weight standpoint, I believe spokes+brass nipples generally weigh around 5.5g. I very much doubt I'd be able to feel the difference of 22-44g.
Some examples from ENVE since they publish rim weights:
ENVE SES 3.4 tubular rim: 402g front, 409g rear
ENVE SES 3.4 clincher rim: 432g front, 439g rear
ENVE SES 3.4 clincher disc: 390g front, 397g rear
ENVE SES 4.5 tubular rim: 361g front, 399g rear (27mm/25.5mm)
ENVE SES 4.5 clincher rim: 469g front, 489g rear (27mm/25.5mm)
ENVE SES 4.5 AR tubular disc: 388g front, 396g rear (31mm/30.5mm)
ENVE SES 4.5 AR clincher disc: 440g front, 450g rear (31mm/30.5mm)
ENVE SES 7.8 tubular rim: 436g front, 468g rear
ENVE SES 7.8 clincher rim: 541g front, 578g rear
ENVE SES 7.8 clincher disc: 514g front, 549g rear