This question may have been asked before on this forum but it is always conforming to ask the gurus on this site before deciding on a purchase. In my search attempts of the net I could not find an answer.
I wanted to know that sort of time saving (say over the standards 40km) I could expect by upgrading my Specailzed tri-spoke rear to a Renn disc (I currently run the Specailzed tri-spoke front and rear).
In my search attempts of the net I could not find an answer.
I would be surprised if it was as much as 30 seconds. Both the sites mentioned above, along with others, say that the difference between 32-spoke box rims and a disc/trispoke combo is about 2 minutes, 2:30 tops. Everyone agrees the front wheel is more important (at least 2/3 of the savings) because it hits clean air. That means disk vs. 32-spoke box rim rear is probably about 40 seconds, maybe 45. HED says that the difference between its trispoke and its disk is 10-20% (depending on crosswinds). That would make the difference between a trispoke and a disk 10 seconds or less.
According to Jim Martin/John Cobb in Chapter 10 “Bicycle Frame, Wheels and Tires” in the book “High Performance Cycling” by Asker Jeukendrup PHD, the difference between a rear disc and good composite wheel (tri spoke) is 12 seconds over 40 kms. I’ve noticed on Cobb’s forum he is now claiming about thirty seconds, which contradicts what he and Martin wrote in this book.
The tri spoke is a bit more versatile for those very few races that don’t allow disks or for those really, really hilly races. I don’t think your going to be wrong with either wheel. IMO if I’m saving only 12-20 seconds its not worth the hassle to switch wheels, tires, cogs etc. I’ve been in only maybe 6-7 tris or duathlons out of 120+ where 20 seconds made a place difference. Only 1 where I missed prize money which would not have covered the cost difference between the wheels.
John Cobb was a panalist at the science of speed conference in Kona. He stated that a disc is faster than any other wheel in ANY triathlon on the planet.
The point was to respond to an earlier post suggesting that a disc would not be faster on a “hilly” course. Cobb seemed to think that there were no tri courses hilly enough to negate the advantage of a disc.
