It is true, must often savings are quoted in time over a 40km TT at ~30mph. But since most of us are somewhat shy of that the quotes don't help much. Contrary to Pedro's estimate of a 40 sec saving reducing to 30-33 secs for a slower rider, I would argue that actually the time saving could be greater.
Rather relevantly, this becomes clearer if you think in terms of power saving (thread on power
), rather than just time.
Consider this:
The time saving going from 25-26 mph (55 seconds for 10 mile) will be greater than the time saving going from 30-31mph (39 seconds for 10 mile).
The power needed to go from 25-26 mph will be much less than that needed to go from 30-31 mph (Google it and look at the equations, or simply use a cycling power calculator website and hold everything constant other than the speed and see the resulting power figures)
The faster rider will likely save a few W more from the disc.
If you think in terms of power savings, even if the faster rider saves more power from the disc, it is entirely possible that this saving doesn't outweigh the fact that to speed up, a hugely larger amount of power is needed than for the slower rider, so actually, while the slower rider saves a few W less, they actually gain the most speed (or even if they gain the same amount of speed) and thus save the most time.
Now I am not sure of the fine details, but in theory, if the numbers are right, it will be the case and in my experience, I gained maybe 30 seconds over 10 miles when I 1st put my disc on, let alone the time saved over 25 miles.
For reference the disc I use is a FFWD lenticular disc wheel with tubular tyres.
