So a roady buddy of mine and I are arguing about TT wheelsets.
I argued the following wheel choices seemed appropriate based on average rider speed.
Speed - Rear wheel/front wheel
25 MPH + - Disc / Hed Deep 3 or Zipp 1080
23 - 25 MPH - Disc / Hed Stinger 9 or Zipp 1080
21 - 23 MPH - Zipp 1080 or Stinger 9 / Zipp 808 or Stinger 6 or FP 80
< 21 MPH - Zipp 808 or Stinger 6/ Zipp 404 or Stinger 6 or FP 60
He pretty much argued that everyone should ride a disc in the rear and either Hed Deep 3 or Hed 3 on the front. Faster guys a deep 3 and slower guys a normal Hed 3.
We pretty much ignored issues such as dimples, clincher vs tubular, and types of rear discs. We also assumed a “typical course” with some rollers, turns, and wind but not some monster winds nor freakish climbs. So what does everyone think?
Note: 25 mph is roughly 40 KPh; 23 MPH is roughly 37 kph; 21 mph is roughly 34 kph.
In general most people riding less than 23 mph would seem to fall in three categories
Someone going long (e.g. IM) and a spoke wheel will be more comfortable than a disc
Someone riding a technical course and a disc simply doesn’t handle as well nor accelerate as well as spoke wheel
Someone with less power - the gains from the disc over an 1080 are quite small at lower speeds even on flat courses without sidewinds. If someone is going 19 mph on a flat 20k TT I would guess they were lighter than average (or could be new to sport).
Thus, something like an 808 with wheel cover would then give this person the option to go psuedo disc or non-disc depending on the course conditions. Those in category 3 would seem to gain more from the better handling than the few extra seconds. In contrast the person going 27 mph would use a disc wheel on practically all courses and it would seem worthwhile to get a good disc instead of messing around with a wheel cover.
In general I think my buddy is only considering the areo properties and not considering comfort or handling at all. A hed3 for 112 miles does not seem terribly comfortable to me (they seem to jar more than a spoke wheel). Slower speed rides occur for a reason (length of course, technical course, etc) and these should be factored into any speed based guide for wheel choices it seems to me. At least this was my argument.
the time gains from a disc are higher for a less powerful rider, not lower.
a disc really, I swear to jesus, allah, and science, is not hard to handle in the wind.
In general most people riding less than 23 mph would seem to fall in three categories
Someone going long (e.g. IM) and a spoke wheel will be more comfortable than a disc
Someone riding a technical course and a disc simply doesn’t handle as well nor accelerate as well as spoke wheel
Someone with less power - the gains from the disc over an 1080 are quite small at lower speeds even on flat courses without sidewinds. If someone is going 19 mph on a flat 20k TT I would guess they were lighter than average (or could be new to sport).
Thus, something like an 808 with wheel cover would then give this person the option to go psuedo disc or non-disc depending on the course conditions. Those in category 3 would seem to gain more from the better handling than the few extra seconds. In contrast the person going 27 mph would use a disc wheel on practically all courses and it would seem worthwhile to get a good disc instead of messing around with a wheel cover.
In general I think my buddy is only considering the areo properties and not considering comfort or handling at all. A hed3 for 112 miles does not seem terribly comfortable to me (they seem to jar more than a spoke wheel). Slower speed rides occur for a reason (length of course, technical course, etc) and these should be factored into any speed based guide for wheel choices it seems to me. At least this was my argument.
Hed 3 are old technology and not as fast as newer wheels. We can thank Lance for keeping that particular wheel alive for years longer than it needed to be.
Your thinking for slower riders is also flawed. Slower riders gain less advantage, but for a longer period of time. A faster wheel is faster for all users, regardless of speed. Frankly, the best set-up is Zipp 808/Hed 90 with rear wheelcover with a 1080 or Hed 90 front in perfect conditions. In higher wind, an 808 might be a better choice if handling is an issue.
I have never bought the argument that a real disc is faster for everyone all the time. Yes, the areo properties at speed provide a benefit across the board that actually provides a greater time savings for slower riders relative to faster rider. However, the operative term here is at speed because once you start adding accelerations (e.g. corners) a slower rider is more heavily penalized by getting the heavier disc wheel back up to speed. Thus, in a pure straightline course a real disc is faster for slower riders. Once you add corners that require slowing and speeding back up the answer is less obvious at slower cycling speeds. Now once you include spoke wheels with a wheel cover it changes the analysis a bit. Even though I ride a wheel with cover this seems more like a wheel with a fairing added instead of an actual disc. A quick read of the UCI regs suggests they are not permittted for roadies.
So I got curious and I am too lazy to work out the calculations myself. However, cycling analytics has the nifty tool on their website for analyzing differing wheel choices. So i just did a quick analysis using their default settings for the bike and choose 75 kilo rider that could generate either 200, 250, or 300 watts. I compared two wheel set choices: Rear Disc and Zipp 404 front versus a Zipp 404s on back and front. Using a relatively straight 40k TT course (the florida tt course). The 300 watt rider gained 19.7 seconds, the 250 watt rider gained 21.4 seconds, and the 200 watt rider gained 23.5 seconds from using a rear disc relative using a zipp 404 as the rear wheel. This goes along with the conventional wisdom that slower riders gain a bit more in using disc wheel relative to the slower rider.
However, when I did the analysis using the sydney TT course which as lots of turns the results were quite different (3 laps equals 40k). Both the the 250 watt and 300 watt rider saved roughly 15 seconds using a disc wheel over the zipp 404. However, the 200 watt rider actually gained time on this course from using a rear disc instead of the Zipp 404. Now this seems more like the typical triathlon course that has to put next to a body of water and is filled with riders from other waves.
curious - what was the weight difference between the 404 and disc in that model, and what was the wind speed? On HED’s website, a disc is only 250grams heavier than their jet 60
zipp sub 9 disc vs zipp 404 is only 138 grams difference
did the analysis assume some sort of average wind yaw angle and speed or did it ignore wind?
However, when I did the analysis using the sydney TT course which as lots of turns the results were quite different (3 laps equals 40k). Both the the 250 watt and 300 watt rider saved roughly 15 seconds using a disc wheel over the zipp 404. However, the 200 watt rider actually gained time on this course from using a rear disc instead of the Zipp 404. Now this seems more like the typical triathlon course that has to put next to a body of water and is filled with riders from other waves.
the time gains from a disc are higher for a less powerful rider, not lower.
a disc really, I swear to jesus, allah, and science, is not hard to handle in the wind.
In general most people riding less than 23 mph would seem to fall in three categories
Someone going long (e.g. IM) and a spoke wheel will be more comfortable than a disc
Someone riding a technical course and a disc simply doesn’t handle as well nor accelerate as well as spoke wheel
Someone with less power - the gains from the disc over an 1080 are quite small at lower speeds even on flat courses without sidewinds. If someone is going 19 mph on a flat 20k TT I would guess they were lighter than average (or could be new to sport).
Thus, something like an 808 with wheel cover would then give this person the option to go psuedo disc or non-disc depending on the course conditions. Those in category 3 would seem to gain more from the better handling than the few extra seconds. In contrast the person going 27 mph would use a disc wheel on practically all courses and it would seem worthwhile to get a good disc instead of messing around with a wheel cover.
In general I think my buddy is only considering the areo properties and not considering comfort or handling at all. A hed3 for 112 miles does not seem terribly comfortable to me (they seem to jar more than a spoke wheel). Slower speed rides occur for a reason (length of course, technical course, etc) and these should be factored into any speed based guide for wheel choices it seems to me. At least this was my argument.
The default setting in the model is 100g difference in weight. Since this understates the difference and biases it against my argument I left it as is. The default wind settings are
Speed: 5 m/s
Wind Direction: 315% from North
Var: 0 m/s
Air Density 1.226
I left the wind settings unchanged from the default as i had no idea the typical wind angle in Sydney. Increasing the weight difference to either 138 or 250 gram makes the rear disc even worse for the 200 watt rider.
does the site break down the factors causing the slowdown?
got a link?
The default setting in the model is 100g difference in weight. Since this understates the difference and biases it against my argument I left it as is. The default wind settings are
Speed: 5 m/s
Wind Direction: 315% from North
Var: 0 m/s
Air Density 1.226
I left the wind settings unchanged from the default as i had no idea the typical wind angle in Sydney. Increasing the weight difference to either 138 or 250 gram makes the rear disc even worse for the 200 watt rider.
Here is the website http://analyticcycling.com/DiffEqWindCourse_Page.html
This seemed much easier than doing it myself, especially for dealing with the changes in speed at corners (or due to other riders from passing or being passed).
Well unfortunately I have realized I did something wrong. I had also adjusted the riders weight (not a lot of 65 kg triathletes) and minimum speed (11 mph seemed too slow). However, the minimium speed I put in seemed right for a 300 watt rider but was not appropriate for the 200 watt rider. After adjusted this appropriately I also get the disc is slightly faster than the zipp 404 rear wheel for the 200 watt rider (about 15 seconds per 40k). Comparing the disc to a something deeper than the zip 404 gives a savings about 7 seconds per 40K for the 200 watt rider.
oh thank goodness I almost had to change my sig to
“Always use a disc unless you are slow as shit on a twisty course”
Well unfortunately I have realized I did something wrong. I had also adjusted the riders weight (not a lot of 65 kg triathletes) and minimum speed (11 mph seemed too slow). However, the minimium speed I put in seemed right for a 300 watt rider but was not appropriate for the 200 watt rider. After adjusted this appropriately I also get the disc is slightly faster than the zipp 404 rear wheel for the 200 watt rider (about 15 seconds per 40k). Comparing the disc to a something deeper than the zip 404 gives a savings about 7 seconds per 40K for the 200 watt rider.
