I am a 22 1/2 mph rider in a 25mile bike portion of the tri. How much time will I save changing from a pair of 770c HED3’s to a HED3 in front and full disc in back, leaving everything else equal?
According to Jim Martin a tri spokefront a rear disc saves a minute and a half over non aero wheels over 40 kms. http://home.hia.no/~stephens/aero.htm I read somewhere, but can’t remember the reference, that the difference with a rear disc to tri spoke is something around twenty seconds.
I ran the test (using the Florida State TT course, which is 40 km) at: http://www.analyticcycling.com/DiffEqWindCourse_Page.html
Fiddled with the wattage so that the resultant elapsed time for the non-test rider reached ~1:06.17 (which is 22.5 mph – setting it at 213 watts does it), and also equalized the values for weight and inertia.
For the default wind and rider weight settings, it yields the opinion that, over 40km (~25 miles), a Hed-3 front and Hed disc rear is 20.63 seconds** **faster than a Hed-3 on both wheels (all else being equal).
So make that two votes for 20 ticks. 
I did a search to find out the stats on these time differences. Yesterday I tried my disc out for the first time, after practicing for a week on an H3 in the front and rear. I expected a faster bike, and it actually felt slow. This is not a scientific lab test or anything, but I just remember when I put on my H3s from my non-aero wheels, I felt like I was flying, but yesterday it felt kind of like my rear tire was flat. I have an ironman distance competition this weekend. Should I go ahead and try out the disc for the race (because it’s officially faster than the trispoke), or go with felt faster before?
Another question: maybe the tired really WAS flat. I’m having trouble getting accurate tire pressure from my pump when using the silca valve converter to pump up the H3s and the disc. Does anyone else have this problem? I want to make sure I’m riding on at least 110 pounds of pressure.
Thanks.
the key to using a crack pipe (as in the converter for the H3 cuoput) is (a Les at InsideOut Sports reminds me every IM) a “CPH” - Crack Pipe Holder. It often works best to have one hand, or and extra person, to hold the crack pipe against the Presta valve to ensure it stays sealed at higher pressures. You can do this yourself, as long as you brace the pump with your knee…
If I recall correctly, aero wheels and disc provide a bigger time savings for slower than faster riders, since they are out ther much longer. the speed difference is less, but the time savings is greater. I don’t remember if it was John Cobb, or who…???
If I recall correctly, aero wheels and disc provide a bigger time savings for slower than faster riders, since they are out ther much longer. the speed difference is less, but the time savings is greater. I don’t remember if it was John Cobb, or who…???
It was Isaac Newton. 
It’s really just a conclusion that falls out of the Physics 101 equations. No road testing needed – just a little algebra.
Try, but I’m not knowlegeable about all the drag, RR equations. I leave that to you, JC, Jens, sojourner, Dan and whoever…Klehner? I could run them through one of my slide rules, though.
Try, but I’m not knowlegeable about all the drag, RR equations.
I’m sorry if that came across as glib. No offense was intended. I only figured this stuff out after asking a hundred stupid questions on the wattage forum.
No offense taken. I should educate myself, but time is limited. With my schedule and Frenchy’s training regimen, I don’t have a ton of extra time for that. Maybe in the off season.
I did a search to find out the stats on these time differences. Yesterday I tried my disc out for the first time, after practicing for a week on an H3 in the front and rear. I expected a faster bike, and it actually felt slow. This is not a scientific lab test or anything, but I just remember when I put on my H3s from my non-aero wheels, I felt like I was flying, but yesterday it felt kind of like my rear tire was flat. I have an ironman distance competition this weekend. Should I go ahead and try out the disc for the race (because it’s officially faster than the trispoke), or go with felt faster before?
Another question: maybe the tired really WAS flat. I’m having trouble getting accurate tire pressure from my pump when using the silca valve converter to pump up the H3s and the disc. Does anyone else have this problem? I want to make sure I’m riding on at least 110 pounds of pressure.
Thanks.
I also have HedH3Carbons on my Blade.
I strictly use them on race day and the day prior , only.
I train with Mavic Ksyriums’. When I put on my Hed’s I feel like the fifference between fist swimming and normal freestyle , if you get my drift.
I have the “crackpipe” per-se to use in emergency with my handpump or CO2. Never had to use it in a race and hope I never have to. I would lover to see how the hell this is done.
Anybody from Hed want to advise , PLEASE ?
I’ve used a crack pipe for…oh, 9 years or so. Its connected directly to my Silca Pump. I thread the hose through the wheel and attach it to the valve. This puts the pipe/valve on the opposite side from me and the pump. I hold the crack pipe on with one hand and pump with the other. The pump is directly between my knees and feet. I bend my knees as I push straight down on the pump. I can pump the tires to over 200 psi (don’t ask) this way. Its very easy. I normally run 140-150psi.