Disk wheels for TTs

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I'm a competitive state-wide age-group time trialer (5 and 10K). My TT bike is a Cervelo P3 with Hed tri-spokes front and rear. I didn't elect to get a disk wheel for the rear initially because it's always windy here in Florida and I was afraid of getting pushed around too much. Now I'm noticing that the only people who beat my times are using disks on the rear. Since I took logic in college, I'm starting to go "hmmm ..." Can those of you with TT experience give me your opinion? Does a disk make you more than marginally faster? And what if the wind is coming at you at an angle?

I'm a competitive state-wide age-group time trialer (5 and 10K). My TT bike is a Cervelo P3 with Hed tri-spokes front and rear. I didn't elect to get a disk wheel for the rear initially because it's always windy here in Florida and I was afraid of getting pushed around too much. Now I'm noticing that the only people who beat my times are using disks on the rear. Since I took logic in college, I'm starting to go "hmmm ..." Can those of you with TT experience give me your opinion? Does a disk make you more than marginally faster? And what if the wind is coming at you at an angle?
I am very competitive too, and will race your sister ANYTIME! But I have noticed that the only people to beat my times are faster than I am.


Seriously- If the time difference is within seconds (2 to 5) then a rear disc might have an impact, but if the margin exceeds 5 seconds consistently, then you are just slower.

Actually the more windy it is, the more the disc will be an advantage... it is counter-intuitive, but look at some of the wind tunnel data and you will see that at effective yaw angles of more than 15deg discs can actually have negative drag (they push you slightly)... it made no sense to me until I read more about how sails work... but yeah, I started TT'ing with a cover in the rear, then got a full disc and used the cover on the front... my times improved dramatically but too many variables to say what gave me the speed (went from 22:30 in 10 mile TT to 20:46 over the season with various position and equipment tweaks), let alone give the total time to the disc... I will say that a cover will give you most(all) of the aero benefit with only a slight weight penalty (meaningless weight penalty you could argue).
Try that first to see.

Lots of good info and ideas how to get faster here:
www.biketechreview.com

Seriously- If the time difference is within seconds (2 to 5) then a rear disc might have an impact, but if the margin exceeds 5 seconds consistently, then you are just slower.
I guess that's true if the TT is short enough, but for a 40K TT, the difference would be on the order of about a minute or more with slower riders saving more time, faster ones less. http://www.zipp.com/portals/0/technology/documents/aerowheelcomparison.pdf

if you have H3's front and rear, i dont think a disc would be a significant advantage. however, it all depends on your version of "significant". you may think 3-5 seconds is a lot or anything more than 30 seconds is a lot. also, this depends on your budget. if money is no object, get a disc! always remember that your body create the most drag. something im going to play around with is getting ahold of a vid cam and setting the cam up in front of me and hook it up to a TV and display myself live. then i will find a good position that works for me and run with it. not exactly like a wind tunnel, but its free!

Thanks for the replies, guys. I've decided that I'm just going to continue to go with what I have, the two H3s. If I lose out on a podium position by only a few seconds, no problem - I'll just kill myself.

I'm also going to sit side-saddle on the bike to present a thinner profile to the wind, and that should more than make up for not having a disc wheel on the back.

Thanks for the replies, guys. I've decided that I'm just going to continue to go with what I have, the two H3s. If I lose out on a podium position by only a few seconds, no problem - I'll just kill myself.

I'm also going to sit side-saddle on the bike to present a thinner profile to the wind, and that should more than make up for not having a disc wheel on the back.
The race was this morning. I missed the state 10K TT age-group gold by three seconds. I'm trying to decide between draino and radioactive polonium.

The race was this morning. I missed the state 10K TT age-group gold by three seconds. I'm trying to decide between draino and radioactive polonium.
Wow, and a $50 wheel cover would have given you the win... of course if you are like me, you feel like you could have pulled that 3 seconds out by digging deeper after the fact... unless you have a russian connection I would go with the draino.

Next time don't forget you can buy speed...

[QUOTE=wilmar13]of course if you are like me, you feel like you could have pulled that 3 seconds out by digging deeper after the fact.

No doubt. If during the race I could have seen a split-screen side-by-side of me and him (like they do with skiing in the Olympic TV coverage) I'd have eaten that three seconds up like popcorn.

Of course, if he had the same view, he'd see me starting to overtake and then he'd give enough to prevent it. And then in my view I'd see that I'd have to go even faster. So in the end I'd probably still lose by three seconds, except we'd both be going 52 mph.

This reminds me of a marathon several years back where the two lead guys were shoulder-to-shoulder for the last few miles, matching surges, until one guy hit the tape about a step ahead. The interviewer asked the runner-up why, after all that effort for over two hours, he couldn't have just summoned up that little bit more to win. And the guy said, "That's exactly what the other guy did."