Road Bike Racing - Need a Disk?

I currently have a Zipp 404 set-up for my road bike and a Zipp 808 set-up on my TT bike.

I am converting over from Triathlon where the 808 made more sense for Tris and the 404 swapped in nicely (windy days).

Is there any point to having a disk wheel if I already have an 808. Are the advantages really there?

Having a disc wheel is great when the conditions are right (no wind/tail wind/head wind) but they are deadly in a cross wind. I don't know the numbers but I wonder how much more you'd gain with full disk over the 808, which are pretty aero. The real benifiet of a disc is the look and sound, that just can't be beat! ;)

A rear disc is going to be a little faster than an 808. Perhaps 20-30 seconds in a flat 40k. Take a look at http://www.analyticcycling.com/DiffEqWindCourse_Page.html The model doesn't have a Zipp 808, but you can get an idea if you play around with the other wheels in the model.

For real world confirmation, look at a TDF TT, and you'll see that teams that ride Zipp wheels typically set up with an 808 front, and a disc rear.

Now do you need it? the question is whether 20 seconds in the number of TT s you do is worth the cost to you.

The real benifiet of a disc is the look and sound, that just can't be beat!

Plus you can paint fancy logos on it.

If you want to impress your neighbors, get a disk.

If you're challenging for the top spot on the podium, get a disk.

If you're finishing every time trial just before sunset, don't get a disk.

It'd be worth it to me, but I'd basically have little use for my 808 unless I am in a wind between a 404 and a Disc.

Now... if a lenticular disc is better if you have to go into the wind... would I be better off with a flat disc like the Renn and just save the 808 rear for when its more of a lenticular deal?

I got question for you guys with disc's. I want to be able to use my PT on the disc as a Hr/cyclocomputer. I do this with my spoked wheels by adding a wheel magnet, any suggetions on how I would do this with a disc? I tried to tape a magnet to the disc last night just to test it but I think it was to far away from the seat stay.

A rear disc is going to be a little faster than an 808. Perhaps 20-30 seconds in a flat 40k. Take a look at http://www.analyticcycling.com/DiffEqWindCourse_Page.html

I've see these formulas, and seen the windtunnel data, but the problem is that they assume clean air and no side winds. That's a big assumption. Even without control issues, a slight sidewind will lead to more drag than with a spoked wheel.
I'd like to see windtunnel data with the bike at 5-10 degrees angle to the wind.

If you want to impress your neighbors, get a disk.

If you're challenging for the top spot on the podium, get a disk.

If you're finishing every time trial just before sunset, don't get a disk.

lol.

Do you really think this Forum is a good place to get an objective opinion on this? Do you really think anyone on here is going to say "no, you don't need more Bike stuff"??? ;)

You don't need more bike stuff. There I've said it.....I don't believe it....but I said it.

doc, I think hed has tested out to 30 degrees, I'm pretty sure up to 15-20 degrees a disc ruins everything else, after that things get a bit iffy, though generally its some form of deep dish or 3 spoke that comes out on top.

YOU guys can correct me if I am wrong, but I believe that a disc is capable of providing negative drag (ie propulsion) at various wind angles. I can check my texts, but I think that DRAG data is always less for a disc up to about 45-55 degrees. In order to have a crosswind affect you at 25 miles per hour (which is an easily doable speed for a TT) the wind would have to be horizonal to the bike and gusting greater than 25 miles per hour. Outside of that kind of force, a disc will always be better. Also important to note, is that even when a disc has a higher coefficient of drag than a spoked wheel (trispoke or 808), it is so miniscule, that the variability in wind direction will more than make up for any small losses you may incur.

The big problem with a disc in the wind is control. If you have never felt that, you may be in for a surprise.

Finally, with regards to the powertap, you can purchase magnets with an adhesive backing, you can use caulk (which is easily removed) or you can do what I do, and use electrical tape to secure the magnet well.

The sad thing is I think I am looking for a reason to justify me getting a disk. LOL

If I were to go with a 909, the part that would screw me is making the judgement call between the 808 and the 909... and then the 808 in front or the 404 in front.

Oh life and its troubles.

If you want to spend that much money, buy two Renn discs and send one to me!

if the less than a handful of seconds you MIGHT gain by getting a disk over an 808 (a very fast wheel already) if going to get you first place rather than second, then yes. if it might move you from 10th to 9th then forget it. if i owned a bike shop near you then the answer is always yes.