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18-07-2011, 15:26   #1
gilleek2
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Zipp 808/1080 combo v 808/disc

Hi Folks,

Wondering whether it's justifiable to splash out on a disc for a possible 2nd tilt at ironman next year. On a flattish course (austria or roth are likely contenders) would there be an appreciable difference between the above 2 combinations given reasonably low winds. Obviously high crosswinds would require a rethink. To give some background i did 10:10 (5:26 bike with 808/1080 set) this year in Austria in my 1st effort but reckon i've potential to do 9:45/9:50.

Thanks in advance for any responses.
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18-07-2011, 16:28   #2
Lumen
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FWIW, from what I've read a disc is better in high winds because (a) it's more aero and (b) it means you can run a deeper front.

If you have a 1080 rear already the money might be better spent on a powermeter or a coach

Unfortunately you can't buy a wheelcover for the 1080. If only you had a rear 808...
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18-07-2011, 16:41   #3
Beasty
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I have a 900 back disc and 808 Firecrest front. I was pleased I didn't get blown off when I did a 25mTT in winds in excess of 50kph a couple of months ago (and was only 90s outside my previous best with bog standard wheels and little wind). The Firecrest are very good in the wind with the 808 handling like a "normal" 404
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18-07-2011, 17:11   #4
Nwm2
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Quote:
Originally Posted by gilleek2 View Post
Hi Folks,

Wondering whether it's justifiable to splash out on a disc for a possible 2nd tilt at ironman next year. On a flattish course (austria or roth are likely contenders) would there be an appreciable difference between the above 2 combinations given reasonably low winds. Obviously high crosswinds would require a rethink. To give some background i did 10:10 (5:26 bike with 808/1080 set) this year in Austria in my 1st effort but reckon i've potential to do 9:45/9:50.

Thanks in advance for any responses.
Here is drag vs yaw for the two (the 1080 is in the light blue, Zipp Sub 9 disk in green):




(BTW, go to http://www.hedcycling.com/aerodynamics.asp for this awesome app).

So, very little difference at up to around 7.5 degrees, then 1080 is ahead until around 14, then disk takes over. So I guess it depends on the winds you will see.

Zipp's own data says 23 seconds over 40k (808/Sub-9 vs 1080/1080), giving you maybe 1.5-2 mins over 112 miles vs your 808/1080:

http://www.zipp.com/_media/pdfs/supp...e_flyer_11.pdf


Not sure what you mean when you raise the issue of crosswinds requiring a rethink - a rear disk has little negative impact on handling in cross winds compared to the front wheel - may even give better handling.
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18-07-2011, 20:59   #5
gilleek2
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Quote:
Originally Posted by Nwm2 View Post
Quote:
Originally Posted by gilleek2 View Post
Hi Folks,

Wondering whether it's justifiable to splash out on a disc for a possible 2nd tilt at ironman next year. On a flattish course (austria or roth are likely contenders) would there be an appreciable difference between the above 2 combinations given reasonably low winds. Obviously high crosswinds would require a rethink. To give some background i did 10:10 (5:26 bike with 808/1080 set) this year in Austria in my 1st effort but reckon i've potential to do 9:45/9:50.

Thanks in advance for any responses.
Here is drag vs yaw for the two (the 1080 is in the light blue, Zipp Sub 9 disk in green):




(BTW, go to http://www.hedcycling.com/aerodynamics.asp for this awesome app).

So, very little difference at up to around 7.5 degrees, then 1080 is ahead until around 14, then disk takes over. So I guess it depends on the winds you will see.

Zipp's own data says 23 seconds over 40k (808/Sub-9 vs 1080/1080), giving you maybe 1.5-2 mins over 112 miles vs your 808/1080:

http://www.zipp.com/_media/pdfs/supp...e_flyer_11.pdf


Not sure what you mean when you raise the issue of crosswinds requiring a rethink - a rear disk has little negative impact on handling in cross winds compared to the front wheel - may even give better handling.

I thought there would have to be some negative effect to having a disc in crosswinds thats what the rethink point was about. 1.5 to 2 minutes over that distance isnt worth the cost for me.
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18-07-2011, 21:16   #6
kennyb3
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Do you mind me asking OP your marathon time for the IM and your straight marathon time?

Anyway im sure there is plenty of scope for improvement in training, nutrition etc if it was only your first without dropping a few k on wheels
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18-07-2011, 21:30   #7
Lumen
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Quote:
Originally Posted by gilleek2 View Post
I thought there would have to be some negative effect to having a disc in crosswinds thats what the rethink point was about.
http://forum.slowtwitch.com/cgi-bin/...?post=2714622;

Quote:
A deep wheel on the front tends to put a torque on the steering axis that turns the wheel away from the side wind since the center of pressure is in front of the steering axis...BUT, what does that do? It actually causes the bike to turn INTO the wind due to the countersteering effect (i.e. to initiate a turn to the right, one actually starts the turn by steering the wheel to left. This causes the CG of the bike to shift down and to the right, initiating the right lean of the bike).

Now then, what happens at the rear with the disc? Well, the wind will tend to tilt the bike AWAY from the wind gust...thereby counteracting the front wheel wanting to tilt the bike INTO the gust. Make sense?

Of course, all of that also doesn't take into account any "splitter plate" effect of a solid disc on the rear of a bike, which can actually help decrease the drag at zero yaw
I have experienced the "blown into the wind" effect riding 50mm rims in a strong crosswind with no hands. It feels odd.
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