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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 07-02-09, 05:55 PM   #1
merlinextraligh
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25mm tires on Zipp 808's

Cross post from the Road Forum ( my guess is the Road poster have more experience with Zipps, You guys obviously have tandem experience.)

First, I understand this is not the best answer from an aerodynamic point of view. However these wheels are 808 rims, (520's) laced to tandem hubs, and are going to be used on a tandem. For crits, I want to use 25mm tires (Continental 4000's) for the flat protection, and cornering grip.

However Zipp says to only use 18-23mm tires with the wheels. My first thought was to check Sheldon's website. From that it would appear even the narrowest rims will work with 25mm tires.

http://www.sheldonbrown.com/tire_sizing.html

Unfortunately the interior dimension of the 520 Zipp rim is not readily available. The website lists the "aero rim width" at 24mm, but that does not refer to the interior rim width.

The tires mount on the rims with no issues, and are very tight on the rims.

So HTFU,and go ride them, or listen to Zipp?
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Old 07-02-09, 06:12 PM   #2
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Waldo was quick and helpful with theanswer in the road thread, so I'm copying it here, so anyone interested will have it.

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Originally Posted by Waldo View Post
Actually, as our clincher bead is governed by the ISO/ETRTO standard that dictates that a road racing rim be compatible with tires between 18-25 mm, those tires are just fine. The aero penalty is on the order of approximately 6 Watts, though that figure is affected by frame configuration on the rear wheel. Can you let me know where you got the info on tire compatibility and I will rectify the misstatement?
thanks for the info. It's on a sticker by the valve on the rims, not to use only 18-23mm tires, and not to exceed 125psi.

I believe these wheels were actually built in 2005 (based on some writing on the rim bed with a sharpie, if that helps.)
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Old 07-03-09, 08:40 AM   #3
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Two thoughts....

1. If it was me and I'd just dropped some serious coin on a set of wheels like the 808's, I would pick up the phone and call Zipp with my questions regarding total load weight, tire size, psi and the like to get a no-kidding answer as to what the implications might be. While it could be simply assumed the major impetus behind limiting tire size to 23mm is to ensure the wind-cheating characteristics of the 808's 4,000 dimples and toroidal shaping are not compromised, there may be concerns regarding the integrity of the rim. After all, there's a reason most rim manufacturers have psi and tire size limits and in most cases it's not related to aerodynamics.

2. Why would you opt to use the 808's for a crit instead of your Rolfs?
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Old 07-04-09, 03:44 PM   #4
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TG's got it. Though the fastest tandem team I know rides 23's on both ends, with no flat or cornering problems, and are about 300 lbs. Tire pressure will be the thing to watch, all right. IIRC, Zipp has special 24mm tires also with dimples, just for their rims.
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Old 07-05-09, 02:26 PM   #5
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As for talking to Zipp, I was in the process of doing that when Waldo, who is a Zipp engineer, resonded.

As for 23mm, we've TT'd on 23's. I'm thinking though at 340lbs team weight we're pushing it riding 23c's. We might try Continental Attacks front and back which are 24mm and split the differenc.

And for the Rolfs, they're a bit lighter, which would help acceleration out of corners, but the Zipps are so much more aero, I think the Zipps will be faster even in a crit. Also, after 3 rides, I'm finding that the Zipps are a lot stiffer than the Rolfs, which is making for more confident cornering.
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Old 07-06-09, 05:00 AM   #6
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tandem + crit?
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Old 07-06-09, 06:20 AM   #7
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Quote:
Originally Posted by merlinextraligh View Post
As for talking to Zipp, I was in the process of doing that when Waldo, who is a Zipp engineer, resonded.
Got; didn't click at first.


Quote:
Originally Posted by merlinextraligh View Post
And for the Rolfs, they're a bit lighter, which would help acceleration out of corners, but the Zipps are so much more aero, I think the Zipps will be faster even in a crit. Also, after 3 rides, I'm finding that the Zipps are a lot stiffer than the Rolfs, which is making for more confident cornering.
There's not much in the way of wheels that aren't stiffer than Rolfs; just not their strong suite. However, I guess I was thinking more in terms of risk vs. reward in that with few exceptions (e.g., one or two tire roll-offs or blow outs at the bottom of descents on road races at the Burley / Co-Motion), most of the crashes I've seen or heard of during tandem races have been during crits and, well, Rolfs are downright disposable compared to the Zipps
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Old 07-06-09, 06:39 AM   #8
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Nice wheels. Can we see a picture?
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Old 07-06-09, 06:47 AM   #9
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I have tried 23mm and 25mm tyres on my Bontrager tandem rims. Both work OK. I ended up sticking with the 25mm tyres as I felt they were better overall.

- I felt the 23mms needed too many psi to avoid huge deflection ~130psi, which is also more than most rim manufacturers state as maximum
- The 25mms seemed to roll better, offer more pinch protection in case of impact, had better ride at same psi and noticeably better ride at slightly lower psi. Stoker also mentioned better ride, so it wasn't just me

If I were doing a time trial I would perhaps go for a 23mm front and 25mm rear to get back most of the 6 watts. Only 5 minutes to change it - much less than the training needed to gain 6W!
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Old 07-06-09, 07:07 AM   #10
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Nice wheels. Can we see a picture?
New wheels
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