Barrettscv 

I'm considering upgrading to aero wheels such as Zipp 303 clincher, Sram S40 and others.

The bike is used for longer rides in the 40 to 100 mile range and I would like to use 700 x 25 tires to preserve some ride quality on the really poor pavement here.

What will be the outcome of aero wheels and a wider tire? Does the wider tire significantly reduce the aero benifit of the wheel?

Michael

botto 

i'm sorry, but i don't quite see the point in putting 25s on aero wheels.

when you write "poor pavement", do you mean something like this?

Barrettscv 

Just about, imagine mile after mile of patched potholes and 40 year old concrete. Plus I'm a larger rider at 210 lbs who likes a little comfort for long distance rides.

botto 

if that's the case, wy do you feel the need to purchase zipps?

Barrettscv 

I'd like to do a century in 5 hours.

Michael

botto 

aero wheels are not the answer.

Barrettscv 

I know, its the motor. The motor's ready... nothing wrong with having the right tools for the job.

merlinextraligh

Go to Zipp's web page. There's a technical paper on the aerodynamic interface of tire and rim. It will basically explain how the wrong sized tire is going to give back a lot of the aero advantage you paid $2000 to buy.


The terroidal shaped rims,and dimples on zipps are designed to overcome this somewhat, but again its not a great idea to put 25c's on Zipps.

DrPete 

Most manufacturers do their wind tunnel testing with 21's or 22's, 23 if you're talking about clinchers.

I tend to agree, though, that if you're running 25's and want to go fast, maybe the Zipps are the wrong choice.

Barrettscv 

So I should use 23's or forget the aero wheels...? (it does sound logical)

Jynx

If the roads are that bad forget deep section wheels. They are very stiff. Also if the roads are that bad zipp 303's are not something I would risk.

Barrettscv 

Agreed. I'm going to stick with my Open Pro's for now.

Zen Cyclery

Dont get the 303s they are flexy.
Dont get the Srams they are boat anchors.
Get some Edge composites clinchers. You can get them in 45mm and 68mm.

AEO

flexy in which direction? vertical or lateral?

box section rims give a nicer ride compared to deep section rims. they deflect vertically more so than deep sections.

your body is, by far, the least aero thing on a bike, no matter how large or heavy the rider is.

DrPete 

Yeah, the '09 303s are so flexy that Thor Hushovd raced them to third at Paris-Roubaix. And he's such a small, weak rider.

Jay Olson

I suppose something from HED might work. With the wider C2 rim, a 25mm tire will only be slightly wider than the rim, so you won't lose very much from an aero point of view. The C2 rim is also supposed to be more comfortable and allow you to run lower pressure (compared to a "normal" width rim). HED has wheels using the same rim with depths ranging from basically box-section to 90mm.

I ride 25mm Continental Gatorskins on Bastogne rims (32-hole, laced to PowerTap rear and Veloce front hubs), and they seem to be quite comfortable on the rough stuff. Because the spokes are attached to the aluminum rim on the HED wheels, the ride comfort should be similar across the range of rim depths.

Barrettscv 

https://www.hedcycling.com/wheels/ardennes_c2.asp

Those look excellent, and it's good to hear from an actual user.

I could see using 23's on the front and 25's on the rear.

Thanks

Waldo

It looks like the OP has settled on continuing with his current wheels but I wanted to chime in on some of the points made here in case anyone searching later on wanted this info.

To answer the original question, the rim profiles on both the 303 and Flash-point 40/S40 were optimized around 21-23 mm tire widths. We made this change starting in 2001, when most companies were using 19 mm tires in their wind tunnel tests (though some still do). We've been further evaluating rims with wider tires since we started developing the 202, 1080, and Sub-9 in parallel 3 years ago and even went as far as evaluating the new 303 with 27 mm tires during the last year or so. The neat thing with that rim is that it actually performs as well with a 24 mm tire as the previous 303 did with a 21 mm tire.

All that said, increasing tire width to a 25 will increase drag on the wheel/tire system approximately 5% depending upon the tire model in question (bear in mind, of course, that this accounts for a small portion of the overall system drag to begin with). However, we've consistently demonstrated in the tunnel that this increase corresponds to that one would expect given an increase in frontal area of the tire alone (granted, that gets a bit more complicated once you get into specific angles of incidence for your effective yaw values and the 5% is most definitely not constant across the range of likely effective yaw angles). The toroidal rim profile means the rim is much less affected by tire selection than a conventional v-shaped (or close approximation thereof) rim profile; in this case the aerodynamic width of the rim itself and the location of that widest part on the chord length of the profile are the dominant factors in aerodynamic performance of a toroidal wheel.

Radial wheel stiffness is one of those subjects about which there exists a great deal of misinformation on the internet. Obviously, any comparison is going to be specific to material usage, construction methods, etc., but one of the patents we have concerns using the toroidal shape as a bit of a leaf spring. In fact, all our rims are less radially stiff than a standard aluminum box section rim (we've used the Ambrosio Chrono as a reference as it was suggested by some of the teams with which we work). The deeper rims are actually less radially stiff than shallower rims as we are able to tune the laminate a bit more. Of course, the tire, rim, and spokes/hub are springs in series so the tire obviously dominates the equation in terms of ride comfort due to its much lower effective spring rate. We've got some pretty charts to go along with all this but unfortunately I can't get to them from this hotel.

Well, to be fair, he completed the bulk of the race on 202s (gasp, they must be like noodles! ) after a bike change after his first crash. His rear brake had come loose, necessitating the switch. It's always interesting to see stiffness discussions on forums considering that our team guys are riding off-the-shelf product and are certainly not averse to complaining if they're unhappy, much less that it's not verified in the numbers (particularly relative to the wheels Zen cites). That's okay, it's not like Zen uses multiple forums to promote his custom builds

Speaking of forums, I noticed when I logged in that this will be 1800 posts for me; that's a lot of time I could have been riding.
I'm almost feeling a bit nostalgic about that as when I joined I was just a mountain biking shop rat that had never heard of Zipp and now I never really get to spend much time here. How things change...

Barrettscv 

Wow, thanks for the quality info.

It looks like the the wider tire does not cause the air flow to delaminate, it justs adds to the frontal area without changing the CD. Do I have that right?

Michael

DrPete 

And considering the quality of your posts, you've made the equivalent of 15.4 million BF posts.

Waldo

Barrettscv, that's the gist of it. We do see some other very minute changes (and I'd have to pull up some tunnel data to get exact figures) but again that varies with yaw angle, and to a lesser extent, the tire model, in certain cases.

DrPete, belated congrats on the baby. Hope all is well with your family. I did think about the post count a bit last night; 1800 posts to me seems to be a ton but it's also over a long period of time, and that's probably about a week or two for p-cad.

DrPete 

I'll give you the address to send the baby shower gift. A pair of 808 Clydesdale tubulars would be fine.

DannoXYZ 

I wouldn't say "without", but probably not as significantly as the change in CA. It's really the total drag CA*CD that counts.