I recently purchased a used zipp 404 front (2004) and it needs a front tubular. I know that Josh said the Zipp was made to work with a 21 tubular, but I was wondering if it would still be better aerodynamically to run a 19 tubular up front and a 21 on the disc on the rear?
Anyone have any insight on this? They will be going on my Louis Garneau TT frame.
trust josh on this one you won’t find a better answer -21 is the way to go.
I like 21’s front and rear.
“I was wondering if it would still be better aerodynamically to run a 19 tubular up front and a 21 on the disc on the rear?”
I realize my experience in this sport may be more limited than many of yours, but is it actually possible that 2 millimeters of tire width makes an aerodynamic difference?!
I raced on 19 tubulars on my Zipp 404s last year. I have no idea whether I would have been faster or slower on 21s but, if you read the anti-19 posts, I probably would have been safer. Once you decide on the size, good luck getting consensus advice on the psi. There is definitely a conspiracy to keep that info secret. I’m still hard at work trying to crack the psi cabal. I have discovered that it meets regularly in Dearborn, Michigan.
You are right on that PSI thing. People are always telling me to put 120 PSI in my tires that take upto 170. I think they are just trying to screw me up. I always fill to 165. I guess it is a harsher ride, but like someone said in another post if I wanted a comfortable ride I would have stayed on the couch.
I rode at 145 psi last year because i thought the max was 150 psi on my conti comps. it’s not posted on the sidewall. Turns out the max psi is 170, so I will bump it to 165 next year.
Actually 2mm can make a significant difference if you were to subscribe to biketechreview.com. That was what got me started thinking about the difference. I believe the Zipp 404 clincher he tested there was one of the older models, not one designed to work with the 21mm tubular.
I think it will probably have to be the 21 front and rear as we are required to race on Schwalbe tires and their top of the line tubulars are those slow Tufo’s (rebadged). The lower models have regular tubes but only come in a 22mm size.
On the PSI front I remember some tire guru saying it depended on body weight and contact patch, but running a super high pressure over 130 or so wasnt just less comfortable but actually slower as the tire would deflect up and back off surface irregularities. I usually run about 110.
That’s a great idea, if you want to increase (yes, increase) your rolling resistance.
Can you explain to me how increaing the PSI in a tubular will increase rolling resistance. Just wondering.
It’s not a matter of tubular or clincher. A higher air pressure reduces the amount of road inconsistencies your tire can absorb. A higher pressure tire transfers this energy be essentially lifting the entire vehicle. That’s why your over-inflated tires Feel faster - because they’re transfering the road energy up to you, rather than absorbing it in the tire.
Tire pressure between 100 and 125 PSI seems to have the least rolling resistance for most people (obviously the weight of the rider is important).
I do weigh so I guess i could go a little higher on the PSI.
Rick C. at Zipp told me that a 19mm tire is not wide enough to cover the “bulge” in the newer rims that is the real aero effect of the tire (a 21mm does). The theory as told to me is that you want to have a smooth edge into the airflow and having the 19mm tire and then a thicker rim causes 2 points of turbulance while the 21mm tire is the same as the rim and thus only has one point. Sounds good and the 21mm is more comfy anyway 
That is what I was looking for-thanks. Also the bonus if I get a 404 rear wheel I can use that for road racing if I need to.
"I was wondering if it would still be better aerodynamically to run a 19 tubular up front and a 21 on the disc on the rear? "
Read awhile ago (probably either on Kraig Willet’s site or John Cobb’s old forum) that the front 21mm tire actually has less rolling resistance but the 19mm is slightly more aero making it a tiny bit faster. Can’t imagine it beeing very much faster however. The 21mm would be a bit more comfortable.
I’m currently running 19/21 on my P2K.
On probably every wheel in the world except ours the 19mm tire is more aero, but if you are riding a 2003 or newer 404, a 21 will be faster both aerodynamically and in rolling resistance. The wheels have been very specifically designed around the 21mm tire, so they still work well with 19’s, you really aren’t giving much up aerodynamically, but as a package you are going slower on 19’s on our wheels than with 21’s. For any other carbon wheel made, you essentially have to use a 19 to get the rim to work properly as the tire width and rim width need to be roughly equal (or the tire slightly smaller) for the wheel/tire combo to perform optimally. Our current 404 tubies are 22.25mm wide and our 404 clinchers are 23mm wide to accomodate the more common and popular 23mm clincher tires on the market.
As for all you guys running 170psi or whatever, we are working with a lab in Finland right now on this, and will publish a white paper on it in a few months, but I can tell you that both theoretically (we’ve been talking about this for a long time) and now in lab testing these high pressures are counter productive. Really anything past 120 or 125 is actually making you slower (though you will be vibrating yourself at a high frequency so it sure feels fast). We’ve been saying this for a few years, but as long as the tire companies keep making higher and higher psi tires people will keep thinking this is ideal. The reality is tha the tire companies feel that they lose business to competitors with higher PSI ratings so they are continually upping their specs to try and gain market share. The PSI rating on your tire sidewall is purely a safety/legal disclaimer as to the safest max pressure the tire can handle, and has become a marketing tool for some, but I would bet my entire collection of wind tunnel wheel samples (measures in the 100’s and contains everything you can imagine) that lowering your pressure to something sensible won’t slow you down. At worst, you’ll be just as fast and get significant improvent in tire life and durability while being more comfortable, and at best you’ll go faster while acheiving these same durability and comfort benefits.
josh
its not so much that 165 is harsher, it is slower on road surfaces.
-SD