What difference would wheels have made.

Agree this has been beaten around for years on tri & roadie sites.  Best to ignore anecdotal claims & look for hard data.  My guess is around 45-60sec.

German cycling mag Tour has published fairly technical article on aero wheels, inc. wind tunnel test data (sep 05).  Don't know exactly how your stock wheels would test (Shimano R500, right?), but their estimated time savings between Ksyrium SSC SL and Zipp 808 (over 40k TT (300W ave power, 40kph/25mph ave speed) was 68 sec.  French bike tech site www.rouessartisanales.com published more wind tunnel data in 08.  They found Shimano R550s (similar to yours) were more aero than SSC SLs, and the shorter-rim 404 are slightly less aero than taller 808's.  So time savings switching from your wheels to Zipp 404's would likely be somewhat under 1 min. 
Another source- HED wheels website 2008 (FAQ section) stated potential 40k TT time savings switching to their wheels "depends on the wheels".  The base comparo wheel is not specified, but most tests use 32-spoke/box rim wheels as their baseline.  HED claims a potential 1.5-2min with "deep front and rear disc" or 1min with their J2s (semi-aero wheel).  Assuming your stock wheels are closer to J2's than 32-spoke/box, and Zipp 404s are not quite as aero as deep front/disc rear combo, HED site would also appear to suggest a time savings a bit under 1 min for your hypothetical wheel swap.

Edited by Oldteen 2009-08-23 5:11 PM

Could be up to a minute, or you could loose time. Keep in mind that body position is the biggest contributor to wind resistance... no wheels will change that. With just a slight cross wind, you might actually loose time, if you're not used to controlling it with deeper rims... weight is another factor coming into play.

Most of the time, I'm certain that I ride that extra few seconds faster when I toss on the race wheels from pure motivation...

Agree with previous data, but it somewhat depends on the speed of the rider. A faster/powerful rider will get more time decrease from said wheel package. Recent studies show for the money a helmet is your first and least expensive time saver at ~1 second/mile. Of course there are variables. If you look side to side often to enjoy the view or put your head down to throw up or whatever your new helmet just became a parachute. So for $100 a little discipline you have about $1400 to blow on tires with less rolling resistance, aerobars and aerobottle, one of the fancy new tri swimsuits from blueseventy, a pair of race only liteweight running shoes, and a host of other gadgetry and goodies. With the goods you got you can eek out another :30 refining your workouts. All that said, this sport is motivation as much as anything else and if you will be motivated to ride more on your new faster wheels then get them...besides, is there anything more beautiful than a pair of 404's?? Hmmm? Maybe a woman on 404's.

I'd say a minute, maybe two, depending on what kind of wheels you're riding and which Zipps you get.

That's if you're just talking about aerodynamics--the extra push/motivation/placebo of bringin' the good stuff on race day is good for a little extra time.

I ride an S32 as well and have the stock wheels on them (non-aero). This weekend was 4/124 on the bike in AgeGroup at about 23mph avg over 13 mile (Sprint) on a rolling course with no wind. My buddy has a nice blingy set of HED full carbon tubulars that cost 1.5X my bike and his speed was 20mph. So my recommendation is continue to work on the motor, cheapest investment you can make!

For what it's worth, I have been contemplating a disk cover for the back at what sounds like around $80-$100 which should get you close (but not all the way there) to the benefit of the high dollar wheelsets.

I agree with the last post though, mentally you may feel faster and get a minute or two from the placebo effect + a minute with the premium wheels.

I ride an S32 as well and have the stock wheels on them (non-aero). This weekend was 4/124 on the bike in AgeGroup at about 23mph avg over 13 mile (Sprint) on a rolling course with no wind. My buddy has a nice blingy set of HED full carbon tubulars that cost 1.5X my bike and his speed was 20mph. So my recommendation is continue to work on the motor, cheapest investment you can make!

For what it's worth, I have been contemplating a disk cover for the back at what sounds like around $80-$100 which should get you close (but not all the way there) to the benefit of the high dollar wheelsets.

I agree with the last post though, mentally you may feel faster and get a minute or two from the placebo effect + a minute with the premium wheels.

Oh, different wheels.