skydive69

I'm curious as to your input on the following:

I just purchased a new set of AC Carbon 58 wheels with the ceramic bearings and Sapim spokes upgrade. I noticed that when the bike is on a repair stand and the front wheel is spun it seems to take forever for the wheel to spin down. I decided to try an experiment and put two bikes side by side on the stand. One bike with the new AC wheels, and the other with a set of Zipp 404 clinchers with standard bearings. When the wheels were spun simultaneously with the same amount of force the Zipp wheel continued spinning about a minute and a half longer than the AC wheel. I would have thought just the opposite would have occurred. Any thoughts on this? Thanks.

As an aside, I am the owner of both wheelsets. The local bike mechanic that I use who also happens to be a wheel builder opines that the AC hubs are superior to those of the Zipp. Assuming that they build comparable hubs, I would have thought that the ceramic bearings would have won a rollout contest. Perhaps there are other factors that I am not considering.

patentcad

This isn't a shootout. The AC's are like Custer @ Little Bighorn.

Zipps RULE. At any rate they do have a cooler brand name and stickers.

recneps

The AC wheels use smaller and lighter bearing, good for weight savings but bad for stiffness and longivity, I would assume that this would have something to do with the drag your refering to.

recneps

hahahahaha, oh marketing hype.

Coyote2

That test is valid only if your bike rides around without a person on top. The real test is how the hubs perform under load, and I would suppose that you have neither the knowledge nor equipment to test that.

skydive69

Perhaps once the heavier bearings gain momentum, they tend to follow Newton's laws of motion a bit better. Also, the Zipp clincher is considerably heavier than the AC tubular, and perhaps that also would help momentum once established. Although I road race on carbon, I time trial on aluminum, and once you get that sucker going with its Zipp 999 wheelset, there is no stopping that beast!

patentcad

No hype, simple observation. Zipps have a cooler name and stickers. We can all agree on that.

cslone

I've always been told it doesn't matter until there's weight on them.

skydive69

Perhaps what I did was totally meaningless then.

I agree about the looks - the Zipps have killer looks, especially mounted on my red and black Guru Geneo - I can't stop looking at that bike!

NoRacer

The new seals in the bearings of the AmClass wheels will cause the wheels to be tighter until you get a few hundred miles in on them--try your test again in about 6 months.

skydive69

That is probably the answer! The Zipps are new also - just replaced by the factory - but they do have 555 miles of hard riding on them.

merlinextraligh

Zipps, even the non ceramic bearings, are purported to have very low friction in the bearings. So it's possible the friction loss in the Zipps is less, even without ceramic bearings.

But as mentioned the real test is loaded. This is probably even moreso with Zipps because the bearings are non preloaded.

fly:yes/land:no

are you sure about the same force? my guess would be that you got them to the same speed and then watched them wind down. this would account for the zipp clinchers spinning longer because they will have a higher inertia at the same speed than an ac tubular.

skydive69

I did try the "experiment" twice being very careful to apply the same force to each wheel. I did it once by gently spinning both at the same time, and on the second one I spun them both hard simultaneously with the same result. It would be interesting to know who builds the hubs for AC - I didn't know until very recently that Zipp supplies the carbon rims to AC. I discovered that when I inquired as to what was holding up my wheel build at the factory, and was told they were awaiting a shipment of rims from Zipp.

asmallsol

Tape a bunch of weights to the tire on one of the wheels and it will spin forever. Its about rotational inertia. The only way this test could even be semi valid is if both wheels had equal rotational inertia. Hell my bench sander at work will spin for 15 minutes after it's turn off, because its heavy as hell.

skydive69

Maybe I should mount a couple of bench sanders on my machine and get rid of both wheelsets!

jrennie

Sounds good except you are backwards, zipp uses smaller bearings:
15X24X5 Zipp bearings

17X30X7 American classic bearings

daytonian

I'm sure both are laterally stiff and vertically compliant.

kensuf

Meh, it's about the motor. A friend of mine just won a pro/1/2 GA Cup race on a set of Aksiums.

curveship

30mm bearings in a front hub? I think you read the wrong spec. 30mm is bottom bracket size.

skydive69

Of course the typical wheel sucker can get by with crap wheels, but if you enjoy winning on breakaways (which I do), you need something that can save you a couple of watts (like a nice deep rimmed wheel ala Zipp 404 or AC Carbon 58). But that's a whole other discussion. We know how important the motor is, and to confirm it gets a bit clicheish at this point. It's like the people at golf tournements who have to bleat the obligatory "get in the hole" on every shot close to the green.

jrennie

those are rear hub bearings. Sorry, should have specified.

kensuf

Yeah. My buddy with the aksium's was in a 2 man break for 45 minutes and still won the race. I guess he's just a chump.

He used to win cat 3 races on a 1989 trek with downtube shifters and openpros but decided to upgrade to STI the same weekend he became a cat2.

Rutnick

The advantage of ceramics is when there is a load applied. NOT putting the bike in a stand and spinning the wheel.

LOAD is the key for ceramics.

skydive69

No, he sounds like a hell of a rider! I know how painful it can be. I was in a two man breakaway last December and everytime I looked at my heart rate monitor, it confirmed the pain - I was running in the 180s. I wound up averaging a higher heart rate in the road race than I did in a time trial competition a couple days previous. The guy would be scary with some real equipment!