Yesterday, I rode a pair of older model Zipp 404’s I had bought on Ebay. I didn’t notice this slight bounce until I slowed down after my hard ride effort to test my new wheels. When I got home I checked it out more and could pick up the rear end spin the crank and feel the bounce. Seems again that it must be out of true but when looking at them while spinning , no obvious wobble. My next assumption was the tire and it does show some slight cracking I wasn’t aware of before the ride. I plan on taking it to the LBS, but wanted a second opinion as to the “bounce” effect I was getting? Thanks.
Tubular or clincher? I felt a slight bounce about a half hour before this happened…
Jodi
Tubulars so that kind eliminates the issue of having a the tube bubble.
looks like someone did not seat the tire properly. Hint, when changing, start at the stem, when placing the tire back on the rim.
looks like it, huh?
Tire had been on for about 600 miles before this happened with no problems. No one can really explain it. I felt the bump only about 30 minutes before it blew. I had just descended a VERY bumpy mountain road. Weird.
Jodi
I used to use the ultra light tubes, but stitched to a heavier tube as they used to blow pretty dramatic like this, but never like this. Mine would blow the hole through the tire.
I always had that “bounce” when I had a deep carbon tubular rear wheel. Never noticed it when riding but if you cranked the pedals on the repair stand it would get bouncing pretty good.
I think it was just a combination of the area around the valve stem not seating quite as tight on the rim when gluing it down and the slight bit of extra weight from the valve and extender. Spin it fast and it just kind of ocislates or bounces.
Even with my deep clinchers, you can detect it when the bike hangs in the repair stand & you crank the pedals; presumably from the weight of the valve extenders.
I’d still get your wheel checked out to make sure is ok.
Since you dont know the history of the wheels this is what I would do.
take tires off clean the rims Put them on a wheel stand check Radial trueness / *lateral *trueness / & Dish check spoke tension correct if needed remount new tires (if needed) make sure valve stem is centered and seated correctly
I have observed this before. Slight bouncing of wheel when spun at high speeds with wheel off of the ground but not perceived while riding. I think that it is due to slight weight imbalance from the weight of the long valve stem or valve extender needed with deep rims. Under load and with the friction of road, the combined weight of bike/rider, and compliance of the tire, it is not enough of an issue to feel while actually riding on the road.
BK; that was exactly what I was experiencing and upon closer exam there was a bulge near the stem. I am having my LBS remove and install a new tire as the one on there did have some cracking. Hopefully the LBS will do it right. I didn’t notice the bounce when I was going fast, only when I was done hammering and rode a few cool down miles I started to notice it and really noticed it in the garage when I lifted the rear and and cranked. Hopefully the new tire, propery installed will fix the problem.
Do you think the bounce you noticed hurt performance?
thanks!
It’s a non issue. Lots of deep wheels will bounce some when spun at high rpm in a repair stand but roll smoothly when on the road.
As Meebo said. It is not at all uncommon to have a bounce in the stand. Think about it…when your car gets new tires they balance to 1/4oz. Spinning at 50mph 1/4oz is alot to be off. Campagnolo and some others have put in some counter weights and or took weight off the valve side of things…Zipp has not. In the stand I can crank out 70mph with my hand at 53x11…yup, the bike bounces.
Or, if you feel it riding I bet it is a high spot at the valve stem.
sometimes the “bounce” with tubular can come from a bad tube inside where it becomes bunched up all in one spot… i have seen it in bad manufacturing… and or bad glue…