High Speed Whump!
 

It is hard to describe but i will try. My road bike seems fine until i get over 25 mph. Then it seems like there is a whump, whump that seems to be originating from one of the wheels and/or tires. It seems pretty normal in the stand and although the rear wheel is a bit out of true, it really isn't bad.

What could cause this? Again, i only notice it at high speed.

1. A tire may not be seated evenly on the rim. Look where the bead seats on the rim and check to see if it is even all around.

2 A patch on a tube may cause a lump in the tire.

3. Take off the silly CPSC-mandated spoke reflector.

Could it be that you're hitting the natural frequency of the bicycle/rider combination at that speed? I think there have been some threads here about this phenomenon...

1. Tire not "round". Can often fixed by letting the air out and "re-seating" the tire. I've had tires that I just could not get "rounded", though.
2. Rim not "round". Can adjust the spokes to round it out. Tighten spokes at a high spot, loosen at a low spot.
3. Rim has flat spot. Adjusting spokes may not be able to fix this.

Well, i took the tire and tube off the rim and put the rim alone in the dropouts. I then laid a flat ruler across the tops of the brake pads to act as a guide. It looks like there is about 1 mm of hop in at least one spot on the rim. It really doesn't look that bad, but considering i am new to road bikes and more familiar with mountain bike rims, maybe it is?

Maybe i will read up on how to true a wheel and give it a "spin" so to speak. EVen though i am not sure if truing will help.

I did remount the tire and rim and retest the wheel spin. It seemed like the hop was still there but maybe not as pronounced. The tire on the rim only has about 300 miles on it so it is odd that anything would be wrong with it. I never noticed it for the first few rides after i installed the new tire. It just showed up on my century ride a week ago.

That's likely to be the seam where the rim is joined. If so it will be directly across from the stem hole. Doubt if that's your problem, a defect in the tire would be more likely.

Al